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Rise of the Planet of the Ants

These days, we’ve been hearing quite a bit about a future in which humans find their dominion over the planet suddenly challenged by a group of super intelligent apes. This may make for an exciting Hollywood movie plot and some stunning visual effects, but I wonder whether we really need to look to humanoid science fiction in order to feel a shiver of doubt regarding our supremacy as a species.

Maybe all we need to do is to look at the world the way it is, a world that could well be called … The Planet of the Ants!

So, why is it that we should feel just a wee bit threatened by these small six-legged colonizers? Here are just a few reasons.

Quadrillions of Ants

Burning Man seems more crowded every year, doesn't it? (photo credit: Mehmet Karatay)

Like us, ants thrive just about anywhere, with the exception of Antarctica and a few isolated islands. Moreover, while there are approximately seven billion of us on the planet, conservative estimates put the number of ants at between one and ten quadrillion.1 That’s between 150,000 and 1,500,000 ants for each and every one of us. At the higher figure, this means that, if you were to put all the world’s ants onto a giant scale, they would weigh about as much as all of the humans on the planet put together.2 In fact, on average, it has been estimated that ants make up 15–20% of the terrestrial animal biomass on Earth (and more than 25% of the animal biomass in tropical regions).3

Our tendency as humans is to unquestioningly assume that we are far and away the most successful species that has ever been. If we take a step back, though, and simply consider the above numbers and the possibility that an animal’s success is most properly measured by the degree to which it has been able to thrive in various environments, perhaps we should already be feeling a pang of doubt about how incontestable our supremacy really is.

Ants Teach

While many animals are able to learn through imitation, ants are the only non-mammal known to engage in interactive teaching.4 In at least one species of ant, knowledgeable workers actively teach inexperienced nest mates where to find food through a process known as “tandem running,” in which the lead worker ant recruits an inexpert follower, and then makes sure that the follower stays on track, slowing down when it lags and speeding up when it gets too close.

Ants Learn

Ants are also able to engage in so-called latent learning, whereby they memorize information that they cannot use at once, but that may be useful later on – a behavior that’s been labeled as “planning.”5 Specifically, ants have been shown to be able to reconnoiter potential new living spaces, retaining information about relative desirability and tailoring their choices based on how urgently the need to move is.

Ants Can Learn to Navigate Mazes

Ants can be trained to remember multiple visual patterns presented in a fixed sequence, enabling them to navigate mazes.6 Ok, I’m not sure how exactly this leads to world domination, but it is definitely pretty cool.

Ants Practice Agriculture

Approximately 50 million years ago (and, accordingly, approximately 49+ million years before Homo Sapiens first arose as a species), ants began engaging in agriculture.7 Today, different species of leafcutter ants have adopted a purely agrarian lifestyle, feeding exclusively on gardens of fungus that they actively weed and cultivate, feed with fresh-cut leaves, and keep free from parasites and other pests.8 Here’s a video of some fungus farming ants:

Ants Engage in Animal Husbandry

Some ants raise aphids and feed on the sugary honeydew the aphids secrete when “milked” by the ants’ antennae. The ants are careful with their herds, keeping predators and parasites away, moving the aphids from one feeding location to another, and often bringing the aphids with them when they migrate.9 Here’s a video of ants tending to their aphids:

Ants Sometimes Enslave Other Ants

Certain types of ants are incorrigible slave-makers, raiding other colonies of ants and making captured slaves perform all routine tasks for their masters, including brood care, foraging, and even feeding slave-maker workers who are unable to feed themselves.10 Obviously, this isn’t a particularly attractive ant characteristic, but unfortunately it is one that may seem all too familiar to us humans.

Ants Use Tools

That’s right, tools. For example, some ants transport liquid and other non-solid food by dropping bits of leaves, sand or mud pellets or pieces of wood into a pool of food and, after the food has soaked in, using these objects to carry the meal back to their nests.11 Other ants use pebbles and soil pellets as weapons, dropping them on other ants or ground-dwelling bees, and then attacking and killing their competitors.12

Ants Build Cooperative Solutions

Hey, watch your foot! You're stepping on my head! (photo: Mlot, Tovey & Hu)

Ants, including army ants, are known to self-assemble into living bridges or ladders that allow them to cross gaps while on the move. When a single ant cannot make it across alone, other ants will successively grab on, steadily lengthening the bridge until it’s long enough to reach the destination. These structures, which can span significant distances and can even cross water, are then used by the rest of the colony and may stay in place for hours, until traffic dies down.13 Comparably, fire ants self-assemble into waterproof rafts to survive floods. These rafts can be made up from anywhere from a few hundred to many thousand ants and are incredibly durable, allowing ants to sail for months at a time as they migrate.

Ants Have “Collective Intelligence”

The concept of collective intelligence has been hot lately, with a number of books and articles describing how groups can make collectively make sophisticated decisions and solve complex problems, even where each individual in the group knows very little, collectively a g (think of the analogy of each individual acting as a neuron, and the group as a whole acting as a collective brain). Collective intelligence is a topic unto itself, one we may address in future posts, but for now suffice it to say that if ants truly can make wise decisions as a group, we humans may really have something to envy!

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ResearchBlogging.org1Holldobler, B & E. O. Wilson (2009). The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies. New York: W. W. Norton. p. 5. ISBN 0-393-06704-1.

2Ibid.

3Schultz, T. (2000). In search of ant ancestors Proceedings of the National Academy of Sciences, 97 (26), 14028-14029 DOI: 10.1073/pnas.011513798.

4Franks, N., & Richardson, T. (2006). Teaching in tandem-running ants Nature, 439 (7073), 153-153 DOI: 10.1038/439153a; Richardson, T., Sleeman, P., McNamara, J., Houston, A., & Franks, N. (2007). Teaching with Evaluation in Ants Current Biology, 17 (17), 1520-1526 DOI: 10.1016/j.cub.2007.08.032.

5Franks, N., Hooper, J., Dornhaus, A., Aukett, P., Hayward, A., & Berghoff, S. (2007). Reconnaissance and latent learning in ants Proceedings of the Royal Society B: Biological Sciences, 274 (1617), 1505-1509 DOI: 10.1098/rspb.2007.0138.

6Chameron, S., Schatz, B., Pastergue-Ruiz, I., Beugnon, G., & Collett, T. (1998). The learning of a sequence of visual patterns by the ant Cataglyphis cursor Proceedings of the Royal Society B: Biological Sciences, 265 (1412), 2309-2313 DOI: 10.1098/rspb.1998.0576; Reznikova, Z. 2008: Experimental paradigms for studying cognition and communication in ants (Hymenoptera: Formicidae). Myrmecological News 11: 201-214.

7Schultz, T., & Brady, S. (2008). From the Cover: Major evolutionary transitions in ant agriculture Proceedings of the National Academy of Sciences, 105 (14), 5435-5440 DOI: 10.1073/pnas.0711024105.

8Ibid.; Schultz, T. (1999). Ants, plants and antibiotics. Nature, 398 (6730), 747-748 DOI: 10.1038/19619.

9Nielsen, C., Agrawal, A., & Hajek, A. (2009). Ants defend aphids against lethal disease Biology Letters, 6 (2), 205-208 DOI: 10.1098/rsbl.2009.0743; Styrsky, J., & Eubanks, M. (2007). Ecological consequences of interactions between ants and honeydew-producing insects Proceedings of the Royal Society B: Biological Sciences, 274 (1607), 151-164 DOI: 10.1098/rspb.2006.3701.

