03 June 2010

Adoption among red squirrels

A press release at Science Daily describes cases of adoption in red squirrels.

The study of adoption across a range of animal species is a crucial aspect of the study of the evolution of altruism. Most (but not all) cases of adoption take place among closely related members of highly social species, like lions or chimps. The evolutionary explanation of this behavior ultimately derives from the work of W. D. Hamilton, who showed that altruistic behavior, such as adoption, could increase the altruistic individual's "fitness" (in an evolutionary sense) if the beneficiary of the altruistic behavior was sufficiently closely related to the altruist—that is, if they shared a sufficient number of genes.  This relationship is described by "Hamilton's rule," the simple but profoundly influential inequality

c < rb

where c is the fitness (reproductive) cost to the altruist (here the adoptive parent), r is the degree of genetic relatedness between the altruist and the beneficiary (for example, for full siblings, r = 0.5, for half siblings r = 0.25), and b is the fitness benefit to the beneficiary.

Red squirrels, unlike lions and chimps, are highly solitary. Adoption of related orphan pups among red squirrels is rare, but what's notable is that is exists at all.

The article is:

Jamieson C. Gorrell, Andrew G. McAdam, David W. Coltman, Murray M. Humphries, Stan Boutin. "Adopting kin enhances inclusive fitness in asocial red squirrels." Nature Communications, 2010. http://dx.doi.org/10.1038/ncomms1022

At least a the moment, the article can be downloaded for free.
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