CONSEQUENCES OF A CATADROMOUS LIFE-STRATEGY FOR LEVELS OF MITOCHONDRIAL-DNA DIFFERENTIATION AMONG POPULATIONS OF THE AUSTRALIAN BASS, MACQUARIA-NOVEMACULEATA

The influence of a catadromous life-strategy on levels of spatial gene tic structuring in fish is poorly understood. In an effort to gain a b etter appreciation of how this specialized life-strategy determines po pulation genetic structuring, we assessed variation in the mitochondri al DNA (mtDNA) control region in a catadromous perciform, the Australi an bass Macquaria novemaculeata. Nineteen putative haplotypes were res olved using temperature gradient gel electrophoresis from 10 geographi cally distinct populations. Significant heterogeneity was revealed in haplotype frequencies and their spatial distributions among many local es. Gene partitioning statistics (AMOVA) for both raw haplotype freque ncy data and frequency data with sequence divergences were concordant, indicating that M. novemaculeata populations were moderately genetica lly structured (Phi(ST) = 0.05, 0.06; P < 0.001, respectively). Isolat ion by distance seems to be a strong structuring force in M. novemacul eata, culminating in no detectable phylogeographic structuring among h aplotypes. Low sequence divergences were observed among many haplotype s and it is suggested that these are the result of pruning of maternal lineages by cyclical variations in female reproductive success. This study highlights the importance of life-history patterns and, in parti cular, spawning locality, in determining spatial structuring of mtDNA variation in catadromous species.