Morphological and genetic differentiation between populations of river crabs (Decapoda: Potamonautidae) from the Western Cape, South Africa, with a taxonomic re-examination ofGecarcinautes brincki

Abstract

As part of a larger study on the systematics of river crabs of the family Potamonautidae in southern Africa, several populations of potamonautid crabs were collected from the Cape Peninsula and surrounds, Western Cape. Two species were represented:Gecarcinautes brinckiandPotamonautes perlatus. The structure of the mandibular palp in the eight populations ofG. brinckiexamined was variable, and in four populations, the structure of this palp was the same as that which can be found in species ofPotamonautes. This paper re-examines the taxonomic status ofG. brincki, quantifies the morphological and genetic differentiation between populations ofG. brinckiandP. perlatusfrom the Cape Peninsula, and determines the extent of morphological and genetic differentiation among geographically separated populations ofG. brincki. Examination of type and other material confirmed thatGecarcinautes brinckiconforms to the current diagnosis of the genusPotamonautes(family Potamonautidae) to which it is therefore transferred. Discriminant functions analysis and protein gel electrophoresis showed thatP.perlatusandP. brinckiare morphometrically and genetically distinct, with the threeP. perlatuspopulations separating from the sixP. brinckipopulations at a genetic identity value of I = 0·66 (D = 0·419). The results also showed thatP. brinckiis a highly structured entity, with the populations collected from the Cape Peninsula clearly separating both genetically (I = 0·75, corresponding to D = 0·296), and morphologically (presence or absence of a flange on the terminal segment of the mandibular palp) from those collected further east. The lack of gene flow between populations of this species is discussed in the light of current species concepts.