The varying rates of phenotypic evolution and historical processes reconstruction: Consequenses for the metabolic theory of ecology and adaptive radiation.

Abstract

The rate at which phenotypic evolution proceeds varies widely across the tree of life, and this variation is fundamental to make accurate inferences about the evolutionary mechanisms that explain the origin of present-day biodiversity. In this thesis I evaluated the evolutionary prediction of two universal theories that makes clear assumptions about the rate of phenotypic evolution in order to explain all diversity patterns and the striking number of species reached by some clades: The Metabolic Theory of Ecology (MTE; chapter one), and Adaptive Radiation (chapter two). The MTE attempts to predict biodiversity patterns by the Basal Metabolic Rate (BMR) of organisms. Assuming that BMR is a direct consequence of temperature, it also predicts that BMR and Body Temperature (Tb) should evolved at constant rates, and hence in a correlated fashion during mammalian radiation. On the other hand, Adaptive Radiation predicts that the impressive species richness reached by some clades is caused by frequent episodes of past disruptive selection and speciation. I evaluated these predictions with new phylogenetic statistical methods that assumes evolution proceeds at variable rates. By accommodating shifts in the rate of phenotypic evolution across each branch of a time-calibrated phylogenetic tree, these methods have demonstrated that is possible to detect and reconstruct accurate historical evolutionary processes, even from data of extant species only. Our results reveal that BMR and Tb were decoupled during the 160 million years of mammalian evolution because they evolved at contrasting rates across each branch of the phylogeny. The observed accelerated evolution of BMR, caused by the abrupt changes in the environmental temperature, was the pivotal process explaining this decoupled scenario. This demonstrates that neither the kinetic effect of Tb nor the functional mechanisms between both traits, constrained BMR to evolve as a direct response of Tb evolution. On the other hand, I find that the distinction between species originated by divergent and directional selection was fundamental to identify the proportion of species originated by an Adaptive Radiation in Sigmodontinae rodents, and these distinction was possible only by studying the rate of body size evolution, branch per branch in the phylogeny. This thesis brings new empirical information that support the importance of variation in the rate of evolution to make appropriate evolutionary predictions expected under the MTE. Furthermore, this thesis provides a new theoretic-based approach that allows to detect the species in a clade originated by an adaptive radiation. These findings arise by the idiosyncrasy of rate variation within the lifespan of species. Consequently, any study that seeks to understand current biodiversity patterns by studying the historical process of phenotypic evolution, should evaluate to what extent the rate of phenotypic evolution varies in both ancestral and extant species, and therefore, in each branch of the phylogenetic relationships.