Evolution of life history in Serpulimorph polychaetes: a phylogenetic analysis.
The widely accepted hypothesis of plesiomorphy of planktotrophic, and apomorphy of lecithotrophic, larval development in marine invertebrates has been recently challenged as a result of phylogenetic analyses of various taxa. Here the evolution of planktotrophy and lecithotrophy in Serpulimorph polychaetes (families Serpulidae and Spirorbidae) was studied using a hypothesis of phylogenetic relationships in this group. A phylogenetic (parsimony) analysis of 36 characters (34 morphological, 2 developmental) was performed for 12 selected serpulid and 6 spirorbid species with known reproductive/developmental strategies. Four species of Sabellidae were used in the outgroup. The analysis yielded 4 equally parsimonious trees of 78 steps, with a consistency index (CI) of 0.654 (CI excluding uninformative characters is 0.625). Under the assumption of unweighted parsimony analysis, planktotrophic larvae are apomorphic and non-feeding brooded embryos are plesiomorphic in serpulimorph polychaetes. The estimated polarity of life history transitions may be strengthened by further studies demonstrating an absence of a unidirectional bias in planktotrophy-lecithotrophy transition in polychaetes.