Shell shape and mating behaviour in pulmonate gastropods (Mollusca)

Enhanced susceptibility to predation in corals of compromised condition

The marine gastropod, Coralliophila abbreviata, is an obligate corallivore that causes substantial mortality in Caribbean Acropora spp. Considering the imperiled status of Acropora cervicornis and A. palmata, a better understanding of ecological interactions resulting in tissue loss may enable more effective conservation strategies. We examined differences in susceptibility of A. cervicornis to C. abbreviata predation based on coral tissue condition. Coral tissue condition was a strong determinant of snail prey choice, with snails preferring A. cervicornis fragments that were diseased or mechanically damaged over healthy fragments. In addition, snails always chose fragments undergoing active predation by another snail, while showing no preference for a non-feeding snail when compared with an undisturbed prey fragment. These results indicate that the condition of A. cervicornis prey influenced foraging behavior of C. abbreviata, creating a potential feedback that may exacerbate damage from predation in coral populations compromised by other types of disturbance.

Reproductive strategies in hermaphroditic gastropods: conceptual and empirical approaches

An individual optimizes its reproductive success by adopting a particular reproductive strategy. Studying the details of a reproductive strategy leads to an understanding of how sexual selection acts, as the former is the process via which the individual reproduces successfully. Hermaphroditic gastropods display a bewildering diversity of reproductive strategies, which may be due to their mode of gender expression, when compared with well-studied separate-sexed species. Extensive theoretical, observational, and experimental research has been conducted on this topic. However, despite our knowledge about the reproductive system of hermaphroditic gastropods, we still need to fill the gap between pre- and post-copulatory processes and reproductive success. Here, we review and propose conceptual and empirical approaches aimed at understanding reproductive strategies of hermaphroditic gastropods. In sum, our suggestions are (i) to focus on sex-biased traits, (ii) to take biologically reliable measurements at both the pre- and post-copulatory level that relate to reproductive success, and (iii) to examine the fitness consequences of biased sex allocation.

Burrowing in the freshwater mussel Elliptio complanata is sexually dimorphic and feminized by low levels of atrazine

The widely used herbicide atrazine (ATR) may have endocrine-associated adverse effects, including on behavior. In this study, 120 adult freshwater mussels, Elliptio complanata, were exposed to ATR at the environmentally relevant concentrations of 1.5, 15, or 150 μg/L. Burrowing depth was evaluated hourly for 6 h and at sacrifice animals were sexed by gonad smear. Female controls burrowed overall approximately 30% less than males, the first report of sexual dimorphism in this behavior. Atrazine at 15 μg/L feminized burrowing in both sexes, in that exposed animals burrowed 20% less than their same-sex controls. Males treated with 1.5 μg /L ATR displayed approximately 20-fold higher vitellogenin (VTG) levels than same-sex controls. Higher concentrations of ATR were not associated with increasing effects. A scatterplot showed a weak binomial curve associating low burrowing with high VTG levels. Taken together, these data suggest a nonlinear dose response in behavioral and physiological feminization produced by ATR and support the need to reconsider the widespread use of this compound.

A speciation gene for left-right reversal in snails results in anti-predator adaptation

How speciation genes can spread in a population is poorly understood. In land snails, a single gene for left-right reversal could be responsible for instant speciation, because dextral and sinistral snails have difficulty in mating. However, the traditional two-locus speciation model predicts that a mating disadvantage for the reversal should counteract this speciation. In this study, we show that specialized snake predation of the dextral majority drives prey speciation by reversal. Our experiments demonstrate that sinistral Satsuma snails (Stylommatophora: Camaenidae) survive predation by Pareas iwasakii (Colubroidea: Pareatidae). Worldwide biogeography reveals that stylommatophoran snail speciation by reversal has been accelerated in the range of pareatid snakes, especially in snails that gain stronger anti-snake defense and reproductive isolation from dextrals by sinistrality. Molecular phylogeny of Satsuma snails further provides intriguing evidence of repetitive speciation under snake predation. Our study demonstrates that a speciation gene can be fixed in populations by positive pleiotropic effects on survival.

A mechanism aiding simultaneously reciprocal mating in snails

The majority of hermaphroditic animals mate on a given occasion as either male or female, but terrestrial snails and slugs generally mate reciprocally with each partner participating in both sexual roles. This manner of mating requires that the genitalia be exactly opposed prior to copulation attempts, a task made difficult in snails and slugs by the absence of hearing and very limited vision. In the brown garden snail, Cornu aspersum (Müller, 1774), we found that a small protruding structure associated with the genital atrium plays an important role in positioning the snails prior to copulation. Lesions of the penial lobe reduced mating success rates, delayed mating, increased the number of attempted intromissions, and increased the number of unilateral intromissions. The sensory capacity of the penial lobe is demonstrated by histological and electrophysiological evidence, and behavioral data suggest that the lobe is also a stimulus for the partner snail. A literature review suggests that structures functionally equivalent to the penial lobe may be present in many gastropod molluscs that mate simultaneously and reciprocally, but in none that mate in other ways.