10Pohl, S., & Foitzik, S. (2011). Slave-making ants prefer larger, better defended host colonies Animal Behaviour, 81 (1), 61-68 DOI: 10.1016/j.anbehav.2010.09.006; Brandt M, Foitzik S, Fischer-Blass B, & Heinze J (2005). The coevolutionary dynamics of obligate ant social parasite systems–between prudence and antagonism. Biological reviews of the Cambridge Philosophical Society, 80 (2), 251-267 PMID: 15921051; Hölldobler, B. & Wilson, E.O., 1990. The Ants, Harvard University Press.

11FELLERS, J., & FELLERS, G. (1976). Tool Use in a Social Insect and Its Implications for Competitive Interactions Science, 192 (4234), 70-72 DOI: 10.1126/science.192.4234.70.

12See, e.g., Pierce, J. (1986). A Review of Tool Use in Insects The Florida Entomologist, 69 (1) DOI: 10.2307/3494748.

13Mlot NJ, Tovey CA, & Hu DL (2011). Fire ants self-assemble into waterproof rafts to survive floods. Proceedings of the National Academy of Sciences of the United States of America, 108 (19), 7669-73 PMID: 21518911.

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Multi-Modal Monkey Memory

Recognizing someone you know is actually not a simple cognitive task – it requires you interpret the information you’re currently receiving through your senses, and then link back to a previously-formed conceptual representation you have of the individual in question. It’s especially difficult if you are acting cross-modally, for example matching someone’s voice to a photograph or vice versa.

Oh yeah, I remember him. He's the one with the high squeaky voice, isn't he? (photo credit: Joe Kegley)

Recently, two separate studies have shown that rhesus macaque monkeys (Macaca mulatta) are quite up to this challenge, reflecting that they possess a considerable degree of social memory and engage in complex conceptual thinking about other individuals.

French Pictures

In the first study1, published earlier this year in Proceedings of the National Academy of Sciences, a French research team headed by Julian Sliwa of the University of Lyon confirmed that rhesus macaques are able to spontaneously match the faces of known macaques and humans to their voices.

In their experiments, the research team gave six macaques a large number of tests in which they played short voice samples of known individuals (coos and grunts for other macaques, short French sentences and phrases for humans) and then measured how long the macaques spontaneously looked at cropped photographs of two known faces, only one of which matched the voice they had heard. The researchers statistically analyzed whether the macaques spent more time looking at specific photos after hearing the matching voice than they did after hearing a different voice, and found that the macaques did indeed stare significantly longer at a photo – whether of another macaque or a human – if the matching voice had been played first.

In reviewing individual performance, the researchers observed that five of six of the macaques displayed this effect overall, and that a greater number were better at recognizing photos that matched human voices than ones matching the voices of fellow macaques (the researchers noted that they were surprised at this finding, but pointed out that perhaps the explanation was that there were more useful auditory cues in the human speech samples than there were in the monkey coo vocalizations). Finally, the researchers found that five of the six monkeys showed preferences for specific faces, spending an especially long time looking at matching” photos of certain individuals – often a “neighbor” monkey or the researcher who was their main caregiver.

The researchers concluded that rhesus macaques can recognize individuals, linking together abbreviated visual and auditory perceptual cues (small, two-dimensional photos and short sound samples) to spontaneously identify other macaques and socially-relevant humans, and even to reflect the preference biases they have towards specific individuals.

At the Movies

The second study2, published last week in PLOS ONE, extended the findings to show that rhesus macaques can also recognize photos of other macaques whom they had seen during video clips, an additional challenge because specific features can be harder to identify in dynamic movies than in still images.

In this study, researchers led by Ikuma Adachi of the Yerkes National Primate Research Center began by training five macaques to watch brief silent video clips of familiar individuals before identifying which of five randomly placed photos represented the individual in the video. At first the macaques were allowed to continue to look at the last frame of the video before having to choose the correct photo, but in a second phase of the experiment the screen went black after the video was played, and the monkeys had to choose the correct photo after a time lag.

In each case the macaques became proficient at the task, even performing well after seeing videos taken from a novel perspective that was substantially different than the view in the training videos. Thus, their performance suggested that they were able to recognize specific features of known individuals as they appeared in dynamically-changing scenes in a range of videos, and then extract that information to identify those individuals later on in still images.

Next, the researchers repeated the testing, but this time they tweaked the conditions by playing a brief vocalization right after showing the last frame of the some of the videos – either a vocalization of the macaque in the video (the “congruent condition”) or of a different macaque (the “incongruent condition”). Only two of the macaques participated in this testing, as apparently the other three weren’t comfortable with working in the sound isolation booth necessary for this phase.

The researchers found that the macaques, who had never been trained to use vocalizations to guide their test responses, continued to be good at choosing the “correct” photo, but that when they made errors, they were statistically more likely than chance to pick the image of the vocalizing monkey, rather than the one in the video.

In other words, hearing the vocalizations systematically biased the macaques’ choice behavior, indicating that the voices may have activated visual representations of the vocalizing monkeys that occasionally superseded the impact of what had been seen in the video. Again, the macaques were demonstrating how they processed the information they used to recognize information cross-modally.

So, clearly “see no evil” is linked to “hear no evil” – perhaps we’ll see how “speak no evil” fits into the picture in a later post.

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ResearchBlogging.org

1Sliwa J, Duhamel JR, Pascalis O, & Wirth S (2011). Spontaneous voice-face identity matching by rhesus monkeys for familiar conspecifics and humans. Proceedings of the National Academy of Sciences of the United States of America, 108 (4), 1735-40 PMID: 21220340.

2Adachi, I., & Hampton, R. (2011). Rhesus Monkeys See Who They Hear: Spontaneous Cross-Modal Memory for Familiar Conspecifics PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0023345.

Grandmothers and Menopause in Cetaceans and Humans

As single income families become rarer and aging baby boomers begin to play a greater role in caring for their grandchildren, people have increasingly come to appreciate how much help a doting grandmother can provide. In fact, interest in the helpful role played by the elderly has given rise to the so-called grandmother hypothesis, which posits that women have evolved to live well past their reproductive years because, free from the costs of childbearing, they are able to invest more time into benefiting their grandchildren and other younger family members, raising the odds that their genes will be carried on to future generations.1 While the strength of the evidence for the grandmother hypothesis is still being debated2, it’s certainly got some intuitive appeal (especially, perhaps, to harried young parents).

What’s also quite fascinating is that the long post-reproductive life of human females – up to a third of a woman’s lifespan or more – is extremely rare: menopause appears to be unique to humans and (somewhat controversially) certain other great apes, as well as to certain toothed whales, including short-finned pilot whales and killer whales. (It’s possible that other species of cetacean may undergo menopause, but this hasn’t been established yet; also, more to come about elderly elephant matriarchs in a later post…)

To grandmother's house I go! (Photo: © Alice MacKay, Cascadia Research)

So, why is post-reproductive life is so rare? If the grandmother hypothesis applies to great apes and toothed whales, why isn’t it at work with other long-lived animals who live in socially-cooperative societies? Also, if evolution favors post-reproductive life because it provides distinct social advantages, why did menopause evolve in humans and toothed whales, given the very different social structures of humans and whales?

A fascinating study published last year in Proceedings of the Royal Society B3 by Rufus Johnstone of the University of Cambridge and Michael Cant of the University of Exeter may offer plausible answers to these questions.

In a nutshell, they found that, although humans, pilot whales and killer whales have quite different social systems, in each case older females become, on average, more genetically related to those with whom they associate. By contrast, in most other long-lived complex mammal societies, older females become increasingly less related to those in their local groups as they age.

