38.5  Wednesday, Jan. 5  More than meets the nose: rapid adaptation to social complexity in laboratory-reared wild mice may be mediated by epigenetic inheritance. NELSON, A.C.*; POTTS, W.K.; University of Utah; University of Utah adam.nelson@utah.edu

Mice in large populations have a complex social structure and large variance in mating success; as a result, social and sexual selection are predicted to have strong effects on trait evolution. Conversely, mice undergoing laboratory adaptation experience relatively low population density and isolation from social and sexual selection, and are expected to down-regulate or eliminate traits used in social competition. We are conducting a selection experiment to assess the impact of returning wild-derived, laboratory-adapted house mice to natural social conditions. Nonselected mice breed in cages under enforced monogamy, and Selected mice breed in semi-natural populations of 30 individuals. Effective population size is held constant and inbreeding is minimized. All offspring are born in cages to facilitate comparisons between treatments. Data from these comparisons at successive generations show that Selected males have increased mating success (F2), increased attractiveness to females in odor- and mate-choice experiments (F3), and increased expression of major urinary protein (MUP), a primary pheromone in urinary scent marks (F4). MUP expression is potentially very costly to males (wild mice excrete roughly 30mg/ml in urine). Our data suggest that up-regulation of MUPs is beneficial in a socially competitive environment. A genetic mechanism that could account for this rapid, heritable effect is suggested from previous studies showing that MUPs undergo transgerational epigenetic inheritance. Thus, Selected parents might “prime” their offspring to express more MUPs by demethylating MUP gametic DNA. Consistent with this hypothesis, we demonstrated reduced DNA methyation in a MUP promoter in Selected males. If confirmed, this would represent an environmentally-induced adaptation caused by a transgenerational, epigenetic modification in vertebrates.