Contributions to Zoology, 81 (3) – 2012Kristine N. White; James D. Reimer: DNA phylogeny of Ryukyus Leucothoidae (Crustacea: Amphipoda)

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Maximum likelihood (ML) analysis of partial 18S rDNA sequences of all available Ryukyus species’ sequences resulted in a tree with generally high bootstrap support values for most nodes. Neighbor Joining (NJ) analysis resulted in an identical distance tree with high bootstrap support values. Bayesian analysis (B) resulted in a phylogenetic tree identical to the ML tree with high posterior probabilities.

The resulting 18S rDNA tree depicted two major clades (Fig. 1), one composed of Anamixis and Para­namixis species (ML = 100%, NJ = 100%, B = 1.00) and the other containing Leucothoe species (ML = 92%, NJ = 72%, B = 1.00). The anamixid clade did not have prominent subclades, grouping Anamixis sentan White and Reimer, 2012c and Paranamixis thomasi White and Reimer, 2012a into one clade. The 18S rDNA sequence data also supported the connection of leucomorphs and anamorphs of P. thomasi (ML = 69%, NJ = 99%, B = 1.00). The connection of anamorphs and leucomorphs was not possible for A. sentan as only leucomorphs were sequenced. The leucothoid clade depicted two distinct subclades within the genus Leucothoe. A new generic-level subclade grouped morphologically similar species (Leucothoe toribe White and Reimer, 2012b, Leucothoe obuchii White and Reimer, 2012a, Leucothoe enko White and Reimer, 2012c, and Leucothoe kebukai White and Reimer, 2012c) together (ML = 100%, NJ = 100%, B = 1.00). Within the larger Leucothoe subclade (ML = 86%, NJ = 98%, B = 1.00), multiple specimens of each species formed subclades.


Fig. 1. Maximum likelihood (ML) phylogenetic tree of ‘long’ partial 18S ribosomal DNA gene sequences from replicates of 21 Leucothoid taxa collected from depths of 1-33 meters, rooted with an outgroup of two Liljeborgiid species. Numbers at branches represent ML/Neighbor joining (NJ) bootstrap values. Thick lines represent Bayesian posterior probabilities >0.95.

Four morphologically similar species (Leucothoe vulgaris White and Reimer, 2012a, Leucothoe ama­miensis White and Reimer, 2012a, Leucothoe akuma White and Reimer, 2012c, and Leucothoe akaisen White and Reimer, 2012c) formed a subclade separate from all other Leucothoe species within the leucothoid subclade (ML = 92%, NJ = 100%, B = 1.00). Five specimens of Leucothoe elegans White and Reimer, 2012a formed a subclade with Leucothoe hashi White and Reimer, 2012b, Leucothoe zanpa White and Reimer, 2012b and Leucothoe lecroyae White and Reimer, 2012b, depicting minor population differences between Okinawa–jima, Amami–oshima, and Hiroshima populations of L. elegans (ML = 90%, NJ = 67%, B = 1.00). The final subclade in the Leucothoe subclade was comprised of morphologically similar species (Leucothoe trulla White and Reimer, 2012a, Leucothoe bise White and Reimer, 2012b, Leucothoe nurunuru White and Reimer, 2012b, Leucothoe daisukei White and Reimer, 2012b, and Leucothoe akaoni White and Reimer, 2012b) (ML = 68%, NJ = <50%, B = 1.00).