Did grandma pinch you on the cheek too? (photo credit: NOAA)

The researchers began by developing a mathematical model that would allow them to draw general conclusions about age-related changes in the genetic relatedness of long-lived social animals as individual group members disperse, die and are replaced over time. (For those interested in such things, they based their approach on the “infinite island” model that is commonly used in considering the process of gene flow among a set of subpopulations.)

With their model in hand, the researchers analyzed three relevant social scenarios:

  1. Males Move On. In the large majority of social animal societies, males tend to move on as they mature, ultimately mating with unrelated females they find within new social groups. In this type of society, the researchers’ model determined that, over time, an older female will become less related to her group mates as she ages. She starts out in a highly related group that includes her father, but over time her older male relatives die, and her sons, and the sons of her relatives, leave the group and are replaced by unrelated males from other groups. Her average genetic relationship to the females in the group doesn’t change much, but since her relatedness to local males declines, overall her genetic connection to the group lessens as she gets older.
  2. Females Move On. Conversely, evidence suggests that during the course of human evolution, women were the ones that were more likely to move on to start families in new environments. (In support of this proposition, Johnstone and Cant cite the behavior of other great apes, human DNA variation patterns, and social patterns among human forager societies, evidence they concede is “far from conclusive.”) In this type of society, where males stay at home and females disperse, an older female tends to become more related to her fellow group members over time. She begins her reproductive life in new surroundings where she has few genetic ties to those around her, but as she produces sons who are likely to remain in the group, her relatedness to local males builds up over time. Again, because the degree of her relatedness to other females stays fairly constant – she starts out with little relation to the females in her new group and this doesn’t change much as her daughters leave and are replaced by new unrelated females – her overall genetic connection to the group increases as she ages.
  3. Males and Females Stay Put, But Mating Occurs Between Different Groups. In the resident killer whale and pilot whale societies studied, males and females stay with their natal groups for life, but mating occurs non-locally, that is, between females and males from other groups. In this final scenario, even though the social structure is quite different from “female moves on” societies, the results are the same: an older female tends to become more related to her fellow group members over time. A female begins her reproductive life separate from her father and her paternal relatives (who belong to a different group), but as she has male offspring her relatedness to males within her group grows over time. Once again, her relatedness to other females stays more or less constant, meaning that her overall genetic affinity with her group increases as she grows old.

Thus for human and certain whale societies, in contrast to most other social animal groupings, a female’s relatedness to her group increases as she becomes older.

Johnstone and Natal next considered the fitness costs of reproduction. They noted that having children imposes costs on other breeders within one’s group due to increased competition for food, resources and mating opportunities, whereas cessation of reproduction confers a benefit, due to a corresponding reduction in competition. Then, using a using a statistical model involving an “inclusive fitness” approach to generate quantitative results for the three scenarios described above, they reached a not-surprising conclusion: in scenario 1 (males move on), it is less advantageous for older females to “help” younger generations by stopping their own breeding, whereas in scenarios 2 and 3 (the human and toothed whale scenarios), non-breeding “help” is favored by evolution, as it confers advantages on a younger generation that is progressively more related to the older helper.

So there you have it. Does Johnstone and Natal’s analysis sound plausible? It certainly offers a neat way of finding an underlying similarity in great ape and whale societies that may explain menopause and support the grandmother hypothesis in these very distinct groups.

No wonder cetaceans often look like they’re grinning – they’ve been spoiled by their grandmothers!

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ResearchBlogging.org1See, e.g., Lahdenperä, M., Lummaa, V., Helle, S., Tremblay, M., & Russell, A. (2004). Fitness benefits of prolonged post-reproductive lifespan in women Nature, 428 (6979), 178-181 DOI: 10.1038/nature02367; Shanley, D., Sear, R., Mace, R., & Kirkwood, T. (2007). Testing evolutionary theories of menopause Proceedings of the Royal Society B: Biological Sciences, 274 (1628), 2943-2949 DOI: 10.1098/rspb.2007.1028.

2See, e.g., Kachel, A., Premo, L., & Hublin, J. (2010). Grandmothering and natural selection Proceedings of the Royal Society B: Biological Sciences, 278 (1704), 384-391 DOI: 10.1098/rspb.2010.1247.

3Johnstone, R., & Cant, M. (2010). The evolution of menopause in cetaceans and humans: the role of demography Proceedings of the Royal Society B: Biological Sciences, 277 (1701), 3765-3771 DOI: 10.1098/rspb.2010.0988.

The Honeybee Waggle Dance – Is it a Language?

The Dance

More than half a century ago, Karl von Frisch rocked the world of behavioral biology with his conclusion that the honeybees (Apis mellifera) can actually communicate the distance to and direction of valuable food sources through an elaborate “waggle dance.” In what later led to his receipt of the Nobel Prize in Physiology or Medicine, von Frisch determined that bees recruited by this dance used the information encoded in it to guide them directly to the remote location of the resource.

In the typical waggle dance, a foraging worker bee who has found by a rich food source returns to the hive, is greeted by other bees, and commences dancing on the vertical comb surface within the dark nest (in other species of bee, like Apis florea, the dance is performed on a horizontal surface in direct view of the sun and/or other landmarks). She dances in a figure-eight pattern, alternating “waggle runs,” during which she vigorously waggles her body from side to side in a pendulum motion at about 13 times per second as she moves forward in a straight line, with return phases in which she circles back to the approximate starting point of the previous waggle run, alternatingly between clockwise and counter-clockwise returns. Here’s a video of a bee doing the waggle dance:

As the video indicates, the honeybee’s dance encodes key information about the resource. For instance, as she performs waggle runs on the vertical comb surface, her average body angle with respect to gravity corresponds to the direction of the food source relative to the current position of the sun (the sun’s azimuth). Accordingly, if the food source lies in the exact direction of the sun, she will waggle straight upwards; if the food lies, say, 30 degrees to the right of the imaginary line to the sun, she will angle upwards 30 degrees to the right of vertical. Also, the duration of her waggling runs is directly linked to the flight distance from the hive to the food source, with (for many bee subspecies) every extra 75 milliseconds of waggling adding roughly another 100 meters to the distance. Further, the more attractive the destination, the longer and more vigorously she dances, and the more quickly she returns for the start of each waggle run. Depending on the richness of the food source, she may perform up to 100 waggle runs in a single dance.

Next week ... the Tango!

Cognitive Complexity

It seems, then, that honeybees have evolved an extraordinary complex form of symbolic communication about distant resources, one that is beyond the capabilities of virtually every other species except for humans. Not bad for an insect.

The cognitive tasks implicated by the waggle dance are not insignificant: the dancer must remember the location and characteristics of a specific site she has seen on her foraging trips, and translate this information into the appropriate dance characteristics. She must also remember and take into account the position of the sun, and update that position as the sun moves (the ability to compensate for the sun’s movement by memory has been documented by researchers observing dances over several hours of overcast weather, when there are no celestial cues to be seen). The observing bees must “read” the dance, translate their sensory input into a resource location, and then find the resource, navigating as necessary around hills, houses and other obstacles.

In fact, the feat is so stunning that von Frisch’s findings were initially met with significant skepticism and controversy.1 At this point, the controversy has essentially been settled, with scientists recognizing that there is compelling evidence that honeybees really do communicate and act on the information encoded in the waggle dance, even though uncertainty remains regarding exactly which signals (tactile, odor, vibrations, air flows, etc.) the observing bees use to translate the dance into actionable information regarding the resource location.2

Is the Waggle Dance a “Language”?

So, the waggle dance is an extremely complex communication system, but is it a language?

