Head and body shape is modular, but there is integration across
all body regions
We assessed two hypotheses using modularity and integration tests.
First, we asked whether there was evidence for modularity and
integration between the head (snout – head top – neck) and body
regions (belly – tail base – back). Second, we asked whether there was
evidence for modularity and integration between the back of the head
(head top – neck – back) and the front of the body (snout – belly –
tail base).
We found evidence for modularity between the head and body (Fig. 6A).
The analysis of modularity showed that the observed CR was significantly
different to the distribution of variables randomly assigned to modules
(CR = 1, CI = 0.00, p < 0.05). Therefore, this suggested that
there was a high level of coordination between shape variables within
the head and within body regions compared to between them. Our
integration test between the head and body modules suggested that they
also respond to predation risk in an integrated manner (r-PLS: 0.825, p
= 0.001). Fig. 6B showed that, moving from the origin out, as the neck
region enlarged, the back moved higher, the tail was drawn towards the
front of the body and the snout shifted backwards.
We found no evidence for modularity (CR = 1.29, CI = 0.00, p = 0.54;
Fig. 6C) in the back and front regions. However, our integration test
suggested that these two groupings of landmarks do respond to predation
risk in an integrated manner (r-PLS: 0.917; p = 0.001). Fig. 6D showed
similar results to Fig. 6B; moving from the origin out, as the back was
expanded by the inducible defence, the back moved higher, the tail was
pulled towards the front of the body and the snout was pulled towards
the back.