Preliminary observations on change of sex by the coral-inhabiting snails Coralliophila violacea (Lamarck) (Gastropoda: Coralliophilidae)

The coral-inhabiting snails, Coralliophila violacea (Lamarck), are widely distributed in the Indo–Pacific region. It has been inferred from field data that sex changes have occurred and might be influenced by neighbors. In this study, we designed a field experiment with 2 treatments, i.e. ‘single males' and ‘male–female pairings' to test the hypothesis of sex changes as well as the role of neighbors on sex changes. Snails were collected by SCUBA diving from the surface of massive coral Porites lobata in shallow waters (<6 m) in southern Taiwan. A total of 73 males and 32 females were marked and returned to the surface of a colony of the massive coral, P. lobata. After 4–5 months, a total of 25 marked males and eight marked females were recaptured. In the treatment of ‘single males', eight of 17 males had changed their sex. None of eight recaptured males in the treatment of ‘male–female pairings' had changed their sex. The occurrence of sex changes is dependent on the presence or absence of a female neighbor (P<0.05, Fisher's exact test). In this study, we have provided direct evidence of socially controlled sex changes in Coralliophila violacea.