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 genetic structuring in fish is poorly understood. In an effort to gain a better appreciation of how this specialized life-strategy determines population genetic structuring, we assessed variation in the mitochondrial DNA (mtDNA) control region in a catadromous perciform, the Australian bass Macquaria novemaculeata. Nineteen putative haplotypes were resolved using temperature gradient gel electrophoresis from 10 geographically distinct populations. Significant heterogeneity was revealed in haplotype frequencies and their spatial distributions among many locales. Gene partitioning statistics (AMOVA) for both raw haplotype frequency data and frequency data with sequence divergences were concordant, indicating that M. novemaculeata populations were moderately genetically structured (phi ST = 0.05, 0.06; P < 0.001, respectively). Isolation by distance seems to be a strong structuring force in M. novemaculeata, culminating in no detectable phylogeographic structuring among haplotypes. Low sequence divergences were observed among many haplotypes 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 particular, spawning locality, in determining spatial structuring of mtDNA variation in catadromous species.