Phylogenetic relations among spirorbid subgenera and the volution of opercular brooding

摘要

Spirorbid olychaetes are a common and often conspicuous elemnt of marine,hard-bottom environments world-wide.Because they exhibit a surprisig variety of brooding modes,they offer an opportunity to study the evolution of alternative life=history strategies.A preiminary investgiationof their phylogenetic relationships was conducted on morphological data amalgamated from pubished species descriptions and ligyht microscopyCladistic analyssi was parsimony-based and was done at the subgenus level.All 27 spirorbid genera and subgenera are represented,along with 7 serpulid outgroups.The phylogenetic hypoteses were used to explore the origin of opercular brood chambers in the Pileolariinae and the Januinae.Both weightted and unweighted analyses strongly supported the monophyly of the Spirorbidae,and yielded three and a single most parsimonious tree respectively.All spirorbid subfamilies were monophyletic except two:the Pileolariinae,from which the Januinae seem to have arisen,and the Romanchellinae,which were polyphyletic inthe unweighted analysis and paraphyletic with Paralaeospira in the weighted analysis.HOwever,support for the hypothesized relationships among spirorbid subfamilies was generally weak.A weakly supported clade of opercular brooders occupied the most derived position on the tree,and the strnlgy supported monophyletic Januinae comprise a derived clade within the Pileolariinae.This analysis suggests that the evolutionary novelty of opercular brooding arose only once,and the simple cylindrical januin brood chamber is a simplification of the more complex pileolariin form.