SEX-RATIOS OF COROPHIUM-VOLUTATOR (PALLAS) (CRUSTACEA, AMPHIPODA) IN BAY OF FUNDY POPULATIONS

Previous work on the tube-dwelling intertidal amphipod Corophium volut ator (Pallas) has shown that adult sex ratios are female-biased for po pulations along the Bay of Fundy, Canada. The causes of these biased s ex ratios, and many other aspects of the life history of this importan t prey species, are unknown. Some authors have suggested that biased s ex ratios for adults may be due to differential predation on adult mal es by migrant shorebirds. Such differential predation is not expected for juvenile C. volutator, which differ in behaviour from adult males. In this study, we first demonstrate an accurate method of sexing juve nile C. volutator that is based on sex differences shown by adults. Th is method will enable more detailed ecological studies of C. volutator . We then show that sex ratios are female-biased for juvenile C. volut ator, which is probably a more important determinant of a biased sex r atio for adults than is differential shorebird predation on adult male s. We demonstrate that biased sex ratios also appear to occur for newl y hatched C. volutator, indicating that some form of asexual reproduct ion (e.g., automixis) may exist within Bay of Fundy populations of C. volutator.