On the relationship between species age and geographical range in reef fishes: Are widespread species older than they seem?

Abstract

Aim: In order to better understand processes of speciation, range-size transformation and extinction, macroecological studies seek to identify the evolutionary dynamics of species geographical ranges. This requires accurate estimates of range size and species age. Species ages are attainable through recent success with techniques to estimate phylogenetic divergence time. Conceptual synthesis of the inherent problems with these techniques has been limited. Our aim is to address the effects of estimation of phylogenetic divergence time on the relationship between species age and geographical range. Innovation: Commonly, estimates of divergence time from the nodes of a time-calibrated phylogeny are used as indicators of ages of extant species. However, this method can sometimes produce misleading age estimates, specifically in the presence of extinction and ancestral persistence. An example of this is illustrated using a comprehensive genetic dataset of genera with near-complete sampling of species from four of the major coral reef fish families. We present a method to minimize the impacts of extinction and ancestral persistence on divergence time estimation. The method focuses on recent divergences and involves pairing minimum divergence time estimates (as indicators of species ages) with the minimum geographical range area between two sister-species, for all sister-species pairs. Main conclusions: When applied to coral reef fishes, this method revealed trends in the relationship between species age and geographical range. The difference in the trend recovered from excluding potential biases associated with ancestral persistence suggests that ancestral persistence may be prevalent among coral reef fishes, with successive peripheral speciation affecting area-age relationships. The method may reveal the occurrence of successive peripheral speciation events across a broad range of taxa.