Population structure and natural selection across a flower color polymorphism in the desert plant Encelia farinosa.

Premise: Clines-or the geographic sorting of phenotypes across continual space-provide an opportunity to understand the interaction of dispersal, selection, and history in structuring polymorphisms.

Methods: In this study, we combine field-sampling, genetics, climatic analyses, and machine learning to understand a flower color polymorphism in the wide-ranging desert annual Encelia farinosa.

Results: We find evidence for replicated transitions in disk floret color from brown to yellow across spatial scales, with the most prominent cline stretching ~100 km from southwestern United States into México.

Diversification, disparification and hybridization in the desert shrubs Encelia.

There are multiple hypotheses for the spectacular plant diversity found in deserts. We explore how different factors, including the roles of ecological opportunity and selection, promote diversification and disparification in Encelia, a lineage of woody plants in the deserts of the Americas. Using a nearly complete species-level phylogeny based on double-digest restriction-aided sequencing along with a broad set of phenotypic traits, we estimate divergence times and diversification rates, identify instances of hybridization, quantify trait disparity and assess phenotypic divergence across environmental gradients.

Natural selection maintains species despite frequent hybridization in the desert shrub .

Natural selection is an important driver of genetic and phenotypic differentiation between species. For species in which potential gene flow is high but realized gene flow is low, adaptation via natural selection may be a particularly important force maintaining species. For a recent radiation of New World desert shrubs (: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions.

Spatial and temporal patterns of seed dispersal: an important determinant of grassland invasion.

We measured spatial and temporal patterns of seed dispersal and seedling recruitment for 58 species in a grassland community to test whether seed dispersal could predict patterns of invasion after disturbance. For the 12 most abundant grasses, recruitment of native species was dependent on the propagule supply of both native and exotic species. Variability in seed rain on small spatial (1-10 m) and temporal (within season) scales led to qualitative differences in the outcome of disturbance colonization such that native species dominated disturbances when exotic seed supply was low but failed to establish when exotic seed supply was high.