Imposex response in shell sizes of intertidal snails in multiple environments

Abstract

Imposex affect shell growth in females as well as the reproduction of gastropod species causing a reduction in sexual allocation and a consequent increase in somatic allocation that can be verified by the growth of the shell. The objective of this study was to evaluate the effects of imposex in conjunction with environment categories (i.e. substrate geology, wave exposure, sand deposition and transport, and presence of harbors and marinas near the collection area classified) on shell sizes of two species of marine gastropods, Leucozonia nassa and Stramonita brasiliensis (Caenogastropoda–Neogastropoda). Both gastropod species were sampled during the summer between 2006 and 2014 along the Espírito Santo coast at 35 sites classified according to environment categories. The total length of the specimens, percentage exhibiting imposex and severity of imposex features (using the vas deferens sequence index, VSDI) were determined. Imposex analysis showed that both species were affected; the percentage of individuals with imposex was ≥60%. As expected, the imposex-affected females are significantly larger than healthy females and males in the gastropod species analyzed. Furthermore, the shell size of imposex-affected females increased as the VDSI stages increased for the both species. A first attempt to verify that the females affected by the imposex are always larger than the healthy females and males regardless of environmental factors suggests that for shell size, the imposex effect overwhelms the effects of plasticity in response.