Eileen Crist, Associate Professor in Science and Technology in Society at Virginia Tech, makes a rather compelling case that the waggle dance embodies many of the attributes of a true language.3 After noting that the waggle dance is always performed in front of an audience and is clearly communicative in nature, she describes some of the principal features that support its being characterized as a language:

  1. Rule-Governed. If a communication system is to be considered linguistic in nature, it generally must be based on a set of rules that are structured and used with regularity. This is the case with the waggle dance: the dance is always performed in a designated place within the hive, it is never done unless an audience is present, and it always follows a standard template for conveying direction, distance, and desirability. While the general rule is that the waggle dance is to be used to inform other bees about sources of nectar, when the colony has a special requirement (e.g., locating water when the hive is overheating or finding a new home when part of the colony must relocate) then the rules dictate that the dance purpose switches to this pressing need. Also, the general rule is that foragers dance about rich, reliable and near resources, but in times of need the “dance threshold” for less desirable resources is lowered.
  2. Complexity. A key dimension of a true language is its complexity, as it is unlikely that a communication system based on just a few rules will qualify as a language. The bee dance rules are not only extremely intricate, but they are applied in a versatile and complex fashion to respond to differing environmental factors and hive requirements.
  3. Stability and Dynamism. A core feature of human language is that a relatively fixed and stable syntax enables the dynamic generation of an indefinite number of new sentences. Similarly, while the waggle dance always takes the same recognizable forms, it “accommodates different purposes, shifting circumstances, urgent needs, and unprecedented events; while structurally identical every time, it is also contextually flexible.”
  4. Symbolic. By itself, the symbolic nature of the waggle dance has led to its being called a language. The dance symbolically represents conditions existing in the real world, actually enabling human researchers to “read” the information encoded in the dance to find specific honeybee food sources and even to design experiments about honeybee foraging behavior.
  5. Performative. According to linguistic theory and as first articulated by John Austin, languages not only describe the world, they also include what he called “performative” utterances, which are used to carry out actions.4 Not only is the waggle dance symbolically descriptive, but it has performative force in the sense that it elicits action from the bees who watch it (as Crist notes, the performative nature of the waggle dance is implicit in the way in which scientists “routinely deploy a vocabulary of announcing, reporting, summoning, recruiting, soliciting, inviting, commanding, and guiding” in describing it).

James Gould, Professor of Ecology and Evolutionary Biology at Princeton University, summarized both the controversy over the issue and the nature of honeybee dance communication as follows:

Some of the resistance to the idea that honey bees possess a symbolic language seems to have arisen from a conviction that “lower” animals, and insects in particular, are too small and phylogenetically remote to be capable of “complex” behavior. There is perhaps a feeling of incongruity in that the honey bee language is symbolic and abstract, and, in terms of information capacity at least, second only to human language.5

Gould estimates that the waggle dance is capable of communicating at least 40 million unique messages (“sentences”), more than 10 times as many as any other animal except for man.6

Not surprisingly, not everyone agrees that the waggle dance constitutes a true language. For example, Stephen Anderson, Professor of Linguistics at Yale University, acknowledges that honeybee dance communication is elaborate and cognitively rich, but concludes that it is unlike human natural language in that, for example, it is genetically fixed rather than learned through environmental interactions, it lacks a syntax in which the order of the communicative elements (words or actions) impacts meaning, and there is a close correspondence between the structure of the dance signals and the nature information to be conveyed (e.g., orientation of the waggle run and the direction to the resource).7

Some bees are better at the dance than others...

To Bee or Not to Bee

In the end, there will probably always be debate and disagreement over whether the waggle dance is a true language. Clearly, the waggle dance and human language are vastly different communication systems, and how we label the waggle dance in human terms may be missing the point. From the honeybee standpoint, the dance serves its purposes and contains all of the communicative nuances that the bees need within their environment. Maybe, the real point is that we should sit back and appreciate the fact that the honeybee, a small insect with tiny brain, has been able to evolve a system of communications that is so sophisticated that it has challenged human linguists to wrestle with the question of what distinguishes a true language and whether human language is really so unique.

Anyhow, time to stop droning on and sign off!

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1See, e.g., Gould, J. (1975). Honey bee recruitment: the dance-language controversy Science, 189 (4204), 685-693 DOI: 10.1126/science.1154023.

2See, e.g., Landgraf, T., Rojas, R., Nguyen, H., Kriegel, F., & Stettin, K. (2011). Analysis of the Waggle Dance Motion of Honeybees for the Design of a Biomimetic Honeybee Robot PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0021354; Gil, M., & De Marco, R. (2010). Decoding information in the honeybee dance: revisiting the tactile hypothesis Animal Behaviour, 80 (5), 887-894 DOI: 10.1016/j.anbehav.2010.08.012.

3Crist, E. (2004). Can an Insect Speak?: The Case of the Honeybee Dance Language Social Studies of Science, 34 (1), 7-43 DOI: 10.1177/0306312704040611.

4Hymes, D. (1965). : How to Do Things with Words . John L. Austin. American Anthropologist, 67 (2), 587-588 DOI: 10.1525/aa.1965.67.2.02a00970.

5Gould, J. L. Ibid. at 692.

6Gould, J. L. Ibid. at note 37.

7Anderson, S. R. 2004. Doctor Dolittle’s delusion: Animals and the uniqueness of human language. New Haven, Conn.: Yale University Press. ISBN-13: 978-0300115253.

Be Kind to Cattle

The AnimalWise Soapbox

In a more ideal world, cattle would be free to lead lives consistent with their ancestry as nomadic grazers covering wide ranges. Of course, this isn’t a perfect world, particularly for the cows and other farmyard animals whose entire existence we have repurposed into the provision of meat and dairy products.

Without wading too deeply into the morass of moral issues raised by how we humans have transformed the environment and put other animals to work to serve our needs, it’s pretty clear that we have assumed a responsibility for the well-being of these animals who depend on us for everything.

Now, jumping down from the soapbox, what’s interesting is that, even if we were to disavow any ethical obligation to our bovine helpers, research continues to underscore how much it is in our own selfish interest to treat them with kindness and care.

A Cow by Any Other Name…

For example, one recent study1 that enjoyed some popular press attention found that named cows were better milk providers. That’s right, cows with names.

Uh oh, here comes what's-his-name...

In this study, researchers led by Catherine Bertenshaw and Peter Rowlinson of Newcastle University sent a detailed survey to every fourth dairy farm in England and Wales (1,000 in total), asking, farmers a number of questions regarding their attitudes toward cattle, how they managed dairy herds, and their perceptions of cows’ emotional and cognitive capacities. The response rate was 56% (52% after weeding out respondents who had recently ceased farming), with 90% coming from experienced stock managers who had worked with cattle for more than 15 years.

As noted above, cows don’t appear to enjoy toiling away in obscurity. On 46% of the surveyed farms, cows are called by name, and these cows produced an average of 258 liters more of milk per 10 month lactation period than did their anonymous peers (7938 liters versus 7680 liters). Moreover, on farms where the stock manager thought it important to know every individual animal, heifers had a 197 liter higher average milk yield over their first lactation than on farms where the manager thought it wasn’t important (6931 liters versus 6734 liters).

Does this mean that cows recognize their own names and appreciate it when they hear themselves being singled out?

While this is possible, the more likely explanation is that farmers who name and individually recognize dairy cows are more likely to treat them well. Bertenshaw and Rowlinson cite previous research finding attitude to be a reliable predictor of a person’s behavior around animals and that those having a positive attitude towards cows are “likely to handle animals patiently, to believe that regular positive contact is important, and to show positive behaviors towards the cows.”

