Species boundaries in carp gudgeons (Eleotrididae: Hypseleotris) from the River Murray, South Australia:: evidence for multiple species and extensive hybridization

Allozyme analyses of carp gudgeons (Hypseleotris) from five sites in the lower River Murray revealed three distinctive taxa designated HA, HB and HC, diagnosable from one another by fixed differences at 3 5 loci, and three apparent F-1 hybrid forms, HAxHB, HAxHX and HBxHX, where HX denotes a taxon not sampled in its 'pure' form. Of all fish sampled, 25% were hybrids, although only one hybrid form was found at any one site, and never in company with both parental taxa. No hybrids involving HC were found, although this was the most common taxon, and no HAxHB hybrids were present at the one site of demonstrated sympatry between the parental taxa. Morphological analysis and the lack of introgression confirm that HA, HB, and HC are distinct biological species. Partial meristic data suggest that HC corresponds to H. klunzingeri s.l., 'Midgley s carp gudgeon is a composite of HA, HB and HAxHB hybrids, and 'Lake s carp gudgeon may be a composite of HX and one of its hybrids (HBxHX). We speculate that one or more of the hybrid classes may be 'unisexual lineages' (clonally reproducing, usually all-female forms derived from hybridization between congeners).