Sex-Specific Routes to Independent Breeding in a Polygynous Cooperative Breeder

How can individuals obtain a breeding position and what are the benefits associated with philopatry compared to dispersal? These questions are particularly intriguing in polygamous cooperative breeders, where dispersal strategies reflect major life history decisions, and routes to independent breeding may utterly differ between the sexes. We scrutinized sex-dependent life-history routes by investigating dispersal patterns, growth rates and mortality in a wild colony of the cooperatively breeding cichlid Neolamprologus savoryi. Our data reveal that female helpers typically obtain dominant breeding positions immediately after reaching sexual maturity, which is associated with strongly reduced growth. In contrast, males obtain breeder status only at twice the age of females. After reaching sexual maturity, males follow one of two strategies: (i) they may retain their subordinate status within the harem of a dominant male, which may provide protection against predators but involves costs by helping in territory maintenance, defence and brood care; or (ii) they may disperse and adopt a solitary status, which diminishes survival chances and apparently reflects a best-of-a-bad-job strategy, as there are no obvious compensating future fitness benefits associated with this pathway. Our study illustrates that sex-dependent life history strategies strongly relate to specific social structures and mating patterns, with important implications for growth rates, the age at which breeding status is obtained, and survival.

Phenotypic Signals of Sexual Selection and Fast Life History Dynamics for the Long-Term but Not Short-Term Mating

Mating patterns are crucial for understanding selection regimes in current populations and highly implicative for sexual selection and life history theory. However, empirical data on the relations between mating and reproductive outcomes in contemporary humans are lacking. In the present research we examined the sexual selection on mating (with an emphasis on Bateman's third parameter – the association between mating and reproductive success) and life history dynamics of mating by examining the relations between mating patterns and a comprehensive set of variables which determine human reproductive ecology. We conducted two studies (Study 1: N = 398, Study 2: N = 996, the sample was representative for participants’ sex, age, region, and settlement size). The findings from these studies were mutually congruent and complementary. In general, the data suggested that short-term mating was unrelated or even negatively related to reproductive success. Conversely, long-term mating was positively associated with reproductive success (number of children in Study 1; number of children and grandchildren in Study 2) and there were indices that the beneficial role of long-term mating is more pronounced in males, which is in accordance with Bateman's third principle. Observed age of first reproduction mediated the link between long-term mating and number of children but only in male participants (Study 2). There were no clear indications of the position of the mating patterns in human life history trajectories; however, the obtained data suggested that long-term mating has some characteristics of fast life history dynamics. Findings are implicative for sexual selection and life history theory in humans.

Size-assortative mating in explosive breeders: a case study of adaptive male mate choice in anurans

Exploration of size-assortative mating (SAM) in animals has led to a near consensus that it arises through constraints in choice, such as preference for large females combined with a large male advantage during intrasexual competition. Although such ‘apparent’ SAM is well explored, whether SAM arises because of specific preferences for size-matched mates has been less thoroughly considered. We tested for ‘preference-based’ SAM in an explosively breeding frog (Rana sylvatica), quantifying how male and female sizes affected fertilization and if males preferred size-matched females. We found that size mismatch severely reduced fertilization. Furthermore, males preferred size-matched, not larger, females in mate choice trials. Because males that mated with much larger females fertilized fewer eggs overall than they would have with size-matched females, male preference for size-matched females may be adaptive. Our results expand understanding of the mechanisms underlying SAM, suggesting that multiple mechanisms may simultaneously cause size-assortative mating patterns to emerge.

Reproductive ecology of short and long-term mating: implications for sexual selection and life history theory

Mating patterns are crucial for understanding selection regimes in current populations and highly implicative for sexual selection and life history theory. However, empirical data on the relations between mating and fitness-related outcomes in contemporary humans are lacking. In the present research we examined the sexual selection on mating (with an emphasis on Bateman’s third parameter – the association between mating and reproductive success) and life history dynamics of mating by examining the relations between mating patterns and a comprehensive set of variables which determine human reproductive ecology. We conducted two studies (Study 1: N=398, Mage=31.03; Study 2: N=996, Mage=40.81, the sample was representative for participants’ sex, age, region, and settlement size). The findings from these studies were mutually congruent and complementary. In general, the data suggested that short-term mating was unrelated or even negatively related to reproductive success. Conversely, long-term mating was positively associated with reproductive success and there were indices that the beneficial role of long-term mating is more pronounced in males, which is in accordance with Bateman’s third principle. Observed age of first reproduction fully mediated the link between long-term mating and number of children but only in male participants. There were no clear indications of the position of the mating patterns in human life history trajectories; however, the obtained data suggested that long-term mating has some characteristics of fast life history dynamics. Findings are implicative for sexual selection and life history theory in humans.

An investigation of MHC-dependent sexual selection in a free-living population of sheep

MHC genes are one of the most polymorphic gene clusters in vertebrates and play an essential role in adaptive immunity. There is evidence that sexual selection also plays a role in maintaining MHC diversity, but the specific mechanisms are controversial. In this study, we investigate evidence for non-random MHC-dependent mating patterns in a free-living population of Soay sheep. Using a large number of sheep diplotyped at the MHC class IIa region and genome-wide SNPs, together with field observations of consorts, we found sexual selection against one of eight haplotypes, C, in males at the pre-copulatory stage and sexual selection on female MHC heterozygosity acting in opposition directions at the pre- and post-copulatory stages. We also found disassortative mating at the post-copulatory stage, along with strong evidence of inbreeding avoidance at both stages. However, results from generalized linear mixed models suggest that the pattern of MHC-dependent disassortative mating could be a by-product of inbreeding avoidance. These results suggest that there is selection on the MHC at the pre- and post-copulatory stages, but that apparent disassortative mating with respect to the MHC may be driven by inbreeding avoidance.