Allopatry, hybridization, and reproductive isolation in Arctostaphylos: phenology and field morphology

Premise of the study: Hybridization plays a key role in introgressive adaptation, speciation, and adaptive radiation as a source of evolutionary innovation. Hybridization is considered common in Arctostaphylos, yet species boundaries are retained in stands containing multiple species. Arctostaphylos contains diploids and tetraploids, and recent phylogenies indicate two clades; we hypothesize combinations of these traits limit or promote hybridization rates. 

Methods: We statistically analyzed co-occurrence patterns of species by clade membership and ploidy level from 87-0.1 ha plots. We sampled multiple sites to analyze for percent hybridization based on morphology. Finally, phenophases were analyzed by scoring herbarium sheets for a large number of taxa from both clades as well as tetraploids, and second, surveying three field sites over two years for divergence in phenological stages between co-occurring taxa.

Key results: Most taxa in Arctostaphylos are allopatric relative to o...