Examining the impact of a symbiotic lifestyle on the fecundity of the marine gastropod Crepidula plana

Abstract

The marine gastropod Crepidula plana has an extensive latitudinal range along the eastern coast of the United States. It is usually found living within gastropod shells occupied by hermit crabs, although individuals can sometimes also be found living on rocks and on the exposed surfaces of shells. Our study sought to determine the extent to which residing inside periwinkle (Littorina littorea) shells occupied by the hermit crab Pagurus longicarpus at a study site in coastal Massachusetts compromises the fecundity of C. plana, through size limitation. The egg masses of symbiotic and free‐living females of C. plana included comparable numbers of egg capsules and embryos per female despite the smaller sizes of the symbionts; symbiotic females compensated for their smaller size by producing significantly more embryos per milligram of female body tissue than their free‐living counterparts. These data raise interesting questions about why—unlike its congener C. fornicata—C. plana has not yet become a successful invasive species.

Size Doesn’t Matter: Integrative Taxonomy ShowsCrepidula aduncaandCrepidula norrisiarumHave Overlapping Shell Sizes and Broadly Concordant Distributions

“…Therefore, while it seems likely that shell morphology and body size are host-dependent, it is also possible that phenotypic variation is related to geographic or bathymetric factors, or that it is the result of genetic differentiation. However, the shell size of Crepidula is necessarily limited by host size (e.g., Pechenik et al, 2020). As a result, and because subtidal host species are generally larger than intertidal ones, C. norrisiarum is twice as large when living on the large subtidal trochid Norrisia norrisii than when living on the small intertidal trochid Calliostoma ligatum.…”

“…Species that form mutualistic relationships are subject to selective pressures imposed by their host and environment, and this can have an important impact on their phenotypic traits, behavior, and geographic range (Boucher, 1982;Afkhami et al, 2014, Pechenik et al, 2020. Well-studied examples of eco-evolutionary changes induced by mutualism are found in terrestrial and marine systems, from viruses to large mammals, including flowering plants and their animal pollinators or seed dispersers (Fleming and Estrada, 1993;Moeller et al, 2012).…”