Admixture between rarely hybridizing milkweeds, Asclepias syriaca and Asclepias sullivantii: Morphological and molecular evidence from populations across the Midwestern U.S.

Interspecific hybridization and subsequent admixture often has important ecological and evolutionary consequences, especially when one of the species involved is relatively rare. Common milkweed (Asclepias syriaca) has been observed to hybridize with its uncommon congener A. sullivantii, but the extent to which hybridization occurs across their range is unknown. The purpose of this study was to quantify the extent of admixture between A. syriaca and A. sullivantii in multiple co-occurring populations across the Midwest U.S. using morphological and genomic data. We collected morphological leaf data and performed ddRADSeq on 276 Asclepias individuals. Morphological analyses indicate distinct parental phenotypes, and moderate phenotypic deviation from parental taxa by putative hybrids. Preliminary STRUCTURE plots indicate extensive admixture in most co-occurring populations, although definitive conclusions cannot be made based on a low burn-in and number of MCMC repetitions for these analyses. Our work represents an important follow up of a previous study into this system, expanding the geographic area sampled and providing high resolution genomic data.Mayer's Undergraduate Research Summer FellowshipNo embargoAcademic Major: Evolution and Ecolog