THE EFFECT OF LOW DENSITY ON THE DEVELOPMENT OF SIMULTANEOUS HERMAPHRODITISM IN MALE CAPITELLA SPECIES I (POLYCHAETA)

¹ Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1
² Marine Biological Laboratory Woods Hole, Massachusetts 02543

In this study it was shown that male Capitella species I may develop into simultaneous hermaphrodites if reared in isolation or at low densities in the laboratory. Since hermaphroditic development is rare in high density non-inbred cultures but becomes frequent in inbred lines which have been selected for high male sex ratios, the ability to become hermaphroditic seems to have a genetic basis. It is also suggested that low density may trigger the hermaphroditic development of males through the absence of animals with female gonads. Excess food resources which could be assimilated at low density and may be directed into the development of a second set of reproductive structures and female gametes, could also be a factor in the male-to-hermaphrodite switch. Capitella sp. I has an opportunistic lifestyle which could accommodate such a sexual adaption. The larvae are widely dispersed which would often cause adults to be at low density where the advantage of being hermaphroditic is well known.