Data from: Identifying environmental correlates of intraspecific genetic variation

Genetic variation is critical to the persistence of populations and their
capacity to adapt to environmental change. The distribution of genetic
variation across a species' range can reveal critical information
that is not necessarily represented in species occurrence or abundance
patterns. We identified environmental factors associated with the amount
of intraspecific, individual-based genetic variation across the range of a
widespread freshwater fish species, the Murray cod Maccullochella peelii.
We used two different approaches to statistically quantify the relative
importance of predictor variables, allowing for nonlinear relationships: a
random forest model and a Bayesian approach. The latter also accounted for
population history. Both approaches identified associations between
homozygosity by locus and both disturbance to the natural flow regime and
mean annual flow. Homozygosity by locus was negatively associated with
disturbance to the natural flow regime, suggesting that river reaches with
more disturbed flow regimes may support larger, more genetically diverse
populations. Our findings are consistent with the hypothesis that
artificially induced perennial flows in regulated channels may provide
greater and more consistent habitat and reduce the frequency of population
bottlenecks that can occur frequently under the highly variable and
unpredictable natural flow regime of the system. Although extensive river
regulation across eastern Australia has not had an overall positive effect
on Murray cod numbers over the past century, regulation may not represent
the primary threat to Murray cod survival. Instead, pressures other than
flow regulation may be more critical to the persistence of Murray cod (for
example, reduced frequency of large floods, overfishing and chemical
pollution).