Morphological and phylogeographic evidence for budding speciation: an example in hominins

Parametric phylogenetic approaches that attempt to delineate between distinct ‘modes’ of speciation (splitting cladogenesis, budding cladogenesis, and anagenesis) between fossil taxa have become increasingly popular among comparative biologists. But it is not yet well-understood how clearly morphological data from fossil taxa speak to detailed questions of speciation mode as compared to the lineage diversification models that serve as their basis. In addition, the congruence of inferences made using these approaches with geographic patterns has not been explored. Here, I extend a previously introduced maximum-likelihood approach for the examination of ancestor-descendant relationships to accommodate budding speciation and apply it to a dataset of fossil hominins. I place these results in a phylogeographic context to better understand spatial dynamics underlying the hypothesized speciation patterns. The spatial patterns implied by the phylogeny hint at the complex demographic processes underlying the spread and diversification of hominins throughout the Pleistocene. I also find that inferences of budding are driven primarily by stratigraphic, versus morphological, data and discuss the ramifications for interpretations of speciation process in hominins specifically and from phylogenetic data in general.