MORPHOLOGICAL AND GENETIC DIFFERENTIATION BETWEEN POPULATIONS OF RIVER CRABS (DECAPODA, POTAMONAUTIDAE) FROM THE WESTERN CAPE, SOUTH-AFRICA, WITH A TAXONOMIC REEXAMINATION OF GECARCINAUTES BRINCKI

As part of a larger study on the systematics of river crabs of the fam ily Potamonautidae in southern Africa, several populations of potamona utid crabs were collected from the Cape Peninsula surrounds, Western C ape. Two species were represented: Gecarcinautes brincki and Potamonau tes perlatus. The structure of the mandibular palp in the eight popula tions of G. brincki examined was variable, and in four populations, th e structure of this palp was the same as that which can be found in sp ecies of Potamonautes. This paper re-examines the taxonomic status of G.brincki, quantifies the morphological and genetic differentiation be tween populations of G. brincki and P. perlatus from the Cape Peninsul a, and determines the extent of morphological and genetic differentiat ion among geographically separated populations of G. brincki. Examinat ion of type and other material confirmed that Gecarcinautes brincki co nforms to the current diagnosis of the genus Potamonautes (family Pota monautidae) to which it is therefore transferred. Discriminant functio ns analysis and protein gel electrophoresis showed that P. perlatus an d P. brincki are morphometrically and genetically distinct, with the t hree P. perlatus populations separating from the six P. brincki popula tions at a genetic identity value of I = 0.66 (D = 0.419). The results also showed that P. brincki is a highly structured entity, with the p opulations collected from the Cape Peninsula clearly separating both g enetically (I = 0.75, corresponding to D = 0.296), and morphologically (presence or absence of. a flange on the terminal segment of the mand ibular palp) from those collected further east. The lack of gene flow between populations of this species is discussed in the light of curre nt species concepts. (C) 1997 The Linnean Society of London.