The Hungry Snail, the Fragile Coral, and the Friendly Microbe

Off the coast of Vietnam, two recent events seem to have contributed to the death of coral reefs: the rapid invasion of a small marine snail called Drupella, and the emergence of a disease that spreads over corals. We decided to investigate whether there is a link between the corals, the snails, and the disease. We analyzed the mucus covering the surface of corals, both in healthy corals and those infested by Drupella snails. Mucus produced by corals is usually full of helpful microbes, protecting the corals from harmful microbes that can make them ill or kill them. Our analyses showed that, when Drupella eats corals, the snail also removes one of the corals’ primary defenses by eliminating most of the tiny protectors in their mucus. This allows harmful microbes to cause additional damage to the corals.

Pronounced phenotypic differentiation in a wide-dispersing marine snail in response to contrasting selection pressures at a local scale

Heterogeneous environments pose a particular challenge for organisms because the same phenotype is unlikely to perform best regardless of the types of stress it encounters. The grain size theory predicts that species with high dispersal potential experience a more heterogeneous, fine-grained environment where phenotypic plasticity may evolve to cope with habitat heterogeneity.To understand how species meet this challenge, we investigated the extent to which contrasting selection pressures induced ecological and phenotypic responses in a natural population of a wide-dispersing marine snail.We collected, measured external and internal characters, weighted, and dissected individuals of Heleobia australis (Rissooidea: Cochliopidae) from heterogeneous habitats from the intertidal area of the Bahía Blanca estuary, Argentina. We also conducted molecular analyses by amplifying the COI gene in individuals sampled from each habitat.We found that subpopulations of H. australis, inhabiting close to each other and without physical barriers, exhibited a strong phenotypic differentiation in shell characters and body weight in response to environmental conditions (thermal, saline, and dehydration stress), crab predation, and parasites. We proved that this differentiation occurred even early in life as most of the characters observed in juveniles mirrored those found in adults. We also found a clear variation in penis size in snails collected from each habitat and raised in common garden laboratory conditions. The COI gene analysis confirmed that the individuals studied constituted a single species despite the strong phenotypic difference among subpopulations.The pronounced phenotypic differentiation in H. australis is all the more remarkable because it occurred at a very small geographical scale, which is rarely documented for a wide-dispersing species. Our findings provide a reasonable ground for advocating that H. australis experienced a fine-grained environment and, thus, benefited from the combined effect of directional selection and plasticity to evolve locally adapted phenotypes to contrasting habitat conditions at a local scale.

Comparing shape along growth trajectories in two marine snail ecotypes of Littorina saxatilis: a test of evolution by paedomorphosis

ABSTRACT Two sympatric ecotypes (‘crab’ and ‘wave’) of Littorina saxatilis are adapted to different microhabitats. It has been claimed, based on the comparison of proteomic differentiation across ontogeny, that the wave ecotype may have evolved by paedomorphosis from an ancestor more similar to the crab ecotype. Here, we test the paedomorphosis hypothesis at a morphological level by comparing crab and wave specimens from two localities using the pattern of shell shape differentiation across ontogeny. The results obtained show a pattern of shell shape differentiation similar to the one observed in previous proteomic studies, but such a pattern could be caused by different modes of evolution, and not necessarily by paedomorphosis. This study emphasizes that in addition to studying the pattern of differentiation, the direction of the evolutionary change across ontogeny has to be analysed before conclusions can be drawn on particular developmental modes of evolution.

The current status of Pogonodon Cope, 1880 (Carnivora: Nimravidae) and a substitution name for its junior homonym Pogonodon Bouchet, 1997 (Caenogastropoda: Triphoridae)

This nomenclatural note addresses the problem regarding the taxonomic status of the extinct large nimravid Pogonodon Cope, 1880 (Chordata. Mammalia, Nimravidae), from the Oligocene of North America and its junior homonym, the recent triphorid marine snail Pogonodon Bouchet, 1997 (Mollusca, ) from the Mediterranean. Here we propose Ionthoglossa nov. gen. as a substitute name for the latter and provide a brief history of the two taxa from the literature available.