Evolution, Genetics and Ecology of Burrowing Behavior in Deer Mice (Genus Peromyscus)

Abstract

Behavioral differences among closely related species can result from adaptation via natural selection, and this is especially true of innately expressed behavior that shows evidence of complex design or function. A major goal of biologists is to understand how and why complex, adaptive behavior evolves. To this end, I investigated the evolution, ecology and genetics of innate burrowing differences in deer mice (genus Peromyscus). First, I show that several species of deer mice recapitulate their natural burrowing habits under laboratory conditions. When I compare these behaviors in a phylogenetic context, I find that burrowing is species-specific and the complex burrows of the oldfield mouse (P. polionotus) likely arose from simple behavior similar to that expressed by two closely related species. Second, I examine the influences of soil composition and genetics on the burrowing behavior of oldfield mice. Although burrow length variation is relatively constant in nature, burrow depth is negatively associated with the silt content of soils. To determine the genetic architecture of complex burrowing, I crossed the oldfield mouse and its sister species, the deer mouse (P. maniculatus), which builds a relatively simple burrow. My results suggest that complexity results from the integration of several component behaviors: the lengthening of entrance tunnels and the construction of an escape tunnel. Additionally, complex burrowing segregates as a dominant trait and I identify four quantitative trait loci that influence burrow variation--three affect tunnel length and a single locus influences escape tunnel construction. Last, I test whether Peromyscus burrow socially. Specifically, I measure burrows constructed by both pairs of mice and individuals across three Peromyscus species with different social systems. Only in the monogamous species (P. polionotus), which is also the only species that builds complex burrows, do pairs of mice coordinate their behavior to build longer burrows. This effect of pairing increases burrow length in same-sex pairs of unrelated individuals, but it is most pronounced in male-female pairs, suggesting that oldfield mice invest most heavily in burrows constructed for the purpose of reproduction.