Overall, the survey results indicate that – at least from the farmers’ perspective – there is a relatively positive relationship between dairy cows and stock persons on UK farms. Ninety percent of the respondents thought that cows had “feelings,” only 21% believed that dairy cattle were fearful of humans, and 78% thought cows were intelligent. (It would be interesting to see what percent think that their human coworkers were intelligent.) Also, on a somewhat reassuring note, 44% gave “love of cows” as a reason why they chose to work with cows.

Obviously, this is a subjective survey from one viewpoint (no word on when the cows will be receiving their questionnaires), but it provides important insight into the importance of our nurturing our relationships with other animals … and lessons that will serve us well when the Revolution comes (hilarious Dana Lyons video below):

♫  ♫  We will fight for bovine freedom, and hold our large heads high!   ♪  ♫  ♪

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1Bertenshaw, C., & Rowlinson, P. (2009). Exploring Stock Managers’ Perceptions of the Human–Animal Relationship on Dairy Farms and an Association with Milk Production Anthrozoos: A Multidisciplinary Journal of The Interactions of People & Animals, 22 (1), 59-69 DOI: 10.2752/175303708X390473.

What’s Up With the Male Dolphins of Shark Bay Who Don’t Use Sponges?

As discussed in detail in a recent AnimalWise post, a group of female bottlenose dolphins in Shark Bay, Western Australia has enjoyed quite a bit of attention of late for creatively using marine basket sponges as tools to assist them in rooting out bottom-dwelling fish. While the spotlight has been on the females, not much has been said about the males who (despite growing up fin-to-fin with sisters who learn how to use sponges) generally do not become spongers. The researchers studying the sponging behavior have not explored the lack of male sponging in depth, but have hypothesized that the males may be too focused on establishing and maintaining “alliances” to be able to devote the time and effort necessary to become specialized sponge-using foragers.1

I can't figure out that sponging thing either... (photo credit: Shark Bay Dolphin Project)

So what are these male alliances all about, and why are they so important?

Fortunately, a study published in the August 23, 2011 issue of Biology Letters2 provides some new detail and insight into male bottlenose dolphin alliances in Shark Bay.

In a surprise to most likely no one, the alliances are all about sex – maximizing a male’s chances of being able to mate. What is surprising, however, is the level of complexity of these male relationships.

Only humans and Shark Bay bottlenose dolphins are known to have multiple-level male alliances within a social network.

The researchers already knew that the Shark Bay males formed two distinct levels of alliance: first-order groupings of three (or, less frequently, two) males who cooperate to establish and maintain “consortships” with females, and second-order alliances comprised of two or more primary groups who band together to take females from other alliances and/or to defend against such “theft” attempts.

In itself, this degree of cooperation is notable, as alliances and coalitions within social groups are considered to be a hallmark of social complexity (for a posting on female elephant social networks, see here, and for hyena social dynamics, see here). The researchers put it succinctly: “Only humans and Shark Bay bottlenose dolphins are known to have multiple-level male alliances within a social network.” (AnimalWise aside: why are males less apt to have multi-tier social networks than females? Ok, perhaps I don’t need to ask….)

Are you in my second-order alliance? This is all so complicated! (photo credit: Shark Bay Dolphin Project)

In this most recent study, the research team describes a Shark Bay male dolphin society that is even more complex than previously reported – one that actually has three levels of nested alliances among males.

The researchers spent over five years observing 121 frequently-seen males in over 500 consortships, concluding that amicable low-level associations (i.e., third-order alliances) were regularly occurring between specific second-order alliances and trios or other second-order alliances. The researchers further noted that fights involving multiple groups of males suggested that the third-order alliances, like the second-order ones, are employed in conflicts over females, as higher-order alliances could be useful if second-order partners were not around when rivals appeared.

A few other interesting research findings include:

  • There was a nearly continuous range in the size of second-order alliances, which had between six and 14 members.
  • There did not appear to be a relationship between the size of the second-order alliances and how stable (long-lasting) their component first-order trios were.
  • Most of the males participated in second-order alliances, but a subset of five trios did not. Of these five trios, four were comprised of older males whose prior second-order alliance partners had disappeared over time. The researchers surmised that these particular dolphins may have participated in third-order alliances because they were particularly in need of assistance in protecting and obtaining females.
  • Most of the first-order trios associated with only one second-order alliance, but a small subset (around 3%) associated with more than one second-order alliance.

So, to sum up, while (a subset of about 1/11 of) the female bottlenoses of Shark Bay are engaging in specialized tool use with marine sponges, the males are absorbed in complex Machiavellian political relationships and sexual maneuvering. Hmm, sounds a bit familiar.

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1Mann, J., Sargeant, B., Watson-Capps, J., Gibson, Q., Heithaus, M., Connor, R., & Patterson, E. (2008). Why Do Dolphins Carry Sponges? PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003868.

2Connor, R., Watson-Capps, J., Sherwin, W., & Krutzen, M. (2010). A new level of complexity in the male alliance networks of Indian Ocean bottlenose dolphins (Tursiops sp.) Biology Letters, 7 (4), 623-626 DOI: 10.1098/rsbl.2010.0852.

Reconciling and Reassuring Ravens

Welcome to the elaborate, conflict-laden world of raven (Corvus corax) social dynamics!

Expanding on prior research demonstrating that ravens sometimes console fellow ravens who’ve been victims of aggression, researchers have now found that ravens who’ve been in conflicts often reconcile with their former opponents, the first time this behavior has been seen in birds.

Reconciling Ravens

In a study published this year in PloS ONE1, University of Vienna biologists Orlaith Fraser and Thomas Bugnyar found that reconciliation behavior does indeed occur between ravens who’ve had conflicts, particularly when the participants share a valuable relationship. While this sort of post-conflict kiss-and-make-up behavior is believed to play an important role in reducing stress and repairing relationships in primates and certain other mammals, it hadn’t been found in prior studies of birds, leading researchers to hypothesize that perhaps birds use different strategies to maintain social harmony or that reconciliation isn’t so important for birds, as their most important relationships are their pair bonds with mates, where they may be able to avoid significant conflicts in the first place.

Will we fight again? Nevermore! (photo credit: Audubon Guides)

Fraser and Bugnyar studied seven captive sub-adult ravens (who were too young to have formed pair bonds) for 13 months, measuring their behavior after a total of 197 aggressive conflicts (defined as incidents involving hitting, chasing or forced retreat). They then documented “affiliative behavior” (friendly interactions involving contact sitting, preening, beak-to-beak or beak-to-body touching) after each conflict, and compared it to the behavior occurring during neutral periods when no aggression had taken place.

They found that reconciliation (friendly contact occurring within 10 minutes of the end of the conflict) occurred after 37 of 197 conflicts and, in a significant majority of the cases, friendly interactions took place more quickly after a conflict than during the matched control period. Moreover, birds who were related or in “high value relationships” (pairs who had previously been observed to preen or sit in contact with one another) were more likely to reconcile. Interestingly, neither the sex-combination of the opponents nor the intensity of the conflict (measured by whether the birds hit each other and how many times a bird was chased or forced to retreat) impacted the likelihood of reconciliation.

The researchers did note that the behavior of ravens in the wild might differ from those in captivity, and that additional study would be needed to determine whether other factors, such as a history of food sharing, might also impact reconciliation behavior.

This study is significant in that it suggests that, through a convergent process and despite very different evolutionary histories, ravens have developed conflict resolution strategies that are similar to those employed by primates, reconciling with each other to preserve valuable relationships and reduce the chance of further discord.

Reassuring Ravens

This 2011 reconciliation research follows closely on the heels of a comparably-structured study2 that Fraser and Bugnyar published in 2010, also in PLoS ONE, establishing that ravens may possess a sense of empathy (yet another trait once thought to belong to humans alone, at least before evidence of empathy began turning up in primates and other animals).

