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

Museo Argentino de Ciencias Naturales Bernardino Rivadavia–CONICET, Avenida A´ngel Gallardo 470 (1405) BuenosAires, ArgentinaThe populations of Buccinanops monilifer (Gastropoda: Nassariidae) from two different sites, Mar del Plata (Buenos Airesprovince) and a close non-polluted locality (Mar Chiquita), are compared in their imposex indices and reproductiveparameters. In Mar del Plata, a beach nourishment (sand filling) remobilized sediment from the harbour area during1999; our results show high imposex percentage and an increase in relative penis size index during and after this beachfilling event, in contrast with the Mar Chiquita population that showed nil values during this study. Comparisons ofreproductive parameters between both populations showed significantly higher frequency of spawning females and numberof egg capsules per female in Mar Chiquita, while female size and number of eggs per capsule did not differ. Females fromMar del Plata that did not succeed in spawning showed higher imposex values than spawning ones. Sex-ratio was notsignificantly different from 1:1 in any of the sites (although male-biased in Mar del Plata and the opposite in MarChiquita). 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 ofintracapsular embryonic cannibalism of other smaller embryos, which was not previously known in this genus, and thatcomplements adelphophagy (feeding on nurse eggs feeding).Keywords: imposex, low fecundity, embryonic development, cannibalism