Morphological integration and evolution of the skull roof in temnospondyl amphibians

Abstract

Morphological integration refers to the phenotypic interdependence of two or more traits and is estimated by the degree of covariation or correlation among traits at different levels, such as at the intraspecific and evolutionary scales. Intraspecific integration of morphological traits results from the interaction among traits at the genetic, developmental, and functional levels and it has been proposed that it channels morphological evolution by modulating variability. In this work, we test whether the intraspecific integration might have channeled the morphological evolution of the skull roof in a major tetrapod radiation, that of extinct temnospondyl amphibians. To do this, we quantified the patterns of intraspecific integration of different species and explored their relationships with the evolutionary patterns of integration and disparity of three clades of temnospondyls using geometric morphometrics. We recovered that, at the intraspecific level, the integration patterns of the total shape of the skull roof are conserved across the clade and over geological time, but that the integration among individual bones varies in every species considered. We did not find a correlation between the patterns of integration among individual bones at the intraspecific and evolutionary levels, nor between the strength of intraspecific integration of each bone and their respective disparity. These results suggest that the intraspecific integration might have not affected significantly the morphological evolution of the skull roof in temnospondyls over geological time. Thus, it seems that the morphological evolution of this skeletal part might have been driven more by selective pressures than by shared developmental constraints inherited from the temnospondyl ancestor.