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BackgroundThe hippolytid genus Lysmata is characterized by simultaneous hermaphroditism, a very rare sexual system among Decapoda. Specialized cleaning behavior is reported in a few pair-living species; these life history traits vary within the genus. Unfortunately, the systematics of Lysmata and the Hippolytidae itself are in contention, making it difficult to examine these taxa for trends in life history traits. A phylogeny of Lysmata and related taxa is needed, to clarify their evolutionary relationships and the origin of their unique sexual pattern. In this study, we present a molecular phylogenetic analysis among species of Lysmata, related genera, and several putative hippolytids. The analysis is based upon DNA sequences of two genes, 16S mtDNA and nuclear 28S rRNA. Phylogenetic trees were estimated using Bayesian Inference, Maximum Likelihood, and Maximum Parsimony.ResultsPhylogenetic analysis of 29 species of Lysmata, eight genera of Hippolytidae and two genera of Barbouriidae based on a single (16S, 28S) and combined gene approach (16S+28S) indicates that three groups of Lysmata differentiate according to antennular morphology: (1) Lysmata, having a multi-segmented accessory branch, (2) Hippolysmata (prior to Chace 1972), with a one-segmented accessory branch, and (3) a third group of Lysmata outliers, with one-segmented unguiform accessory branch, and close affinity to the genera Exhippolysmata and Lysmatella. The monophyly of the clade bearing a multi-segmented accessory branch is robust. Within the short accessory branch clade, species with specialized cleaning behaviors form a monophyletic clade, however, the integrity of the clade was sensitive to alignment criteria. Other hippolytid and barbouriid genera used in the analysis are basal to these three groups, including one displaying simultaneous hermaphroditism (Parhippolyte). The two barbouriid species occur in a separate clade, but among hippolytid taxa.ConclusionsThe data support the historical morphological division of Lysmata into clades based on accessory branch morphology. The position of the "cleaner" shrimps, indicates that specialized cleaning behavior is a derived trait. The topologies of the cladograms support the monophyly of the barbouriids, but do not support their elevation to familial status. Taxa ancestral to the genus Lysmata display simultaneous hermaphroditism, suggesting that this life history trait evolved outside the genus Lysmata.

Mitochondrial genes for cytochrome oxidase I (COI) from hydrothermal-vent-endemic gastropods of the genus Alviniconcha were sequenced to determine the phylogenetic relationships among specimens from three areas in the western Pacific. Individuals of Alviniconcha hessleri were collected at two vent fields (depths 1470 m and 3600 m) in the Mariana Trough. Specimens collected in the North Fiji Basin could be divided into two genetically distinct groups, both of which also differed from A. hessleri from the Mariana Trough. None of the specimens of the genus Alviniconcha collected in the Manus Basin differed genetically from the dominant group from the North Fiji Basin. We suggest that the specimens of the genus Alviniconcha analyzed in the present study can be tentatively classified into A. hessleri and two undescribed species.

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The population structure of Bothrocara hollandi, a dominant deep-sea demersal fish in the Japan Sea, was analyzed on the basis of the nucleotide sequence of part of the mitochondrial control region. The 296 individuals analyzed were collected at 17 sites at depths between 375 and 1677 m, and could be divided into a distinct monophyletic group of haplotypes and a paraphyletic group that contained the remaining haplotypes. Individuals in the first group were collected only from shallower sites at depths less than 1100 m, and they were found predominantly off the western part of Honshu Island (the Japanese mainland). Individuals in the second group were collected from all sites at which fish were sampled. The genetic diversity of the first group was greater than that of the second group. As a consequence, the genetic diversity of populations showed a tendency to decrease with increasing depth. The divergence of the 2 groups was estimated to have occurred during the early part of the last glacial period. The geographical pattern of distribution of haplotypes might be attributable to the accumulation of unique genetic characteristics in different refuges during the last glacial period and to secondary contacts as a result of migration from such refuges after the last glacial period. No genetic differentiation between the 2 morphotypes of this species was detected. KEY WORDS: Phylogeography · Deep-sea demersal fish · Bothrocara hollandi · Japan Sea · Mitochondrial DNA Resale or republication not permitted without written consent of the publisher