Phylogenetic relationships and remarkable radiation in Parartemia (Crustacea: Anostraca), the endemic brine shrimp of Australia: evidence from mitochondrial DNA sequences

The Australian continent is notable for the faunal radiations which have occurred in its saline inland waters. The endemic brine shrimp genus Parartemia inhabits many of these habitats. The complex pattern of morphological variation in parartemiids has impeded the establishment of a sound scheme of species relationships. The present study provides an explicit hypothesis of relationships for the genus based on nucleotide sequence data from a segment of mitochondrial DNA coding for the large subunit rRNA gene. Phylogenetic analyses indicated that the eight known species are genetically distinct, and revealed the existence of at least two new species. The molecular data support certain morphology-based relationships among species, but are inconsistent with other hypotheses. There is evidence that most members of the genus arose in a short interval, followed by remarkable genetic divergence. Comparisons of levels of mt DNA sequence divergence between lineages from saline inland waters and freshwaters using representative crustacean groups from Australia that included parartemiids indicated profound differences in rates of evolution, with halophiles exhibiting greater rates of change than their counterparts from freshwaters.     

MOLECULAR SYSTEMATICS OF THE FRESHWATER SNAIL FAMILY LYMNAEIDAE (PULMONATA: BASOMMATOPHORA) UTILISING MITOCHONDRIAL RIBOSOMAL DNA SEQUENCES

Nucleotide sequences were obtained from a region of the largesubunit mitochondrial ribosomal RNA gene from 18 lymnaeid taxaand a planorbid out-group. A molecular phylogeny was constructedutilising maximum-parsimony and distance analyses of the data.This agreed with certain aspects of kary-ology and immunology-basedlymnaeid taxonomy, but failed to support the only previouslypublished phylogenetk scheme or past inferences regarding basalrelationships in lymnaeids. The molecular phylogeny is alsoincongruent with previous progressive-evolution models basedon chromosome numbers because European genera having n = 18formed a group basal within lymnaeids whereas taxa belongingto the n = 16 group included the most derived lymnaeids. Relationshipsof selected problematic taxa inferred from the molecular phylogenywere compared to previous hypotheses based on other data sets.A partial, tentative bio-geographical hypothesis was derivedfrom this phylogeny. We propose a Laurasian origin for lymnaeidsin the late Jurassic. (Received 14 August 1996; accepted 3 October 1996)