Neither larval duration nor dispersal distance predict spatial genetic diversity in planktonic dispersing species

Abstract

The increase in genetic distance between marine individuals or populations with increasing distance has often been assumed to be influenced by dispersal distance. In turn, dispersal distance has often been assumed to correlate strongly with pelagic larval duration (PLD). We examined the consistency of these assumptions in species with long planktonic durations. Reviewing multiple marine species, Selkoe & Toonen (2011; Mar Ecol Prog Ser 436:291-305) demonstrated significant fit of a species’ PLD with metrics of genetic distance between sampling sites. However, for long dispersers (PLD >10 d) whose dispersal is more influenced by ocean currents, the fit of PLD and genetic connectivity metrics was not significant. We tested if using realistic ocean currents to determine simulated dispersal distances would produce an improved proxy for larval dispersal that correlates more strongly with genetic connectivity metrics. We estimated the dispersal distance of propagules for locations in the genetic studies compiled by Selkoe and Toonen with a global ocean model (Mercator, 1/12° resolution). The model-derived estimates of dispersal distance did not correlate better than PLD against the genetic diversity metrics global FST km-1 and isolation-by-distance (IBD) slope. We explored 2 explanations: (1) our ocean circulation-based dispersal distance estimates are too simple to produce biologically meaningful improvement over PLD, and (2) IBD slope is not a powerful predictor of variation in dispersal distance between species with long PLD. Exploring these explanations suggests directions for future research which will enable better quantitative understanding of genetic diversity and its spatial distribution in coastal marine organisms.