Effect of evolutionary miniaturization on the tempo and mode of diversification - An example from marine angelfishes

Evolutionary change in body size is a widespread phenomenon in animals. Numerous studies have highlighted evolutionary miniaturization, referring to the evolution of small body size, in various taxa. As other traits shift, decrease in size can be viewed as a morphological novelty that enables colonization of new “adaptive zones” and subsequent diversification (i.e. a “key innovation”). Thus, evolution to small body size is hypothesized to influence lineage, morphological and ecological diversification. Until now, few studies have tested this hypothesis and current supports are mixed. Here, we present a quantitative analysis of the radiation of Pomacanthidae (angelfishes), an iconic coral reef fish family where small taxa, the so called “pygmy angelfishes” of the genus Centropyge, appear to have evolved three-times. If an evolutionary decrease in size has acted as a key innovation during the evolutionary history of Pomacanthidae, we predict that diversification rates would be the highest in clades of pygmy angelfishes. We produced a time-calibrated phylogeny including 67 species, collected ecological data and quantified the body shape of 80 species using geometric morphometrics. Then, we tested the prediction by modelling macroevolutionary dynamics of diversification using the Bayesian Analysis of Macroevolutionary Mixture (BAMM) framework. BAMM results do not support a common macroevolutionary regime for every pigmy angelfish clades. Only the clade Centropyge Xiphypops shows higher rates of lineage and morphological diversification than the other clades of angelfishes. We show that miniaturization has few effects on the rate of diversification. The shifts in the tempo of diversification observed in C. Xiphypops might instead be related to a functional innovation of the feeding apparatus. Using the Pomacanthidae, we illustrate that miniaturization may not be a main factor in triggering increased of diversification rates at the family level.