(b) Mitochondrial diversity
Globally, average mitochondrial genetic diversity was higher in the
western Pacific Ocean and lower along North American and European
coastlines (Fig. 2A & B, S4A & B). For both Hdand π, diversity peaked at low-to-mid latitudes and declined towards the
poles, particularly in the Northern hemisphere (Fig. 2A & B, S7A & B).
Diversity was also consistently higher in the Coral Triangle and
elsewhere in the western Indo-Pacific (Fig. 3A & B). For mitochondrial
genetic diversity (either Hd or π), we found that
all latitude and longitude models performed better than the baseline
(null) model (Table 1). Latitude, absolute latitude, and longitude were
significant predictors of mitochondrial genetic diversity (Table 1, Fig.
S8). As expected, Hd increased consistently with
the length of the locus in base pairs (Fig. S9) and decreased towards
species range edges (although π did not) (Fig. S10).
Both environmental drivers were significantly correlated with
mitochondrial genetic diversity (Hd and π) and
performed better than the null model (Table 2). Sea surface temperature
was positively related with mitochondrial diversity (Fig. 4A & B),
while chlorophyll-a concentration followed a quadratic relationship with
diversity highest at mid-to-upper chlorophyll-a concentrations (5-10
mg/m3) (Fig. 4D & E).
When looking at how these global patterns differed across a subset of
families represented in our dataset, we found substantial variation.
While the majority of the 10 families followed the same overarching
patterns (e.g. reduced mitochondrial genetic diversity at higher
latitudes, increased diversity at elevated SST, and a quadratic
relationship with chlorophyll-a concentration), several did not (Fig.
S11-S13). Gadidae (cods) and Sebastidae (rockfishes) showed elevated
mitochondrial diversity at higher latitudes and lower SST for bothHd and π, while the relationships between
latitude and SST varied in Carcharhinidae (requiem sharks), Engraulidae
(anchovies), and Rajidae (skates) by marker type.