On the reproductive biology and impact of imposex in a population of Buccinanops monilifer from Mar del Plata, Argentina

The populations of Buccinanops monilifer (Gastropoda: Nassariidae) from two different sites, Mar del Plata (Buenos Aires province) and a close non-polluted locality (Mar Chiquita), are compared in their imposex indices and reproductive parameters. In Mar del Plata, a beach nourishment (sand filling) remobilized sediment from the harbour area during 1999; our results show high imposex percentage and an increase in relative penis size index during and after this beach filling event, in contrast with the Mar Chiquita population that showed nil values during this study. Comparisons of reproductive parameters between both populations showed significantly higher frequency of spawning females and number of egg capsules per female in Mar Chiquita, while female size and number of eggs per capsule did not differ. Females from Mar del Plata that did not succeed in spawning showed higher imposex values than spawning ones. Sex-ratio was not significantly different from 1:1 in any of the sites (although male-biased in Mar del Plata and the opposite in Mar Chiquita). We found no malformations or abnormalities during intracapsular development in the imposexed population. Alternatively, we found evidence that suggests that B. monilifer intracapsular development includes the occurrence of intracapsular embryonic cannibalism of other smaller embryos, which was not previously known in this genus, and that complements adelphophagy (feeding on nurse eggs feeding).