Diversification rates in Antirrhineae (Plantaginaceae): The contribution of range shifts and pollination modes

Abstract

The relationship between range and diversification is an enduring evolutionary question. The rich angiosperm diversity stems from several factors including variations in geographical distribution and floral morphology, which tend to correlate with different pollinator preference in many taxa. Pollinator diversity varies among different regions, thus range shifts can play an important role in increasing divergence by predisposing clades to floral shifts. Antirrhineae is an ideal model to examine the effect of range shifts and pollination modes on diversification, because the tribe is distributed in the Old World and the New World with representatives exhibiting hummingbird pollination in the New World, and bee pollination in the Old World and the New World. Using ancestral reconstructions and phylogenetic modeling, this study investigated the effects of geographic distribution and pollination modes on the macroevolution of the tribe Antirrhineae. Our age-range correlation analysis showed young nodes had more range overlap than older nodes in the phylogeny, suggesting sympatric speciation as a contributing factor to the diversification of the tribe. We observed similar rates of diversification throughout time with no evident rate shifts within the tribe. Old World and New World lineages have similar speciation rates in Antirrhineae, and pollination mode did not have a significant effect on the diversification of the tribe. However, we found evidence for increased diversification rates through long-distance dispersal events, which occurred between the Old World and the New World four times throughout the evolutionary history of Antirrhineae. Therefore, we conclude that long-distance dispersal was a strong contributor to the diversity within Antirrhineae.