HART, M.W.: Character conflict and life history evolution of marine invertebrates

The evolution of marine invertebrate larvae includes numerous adaptive modifications of ancestral, complex, feeding larval forms to produce derived, often simplified, nonfeeding or nonplanktonic larvae. These modifications are taxonomically widespread and suggest numerous convergences in the evolution of modified nonfeeding or nondispersing modes of larval development. Molecular phylogenetic analyses of closely related species with diverse modes of development suggest that convergence is common in the evolution of life history traits such as egg size, fecundity, and development time that are correlated with mode of development. I review these studies briefly. Frequent homoplasies in these life history characters would make them inappropriate as phylogenetic characters for inferring relationships. I develop one example in detail from our work on asterinid sea stars in which convergence in life history characters appears to be common. A partition homogeneity analysis shows, not surprisingly, that life history characters and mitochondrial DNA sequence characters conflict strongly. Sequence characters mapped onto the phylogeny inferred from life history characters indicate a large number of unlikely nucleotide and amino acid substitutions. A total evidence analysis leads to some ambiguities in phylogenetic inference that are not evident in the analysis of sequences alone. The adaptive nature of many changes in larval form suggests a likely route for convergences to evolve, leading to homoplasies in life history characters. This observation suggests that such characters should not be used as data in phylogenetic inference, though the distribution of and change in these characters through evolutionary time is of considerable interest.