Multiple paternity does not depend on male genetic diversity

Mate genetic similarity affects mating behaviour but not maternal investment in mice

Maternal investment can affect the survival and development of offspring. Here we experimentally investigated in mice, whether females alter implantation rates and pup survival after embryo transfer depending on the genetic similarity with their vasectomised mating partner. We selected the MHC genotype and genetic background of males and paired females either with males that shared the same MHC haplotype and genetic background (CBA/J inbred males, isogenic group), that shared half of the MHC haplotype and genetic background (B6CBAF1 hybrid males, semi-isogenic group), or that had a different MHC haplotype and genetic background (C57BL/6N inbred males, allogenic group). We performed 304 pairings, resulting in 81 vaginal plugs, which confirmed mating. Plug rates were significantly higher in the semi-isogenic group (36.9%) compared to the isogenic group (19.5%), but not the allogenic group (26%). We found no difference in the number of implantation sites, the number of born or surviving pups until weaning, or litter weight or sex ratio between groups. Even though we found a mating bias, we found no difference in maternal investment under laboratory conditions. At least under pathogen-free conditions our study does not provide any evidence for differential maternal investment when females could increase offspring genetic diversity or heterozygosity.

Polyandry blocks gene drive in a wild house mouse population

Gene drives are genetic elements that manipulate Mendelian inheritance ratios in their favour. Understanding the forces that explain drive frequency in natural populations is a long-standing focus of evolutionary research. Recently, the possibility to create artificial drive constructs to modify pest populations has exacerbated our need to understand how drive spreads in natural populations. Here, we study the impact of polyandry on a well-known gene drive, called t haplotype, in an intensively monitored population of wild house mice. First, we show that house mice are highly polyandrous: 47% of 682 litters were sired by more than one male. Second, we find that drive-carrying males are particularly compromised in sperm competition, resulting in reduced reproductive success. As a result, drive frequency decreased during the 4.5 year observation period. Overall, we provide the first direct evidence that the spread of a gene drive is hampered by reproductive behaviour in a natural population.

This study resolves a long-standing mystery of why t haplotypes, an example of selfish genes, have persisted at unexpectedly low frequencies in wild mouse populations. It shows that multiple mating by females, which is more common at higher mouse population densities, decreases the frequency of driving t haplotypes.

Sexual experience has no effect on male mating or reproductive success in house mice

The ability to learn from experience can improve Darwinian fitness, but few studies have tested whether sexual experience enhances reproductive success. We conducted a study with wild-derived house mice (Mus musculus musculus) in which we manipulated male sexual experience and allowed females to choose between (1) a sexually experienced versus a virgin male, (2) two sexually experienced males, or (3) two virgin males (n = 60 females and 120 males). This design allowed us to test whether females are more likely to mate multiply when they encounter more virgin males, which are known to be infanticidal. We recorded females’ preference and mating behaviours, and conducted genetic paternity analyses to determine male reproductive success. We found no evidence that sexual experience influenced male mating or reproductive success, and no evidence that the number of virgin males influenced female multiple mating. Females always copulated with both males and 58% of the litters were multiple-sired. Females’ initial attraction to a male correlated with their social preferences, but neither of these preference behaviours predicted male reproductive success – raising caveats for using mating preferences as surrogates for mate choice. Male reproductive success was predicted by mating order, but unexpectedly, males that copulated first sired fewer offspring.

Does multiple paternity influence offspring disease resistance?

It has been suggested that polyandry allows females to increase offspring genetic diversity and reduce the prevalence and susceptibility of their offspring to infectious diseases. We tested this hypothesis in wild‐derived house mice (Mus musculus) by experimentally infecting the offspring from 15 single‐ and 15 multiple‐sired litters with two different strains of a mouse pathogen (Salmonella Typhimurium) and compared their ability to control infection. We found a high variation in individual infection resistance (measured with pathogen loads) and significant differences among families, suggesting genetic effects on Salmonella resistance, but we found no difference in prevalence or infection resistance between single‐ vs. multiple‐sired litters. We found a significant sex difference in infection resistance, but surprisingly, males were more resistant to infection than females. Also, infection resistance was correlated with weight loss during infection, although only for females, indicating that susceptibility to infection had more harmful health consequences for females than for males. To our knowledge, our findings provide the first evidence for sex‐dependent resistance to Salmonella infection in house mice. Our results do not support the hypothesis that multiple‐sired litters are more likely to survive infection than single‐sired litters; however, as we explain, additional studies are required before ruling out this hypothesis.

No evidence for the effect of MHC on male mating success in the brown bear

Mate choice is thought to contribute to the maintenance of the spectacularly high polymorphism of the Major Histocompatibility Complex (MHC) genes, along with balancing selection from parasites, but the relative contribution of the former mechanism is debated. Here, we investigated the association between male MHC genotype and mating success in the brown bear. We analysed fragments of sequences coding for the peptide-binding region of the highly polymorphic MHC class I and class II DRB genes, while controlling for genome-wide effects using a panel of 18 microsatellite markers. Male mating success did not depend on the number of alleles shared with the female or amino-acid distance between potential mates at either locus. Furthermore, we found no indication of female mating preferences for MHC similarity being contingent on the number of alleles the females carried. Finally, we found no significant association between the number of MHC alleles a male carried and his mating success. Thus, our results provided no support for the role of mate choice in shaping MHC polymorphism in the brown bear.