Sexual selection is often quantified using Bateman gradients, which represent sex-specific regression slopes of reproductive success on mating success and thus describe the expected fitness returns from mating more often. Although the analytical framework for Bateman gradients aimed at covering all sexual systems, empirical studies are biased toward separate-sex organisms, probably because important characteristics of other systems remain incompletely treated. Our synthesis complements the existing Bateman gradient approach with three essential reproductive features of simultaneous hermaphrodites. First, mating in one sex may affect fitness via the opposite sex, for example, through energetic trade-offs. We integrate cross-sex selection effects and show how they help characterizing sexually mutualistic versus antagonistic selection. Second, male and female mating successes may be correlated, complicating the interpretation of Bateman gradients. We show how to quantify the impact of this correlation on sexual selection and propose a principal component analysis on male and female mating success to facilitate interpretation. Third, self-fertilization is accounted for by adding selfed progeny as a separate category of reproductive success to analyses of Bateman gradients. Finally, using a worked example from the snail Biomphalaria glabrata, we illustrate how the extended analytical framework can enhance our understanding of sexual selection in hermaphroditic animals and plants.

Mating partners often have conflicting interests when copulating. One of the major agents affecting female mating partners is seminal fluid, transferred along with sperm. The role of seminal fluid proteins (SFPs) in reproductive success is well studied in separate-sexed animals but is much less so in simultaneous hermaphrodites. The latter potentially have a unique target to exploit for the sperm donor's own benefit: the male function of their mating partners. Here we show that, in the great pond snail Lymnaea stagnalis, receipt of specific SFPs reduces both sperm transfer and paternity success in a subsequent insemination event. Lowering investment in the mating partner's male function constitutes a novel role for SFPs. This demonstrates for the first time that hermaphrodites alter their mates' male as well as female reproductive output. Although it remains to be tested whether this represents mate manipulation or an adaptive response of recipients, our findings identify male investment as a new target for postcopulatory sexual selection.

Promiscuity, sperm storage and internal fertilization enhance sperm competition, which leads to sexual confl ict whenever an advantageous trait for sperm donors is harmful to recipients. In separate-sex species, such confl icts can severely impact the evolution of reproductive characteristics, physiology and behaviours. For simultaneous hermaphrodites, the generality of this impact remains unclear and underlying mechanisms remain largely unexplored. In the hermaphrodite Lymnaea stagnalis several previous studies showed that investment in eggs diff ers depending on semen receipt, but these were inconsistent about the direction of change. We investigated whether the change in egg laying is caused by a seminal fl uid component. By intravaginally injecting animals, we here reveal that a component of the seminal fl uid inhibits egg laying, thus providing the fi rst direct evidence for involvement of such components in competition for fertilization in hermaphrodites. We discuss the broad implications that this fi nding has on a number of previous studies performed in the same species. © Koninklijke Brill NV, Leiden, 2009.

No abstract

BackgroundSexual conflicts between mating partners can strongly impact the evolutionary trajectories of species. This impact is determined by the balance between the costs and benefits of mating. However, due to sex-specific costs it is unclear how costs compare between males and females. Simultaneous hermaphrodites offer a unique opportunity to determine such costs, since both genders are expressed concurrently. By limiting copulation of focal individuals in pairs of pond snails (Lymnaea stagnalis) to either the male role or the female role, we were able to compare the fecundity of single sex individuals with paired hermaphrodites and non-copulants. Additionally, we examined the investment in sperm and seminal fluid of donors towards feminized snails and hermaphrodites.ResultsCompared to non-mating focal snails, reciprocating individuals as well as male and female copulants experienced a significant fecundity reduction (~40%) after, on average, 3.07 ± 0.12 copulations in their allowed roles (for donors 2.98 ± 0.16 copulations and for recipients 3.14 ± 0.12 copulations). In a single copulation, significantly more sperm was donated to partners that were restricted to mating in the female role than to hermaphrodites, while seminal fluid transfer was unaffected by recipient type.ConclusionsOur data indicate that the costs of mating in both sex functions are high in L. stagnalis. This conclusion is based on fecundity data collected separately for male and female copulants. Male mating costs result from investment in expensive ejaculates, composed of sperm and seminal fluid. For female copulants, fecundity reduction correlated with transferred sperm numbers in the first copulation, while differences in transferred quantities of seminal fluid were not detected. These findings may point toward a "sperm effect" as a novel feature of pond snail reproductive ecology. In conclusion, sex allocation and sexual conflict both contribute to decreased female fecundity in pond snails.

Sexual selection is generally predicted to act more strongly on males than on females. The Darwin-Bateman paradigm predicts that this should also hold for hermaphrodites. However, measuring this strength of selection is less straightforward when both sexual functions are performed throughout the organism’s lifetime. Besides, quantifications of sexual selection are usually done during a short time window, while many animals store sperm and are long-lived. To explore whether the chosen time frame affects estimated measures of sexual selection, we recorded mating success and reproductive success over time, using a simultaneous hermaphrodite. Our results show that male sexual selection gradients are consistently positive. However, an individual’s female mating success seems to negatively affect its own male reproductive success, an effect that only becomes visible several weeks into the experiment, highlighting that the time frame is crucial for the quantification and interpretation of sexual selection measures, an insight that applies to any iteroparous mating system.DOI: http://dx.doi.org/10.7554/eLife.25139.001

Sexual selection is generally predicted to act more strongly on males than on females.The Darwin-Bateman paradigm predicts that this should also hold for hermaphrodites. However, measuring this strength of selection is less straightforward when both sexual functions are performed throughout the organism's lifetime. Besides, quantifications of sexual selection are usually done during a short time window, while many animals store sperm and are long-lived. To explore whether the chosen time frame affects estimated measures of sexual selection, we recorded mating success and reproductive success over time, using a simultaneous hermaphrodite. Our results show that male sexual selection gradients are consistently positive. However, an individual's female mating success seems to negatively affect its own male reproductive success, an effect that only becomes visible several weeks into the experiment, highlighting that the time frame is crucial for the quantification and interpretation of sexual selection measures, an insight that applies to any iteroparous mating system.

Water uptake into seeds is a fundamental prerequisite of germination and commonly influenced by commercial seed enhancement technologies. The effect of fruit orientation and contrasting pelleting materials on germination and biological performance of sugar beet was assessed. The results indicated there was orientation dependent fruit shrinkage of 37% for the operculum side supplied by moisture compared to 4% for the basal pore side. The expansion rate of 5% compared to the original size, which was also observed for non-shrinking seeds, indicated this was a temporary effect. This behaviour has importance for the application pelleting materials to seeds. Pellets composed of materials exhibiting low levels of swelling act as a water distribution layer which increased germination rates. Careful selection of pelleting material is crucial as it has direct implications on germination speed and subsequent establishment rates.