GENETIC-VARIATION IN YABBIES, CHERAX-DESTRUCTOR AND C-ALBIDUS (CRUSTACEA, DECAPODA, PARASTACIDAE), INDICATES THE PRESENCE OF A SINGLE, HIGHLY SUB-STRUCTURED SPECIES

The high degree of morphological variability exhibited by yabbies (Che rax destructor Clark and C. albidus Clark) prompted this investigation of genetic variation, specifically addressing the taxonomy and popula tion structure of these freshwater crayfish. Yabbies from 14 localitie s in South Australia and Victoria were classified morphologically and examined electrophoretically at 35 gene loci. Morphometric analysis co nfirmed the existence of two morphotypes with allopatric distributions . Genetic divergence between morphotypes was relatively low (average f ixed differences = 4.72%, average Nei D = 0.085) compared with known i nterspecific levels-both generally and within the genus Cherax-and lev els of divergence between populations within the morphotypes. Subspeci fic status for albidus is consequently advocated. This species shows e vidence of a high degree of genetic fragmentation, with significant he terogeneity occurring at two or more loci between even the closest loc alities. Gene flow appears to be severely restricted even within drain age basins and a 'stepping-stone' model of population structure may be appropriate. This high degree of genetic fragmentation may explain th e variable morphology of this species although phenotypic plasticity c ould also play a role. Genetic variation was chaotically distributed ( the only consistent geographic pattern of divergence corresponding to the albidus morphotype), probably reflecting numerous translocations o f this species. The results highlight the need for taxonomy and manage ment to be based on genetic as well as morphological subdivisions.