Life history diversity and evolution in the Asterinidae

Asterinid sea stars have the greatest range of life historiesknown for the Asteroidea. Larval form in these sea stars hasbeen modified in association with selection for planktonic,benthic, or intergonadal developmental habitats. Life historydata are available for 31 species and molecular data for 28of these. These data were used to assess life history evolutionand relationships among asterinid clades. Lecithotrophy is prevalentin Asterinidae, with at least 6 independent origins of thisdevelopmental mode. Morphological differences in the attachmentcomplex of brachiolaria larvae were evident among species withplanktonic lecithotrophy. Some features are clade specific whileothers are variable within clades. Benthic brachiolariae aresimilar in Aquilonastra and Parvulastra with tripod-shaped larvae,while the bilobed sole-shaped larvae of Asterina species appearunique to this genus. Multiple transitions and pathways havebeen involved in the evolution of lecithotropy in the Asterinidae.Although several genera have a species with a planktonic feedinglarva in a basal phylogenetic position, relative to specieswith planktonic or benthic lecithotrophy, there is little evidencefor the expected life history transformation series from planktonicfeeding, to planktonic non-feeding, to benthic non-feeding development.Intragonadal development, a life history pattern unique to theAsterinidae, arose three times through ancestors with benthicor pelagic lecithotrophy. Evolution of lecithotrophy appearsmore prevalent in the Asterinidae than other asteroid families.As diverse modes of development are discerned in cryptic speciescomplexes, new insights into life history evolution in the Asterinidaeare being generated.