Identity evolves

Everyone is special.” The paradoxical refrain of baby boomer parents to their millenial offspring is true, so long as you’re a rodent living in a large, stable group of good communicators.

I recently wrote about the phenomenon of identity signals in animals, where variable colours and patchy-looking patterns can provide signatures of individuality, much like the human face. These are not limited to the visual domain. Think of how easily you can recognize a person’s voice – even someone you don’t know very well – from just a few lines of speech, like when a celebrity turns up in an animated movie.

But I didn’t have a chance to cover the latest news on this topic. In some very plain looking rodents, we now have evidence that individuality evolves1. Some of the plainest looking critters, like the Belding’s ground squirrel shown below, have the most distinctive snarfs and grumbles – and it all has to do with the number of group-mates they typically interact with.

Belding's ground squirrel pups

Two Belding’s ground squirrel pups peek out of a burrow. Photo by Alan Vernon from Wikimedia Commons.

The new results came out this month in the high profile journal Current Biology. Previously, researchers had looked for the evolution of individuality in a handful of bird and bat species. The prior studies examined distinctiveness in the begging calls offspring make to their parents, contrasting pairs of closely-related species that vary in the number of offspring in shared “crèche” or communal nest sites2,3. But nobody had tackled the evolution of individuality in a broad context.

Until Kim Pollard, that is. Pollard, a recent PhD graduate from UCLA, and her supervisor Dan Blumstein decided to look at this question in the social marmots. You might remember Blumstein from another recent post; his interests range from mammal conservation and environmental education to the bioacoustics of movie soundtracks.

For Kim Pollard’s study of identity signalling, marmots were an ideal choice. Marmota is a large genus of 14 different species in the squirrel family, all social, and all with their own alarm calls that they use to warn neighbours and family members about nearby predators. Species like the yellow-bellied marmot and Richardson’s ground squirrel also have the ability to recognize each other based on the unique sound of these calls4,5.

Crucially for Pollard and Blumstein, social group size also varies in the genus, ranging from about 5 to 15 individuals per clan or family group. This allowed the authors to test the hypothesis that group size has been an important factor in the evolution of distinctiveness, since, as they put it, “The bigger the crowd, the more it takes to stand out.”

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How to raise a science major

The newspapers have been abuzz lately about a controversial book: Battle Hymn of the Tiger Mother, by Amy Chua, is a memoir on the rewards and perils of stereotypically strict Asian-American parenting. This week I asked students in my 4th-year biology class to tell me about their earliest memory of being fascinated with something biological, information that could be useful for parents hoping to form their children into university science majors.

And so, some lessons learned:

1. Worms work. Let your kids get close to the ground, outside. At least two students listed earthworms appearing after the rain as their most important early memory. A large portion of the class described similar encounters with tadpoles, snails, caterpillars, ants, spiders and their webs, and other minutiae found on the lawn. Larger examples of charismatic megafauna barely got a mention. Perhaps opportunity plays a role. For instance, one student remembers being particularly enamoured with deer in the backyard.

2. Pain. A wise teacher once told me that “learning hurts”. The converse might also be true: harmful organisms can be educational. An encounter with razor-sharp zebra mussels was particularly salient for one student. Another recounted a family vacation in the New Mexico desert, where a first-hand experience with cacti led to an early lesson in adaptation.

Well-armed cacti

Hidden Valley, Joshua Tree National Park, California.

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Shark Lady and the convict fish

Who’s weirder: the shark lady or the convict fish? It may seem a strange way to get this blog started again, but it turns out to be quite fitting this time of year when we find ourselves cooped up with relatives of all stripes.

My first encounter with the convict fish was this summer. It was one of those enigmatic creatures that blew all of the biologists in the room away, at one of our regular gatherings to watch the BBC’s Life series. Over images of thousands of tiny fish emerging from a burrow on the sea floor, David Attenborough explained the mystery. This was a swarm of siblings, all offspring of the same pair of adults who spend their entire lives in a tunnel. Each day, the young convict fish head out to forage on plankton around the reef, returning home at night. Biologists have no idea how the parents feed, though, because no one has ever seen the adults leave their burrows in the wild. Attenborough left us hanging, suggesting with intrigue that the young fish might have something to do with it.

Could the convict fish be living off of its own offspring? A bit grim, yes, but also a fascinating biological paradox – perfect for this blog on the stranger twists of evolution, I thought. In nature, it might not even be that unusual. The males of plenty of fish species feed on eggs from their own nests. By taking in extra resources, this might allow them to invest more in future nesting attempts1. In fish with especially large broods, once filial cannibalism gets started it could get an evolutionary boost from the fact that many of the offspring in dense egg masses will not survive anyway2.

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