Carapace dentition patterns, morphometrics and allozyme differentiation amongst two toothed freshwater crab species (Potamonautes warreni and P-unispinus) (Decapoda : Brachyura : Potamonautidae) from river systems in South Africa

The taxonomic relationship between two toothed South African river crabs, P otamonautes warreni and P. unispinus, is unclear. The problem stems from th e widespread variation in carapace dentition patterns amongst P. warreni in dividuals over its biogeographic range, where single toothed individuals ma y appear similar in carapace morphology to P. unispinus. Ten populations of P. warreni and 18 populations of P. unispinus were collected and the morph ometric and genetic differentiation between the two taxa quantified. Patter ns of morphometric and genetic variation were examined using multivariate s tatistics and protein gel electrophoresis, respectively. Principal componen t analyses of carapace characters showed that the two species are morpholog ically indistinguishable. However, discriminate functions analyses and addi tional statistical results corroborate the morphological distinction betwee n the two taxa. Allozyme electrophoresis of 17 protein coding loci, indicat ed a close genetic similarity between the two species (I = 0.92). A fixed a llelic difference at one locus (LT-2) and extensive genetic variability at another locus (PGM-1) indicate that two gene pools are present and that the two taxa are genetically isolated. Intraspecific genetic I values for both species were > 0.97 and indicated no apparent genetic structuring on a mic ro or macro-geographic scale. The variation in carapace dentition among P. warreni populations possesses no genetic basis and may possibly toe the pro duct of ecogenesis. The value of dentition patterns in the systematics of r iver crabs is discussed. Dentition patterns among river crab species appear to be conserved and reliable as species specific diagnostic markers, but s hould ideally be used in combination with other morphological data sets and genetic evidence.