Morphological integration during postnatal ontogeny: implications for evolutionary biology

Abstract

AbstractHow covariance patterns of complex phenotypes change during development is fundamental for a broader understanding of morphological evolution. There is compelling evidence that mammalian skull covariance patterns change during ontogeny. However, it is unclear to what extent variation in covariance patterns during ontogeny can impact the response to selection in age-structured populations under directional selection. To tackle this question we explored: i) the extent to which covariance patterns change during postnatal ontogeny; ii) in which ontogenetic stages covariance patterns differ the most, and iii) the extent to which the phenotypic covariance pattern at different ontogenetic stages can be explained by the same processes determining additive genetic covariance. We sampled ontogenetic series for two Didelphimorphia marsupials, and one precocial and one altricial placental at different postnatal ontogeny stages. We calculated phenotypic covariance matrices (P-matrices) for each ontogenetic series at different ontogenetic stages. Within each ontogenetic series, we used Principal Coordinate Analysis, Krzanowski Subspace Comparison for multiple matrices to compare these P-matrices among them. Furthermore, we used Random Skewers analyses to compare these P-matrices to two target matrices [adult P-matrix and an additive genetic covariance matrix (G-matrix)]. Our results show that for all ontogenetic series, covariance patterns from weaning onward are conserved and probably shaped by the same processes determining the G-matrix. We conclude that irrespective of eventual differences on how selection operates during most of postnatal ontogeny, the net response to such pressures will probably not be affected by ontogenetic differences in the covariance pattern.