OPHIR, A.G.*; PHELPS, S.M.; WOLFF, J.O.; Univ. of Florida; Univ. of Florida; Univ. of Memphis: Selection for social but not genetic monogamy in the prairie vole

Perhaps best known for work relating to the study of mechanisms of pair bond formation, the prairie vole (Microtus ochrogaster) has emerged as a �poster child� of monogamous behavior in both popular press and scientific report. The extent to which these mechanisms have been studied, paired with the detailed description of their natural history, positions prairie voles as prime models for investigating how mechanisms underlying monogamous behavior operate under natural conditions. We ran 8 replicates in semi-natural enclosures, using 6 male and 6 female prairie voles per enclosure. We radiotracked subjects to assess association, and assigned paternity to pregnant females using 4 microsatellite loci. We characterized the mating system by comparing in-pair (IPF) and extra-pair (EPF) fertilizations. We found that subjects were neither genetically monogamous nor fully promiscuous (N�s=27; both p�s<.05), and therefore conclude that prairie voles are socially monogamous. We investigated the strength of selection on social and genetic monogamy by comparing the number of offspring produced by paired or single animals and by IPF�s or EPF�s. Paired males and females had higher fitness than single subjects (N_male=46, N_female=39; both p�s<.02), however subjects that engaged in IPF�s or EPF�s had comparable fitness success (N_male=24, N_female=26; both p�s>.10). These results support the hypothesis that selection favors social but not genetic monogamy. Because our experimental design focused on fitness effects of fertilization rates, but not parental care or pup defense, we suggest a primary value of paring emerges from mate-guarding. Prairie voles, which have become a popular species for studies of monogamy and pair bond formation, may serve as a good model for the evolution of mechanisms of �love� but not fidelity.