KEEVER, C.C.*; HART, M.W.; Simon Fraser Univ.; Simon Fraser Univ.: Evolution of reproductive mode in asterinid sea stars
Asterinid sea stars have evolved diverse modes of reproduction and larval development that include planktonic larval dispersal with suspension feeding (or planktotrophy, the ancestral state for the Asteroidea), brief larval dispersal with non-feeding morphology (lecithotrophy), non-dispersing larval development in benthic egg masses, and internal brooding with live birth of juveniles. All three derived modes of reproduction appear to have evolved in parallel several times. Reconstruction of ancestral modes of development at internal nodes in an asterinid molecular phylogeny could be used to infer the order and timing of changes in mode of development. Unfortunately, prior independent attempts by Mike Hart and Cliff Cunningham to do so using 20th century parsimony and likelihood methods produced equivocal results and suggested that this particular problem may be inherently difficult. We have recently attempted to improve upon these results through expanded taxonomic sampling of mtDNA sequences (our own and those of Jon Waters and colleagues) and reproductive characters (especially by Maria Byrne), application of Bayesian methods of phylogenetic inference, and the use of new analytical methods of ancestral character state inference. Bayesian methods gave a well-supported tree topology with some high posterior probability estimates for ancestral states of some life history characters. The results appear to provide a more robust basis for inferring patterns of character change and for exploring correlations between modes of reproduction and genetic, ecological, or historical factors that are causes or consequences of this extensive life history variation. We use the phylogeny as the basis for analyzing correlations between mode of reproduction and population genetic structure.
