Phenotypic divergence
Total length – Model comparisons showed that TL varied across
sites rather than habitats (Table 2). This pattern was predominantly
driven by stickleback from HS2 site being shorter than stickleback from
other sites (Figure 1). TL was negatively correlated with both
temperature (Table 3) and bird density (Table 3), but the model with
temperature as a predictor fit the data better (i.e., had a lower DIC;
Table 3). All traits, except plate number and GRN, were positively
correlated with TL (Table 2), and all results presented hereafter refer
to effects on size-corrected traits.
Defence traits - There were no sex differences in the relative
length of either dorsal or pelvic spines, but males had more armour
plates than females (Table 2). Model comparisons suggested that defence
traits tended to vary according to habitat rather than site, although
there was only very weak statistical support for this effect (Table 2,
Figure 1). Whilst none of the ecological variables predicted relative
length of DS1 and armour plate number (Table 3), relatively length of
DS2 increased as the density of piscivorous birds increased (Table 3)
and relative length of PS increased in deeper water (Table 3, Figure 2).
However, statistical support for these environmental associations was
weak (the ΔDIC to the null model was within 2, and the lower credible
interval of the posterior distribution of the linear coefficient was
only just above zero; Table 3).
Individuals with relatively longer DS1 had correspondingly longer DS2
and PS (pairwise phenotypic covariances (CoV), posterior mode and
95%CI: DS1:DS2 = 0.224(0.165, 0.289);
DS1:PS = 0.133(0.077, 0.190); DS2:PS =
0.122(0.070, 0.190)), indicating that spine traits
covaried at the individual level. However, relative length of spines did
not seem to covary with armour plate number (see Table S2). There was no
evidence for phenotypic covariance across the habitats between any of
the defence traits, suggesting that spatial divergence in defence traits
was not correlated at the habitat level (see Table S2). However, to
increase statistical power for detecting divergence in phenotypic
covariances, greater level of replication is likely needed.
Trophic traits - Males had relatively longer GRL2 and GRL3, and
relatively more gill rakers (GRN), than females (Table 2), but there
were no sex differences in GRW (Table 2). Model comparisons showed that
gill raker traits varied according to site rather than habitat (Table
2), but this variation was not associated statistically with any of the
ecological variables (Table 3). Specifically, stickleback from the CS
site had relatively longer and fewer gill rakers than stickleback from
other sites, and stickleback from site CS and DN had fewer gill rakers
than stickleback from all other sites (Figure 1). There was evidence for
phenotypic covariances at the residual (i.e., individual) level for some
gill raker traits. For instance, individuals with relatively longer GRL2
had correspondingly longer GRL3 (CoV, posterior mode and
95%CI: GRL2:GRL3 = 0.288(0.188,
0.403)). Furthermore, individuals with more gill rakers also had
narrower GRW (CoV, posterior mode and 95%CI: GRW:GRN =
-0.184(-0.311, -0.052))). There was no evidence for
phenotypic covariances at the site level between any of the gill raker
traits, suggesting that spatial divergence in gill raker characteristics
was not correlated (see Table S2).
Gut length - Males had relatively shorter guts than females
(Table 2). Model comparisons suggested that relative gut length varied
among sites (Figure 1, Table 2), but this variation was not associated
to any of the ecological variables (Table 3).