Meeting Abstract
Chitons (Mollusca: Polyplacophora) have eight overlapping shell plates; these contain clusters of sensory cells called aesthetes. In some chiton species, aesthetes are modified to include an eyespot, and in others, aesthetes are present in addition to eyes with a lens and retina. To address the evolution of complexity in chiton eyes, it is necessary to phylogenetically test whether Chitoninae, with eyespots, is sister to Acanthopleurinae + Toniciinae, with lens eyes. To this end, we have taken a phylogenomic approach using transcriptome data. We sequenced cDNA from sixteen chiton species and one aplacophoran with Illumina Hi-Seq. In addition to novel aculiferan data sequenced for this study, we included data from ten species available on SRA, and data from three mollusc genomes. Our final data matrix contains 30 mollusc species and >500 genes. Overall, our phylogenomic results are consistent with previously published chiton phylogenies, with major lineages supported as monophyletic. Chitoninae is sister to Acanthopleurinae + Toniciinae in our analyses, suggesting that eyespots may be the morphological precursors of ‘shell eyes’. However, expanded taxon sampling is needed to address remaining questions. To generate a more taxon-rich phylogeny for Chitonina, we have used our transcriptome-based data matrix to design probes for a genomic-DNA targeted gene capture study. This target-capture study will enable us to more directly address the question of whether or not lens eyes have multiple origins in chitons.
