Macroevolutionary dynamics and comparative methods of morphological diversification

Abstract

Among the comparative approaches that have been used to understand the patterns of morphological diversification, those related to the detection and evaluation of large-scale evolutionary trends have recently been highlighted. A new method known as the analysis of skewness (ANSKEW) allows partitioning between the passive and driven trends associated with the random occupation of a bounded morphological space and a single morphological attractor, respectively. This partitioning provides a better understanding of the relative role of processes that occur at distinct hierarchical levels associated with the macroevolutionary trends of morphological diversification. In this paper, we used this new approach to understand the patterns of morphological diversification in Erodiscini (Coleoptera, Curculionidae, Otidocephalinae) beetles. When genera were used as subclades, ANSKEW revealed that 19.9% of the body size variation in the Erodiscini was attributable to driven trends, i.e., a morphological attractor, whereas 80.1% of the variation was attributable to the occupation of different adaptive zones by distinct subclades (a passive process), with the passive components being significant (based on 5,000 bootstrap samples). This simple approach to partitioning provided insights into the intrinsic dynamics of body size evolution in this group without the need to consider explicit phylogenetic structures. Such analyses could provide a starting point for further evaluation of adaptive variation at multiple hierarchical levels and of the processes underlying the relationship between variation in body size and other ecological, physiological and behavioral aspects.