Large genetic distances within a population of Amphipholis squamata (Echinodermata; Ophiuroidea) do not support colour varieties as sibling species

Abstract

The brittle star Amphipholis squamata is paradoxical in that it lacks an obvious dispersive phase yet has a world-wide distribution. Although individuals from distant populations are morphologically similar, a recent phylogenetic analysis found multiple clades separated by large genetic divergences. These clades were not phylogeographically structured and genetic divergences within populations were typically as high as those amongst populations. The recent suggestion that the sympatric colour varieties 'orange', 'dark brown', 'beige', 'black' and 'grey' represent sibling species, led us to test whether colour variety and phylogeny were congruent. Genetic distances among sequences of the mitochondrial gene 16S rRNA from the colour varieties were surprisingly high (up to 13% uncorrected distance) and phylogenetic analyses using maximum parsimony, maximum likelihood and neighbour joining gave well supported, congruent phylogenies. However, the clades were not consistent with colour variety. When clades were constrained to make colour varieties monophyletic, tree scores were always significantly worse. We conclude from the results of this study that colour varieties do not represent distinct phylogenetic lineages. We discuss the implications of our results in the light of the possibility of clonality or self-fertilization in this species.