COWART,, J.D.; Univ. of Florida, Gainesville: The Mating System of a Pterasterid Sea Star: Hermaphroditism, Sperm Storage, or Parthenogenesis?

The eggs of the sea star Pteraster tesselatus are capable of developing to the juvenile stage without artificial fertilization, without evidence of sperm in the water, and without the elevation of a vitelline envelope. I offer three alternate hypothesis for this phenomenon: 1) hermaphroditism, with internal self-fertilization prior to spawning, 2) outcrossing, with internal fertilization using stored exogenous sperm, and 3) parthenogenesis. Hermaphroditism is the least likely explanation. Sexes are separate in this species and the sex ratio is approximately 1:1. In addition, dissections of reproductive adults reveal no signs of ovotestes. To distinguish between outcrossing and parthenogenesis, I used amplified fragment length polymorphisms (AFLPs) to look for the presence of novel genetic markers (i.e., not present in the mother) in the offspring. Genetic analysis did not support the hypothesis of parthenogenesis and further ruled out self-fertilization. None of the offspring were genetically identical to their mother. Furthermore, novel markers were present in the offspring that were not present in their mother. My results falsify hypotheses 1 and 3 and are only compatible with hypothesis 2. This is the first report of sperm storage in an asteroid. Pteraster tesselatus is unique among the Pterasteridae in that it is free-spawning. Other pterasterids brood in a specialized nidamental chamber. The eggs of P. tesselatus are spawned into the nidamental chamber, where they are more than likely fertilized prior to being released into the water column. Sperm storage most likely evolved in pterasterids after they became specialized for brood protection. If so, P. tesselatus retained the ability to collect and store exogenous sperm after it re-evolved pelagic development.