Cryptic individual-level variation in propensity for selfing in a hermaphroditic snail

For mating-system evolution, individual-level variation is as important as variation among populations. In self-compatible hermaphrodites, individuals may vary in their lifetime propensity for selfing, which consists of a fundamental, likely genetic and an environmental component. According to the reproductive assurance hypothesis explaining partial selfing, a key environmental factor is mate availability, which fluctuates with population density. We quantified individual variation in selfing propensity in a hermaphroditic snail by manipulating mate availability in the laboratory, recording mating behaviour, estimating selfing rates from progeny arrays, and measuring female lifetime fitness. Our results revealed four classes of individuals with different selfing propensities: pure outcrossers, pure selfers, and two types of plastic individuals. These classes only became apparent in the laboratory; the field population is outcrossing. All classes were present both under low and increased mate availability; this large among-individual variation in selfing propensities meant that effects of the pairing treatment on the frequency and extent of selfing were non-significant despite large effect sizes and sufficient statistical power. We believe that selfing propensities may have a genetic component and when selected on cause mean selfing rates to evolve. We propose that heritable variation in selfing propensities offers a reconciliation between the reproductive assurance hypothesis and its weak empirical support: distributions of selfing propensities vary temporally and spatially, thus obscuring the relationship between population density and realised selfing rates.

Three options are better than two: compensatory nature of different pollination modes in Salix caprea L.

Mixed pollination systems have been reported for many angiosperms. Here, we report on a dioecious willow, Salix caprea L., which employs three pollination modes, namely pollination by wind, nocturnal moths, and diurnal bees. In four field populations of S. caprea in Germany, we addressed the following questions: (a) How are the pollination modes affected by local mate availability? (b) What is the contribution of each pollination mode to seed set? (c) How does flower opening time affect pollination? We compared seed set among seven pollination treatments (wind pollination, diurnal pollination, nocturnal pollination, natural pollination, apomictic reproduction, daytime/night-time artificial pollination). Pollen limitation was observed across populations. On the other hand, limitations in mate availability affected the pollination modes differently. Insect pollination outperformed wind pollination in situations where nearby males were few or all positioned in the same direction from the females. The contribution of nocturnal moths was lower than that of the other pollen vectors. However, moth pollination worked complementarily with bee pollination in compensating for the lack of wind pollination. Furthermore, we found that the onset of flower anthesis peaked at sunset, and that cold night temperatures had no negative effect on seed set or pollen viability. Thus, nocturnal anthesis and prior pollination by moths may minimize male fitness loss due to pollen collection and grooming by bees. We suggest that S. caprea maximizes its fitness by combining multiple pollination modes that work in different environmental conditions, while optimizing the anthesis so that more pollen would be delivered to stigmas.

Mate Availability and Sexual Disgust

Objective: One of the factors that sexual disgust should be calibrated to is the size of the mating pool. Previous research provides evidence that low mate availability affects perceptions related to mate choice. However, methodological shortcomings leave the role of sexual disgust in facilitating mate selection unclear. We will examine whether perceptions of mate availability explain variance in levels of sexual disgust towards potential mates.Methods: Participants (N = 1,000) will rate how sexually disgusting they find 60 potential mates that have previously been rated on attractiveness by a separate group of raters. We will measure participants’ perceptions of mate availability in their local environment, self-perceived attractiveness and mate value, and relevant control variables (e.g., age, relationship status). Results: We will use linear mixed effect models to examine (1) the association between sexual disgust towards potential mates and perceived mate availability; (2) the sex difference in sexual disgust; (3) the association between targets’ attractiveness and raters’ sexual disgust; and (4) whether perceived mate availability moderates the association between sexual disgust and targets’ attractiveness. Conclusions: This study will test perceptions of mate availability as an input into the calibration of sexual disgust. The results will clarify the magnitude of mate availability perceptions on mate choice.

Mate availability determines use of alternative reproductive phenotypes in hermaphrodites

In many species, individuals can employ alternative reproductive phenotypes, with profound consequences for individual fitness and population dynamics. This is particularly relevant for self-compatible hermaphrodites, which have exceptionally many reproductive options. Here we investigated the occurrence of reproductive phenotypes in the simultaneously hermaphroditic freshwater snail Radix balthica under experimentally simulated conditions of low versus moderate population density. We captured all mating behavior on camera and measured individual female lifetime reproductive success. We found every possible reproductive phenotype: (1) both male and female (i.e., truly hermaphroditic) reproduction, (2) purely female and (3) purely male reproduction, (4) male reproduction combined with self-fertilization and (5) female mating activity, (6) pure self-fertilization without mating and (7–8) two types of reproductive failure. Variation in alternative reproductive phenotypes was explained by mate availability (10.8%) and individual condition, approximated by a snail’s mean daily growth rate (17.5%). Increased mate availability resulted in a lower diversity of reproductive phenotypes, in particular increasing the frequency of true hermaphrodites. However, it lowered phenotype-specific fecundities and hence reduced the population growth rate. Snails in better condition were more likely to reproduce as true hermaphrodites or pure females, whereas low-condition snails tended to suffer reproductive failure. Overall, we show substantial variation in alternative reproductive phenotypes in a hermaphrodite, which is possibly in part maintained by fluctuations in population density and thus mate availability, and by variation in individual condition. We also provide evidence of an almost 2-fold increase in clutch size that can be ascribed specifically to mating as a female.

Testing the effects of pathogen threat and sexual strategies on political ideology

Disgust has been consistently associated with greater political conservatism. Two explanations have been proposed for this link. According to a pathogen threat model, disgust serves a pathogen-avoidance function, encouraging more conservative ideology, whereas a sexual strategies model suggests that this link is explained by variability in short-term versus long-term mating goals. In two preregistered studies using a college student and community sample (total N = 1,950), we examined whether experimentally manipulating pathogen threat and mate availability produced differences in political ideology and whether these differences were explained by disgust and sociosexual attitudes. Across both studies, we did not find evidence that manipulating pathogen threat or mate availability resulted in change in political ideology. In Study 1, manipulating mate availability was indirectly associated with greater political conservativism through stronger sociosexual attitudes that favor monogamy. These findings failed to replicate in Study 2. Implications for theory and future research are discussed.