Projects

The genetics of reproductive isolation and floral morphology in Ipomopsis

We are exploring the genetic basis of floral divergence and reproductive isolation in Front Range Ipomopsis subspecies. Ipomopsis aggregata subsp. candida grows in grassland habitat interspersed with small patches of mixed Ponderosa pine-Douglas fir forest. The flowers of candida are delicate, with relatively thin/long tubes, inserted anthers, and range in corolla color from pure cream white to light shades of pink. I. a. candida is primarily pollinated by white-lined hawkmoths, Hyles lineata (Sphingidae) and, to a lesser degree, by resident and migratory hummingbirds. Ipomopsis. aggregata subsp. collina, a second subspecies, also occurs on the East Slope and is found primarily in mixed forest and forest-edge habitats. I. a. collina has robust, red flowers, exserted stigmas, with relatively wide/short corollas and is primarily pollinated by hummingbirds. I. a. candida and collina are sister taxa that have only recently diverged, likely during Pleistocene isolation of East slope populations. I. a. candida and collina hybridize across much of the East Slope.

We are interested in understanding the interplay of selection and gene flow in the dynamics of introgression and hybridization between candida and collina. Furthermore, we hope to use several quantitative genetic experiments and QTL mapping to better understand the genetic basis of floral differences between the subspecies. Initial collections from 22 populations have been analyzed for floral morphological variation and genotyped at eleven microsatellite loci. These data were analyzed with a Bayesian clustering approach which allows a flexible evaluation of introgression (Pritchard et. al. 2000). In this method, individuals in a sample are assigned (probabilistically) to populations, or jointly to two or more populations if their genotypes indicate that they are admixed. These data reveal a diversity of local demes including pure subspecies, well-mixed hybrids, and recently admixed individuals. The assignment of individuals from 22 locations into either of two populations [corresponding to putative pure candida and collina] is presented below. Each individual is represented by a bar with the inferred ancestry indicated by the proportion colored either red [putative collina] or white [putative candida]. Collection sites are split by black bars.