Scientific Method / Science & Exploration

Why be social?

A paper in PLOS genetics suggests that a species is more likely to be social …

A recent paper in PLOS Genetics struck me as having a great combination of interesting technique, intriguing conclusion, and a volcanic explosion. The question the researchers were interested in was how social behavior, in terms of group living and sharing of resources, arises. After all, most social species are members of a larger group that includes solitary species as well—for example, the wasps include many social and non-social species. Why have some gone social?

The authors work with the species Ctenomys sociabilis, known among its fans as the colonial tuco-tuco, and the only social member of the tuco-tuco family of rodents from South America. DNA sequencing of small current population suggests that it has undergone a recent population bottleneck, or severe population shrinkage. The authors reconstructed the dynamics of that bottleneck by using what, in my opinion, is an underutilized resource: owl vomit. Owls compress everything indigestible from a meal into a pellet, which they vomit back out. These pellets preserve well, and DNA can be extracted from them, allowing the owl's meals to be reconstructed.

These reconstructions allowed the researchers to track tuco-tuco populations over the last 10,000 years, as the population of the colonial species was slowly reduced by competition with a larger species. Suddenly, 3,000 years ago, over 99 percent of the colonial species vanished at a time of major Andean volcanic activity, leaving only about 300 females behind (with an undetermined number of males). The population's bounced back since, but the authors note that that may have something to do with its social nature. They note that small populations are proposed to force socialization upon a species for two reasons. Since all individuals are likely to be related, the typical level of aggression within the species should be reduced. Meanwhile, if the population's small, living in close proximity greatly increases the chances of finding a mate. As a result, this new data is consistent with a model where the population crash and social nature of these rodents are related.

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