Figure 7: The phenotypically derived species is more robust to environmental change.

Families of LF and TRC were split and reared on distinct diet treatments to mimic benthic and limnetic modes of feeding. (a–c) Along the major axis of variation (PC1) the derived species, LF, shows no difference in craniofacial form when grouped by feeding treatment (t=0.16, n=35, P=0.8723). (a) Depicts an animal at the extreme positive end of PC1. (b) Shows an animal at the extreme negative end of PC1. (c) Illustrates the shape change associated variation along this axis as vector displacements at each craniofacial landmark. We consider this species to be more environmentally canalized. (d–f) Alternatively, in the more intermediate species, TRC, benthic and limnetic fish exhibited a marked shift in craniofaical form along this axis (t=5.89, n=37, P<0.0001). Animals from the benthic treatment developed, on average, more steeply descending craniofacial profiles (that is, positive PC1 scores) (d), whereas those from the limnetic treatment possessed more isognathus jaws (that is, negative PC1 scores) (e). These plastic differences are highly similar to evolved differences among benthic and limnetic species in the wild, including craniofacial profile (black arrows; d,e), as well as a more streamlined head and up turned jaw (vector displacement of craniofacial landmarks, f). Scale bars, 1 cm.