Allozyme analysis reveals a complex population structure in the southern calamary Sepioteuthis australis from Australia and New Zealand

Abstract

Allozyme electrophoresis was used to investigate species boundaries and population genetic structure within the southern calamary Sepioteuthis australis Quoy and Gaimard. Samples collected from 17 localities around southern Australia and northern New Zealand were examined for allozyme variation at 49 loci. Of 13 polymorphic loci detected, 7 were sufficiently variable to be useful as routine genetic markers of population structure. There was little or no genetic differentiation across the entire range sampled at 5 of these 7 loci. In marked contrast, the allozyme data at 2 loci (Fdp and PepD) unequivocally sorted all individuals into 1 of 3 genetic types, the geographic distributions of which exhibited a markedly non-random pattern. One type was mainly found near the western and eastern limits of the sampled area, the other type predominantly in the intervening region. Where these 2 types overlapped, a third hybrid-type was found at frequencies predicted under Hardy-Weinberg expectations. The 2 most-likely explanations for these data are: (1) there are 2 taxa within S. australis which produce only F1 hybrids wherever they overlap, or (2) the 2 loci Fdp and PepD are tightly linked and thus are not independent measures of population structure. Preliminary morphological and reproductive data support the hypothesis of 2 taxa, while mitochondrial DNA-sequence data are inconclusive. It is argued that some combination of the 2 explanations may be operating. Regardless of the final outcome, the data indicate that there are a number of discrete stocks of S. australis in this region, a result at variance with current management perspectives on this important fishery.