Natural Hybridization between Ipomopsis aggregata and I. tenuituba (Polemoniaceae)

Publisher Website
Google Scholar
Abstract
Ipomopsis aggregata and I. tenuituba are sympatric over a wide area in the mountains of western North America. Ipomopsis tenuituba is subalpine and sphingophilous, while the subspecies of I. aggregata that are sympatric with it occur at lower elevations and are ornithophilous. The ecological and floral isolation breaks down locally, and hybridization ensues. A hybrid swarm is reported in northern Arizona. Introgression takes place, and we describe introgressive populations of I. aggregata from several sites in Colorado and Utah and introgressive populations of I. tenuituba from Colorado and California. Individual variation associated with an intermediate character state is a feature of all these populations; indeed, the variability for which the group is noted is largely explained by hybridization. Individual plants in an introgressive population of I. tenuituba in California show gametophyte segregation for pollen color differences between the parental species. Differences between two widespread altitudinal races of I. a. aggregata in the central and western Rocky Mountains of Colorado suggest that the high montane race is an old product of introgression between the middle elevation race and I. tenuituba. The high montane race of I. a. aggregata in the Wasatch Mountains of Utah probably has a parallel origin.