In the 2010 study, Fraser and Bugnyar attempted to measure whether “bystander” ravens (those who’d witnessed but not been involved in an aggressive conflict) would console the conflict victim through “affiliations” (the same sort of friendly behavior – contact sitting, preening, beak-to-beak or beak-to-body touching – as was measured in the more recent “reconciliation” study).

Don't worry, you're much better looking than he is... (photo credit: pdphoto.org)

This time, they studied 11 sub-adult and two adult ravens raised in captivity, reviewing behavior after a total of 152 conflicts and in matching control periods and finding that both spontaneous and solicited (that is, initiated by the victim) bystander affiliations were likely to occur after conflicts.

More specifically, they found that unsolicited bystander affiliations were more likely to occur after more intense conflicts as well as when the ravens were related or shared valuable relationships, factors which suggested to the researchers that the affiliations served a distress-alleviating, or consoling, function. Also, the bystanders generally had stronger ties to the victims than to the aggressors, leading the researchers to conclude that it was unlikely that the bystanders were either acting as proxies for the aggressor to try to repair relationship between the combatants or trying to protect themselves from redirected attacks from the victims.

Based on these findings, Fraser and Bugnyar concluded that the best explanation for the bystanders’ unsolicited friendly behavior was that they were acting to console and alleviate the distress of the victims. The summarized the significance of this as follows:

Consolation is a particularly interesting interaction because it implies a cognitively demanding degree of empathy, known in humans as ‘sympathetic concern’. In order for a bystander to console a victim, they must first recognize that the victim is distressed and then act appropriately to alleviate that distress, requiring a sensitivity to the emotional needs of others previously attributed only to humans.

While the researchers noted some caveats, including the fact that study didn’t attempt to record vocalizations and that research on ravens in the wild was still necessary, they concluded that “the findings of this study … suggest that ravens may be responsive to the emotional needs of others.”

So, before you leave, here’s a multiple choice test regarding the moral of this story:

  1. Ravens are super smart, just like crows, nutcrackers, magpies and other corvids.
  2. We keep finding more and more ways in which other animals are able to do “uniquely human” things.
  3. If you plan on having an argument with a raven, you should make sure you bring all your raven buddies with you for support.
  4. All of the above.

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1Fraser, O., & Bugnyar, T. (2011). Ravens Reconcile after Aggressive Conflicts with Valuable Partners PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0018118.

2Fraser, O., & Bugnyar, T. (2010). Do Ravens Show Consolation? Responses to Distressed Others PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010605.

Asian Elephant Social Networkers

In a terrific new study in this month’s BMC Ecology1, a team of researchers led by Shermin de Silva of the University of Pennsylvania Biology Department has published the results of extensive, multi-year research regarding the social dynamics of a population of Asian elephants (Elephas maximus) at Uda Walawe National Park in Sri Lanka. The researchers studied 286 adult female elephants from September 2006 to December 2008, observing the social relationships they formed on a one-to-one basis, in small groups, and at the overall population level.

While group social behavior in African savannah elephants (Loxodonta africana) has been studied extensively, this new research is the first detailed, quantitative study of a wild Asian elephant population over such a lengthy time period … and what the researchers found was quite surprising.

You spend all your time social networking! First do your homework, then you can go on Facebook (photo credit: HelpElephants.com)

Prior less comprehensive studies had suggested that Asian elephants form less complex social networks than do African savannah elephants, with Asian elephants forming smaller and looser social groups based primarily on mother/daughter bonds, and rarely if ever involving relationships between unrelated females. In this in-depth longitudinal study, though, a different, more nuanced, portrait of Asian elephant society emerged.

Although, on any given day, the researchers would see only small groups of elephants that didn’t appear to interact extensively, over time, individual elephants formed larger social units that could be remarkably stable across years, even while associations among such units varied quite a bit across seasons.

One-to-One Relationships (Dyads)

The researchers started out by measuring how much time pairs of adult females spent together and found that, at a high level, the frequency of their associations was highly correlated across all five seasons in the National Park (Sri Lanka has a highly seasonal environment, with two separate monsoon seasons, two dry seasons, and a transitional season) – that is, pairs who associated in one season tended to associate in all seasons, and those who did not associate in a given season weren’t likely to associate at all.

Yeah, let's just hang and make nice for now, then we'll hit the rice paddies when nobody's looking! (photo credit: EleAid.com)

In studying one-to-one relationships, the researchers turned their attention to 51 “core” elephants who they thought would provide particularly good data, since these elephants were observed frequently and during all seasons of the year. These elephants formed a total of 478 pair relationships, which the researchers divided out statistically as follows:

  • A total of six (1.3%) of the pairings were “strong” and stable relationships, as measured by the relative percentage of time these pairs spent together during all seasons. Nine of the elephants (17.6%) participated in relationships in this category.
  • A total of 433 (90.6%) of the pairings were “temporary,” with the association peaking during a single season (most of the peaks were in either the transitional or dry seasons). All 51 of the elephants had at least one relationship that fell into this category.
  • A total of 39 (8.2%) of the pairings were “cyclical,” with the associations peaking in frequency during the two dry seasons (interesting, the researchers did not find relationships where the peaks were during the two wet seasons). Thirty two (62.7%) of the elephants had relationships that were cyclical.

Next, the researchers analyzed whether the identities of an elephants’ preferred companions changed over time. Overall, they found that the elephants spent slightly more than 20% of their time with their long-term companions (the top five companions over five seasons) and slightly more than 30% of their short-term companions (the top five for the current season). On an individual level, there was quite a bit of variation: eight (15.7%) of the elephants maintained 4 to 5 of their top five companions for all five seasons, while 16 (31.4%) completely changed their top-five companions during the study.

The researchers cite the example of two elephants, Kamala and Kanthi, who spent nearly all their time together – they were part of the “K” unit (Kamala, Kanthi, Karin, Kavitha and Kalyani, but no Kardashians) that was particularly close – and contrasted this kloseness to an individual named “471” that had few stable companions. (I wonder if this was due to distress over only receiving a number for a name.)

Additionally, the researchers noticed that the elephants who had the most relationships tended to form weaker bonds with each individual partner, whereas those with relatively few pairings tended to spend a relatively large amount of time with each of their companions.

Hmm, these elephants are beginning to sound quite a bit like people…

Small Group Associations (Ego Networks)

At the next level up, the researchers studied so-called “ego networks,” social networks consisting of an elephant and all of the other individual elephants with whom she associated at least once. The researchers focused on 88 of the adult females who they observed in every season, and calculated five measurements for each: (1) the number of her direct companions, (2) the number of ties between the direct companions, (3) the total number of potential ties between each of these direct companions, (4) the ratio of actual to potential ties, and (5) the number of individuals within two degrees of separation of the subject (number of friends plus number of “friends of friends”).

(Note that, assuming at least one of the researchers is within five degrees of separation of Kevin Bacon, this would mean that the entire ego network would be within seven degrees of separation of Kevin Bacon.)

Without getting into the full statistical analysis, the researchers’ principal conclusion was that:

[W]hile a subject’s direct companions do change over time, she has a few that are almost always present; even those that are not present continuously may have been companions in previous seasons. Thus, individuals maintain long-term relationships with others even though they may be apart for one or several seasons and [the amount of time spent together is small].

In other words, the elephants remember their friends and reestablish their relationships even after having been apart for long periods.

Population Level

Finally, the researchers looked at the social structure of the entire population. They found that the elephants in the overall popular had an extensive and well-connected social network, and that the distinct social units within the population were two to three times larger than had previously been seen in the field. Moreover, they observed that many of the social units maintained their integrity across seasons, even as individuals switched units and the connections between the units changed.

