Bigger testes increase paternity in a simultaneous hermaphrodite, independently of the sperm competition level

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Inbreeding depression of mating behavior and its reproductive consequences in a freshwater snail

Inbreeding is expected to impair male and female reproductive performance, but little is known on how inbreeding depression varies between sexes and different levels of competition. We studied inbreeding depression in mating behavior and its reproductive consequences in a hermaphroditic freshwater snail and demonstrate that inbreeding depresses mating success in both sex functions. However, the magnitude of inbreeding depression does not differ between sex functions and is not affected by the opportunity for mate choice and male-male competition.Theoretical work predicts that the magnitude of inbreeding depression is particularly high in traits that are closely related to fitness. Despite the extensive work on inbreeding depression of male and female reproductive performance, relatively little is known on how inbreeding impairs male and female mating behavior. We studied inbreeding depression of male and female mating behavior in the simultaneously hermaphroditic freshwater snail Physa acuta to test 1) whether there is inbreeding depression of mating behavior, 2) whether the potential of mate competition and mate choice has an effect on the strength of inbreeding depression, 3) whether the magnitude of inbreeding depression differs between both sex functions, and 4) how inbreeding depression of mating behavior translates into inbreeding depression of reproductive success. For this, we compared the mating behavior between selfed (inbred) and outcrossed (outbred) focal snails in a series of mating trials, in which we manipulated experimentally the potential of mate competition and mate choice. Our results provide evidence for moderate inbreeding depression of the number of copulatory encounters, the number of copulations, and the total time spent mating in both sex functions. The magnitude of inbreeding depression did not differ between the levels of competition and between both sex functions. Finally, our results suggest that inbreeding depression of mating behavior only explains a small fraction of the observed inbreeding depression of reproductive success. We discuss the implications of these findings with respect to precopulatory sexual selection and sex-specific inbreeding depression

No evidence for strong cytonuclear conflict over sex allocation in a simultaneously hermaphroditic flatworm

Abstract Background Cytoplasmic sex allocation distorters, which arise from cytonuclear conflict over the optimal investment into male versus female reproductive function, are some of the best-researched examples for genomic conflict. Among hermaphrodites, many such distorters have been found in plants, while, to our knowledge, none have been clearly documented in animals. Methods Here we provide a quantitative test for cytonuclear conflict over sex allocation in the simultaneously hermaphroditic flatworm Macrostomum lignano. We used a quantitative genetic breeding design, employing pair-wise crosses of 2 × 15 independent inbred lines, to partition the phenotypic variance in several traits (including sex allocation) into its nuclear and cytoplasmic components. Results Although the nuclear genetic background had a significant effect on all traits analyzed, we found significant cytoplasmic genetic variation only for ovary size, there explaining just 4.1% of the variance. A subsequent statistical power analysis showed that the experimental design had considerable power to detect cytonuclear interactions. Conclusion We conclude that there were no strong effects of cytonuclear conflict in the studied populations, possibly because the usually compact mitochondrial genomes in animals have a lower evolvability than the large mitochondrial genomes in plants or because the sampled populations currently do not harbor variation at putative distorter and/or the restorer loci