Low genetic variation reduces cross-compatibility and offspring fitness in populations of a narrow endemic plant with a self-incompatibility system

Genetic variation was shown earlier to bereduced in smaller populations of the narrowendemic putatively self-incompatible Cochlearia bavarica. To test whether thisnegatively affects plant fitness by reducedavailability of compatible mates and byinbreeding depression, we studied effects ofpopulation size and pollination treatments oncross-compatibility and offspring fitness in 16isolated populations of this plant. After openpollination, compatibility of crosses (i.e.,whether at least one fruit developed per markedflower), fruit set of compatible crosses, andcumulative fitness (number of plants permaternal ovule) after 14 months in a commongarden were lower for plants from smallerpopulations. Throughout the study, cumulativefitness was lower after hand pollination withpollen of one donor than after open pollination(finally 73.4% lower), suggesting that severalpollen donors or single pollen donors of higherquality are involved in open pollination.Moreover, cumulative fitness was lower afterhand selfing than after hand outcrossing(finally 69.4% lower), indicating bothinbreeding depression and reduced compatibilityafter selfing. High self-compatibility(40.6%), dry stigmas, and differences in thecompatibility of 11 of 33 experimentalreciprocal crosses between plant pairsconfirmed that C. bavarica has asporophytic self-incompatibility system, as iscommon in the Brassicaceae. Our studydemonstrates, that plants in smallerpopulations of species with a sporophyticself-incompatibility system can experiencetwofold fitness reductions associated withreduced genetic variability, i.e., twofoldgenetic Allee effects: via reducedcross-compatibility and via reduced offspringfitness.     

Factors influencing paternity success in Antechinus agilis: last‐male sperm precedence,timing of mating and genetic compatibility

We describe the patterns of paternity success from laboratory mating experiments conducted in Antechinus agilis, a small size dimorphic carnivorous marsupial (males are larger than females). A previous study found last‐male sperm precedence in this species, but they were unable to sample complete litters, and did not take male size and relatedness into account. We tested whether last‐male sperm precedence regardless of male size still holds for complete litters. We explored the relationship between male mating order, male size, timing of mating and relatedness on paternity success. Females were mated with two males of different size with either the large or the small male first, with 1 day rest between the matings. Matings continued for 6 h. In these controlled conditions male size did not have a strong effect on paternity success, but mating order did. Males mating second sired 69.5% of the offspring. Within first mated males, males that mated closer to ovulation sired more offspring. To a lesser degree, variation appeared also to be caused by differences in genetic compatibility of the female and the male, where high levels of allele‐sharing resulted in lower paternity success.     

Social structure influences extra-pair paternity in socially monogamous mammals

Using the genetic estimates of paternity available for 22 species of socially monogamous mammals, we investigated the impact of the social structure and of the type of pair bonding on the interspecific variations of extra-pair paternity rates. To this purpose, we classified species in three categories of social structure—solitary, pair or family-living species—and in two categories of pair bonding—intermittent or continuous. We show that interspecific variations of extra-pair paternity rates are better explained by the social structure than by the type of pair bonding. Species with intermittent and continuous pair bonding present similar rates of extra-pair paternity, while solitary and family-living species present higher extra-pair paternity rates than pair-living species. This can be explained by both higher male–male competition and higher female mate choice opportunities in solitary and family-living species than in pair-living species.     

When does female multiple mating evolve to adjust inbreeding? Effects of inbreeding depression,direct costs,mating constraints,and polyandry as a threshold trait

Polyandry is often hypothesized to evolve to allow females to adjust the degree to which they inbreed. Multiple factors might affect such evolution, including inbreeding depression, direct costs, constraints on male availability, and the nature of polyandry as a threshold trait. Complex models are required to evaluate when evolution of polyandry to adjust inbreeding is predicted to arise. We used a genetically explicit individual‐based model to track the joint evolution of inbreeding strategy and polyandry defined as a polygenic threshold trait. Evolution of polyandry to avoid inbreeding only occurred given strong inbreeding depression, low direct costs, and severe restrictions on initial versus additional male availability. Evolution of polyandry to prefer inbreeding only occurred given zero inbreeding depression and direct costs, and given similarly severe restrictions on male availability. However, due to its threshold nature, phenotypic polyandry was frequently expressed even when strongly selected against and hence maladaptive. Further, the degree to which females adjusted inbreeding through polyandry was typically very small, and often reflected constraints on male availability rather than adaptive reproductive strategy. Evolution of polyandry solely to adjust inbreeding might consequently be highly restricted in nature, and such evolution cannot necessarily be directly inferred from observed magnitudes of inbreeding adjustment.     

An Analysis of Single Clutch Paternity in the Burrower Bug Sehirus cinctus Using Microsatellites

Recent studies of the burrower bug, Sehirus cinctus, have examined the genetic basis of parental care. An understanding of the burrower bug mating system, and the subsequent pattern of offspring relatedness that this system generates, is critical to further interpret genetic data. To this end, we developed three consistently amplifiable highly polymorphic microsatellite loci and used them to determine genotypic patterns at the level of both the population and the single clutch. We found that all clutches were sired by single males. Further, we find no evidence for inbreeding. We hypothesize that single paternity within a clutch may play an important role in reducing the potential for sibling rivalry, by increasing the relatedness among clutchmates.     

Genetic analysis reveals promiscuity among female cheetahs

Cheetahs (Acinonyx jubatus) have a combination of ranging patterns and social system that is unique in mammals, whereby male coalitions occupy small territories less than 10% of the home range of solitary females. This study uses non-invasive genetic sampling of a long-term study population of cheetah in the Serengeti National Park in Tanzania to infer the mating system. Individual cheetah genotypes at up to 13 microsatellite loci were obtained from 171 faecal samples. A statistical method was adapted to partition the cubs within each litter (n=47) into full-sibling clusters and to infer the father of each cluster using these loci. Our data showed a high rate of multiple paternity in the population; 43% of litters with more than one cub were fathered by more than one male. The results also demonstrated that female fidelity was low, and provided some evidence that females chose to mate with unrelated males within an oestrus cycle. The low rate of paternity assignments indicated that males living outside the study area contributed substantially to the reproduction of the cheetah population.     

Advances in our understanding of mammalian sex-biased dispersal

Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns.     

The frequency of multiple paternity suggests that sperm competition is common in house mice (Mus domesticus)

Sexual selection is an important force driving the evolution of morphological and genetic traits. To determine the importance of male-male, postcopulatory sexual selection in natural populations of house mice, we estimated the frequency of multiple paternity, defined as the frequency with which a pregnant female carried a litter fertilized by more than one male. By genotyping eight microsatellite markers from 1095 mice, we found evidence of multiple paternity from 33 of 143. Evidence for multiple paternity was especially strong for 29 of these litters. Multiple paternity was significantly more common in higher-density vs. lower-density populations. Any estimate of multiple paternity will be an underestimate of the frequency of multiple mating, defined as the frequency with which a female mates with more than a single male during a single oestrus cycle. We used computer simulations to estimate the frequency of multiple mating, incorporating observed reductions in heterozygosity and levels of allele sharing among mother and father. These simulations indicated that multiple mating is common, occurring in at least 20% of all oestrus cycles. The exact estimate depends on the competitive skew among males, a parameter for which we currently have no data from natural populations. This study suggests that sperm competition is an important aspect of postcopulatory sexual selection in house mice.