Abstract:
The apodid sea cucumber Leptosynapta clarki exhibits the three commonly associated traits of small adult size (max. length 113 mm), brooding (intraovarian = viviparity), and hermaphroditism (protandric). Juvenile L. clarki are released from the ovary at a length of 1-2 mm in the early spring (April-May) and are reproductively active as males in the reproductive season (November) following their birth. In their second year, some individuals continue to reproduce as males, but others undergo protandric sex change to reproduce as females. Analysis of the relationship between size and sex revealed a "critical" size for sex change at a weight of 200-400 mg with a 1:1 sex ratio above 500 mg total weight. Transitional gonads with previtellogenic oocytes and mature spermatozoa were observed, suggesting that sex change is initiated prior to reproducing in the current reproductive season. A test of the allometric hypothesis on the association between small size and brooding found no evidence for scaling constraints on brood size in L. clarki. These allometric constraints may be avoided because of potentially low fertilization success and brooding within a distensible structure. The sequential hermaphroditism in L. clarki may additionally be a method to reduce inbreeding in a species with limited dispersal.
