Sperm Competitive Ability and Genetic Relatedness in Drosophila Melanogaster: Similarity Breeds Contempt

Abstract

Offspring of close relatives often suffer severe fitness consequences. Previous studies have demonstrated that females, when given a choice, will choose to avoid mating with closely related males. But where opportunities for mate choice are limited or kin recognition is absent, precopulatory mechanisms may not work. In this case, either sex could reduce the risks of inbreeding through mechanisms that occur during or after copulation. During mating, males or females could commit fewer gametes when mating with a close relative. After mating, females could offset the effects of mating with a closely related male through cryptic choice. Few prior studies of sperm competition have examined the effect of genetic similarity, however, and what studies do exist have yielded equivocal results. In an effort to resolve this issue, we measured the outcome of sperm competition when female Drosophila melanogaster were mated to males of four different degrees of genetic relatedness and then to a standardized competitor. We provide the strongest evidence to date that sperm competitive ability is negatively correlated with relatedness, even after controlling for inbreeding depression.

Sex–specific, counteracting responses to inbreeding in a bird

“…For example, early embryo mortality may reduce the reproductive success of genetically related partners (Birkhead et al 2004). Therefore, the strategies through which each sex influences inbreeding remain poorly understood (Mack et al 2002;Tregenza & Wedell 2002;Bretman et al 2004). Red junglefowl (Gallus gallus) live in small, sexually promiscuous populations where reproductive skew, limited dispersal of both sexes (Collias & Collias 1996) and male sexual coercion create a potential for inbreeding: around 4% of the copulations observed in freeranging, unconstrained groups of red junglefowl occurred between brothers and sisters, and also between mothers and sons (n ¼ 135; Collias & Collias 1996).…”

Kin recognition inDrosophila: the importance of ecology and gut microbiota

“…This is also supported by the level of polyandry exhibited by this species, with females remating every3-5 days (Markow, 1996(Markow, , 2002. Finally, this suggests that there could be a conflict of interest between investing in environmentally similar mates while limiting the investment in related individuals (Mack et al, 2002). Preference for environmentally similar mates accounts for the recent findings that gut bacteria specificity can drive assortative mating, and potentially divergence between populations (reviewed in Brucker and Bordenstein, 2012), and this appears to be the case in D. melanogaster (Sharon et al, 2010(Sharon et al, , 2011.…”

“…Adults expressed a strong homogametic preference in mates presenting similarities in their odours, and gut bacteria were directly implicated in the recognition process. In D. melanogaster, various studies have attempted to test its ability to both recognise kin and avoid inbreeding (Spiess, 1987;Mack et al, 2002;Robinson et al, 2009Robinson et al, , 2012Tan et al, 2012), but controversies remain. It is clear that mating with related individuals leads to inbreeding costs, but uncertainty remains on the costs/benefits associated with mating with individuals of varying degrees of relatedness.…”

Cryptic female preference for genetically unrelated males is mediated by ovarian fluid in the guppy

“…It has been suggested that female multiple mating (polyandry) may have evolved as an inbreeding avoidance strategy mediated by post-copulatory mechanisms such as sperm-egg or sperm-female environment interactions [3][4][5], which could bias paternity towards unrelated or genetically compatible mates and hence reduce the costs of inbreeding. While growing evidence suggests that the genetic relatedness (or genetic similarity) between mating partners is associated with competitive fertilization success [6][7][8][9][10][11][12][13][14]although not always in the predicted direction (i.e. fertilization success biased in favour of males that are more genetically similar to the female [15][16][17][18])-most of these studies cannot exclude the influence of pre-copulatory mate choice or behavioural control of post-copulatory processes, which could bias fertilization success towards unrelated mates.…”