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Theory and empirical data showed that two processes can boost selection against deleterious mutations, thus facilitating the purging of the mutation load: inbreeding, by exposing recessive deleterious alleles to selection in homozygous form, and sexual selection, by enhancing the relative reproductive success of males with small mutation loads. These processes tend to be mutually exclusive because sexual selection is reduced under mating systems that promote inbreeding, such as self-fertilization in hermaphrodites. We estimated the relative efficiency of inbreeding and sexual selection at purging the genetic load, using 50 generations of experimental evolution, in a hermaphroditic snail ( Physa acuta ). To this end, we generated lines that were exposed to various intensities of inbreeding, sexual selection (on the male function), and nonsexual selection (on the female function). We measured how these regimes affected the mutation load, quantified through the survival of outcrossed and selfed juveniles. We found that juvenile survival strongly decreased in outbred lines with reduced male selection, but not when female selection was relaxed, showing that male-specific sexual selection does purge deleterious mutations. However, in lines exposed to inbreeding, where sexual selection was also relaxed, survival did not decrease, and even increased for self-fertilized juveniles, showing that purging through inbreeding can compensate for the absence of sexual selection. Our results point to the further question of whether a mixed strategy combining the advantages of both mechanisms of genetic purging could be evolutionary stable.

Sex allocation theory predicts that simultaneous hermaphrodites evolve to an evolutionary stable resource allocation, whereby any increase in investment to male reproduction leads to a disproportionate cost on female reproduction and vice versa. However, empirical evidence for sexual trade-offs in hermaphroditic animals is still limited. Here, we tested how male and female reproductive traits evolved under conditions of reduced selection on either male or female reproduction for 40 generations in a hermaphroditic snail. This selection favors a reinvestment of resources from the sex function under relaxed selection toward the other function. We found no such evolutionary response. Instead, juvenile survival and male reproductive success significantly decreased in lines where selection on the male function (i.e., sexual selection) was relaxed, while relaxing selection on the female function had no effect. Our results suggest that most polymorphisms under selection in these lines were not sex-antagonistic. Rather, they were deleterious mutations affecting juvenile survival (thus reducing both male and female fitness) with strong pleiotropic effects on male success in a sexual selection context. These mutations accumulated when sexual selection was relaxed, which supports the idea that sexual selection in hermaphrodites contributes to purge the mutation load from the genome as in separate-sex organisms., (© 2018 The Author(s). Evolution © 2018 The Society for the Study of Evolution.)

Basic models of mating-system evolution predict that hermaphroditic organisms should mostly either cross-fertilize, or self-fertilize, due to self-reinforcing coevolution of inbreeding depression and outcrossing rates. However transitions between mating systems occur. A plausible scenario for such transitions assumes that a decrease in pollinator or mate availability temporarily constrains outcrossing populations to self-fertilize as a reproductive assurance strategy. This should trigger a purge of inbreeding depression, which in turn encourages individuals to self-fertilize more often and finally to reduce male allocation. We tested the predictions of this scenario using the freshwater snail Physa acuta, a self-compatible hermaphrodite that preferentially outcrosses and exhibits high inbreeding depression in natural populations. From an outbred population, we built two types of experimental evolution lines, controls (outcrossing every generation) and constrained lines (in which mates were often unavailable, forcing individuals to self-fertilize). After ca. 20 generations, individuals from constrained lines initiated self-fertilization earlier in life and had purged most of their inbreeding depression compared to controls. However, their male allocation remained unchanged. Our study suggests that the mating system can rapidly evolve as a response to reduced mating opportunities, supporting the reproductive assurance scenario of transitions from outcrossing to selfing., (© 2016 The Author(s). Evolution © 2016 The Society for the Study of Evolution.)

Background: Sexual minorities are more likely than heterosexuals to engage in unhealthy eating behaviors., Purpose: The purpose of this study is to examine sexual minority stressors and internalizing symptoms as predictors of unhealthy eating behaviors among sexual minority youths., Methods: We used longitudinal data from 1461 sexual minority youths in the Growing Up Today Study, across ages 14-28 years. We hypothesized that sexual minority stressors would predict unhealthy eating behaviors, in part due to internalizing symptoms. Linear regression models fit via generalized estimating equations were stratified by gender and sexual orientation., Results: Significant positive and inverse associations between stressors and eating behaviors were detected among females and males, with more significant associations among females. Associations were attenuated by up to 71 % for females and 12 % for males when internalizing symptoms were added to the models., Conclusions: Sexual minority stressors predicted unhealthy eating behaviors overall and more so for some sexual orientation and gender groups; associations were partially explained by internalizing symptoms. The conceptual model appears to best describe the experiences of bisexual females. Findings have clinical implications for adolescent health.

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre- versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RSm )). However, paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RSm ) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RSm ) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RSm ) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade-offs were detected between different components of precopulatory success, whereas pre- and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species., (© 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.)

Inbreeding depression has become a central theme in evolutionary biology and is considered to be a driving force for the evolution of reproductive morphology, physiology, behavior, and mating systems. Despite the overwhelming body of empirical work on the reproductive consequences of inbreeding, relatively little is known on whether inbreeding depresses male and female fitness to the same extent. However, sex-specific inbreeding depression has been argued to affect the evolution of selfing rates in simultaneous hermaphrodites and provides a powerful approach to test whether selection is stronger in males than in females, which is predicted to be the consequence of sexual selection. We tested for sex-specific inbreeding depression in the simultaneously hermaphroditic freshwater snail Physa acuta by comparing the reproductive performance of both sex functions between selfed and outcrossed focal individuals under different levels of male-male competition. We found that inbreeding impaired both male and female reproductive success and that the magnitude of male inbreeding depression exceeded female inbreeding depression when the opportunity for sperm competition was highest. Our study provides the first evidence for sex-specific inbreeding depression in a hermaphroditic animal and highlights the importance of considering the level of male-male competition when assessing sex differences in inbreeding depression., (© 2013 The Author(s). Evolution © 2013 The Society for the Study of Evolution.)

Inbreeding depression, one of the main factors driving mating system evolution, can itself evolve as a function of the mating system (the genetic purging hypothesis). Classical models of coevolution between mating system and inbreeding depression predict negative associations between inbreeding depression and selfing rate, but more recent approaches suggest that negative correlations should usually be too weak or transient to be detected within populations. Empirical results remain unclear and restricted to plants. Here, we evaluate, for the first time, the within-population genetic correlation between inbreeding depression and a trait that controls the amount of self-fertilization (the waiting time) in a self-fertile hermaphroditic animal, the freshwater snail Physa acuta. Using a large quantitative-genetic design (36 grand-families and 348 families), we observe abundant within-population family-level genetic variation for both inbreeding depression (estimated for survival, fecundity, and size) and the degree of behavioral selfing avoidance. However, we detected no correlation between waiting time and inbreeding depression across families. In agreement with recent models, this result shows that mutational variance rather than differential purging accounts for most of the genetic variance in inbreeding depression within a population.