Marine connectivity: a new look at pelagic larval duration and genetic metrics of dispersal

Understanding connectivity remains a fundamental challenge to marine ecology due to technical limitations of tracking larval dispersal. Marine population genetic analyses are often used to make inferences about the scale of population connectivity. For species with a larval phase, pelagic larval duration (PLD) is assumed to influence the scale of connectivity. If PLD and genetic metrics are reliable proxies of connectivity, the 2 should be well correlated. Previous tests report conflicting results, with many reports that global F-ST (Wright's fixation index) correlates poorly with PLD, and one very high correlation of isolation-by-distance (IBD) slope, which is derived from F-ST, with PLD. First we clarify the expectations for the performance of these different proxies in light of the latest understanding of larval dispersal dynamics. We then test the hypothesis that IBD slope may be a more robust correlate with dispersal scale than global F-ST with a new dataset of recent marine genetic studies. Re-evaluation of previously published and new datasets revealed a consistent, moderate fit (R-2 similar to 0.30) between genetic and PLD proxies of dispersal (using either IBD slope or global F-ST), with significant improvement for small-scale (<650 km) studies (R-2 = 0.50), and important effects of marker type. Significant effects of number of individuals and number of populations sampled on the genetic metrics in our dataset suggest a common need for more robust sampling designs. These results synchronize previous studies on this topic and provide validation that PLD and genetic metrics typically reflect scales of dispersal, as intended, at least when sampling design is robust.