A case of budding speciation in the California Floristic Province and infraspecific divergence in Abronia villosa.

premiseBudding speciation occurs when peripheral populations adapt to local ecological conditions and "bud" off from a widespread progenitor species. Traditionally regarded as rare because of its sympatric and parapatric nature, budding speciation is largely understudied. Moreover, recent evidence signals that this type of speciation is prevalent in plants, especially in biodiversity hotspots. In this study, we tested for budding speciation in the narrow endemic Abronia villosa var. aurita from the California Floristic Province (CFP).

methodsWe used high-resolution phylogenetics, biogeography, and niche modeling to test the predictions of budding speciation for A. villosa var. aurita from its putative progenitor, the more widespread A. villosa var. villosa. Specifically, we tested for nested phylogenetic relationships of sister taxa, asymmetrical range size, and ecological divergence.

resultsOur results revealed that A. villosa var. aurita is a recently budded taxon, which phylogenetically nested within another variety of the same species. Abronia villosa var. aurita showed a clear signal of niche divergence into a montane environment and signals of genetic structure between two geographically divided populations, indicating further local adaptation and divergence potential.

conclusionsWe elucidated a case of budding speciation in the CFP, adding evidence to a growing number of studies that support budding speciation as a prevalent driver of diversification in plants. Furthermore, our analyses uncovered a nuanced history of within-species divergence, illustrating the importance of bridging microevolutionary and macroevolutionary mechanisms.