(c) Nuclear diversity
In contrast to the mitochondrial results, there was no evidence for
strong latitudinal or longitudinal diversity gradients in the nuclear
dataset. Nuclear genetic diversity declined only weakly towards the
poles and did not follow strong longitudinal patterns (Fig. 2C & 3C,
Fig. S7). The null model performed better than any models that
incorporated latitude or longitude predictors, and neither latitude nor
longitude was a significant term in any of the models (Table 3).
However, diversity was consistently lower for loci amplified with
primers originally developed in another species (Fig. S14) and showed a
negative, albeit non-significant, relationship with range position
(Table 3, Fig. S10).
Nuclear diversity was also significantly associated with chlorophyll-a
concentration; all models with chlorophyll-a as a predictor performed
better than the null, and the model with only mean chlorophyll-a
concentration performed best overall (Table 2). Similarly to the
mitochondrial patterns, nuclear genetic diversity peaked at mid-to-upper
chlorophyll-a concentrations (5-10 mg/m3) (Fig. 4F).
Mean SST was not significantly related with nuclear genetic diversity
(Table 2, Fig 4C).
As with mitochondrial genetic diversity, global patterns in nuclear
genetic diversity also appeared to vary across families, although to a
much diminished degree (Fig. S11-13).