(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. S4). 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. S10) and
consistently but weakly declined towards the range edge (Table 3, Fig.
S7).
Nuclear diversity was also significantly associated with chlorophyll;
all chlorophyll models performed better than the null, and the model
including mean chlorophyll performed best overall (Table 2, Table S3).
Similarly to the mitochondrial patterns, nuclear genetic diversity
peaked at upper-range chlorophyll values (5-10 mg/m3)
(Fig. 4F, Fig. S9). Among the SST models, only the one including SST
range performed marginally better than the null model, and no SST
predictors were significantly related with nuclear genetic diversity
(Table 2, Table S2).