Meeting Abstract
106.5 Sunday, Jan. 6 Phylogeny and biogeography of the shell-eyed chitons EERNISSE, D.J.*; BROOKER, L.R.; Cal State Fullerton; Univ. Sunshine Coast, Qld. deernisse@fullerton.edu
Over their half a billion-year history, chitons have had numerous aesthete sensory organs in their shells, with shadow detection as one of their proposed functions. Much more recently, a clade of chitons have diversified that have not only aesthetes but also much larger ocelli, and these are image forming and each has an aragonitic lens, retina, and other hallmarks of animal visual systems. Shell-eyed chitons are not known as fossils older than the Miocene yet since then have become some of the most common reef-dwelling chitons in tropical and southern hemisphere localities worldwide. Despite their ecological importance and their status as the animals with the most recently evolved eyes, their phylogenetic relationships have not been well resolved. They have been classified as either Toniciinae or Acanthopleurinae within Chitonidae based on whether the girdle is nude or is covered with calcareous armor (spines or scales), respectively. We tested this subdivision with DNA sequence comparisons. Our results strongly corroborate the shell-eyed clade but not its internal subdivision into conventional groupings. Instead, our results support separate New World and Old World radiations, with loss of girdle elements corresponding to polyphyletic lineages nested within the shell-eyed clade. There is also intriguing evidence of regional patterns of speciation or phylogeographic divergence. For example, Acanthopleura gemmata from northeastern Australia have closer affinities with western Pacific populations from New Caledonia than they do with A. “gemmata” from Western Australia, and the latter have closer affinities with Indian Ocean populations as far west as Africa. In between, populations north of Australia are different again with likely unrecognized species diversity. Improved phylogenetic and biogeographic resolution will allow us to relate variation in ocelli to the pattern of evolutionary diversification.
