Differences in patterns of variation and covariation for specific
traits
Our PCA investigating patterns across the P-matrices of Caribbean, SSI
generalist-only, and SSI radiating groups indicates that jaw closing
in-lever, maxilla length, and palatine height have strong negative
correlations with PC1(~ -0.96 for all three traits),
while nasal tissue protrusion has the only positive correlation value
for PC1 (0.014; Figure 4; Appendix Table D3, Appendix Figure D2). For PC
axis 2 we observed a strong positive correlation associated with
maxillary head protrusion (0.91), moderate positive correlations for jaw
opening in-lever (0.56) and head depth (0.51), and moderate negative
correlations for lower jaw length (-0.59) and dentigerous arm width
(-0.43; Figure 4; Appendix Table D3, Appendix Figure D2). Similar
correlation values between traits along respective PC axes suggest that
these traits share similar patterns of variation and covariation, while
similar values with opposite signs indicate antagonist patterns. Further
investigation shows that most of the variation along PC1 is contributed
by the SSI generalist-only P matrix (52.5%), while most variation along
PC2 is contributed by the SSI radiating P matrix (84.8%; Appendix Table
D4).
Along PC1, we see that the major loadings of jaw closing in-lever,
maxilla length, and palatine height have a strong relationship in the
negative direction with SSI generalist-only traits, a variable
relationship with SSI radiating traits, and strong relationship in the
positive direction with Caribbean traits (Figure 4; Appendix Table D4).
This suggests that as the covariation of jaw closing in-lever, maxilla
length, and palatine height increases the covariation of other traits in
SSI generalist-only groups also increase, while the covariation in
Caribbean groups decreases. The relationship is more complicated in SSI
radiating groups as the covariation of some traits, such as lower jaw
length and dentigerous arm width, have a positive relationship with the
covariation of jaw closing in-lever, maxilla length, and palatine
height, while others such as nasal tissue protrusion and maxillary head
protrusion have a negative relationship.
The major loadings for PC2 include maxillary head protrusion, lower jaw
length, and jaw opening in-lever (Appendix Table D3). In general, the
variation along PC2 corresponds to the SSI radiation P matrix (Figure 4;
Appendix Table D4). For instance, for the SSI radiating group the
covariation between maxillary head protrusion and jaw opening in-lever
have positive relationship with one another but a negative relationship
with lower jaw length, dentigerous arm width, and dentigerous arm base.
These patterns are either significantly weaker, or opposite in the
Caribbean and SSI generalist only matrices.