REITZEL, Adam M; MINER, Benjamin G; Boston Univ.; Univ. of Florida: Transitions in Marine Invertebrate Life Histories: Reduced Planktotrophy in an Echinoid Larva

Lecithotrophic development has evolved from planktotrophic development numerous times in many marine invertebrates and is generally considered to be irreversible. Lecithotrophic larvae develop from relatively large yolky eggs that provide the organism with sufficient energy to develop to metamorphosis without exogenous food whereas planktotrophic larvae must acquire exogenous food to metamorphose. Intermediate between these two developmental modes is facultative planktotrophy where larvae can develop to metamorphosis without food although functional feeding structures are present. Facultative planktotrophy presumably represents a transitional developmental mode between planktotrophy and lecithotrophy. Here we discuss data testing the hypothesis that facultative planktotrophy is a transitional developmental mode for marine invertebrates with a subtropical echinoid. Facultative planktotrophic larvae of Clypeaster rosaceus were assayed for ability to assimilate exogenous food by measuring energy accumulation and expenditures during development and changes in stable isotopic ratio in life history stages. We found these larvae have an extremely reduced ability for energy assimilation compared to other planktotrophic larvae. Although larvae are still able to ingest food, they apparently have reduced digestive efficiency. These results emphasize that the transition in development modes for marine invertebrates may involve changes in physiology before morphology. We discuss our results in context of other studies investigating facultative planktotrophic larvae from other species.