Unusual high frequency of hermaphroditism in the gonochoric bivalve Megapitaria squalida (Sowerby, 1835) (Veneridae)

Through histological analyses, this investigation reveals an unusual high incidence of hermaphroditism in Megapitaria squalida, a gonochoric species. A total of 684 specimens were sampled at monthly intervals from February 2007 to January 2008 at Bahı´a de La Paz and Bahı´a Magdalena, Baja California Sur, Mexico. Microscopic examination showed that 21.8% of specimens from Bahı´a de La Paz and 23.5% from Bahı´a Magdalena were hermaphroditic; in both areas, hermaphroditism was found throughout the year, although in variable proportions. In general, a significantly higher Lumber of females relative to males (chi-square, P < 0.05) were observed in both areas. Our findings indicate that this unusual incidence of hermaphroditism was likely caused by the low population density resulting from overfishing