Meeting Abstract

4.4  Wednesday, Jan. 4  Ontogenetic evidence and performance consequences of re-acquisition of planktotrophy in the gastropod family Calyptraeidae MCDONALD, K.A.; Smithsonian Tropical Research Institute

Phylogenetic hypotheses suggest that different lineages of calyptraeid gastropods have regained free-swimming, feeding larvae following loss of the ancestral type of planktotrophic development. This runs counter to expectations based in part on other invertebrate phylogenies that losses of complex larval types are irreversible. The potential to regain ancestral characters depends upon the preservation of the developmental-genetic programme that produces the structures, and also upon the ontogenetic and functional constraints that limit changes to the planktotrophic phenotype. The amount of change in ontogeny and performance that can be tolerated without loss of planktotrophic functions will influence the strength of barriers to re-acquisition of planktotrophy. Here I test the hypothesis that plankotrophic calyptraeids vary in ontogeny of swimming structures and in resulting larval performance. Species differ significantly in growth of prototrochal cilia, velum, and shell mass prior to hatching into the plankton, and in indices of swimming ability at time of hatching. Putative re-evolved planktotrophs show significantly higher mass and rates of mass increase than other planktotrophs, and are predicted to show substantially weaker swimming than all but one of the “primary” planktotrophs. The results support phylogenetic hypotheses of re-evolution of planktotrophy, and indicate possible ecological differences between primary and re-evolved planktotrophic veligers.