Phylogenetic signal, function and integration in the subunits of the carnivoran mandible

Abstract

Complex phenotypes could be interpreted as the result of functional integration between identifiable subunits. Common developmental or ecological factors may favour macroevolutionary morphological integration so that functional subunits also covary above the species level. We investigate shape variation and functional integration in two subunits of the mammalian mandible: the corpus and the ramus in a subset of extant terrestrial Carnivora using geometric morphometric and comparative methods. More specifically, we test if corpus and ramus shape exhibit similar degree of homoplasy and if these traits covary above species level. Additionally, broad functional categorisations (predaceous and non predaceous) are investigated to test if differences in morphological variation and integration at macroevolutionary scale occur. Principal components of shape data show a significant phylogenetic signal in both mandibular subunits, with the ramus exhibiting a higher degree of homoplasy than the corpus. Functional groups (predators and non-predators) are significantly distinct in corpus shape, while in the ramus significance emerges only after removing the phylogenetic signal. Partial Least Square shows that mandibular corpus and ramus region covaries above species level even if this trend is not supported when employing comparative methods. Only in a subset of predaceous species covariation still hold. We conclude that mandibular subunits of Carnivora differ considerably in shape among predaceous and non-predaceous species because of the adaptive selection pressure imposed by catching and hold of live prey. This selective process also favoured macroevolutionary integration in predaceous carnivorans.