Abstract
Multiple mating is common in many species, but it is unclear whether multiple paternity enhances offspring genetic diversity or fitness. We conducted a survey on wild house mice (Mus musculus musculus), and we found that in 73 pregnant females, 29% of litters had multiple sires, which is remarkably similar to the 23–26% found in feral populations of Mus musculus domesticus in the USA and Australia, respectively. The question is: How has selection maintained multiple mating in these subspecies since the evolutionary divergence, ca. 2800–6000 years ago? We found no evidence that multiple paternity enhanced females’ litter size, contrary to the fertility assurance or genetic benefits hypotheses. Multiple paternity was associated with reduced mean and variance in offspring body mass, which suggests that females allocate fewer resources or that there is increased intrauterine conflict in multiple-versus single-sired litters. We found increased allelic diversity (though not heterozygosity) in multiple-sired litters, as predicted by the genetic diversity hypothesis. Finally, we found that the dams’ heterozygosity was correlated with the mean heterozygosity of their offspring in single-and multiple-sired litters, suggesting that outbred, heterozygous females were more likely to avoid inbreeding than inbred, homozygous females. Future studies are needed to examine how increased genetic diversity of litters and smaller mean (and variance) offspring body mass associated with multiple paternity affect offspring fitness.
Highlights
Polyandry or multiple mating is common in diverse animal taxa ranging from insects to mammals (Arnqvist and Nilsson 2000; Wolff and Macdonald 2004), and this behavior has been studied extensively over the past decades, there is still continuous debate over its function
We found no difference in the frequency of multiple paternities between the populations (GLMM: v2 = 0.549, N = 73, P = 0.459) or between seasons (GLMM: v2 = 2.658, N = 73, P = 0.264)
We examined whether multiple paternity was correlated with litter size and weanling body mass, and we found that multiple paternity did not affect litter size (LMM: F1,64 = 2.411, P = 0.125) (Fig. 2A)
Summary
Polyandry or multiple mating is common in diverse animal taxa ranging from insects to mammals (Arnqvist and Nilsson 2000; Wolff and Macdonald 2004), and this behavior has been studied extensively over the past decades, there is still continuous debate over its function. 2000; Rolland et al 2003; Westneat and Stewart 2003; Manser et al 2011), despite a variety of potential costs, including an elevated risk of disease transmission, predation and injuries from potential mating partners (Daly 1978; Magnhagen 1991; Siva-Jothy 2006). In nonresource-based mating systems in which males provide no parental care, explanations of polyandry largely rely on indirect or genetic benefits (Simmons 2005). Females can gain such benefits either through (i) good genes (Kempenaers et al 1992; Keller and Reeve 1995; Yasui 1997), (ii) increased genetic compatibility (Zeh and Zeh 1997),
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