Abstract

Females often show multi-male mating (MMM), but the adaptive functions are unclear. We tested whether female house mice (Mus musculus musculus) show MMM when they can choose their mates without male coercion. We released 32 females into separate enclosures where they could choose to mate with two neighboring males that were restricted to their own territories. We also tested whether females increase MMM when the available males appeared unable to exclude intruders from their territories. To manipulate territorial intrusion, we introduced scent-marked tiles from the neighboring males into males' territories, or we rearranged tiles within males' own territories as a control. Each female was tested in treatment and control conditions and we conducted paternity analyses on the 57 litters produced. We found that 46 % of litters were multiply sired, indicating that multiple paternity is common when females can choose their mates. Intrusion did not increase multiple paternity, though multiple paternity was significantly greater in the first trial when the males were virgins compared to the second trial. Since virgin male mice are highly infanticidal, this finding is consistent with the infanticide avoidance hypothesis. We also found that multiple paternity was higher when competing males showed small differences in their amount of scent marking, suggesting that females reduce MMM when they can detect differences in males' quality. Finally, multiple paternity was associated with increased litter size but only in the intrusion treatment, which suggests that the effect of multiple paternity on offspring number is dependent on male–male interactions.

Highlights

  • The adaptive significance of multi-male mating (MMM) or polyandry is unclear and controversial (Jennions and Petrie 2000; Hosken and Stockley 2003; Simmons 2005; Gowaty 2012)

  • To test the effect of intrusion treatment and male scent marking on the rate of multiple-sired litters, we ran a generalized linear mixed effects model (GLMM) with a binomial error distribution and a logit link function

  • Paternity was significantly predicted by the difference in the two males' scent marking: we found that multiple paternity was higher when males showed smaller differences in their marking whereas single paternity was higher when the differences in males marking increased (GLMM, z =−2.472, β =−0.373, SE =0.151, N =44, P=0.013, Fig. 3)

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Summary

Introduction

The adaptive significance of multi-male mating (MMM) or polyandry is unclear and controversial (Jennions and Petrie 2000; Hosken and Stockley 2003; Simmons 2005; Gowaty 2012). Several nonmutually exclusive hypotheses have been proposed to explain how females can potentially gain fitness benefits from polyandry (Jennions and Petrie 2000; Simmons 2005). MMM could provide females with direct benefits, such as parental care, nuptial gifts, or other resources from males (Arnqvist and Nilsson 2000; Hosken and Stockley 2003). In nonresource-based mating systems, polyandry might function to increase females' fertility (fertility assurance hypothesis) (Hoogland 1998) or to obtain a variety of indirect, genetic benefits for offspring (Simmons 2005), such as eliciting sperm competition to gain “good genes” (Kempenaers et al 1992), increasing genetic compatibility

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