Arrested diversification? The phylogenetic distribution of poorly-diversifying lineages.

Rapidly-diversifying lineages have been a major focus of modern evolutionary biology, with many hypotheses seeking to explain how they contribute to the uneven distribution of species in space and among taxa. However, an alternative view that is rarely explored is that some lineages evolve to become depauperate clades and show disproportionately low diversification, in a phenomenon we here call arrested diversification. In this study, we analyse several large-scale datasets including amphibian, squamate, mammal, and seed plant species to assess the extent to which poorly-diversifying lineages show distinct phylogenetic and spatial distributions in relation to other lineages. We found significant evidence that clades with low diversification rates tend to be more phylogenetically overdispersed than expected and show more idiosyncratic spatial distributions. These results suggest that arrested diversification is a real phenomenon that might play an important (yet largely overlooked) role in explaining asymmetries in the distribution of species across lineages.