New Imposex Development Index (IDI) for Stramonita haemastoma (Mollusca: Muricidae): A Transplantation Experiment in the Brazilian Northeast

Abstract

A total of 600 Stramonita haemastoma (Mollusca: Muricidae) individuals, free of imposex, were transplanted into a marina with an intense ship flow. Thirty individuals were collected periodically until 210 days and analyzed according to RPLI (Relative Penis Length Index), RPSI (Relative Penis Size Index), IDI (Imposex Development Index, developed in this study), and imposex percentage. The proposed Imposex Development Index (IDI) presented three developmental paths, being two of them aphallic. The incidence of aphally was quite high along the experiment. An underdevelopment of the male characters in imposexed females was clearly observed. At first sample (15 days) all females showed evidence of imposex. RPLI and RPSI had a strong correlation with time along the transplantation. Correlation of imposex development (IDI) with time was also significant. This index increased gradually, reaching a stage IV at day 210, with all females showing a complete vas deferens.