Taxonomic status and phylogenetic relationships of some species of the genus gammarus (Crustacea, Amphipoda) deduced from mitochondrial DNA sequences

Times Cited: 36International audienceMitochondrial DNA nucleotide sequence analysis was used to determine the extent of genetic differentiation among six species of the genus Gammarus (Crustacea, Amphipoda) common in France (G. fossarum, G. pulex, G. Lacustris, G. wautieri, G. roeseli, G. marinus). From 23 different populations, 104 specimens were compared to examine their taxonomic status and their phylogenetic relationships. Nucleotide sequences for a 376-base segment of the cytochrome c oxidase subunit I (COI) gene were obtained through direct sequencing of amplified DNA. The strong sequence variability found at the interspecific level, generally masked by morphological or ecological similarities, is consistent with that observed for other crustaceans and supports existing species classifications. A high level of genetic variation was observed at the intraspecific level, suggesting that the COI gene will be a powerful marker for amphipod population biology. Based on the mitochondrial DNA results, we propose a phylogenetic hypothesis of the relationships among the six studied species, which is discussed in biogeographic and evolutionary terms. (C) 1997 Academic Press

Pleistocene glaciations and polyphyletic origins of polyploidy in an arctic cladoceran

RFLP analysis of the ND4-ND5 genes of the mtDNA genome in Daphnia middendorffiana and three closely allied species was used to investigate its origin and age. Populations of D. middendorffiana from arctic Canada were found to possess three distinct mtDNA lineages, only one of which appears unique to this species. The other two mtDNA lineages are either closely allied or identical to haplotypes in D. pulicaria, suggesting that it is the maternal parent of many clones of D. middendorffiana. Within D. pulicaria, mtDNA lineages have largely disjunct distributions, suggesting that populations of this species persisted in three glacial refugia (arctic, western, eastern) during the Pleistocene. Hybridizations between these refugial stocks and other species such as D. melanica and D. pulex likely generated many of the polyploid lineages of D. middendorffiana following the Wisconsinan glaciation. The presence of one unique mtDNA lineage in D. middendorffiana suggests that at least some of its clones are more ancient, but further studies are needed to rule out the possibility of their recent derivation from an as yet undetected sexual species. As a general result, this study suggests that polyploid cladocerans are unlikely to predate the Pleistocene