For those of you who like to look at dot patterns, below is a colorful series of diagrams depicting the connections between elephants, measured at different societal levels and during different seasons (T1 is the transitional season, D1 and D2 are the dry seasons, and W1 and W2 are, you guessed it, the wet seasons):

Figure 5 from Research Paper

Recap

While the strength of the associations among these Asian elephants (as measured by percentage of time that individuals spent together) is generally a good bit lower than that of the associations among African savannah elephants, most of these elephants had a few strong ties as well as consistent ties that they maintained over several seasons. Further, the Asian elephants were hardly asocial – while their mix of companions did fluctuate over time, they often returned to a subset of preferred companions.

Moreover, through their years of observation and statistical analysis of the elephants at the population level, the researchers found that the elephants’ social units were much larger than had been observed in prior studies, and that these social units were more stable across the years than were the companions of individual elephants.

The researchers speculated that one reason for the surprising findings is that the elephants stay in touch in ways that are hard for humans to detect, allowing the elephants to maintain bonds and relationships that we fail to observe. For example, elephants can communicate acoustically over great distances, and often use scent to follow one another’s paths at night (and, for that matter, even when the other elephants would be in plain sight, at least from the human perspective).

Finally, the researchers are planning to perform a detailed genetic study of the population in order to analyze the degree to which relatedness impacts the social organization of Asian elephant society. We’ll be waiting!

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1de Silva, S., Ranjeewa, A., & Kryazhimskiy, S. (2011). The dynamics of social networks among female Asian elephants BMC Ecology, 11 (1) DOI: 10.1186/1472-6785-11-17.

Female Dolphins Sponge Their Way to Success

After 27 years, scientists finally appear to have unraveled most of the mystery surrounding a very enterprising group of (primarily) female bottlenose dolphins (tursiops aduncus) who live in Shark Bay, off the coast of Western Australia.

Why are those dolphins looking at me like that? (photo credit: Eric Patterson, Shark Bay Dolphin Project)

The story opens in 1984, when observers first noticed that some of the Shark Bay dolphins were breaking off conical marine basket sponges and wearing them over their beaks (rostra). Because only a small percentage of the dolphins in the area engaged in this behavior and it was very difficult to see what they were doing with the sponges, especially when they were underwater, the first research on this behavior wasn’t published until over a decade later.

Preliminary Findings: Tool Use by a Few Females

In a 1997 article in Ethology1, a team of researchers led by Janet Mann of Georgetown University described their initial findings: five female dolphins were regularly seen with sponges, and four additional dolphins (only one of which was a male) were each seen carrying sponges on a single occasion. The regular sponge users were relatively solitary, tended to use the sponges in a deep water channel area, and did not participate in the group feeding and social aggregations to which other dolphins in the group were attracted.

The researchers weren’t sure what the dolphins were doing with the sponges, but they assumed that there had to be some sort of functional advantage, since the sponges were often quite large, covering a large portion of the dolphin’s face, interfering with normal use of the mouth, contributing to hydrodynamic drag, and potentially impacting the ability to engage in echolocation. They considered three possibilities: that the dolphins were playing with the sponges, that the sponges contained some medicinal or other useful compound, or that the dolphins were using the sponges as a tool to aid in foraging.

They concluded that it wasn’t likely that the sponges were being used as toys, as the spongers were relatively solitary, used the sponges methodically for hours at a time, year after year, and didn’t engage in typical play postures, splashing or vocalizations as they carried the sponges. Similarly, they determined that medicinal or similar uses were unlikely, since, among other things, the regular sponge users all seemed healthy and there were no indications that they were ingesting the sponges (although the researchers conceded that this could be difficult to observe).

Hi ho, hi ho, it's off to sponge I go! (photo credit: Eric Patterson, Shark Bay Dolphin Project)

On the other hand, it did seem likely that the dolphins were using the sponges to help them forage for prey: they were seen eating fish when engaging in sponging behavior; they invested an amount of time in carrying sponges similar to that invested by other foraging dolphins; and they made sounds and generally behaved in ways consistent with foraging. The researchers speculated that sponges might be used to protect the dolphin’s face, either from spines or stingers of prey animals or from the abrasive sea floor as they flushed out burrowing prey. In either case, they believed that this would constitute “tool use,” something that had been reported in captive dolphins but never before in the wild.

Finally, the researchers drew no conclusions on why males didn’t engage in sponging, except to note that perhaps it required a degree of solitary living that was at odds with their need to form and maintain cohesive and cooperative alliances.

Additional Findings: A Cultural Tradition of Tool Use among a Related Group of Females

Next, in 2005, Mann’s researcher team expanded on its findings in a paper published in the Proceedings of the National Academy of Sciences2, with salient points of the research including the following:

  • Sponges Are Foraging Tools. By this time, the researchers had found 15 adults in the community who regularly used sponges, only one of whom was a male. Although not a focus of the paper, it appears that the researchers had concluded by this time that the dolphins were indeed using the sponges as tools to protect their rostra as they foraged for prey on the sea floor.
  • “Sponging Eve.” The researchers tested the mitochondrial DNA of the regular spongers and found that sponging had been passed on mainly along a single matriline (line of descent from mother to daughter) and that, due to the high degree of genetic relatedness, all spongers likely descended from one recent “Sponging Eve.”
  • Female Social Culture. After considering in detail whether the sponging behavior could have resulted from either a genetic propensity or some unique aspect of the deep-water channels where the most of the sponging occurred, the researchers found the evidence for these alternatives lacking and concluded that by far the best explanation was that the sponge use was being socially learned and transmitted from mother to daughter. The researchers weren’t overly surprised by this finding, given that studies had already shown that dolphins have uncommonly complex cognitive and imitative skills and the ability to excel at vocal and social learning.
  • Uncommon Cultural Diversity. It was particularly rare to see this sort of cultural phenomenon in a small subset of the overall population (a single maternal line comprising only about 10% of the females in the group). In other studies (for example, involving apes), this type of culturally learned behavior is seen across the entire population.
  • Can’t Explain Males. Once again, the researchers surmised that perhaps males didn’t engage in sponging because they had to associate at high levels with alliance partners, but they left this point open.

The Story Continues: Spongers Are Fit

The story continued to unfold in 2008, when Mann and her team published a paper in PLoS ONE3 that focused in more on whether sponging was an advantageous behavior, or whether the spongers were in some fashion subordinate or less competitive and were making the “best of a bad situation.”

I don't know what you mean, it's no more elaborate than the other hats at the Royal Wedding... (photo credit: Eric Patterson, Shark Bay Dolphin Project)

By this point, recurrent sponging had been seen in 41 of the dolphins and a few more of them were male (29 were females, 6 were males, and 6 were of unknown sex). This still represented a small percentage (about 11% of adult females were spongers) and, although it now appeared that more than one matriline was involved, the data continued to show that the behavior was consistently passed down from mother to daughter, and less frequently from mother to son: there were no instances observed where a calf adopted the behavior if its mother wasn’t a sponger, and of 19 offspring born to sponger females who could be observed and whose sex was known, 91% of the daughters (10 of 11) and 25% of the sons (2 of 8) adopted sponging.

Further, the researchers found that the spongers were highly specialized, not using other hunting techniques and spending approximately 96% of their foraging time using sponges. In fact, the researchers concluded that, due to their lifestyle and specialization, spongers actually used tools more than any non-human animal.

So, was the sponging advantageous or a way of coping for not particularly well-adapted dolphins? Well, the researchers did find that spongers were more solitary and spent more time foraging at deeper depths and on longer dives, but noted that they really didn’t seem to suffer from any kind of fitness cost, as their calving success was equivalent to that of other females in the population.

