Evolution of life cycle, colony morphology, and host specificity in the family Hydractiniidae (Hydrozoa, Cnidaria).

摘要: Biased transitions are common throughout the tree of life. The class hydrozoa is no exception, having lost feeding medusa stage at least 70 times. family hydractiniidae includes one lineage with pelagic medusae (Podocoryna) and several without (e.g., Hydractinia). benthic colony also varies widely in host specificity form. five-gene phylogeny presented here requires multiple between character states for medusae, specificity, phenotype. Significant phylogenetic correlations exist medusoid form, morphology, specificity. Species nonfeeding usually specialized on a single type, reticulate colonies correlated nonmotile hosts. history less certain. Podocoryna nested within five lineages lacking medusae. This either repeated losses or remarkable re-evolution after 150 million years. Traditional ancestral reconstruction favors regain, but likelihood framework testing biased cannot distinguish versus regain. A hypothesis transient selection pressure favoring such loss. Populations species always locally rare lack does not result restricted distribution around world.