| dc.description.abstract | Indirect genetic approaches such as those based on the association between genetic and
geographic distance (isolation by distance, IBD) may provide one of the best means of estimating
dispersal in marine systems. We evaluated the scale -dependency and the ecological covariates of the
1131) relationship through a combined modeling and meta-analytical approach. Using Wright's
fixation index F-ST, simulations were used to generate IBD relationships, F-ST/(1-F-ST) and
geographic distance, for various combinations of average dispersal distance and number of
generations. 1131) linearity increased with time since colonization and dispersal distance, although
the effect of dispersal distance predominated after initial colonization. Simulations suggest that
declines in the 1131) slope were associated with increases in the spatial scale of observation,
suggesting that the IBD pattern is non-linear at very short and long average dispersal distances. We
hypothesized that non-linear IBD would be common in marine populations, and apparent through a
biologically significant non-zero intercept arid decreasing slope with increasing geographic scale.
Predictions of common non-linearity were examined through IBD relationships (i.e. slope, intercept,
R-2 of the regression) and life history parameters from the published literature for 18 species of
anadromous/philopatric fishes. As predicted, 1131) parameters (intercept and slope) were
consistently correlated with many life history traits (e.g. fecundity, egg size). However, the
statistical removal of adult size eliminated most significant life history-IBD, correlations.
Increases in IBD slope were associated with decreasing gene flow (p = 0.014, R-2 = 0.33), and
decreasing migration distance (p = 0.039, R-2 = 0.23). Non-linearity was further supported by
consistent declines in the 1131) slope with increased geographic scale in anadromous fish as well as
several marine species, suggesting the ubiquity of this phenomenon. We conclude that isolation by
distance patterns may reflect dispersal phenotype and are biologically significant. Nonetheless,
non-linearity in 1131) pattern is probably the norm in aquatic organisms, resulting from large
ranges and limited dispersal. Accordingly, approximations of demographic parameters based on the IBD
must be made cautiously, taking into account possible non-linearity, scale dependencies, and
assumptions of genetic drift-dispersal equilibrium. | en_US |