Since there was no evidence that any kind of competition for food was relegating the spongers to their strategy, the research concluded that sponging simply seemed to be an “all-or-none phenomenon,” that required a specialized approach and a commitment to a single foraging type, but that most likely opened up a particular hunting niche in a diverse environment. While other dolphins could theoretically adopt the strategy, the researchers noted that daughters in particular tend to adopt their mothers’ foraging strategy, and unless the mother was a sponger, a daughter might simply not have had sufficient exposure to develop this highly specialized technique while a calf.

Once again, the team hypothesized about the males, stating: “Male offspring are exposed to sponging as often as female offspring, but do not seem to adopt the behaviour early, if at all. … [M]ales likely range more widely post-weaning, focus on establishing long-term alliances, and cannot afford to adopt foraging tactics that both demand extensive effort and specialization and limit their range and access to females.”

The researchers offered no opinions about whether the male dolphins were simply slow on the uptake or whether they associated sponges with housework to be avoided.

The Latest Chapter: Explaining the Purpose of Sponging

While all of this research had answered many questions and shed light on a fascinating example of tool use in wild female dolphins, one fundamental question remained. Dolphins are great at using echolocation to detect prey (even prey that is buried), so why do the Shark Bay spongers probe the debris-covered sea floor with their noses, risking injury (even with the protection afforded by the sponges) instead of minimizing sea floor contact by simply echolocating for buried prey as they do in other locations (for example, the Bahamas)?

What a mess! This sea floor needs a good sponging! (photo credit: Eric Patterson, Shark Bay Dolphin Project)

This is the question is answered in the latest chapter, a research paper published last week in PLoS ONE4. Mann’s research team had fun with this one, grabbing poles and going sponging themselves. What they found, aside from the fact that dolphins are far more graceful than people, was that the nature of the prey turned up by sponging helps explain the dolphins’ behavior.

It turns out that most of the bottom-dwelling fish that hide in Shark Bay the sea bottom lack swim bladders, gas-filled chambers used by fish to control their buoyancy as they swim up and down. Because they lack the major characteristic that distinguishes their density from sea water, they generate relatively weak acoustic signals and are difficult to detect with echolocation. In addition, the debris (rock, shell and coral) on the sea floor in the area seemed likely to cause “interfering reverberation and echo clutter,” which would further reduce the effectiveness of echolocation.

Moreover, it’s worth it to go after these swim bladderless fish. They are attractive targets, as they are reliably present on the sea floor and exhibit consistent, predictable behavior when rousted out of their hiding places, allowing the dolphins to adopt a single efficient technique as they sponge. Further, bladderless fish tend to have a relatively high fat content, providing hungry dolphins with a particularly energy-rich meal.

So, the sponging female dolphins of Shark Bay really are quite remarkable. They have established a mother-daughter subculture of tool use in the wild, successfully devising a highly specialized way of exploiting an attractive niche in their diverse environment.

You go girl(s)!

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1Smolker, R., Richards, A., Connor, R., Mann, J., & Berggren, P. (2010). Sponge Carrying by Dolphins (Delphinidae, Tursiops sp.): A Foraging Specialization Involving Tool Use? Ethology, 103 (6), 454-465 DOI: 10.1111/j.1439-0310.1997.tb00160.x.

2Krutzen, M. (2005). Cultural transmission of tool use in bottlenose dolphins Proceedings of the National Academy of Sciences, 102 (25), 8939-8943 DOI: 10.1073/pnas.0500232102.

3Mann, J., Sargeant, B., Watson-Capps, J., Gibson, Q., Heithaus, M., Connor, R., & Patterson, E. (2008). Why Do Dolphins Carry Sponges? PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003868.

4Patterson, E., & Mann, J. (2011). The Ecological Conditions That Favor Tool Use and Innovation in Wild Bottlenose Dolphins (Tursiops sp.) PLoS ONE, 6 (7) DOI: 10.1371/journal.pone.0022243.

Chimps Don’t Ape Humans – Develop Tools Independently

The more we learn about the capabilities of animals, the less it seems we can claim as uniquely our own. Now it appears that we may even have to share our treasured Flintstones cartoons, as we have learned that we aren’t the only species to have enjoyed an ancient Stone Age history.

Chimp eating nuts and thinking about upcoming Chimpanzee Iron Age

A few years ago, archeologists led by Julio Mercader of the University of Calgary discovered that chimpanzees in West Africa were using stone tools to crack nuts thousands of years ago, before humans had begun engaging in agriculture in the area. The research team, exploring sites located in the Ivory Coast’s Taï National Park, found stone “hammers” that were 4,300 years old and that had all the hallmarks of chimpanzee tools, rather than human ones. Science 2.01 described the tool findings as follows:

The stone hammers that the team discovered, essentially irregularly shaped rocks about the size of cantaloupes – with distinctive patterns of wear – were used to crack the shells of nuts. The research demonstrates conclusively that the artifacts couldn’t have been the result of natural erosion or used by humans. The stones are too large for humans to use easily and they also have the starch residue from several nuts known to be staples in the chimpanzee diet, but not the human diet.

The research team elaborated further in the paper it published in the Proceedings of the National Academy of Sciences2:

This discovery speaks of true prehistoric great ape behavior that predates the onset of agriculture in this part of Africa. The chimpanzee assemblages are contemporaneous with the local Later Stone Age; thus, they represent a parallel “Chimpanzee Stone Age”….

The systematic archaeological study of prehistoric chimpanzee cultures suggests that the “Chimpanzee Stone Age” started at least 4,300 years ago, that nut-cracking behavior in the Taï forest has been transmitted over the course of >200 generations, and that chimpanzee material culture has a long prehistory whose deep roots are only beginning to be uncovered. These findings substantiate the contribution of rainforest archaeology to human evolutionary studies in areas other than the classical savanna-woodlands of East and Southern Africa and add support to fossil discoveries from these other regions indicative of an ancient chimpanzee past.

I love it: the Chimpanzee Stone Age! Also, it’s amazing that this tool use tradition has been passed down over 200 generations, and is still in use today.  Here’s a nice BBC video clip that shows today’s generation of chimps using the same sort of tools to expertly crack open nuts.

Archeology3, the official publication of the Archeological Institute of America, haled Mercader’s research as one of the “Top 10 Discoveries” of 2007, noting that:

The discovery shows that stone tool use is not a behavior that chimpanzees learned recently by watching the farmers who live in the area, as some skeptics believe. Mercader thinks that humans and chimpanzees may have inherited stone tool use from an ancestral species of ape that lived as long as 14 million years ago.

At this point, Mercader’s views on the origins of tool use are still open to debate and further research. The fact, though, that there can even be such a discussion about tool use, a capability once thought to so uniquely identify the human species, illuminates how much thinking we have had to do recently about the common characteristics we share with other animals. Interesting stuff.

We’ll keep you posted as the story unfolds, and let you know as soon as they discover the first prehistoric chimpanzee satellite TV dishes and computer operating systems.

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1Science 2.0, “Hammer Using Chimps Make Us Wonder Where They Learned It,” February 13, 2007.

2Mercader, J., Barton, H., Gillespie, J., Harris, J., Kuhn, S., Tyler, R., & Boesch, C. (2007). 4,300-Year-old chimpanzee sites and the origins of percussive stone technology Proceedings of the National Academy of Sciences, 104 (9), 3043-3048 DOI: 10.1073/pnas.0607909104.

3Archeology, “Ancient Chimpanzee Tool Use,” Volume 61, Number 1, January/February 2008.

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