Diverging evolutionary trajectories for palm seed sizes in mainland Africa and Madagascar.

Abstract

Seed size is a trait which determines survival rates for individual plants and can vary as a result of numerous trade-offs. In the palm family (Arecaceae) today, there is great variation in seed sizes. Past studies attempting to establish drivers for palm seed evolution have sometimes yielded contradictory findings in part because modern seed size variations are complicated by long-term legacies, including biogeographic differences across lineages. Here, we examined palm seed size evolution in two adjacent regions (mainland Africa and Madagascar) utilizing single- and multi-regime Brownian Motion and Ornstein-Uhlenbeck processes. We explicitly take into account species' evolutionary histories to investigate whether there may be shared evolutionary pressures over regional scales. We found that regional selection pressures do exist for palm seed lengths, but these pressures are distinct in mainland Africa and Madagascar, despite the two regions' proximity. Our study indicates that evolutionary drivers may differ in these two regions, highlighting the importance of re-considering the widespread assumption to view mainland Africa and Madagascar as a single evolutionary region.