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Premise of the Study: Novel microsatellite primers were developed for the native wildflower Ipomopsis aggregata to facilitate ongoing studies of the genetics of local adaptation and patterns of hybridization with closely related species within the genus., Methods and Results: Thirteen primer sets were successfully developed and tested using populations from the Rocky Mountains of Colorado, USA. The primers amplified di-, tri-, and tetranucleotide repeats with 1-15 alleles per locus. All primers also amplified fragments with varying success in closely related Ipomopsis species and more distant members of the Polemoniaceae., Conclusions: The polymorphism levels observed across all loci suggest that these microsatellites may be useful for population genetic studies in Ipomopsis, as well as in studies of other related taxa in the Polemoniaceae.

Natural hybridization can produce individuals that vary widely in fitness, depending upon the performance of particular genotypes in a given environment. In a hybrid zone with habitat heterogeneity, differences in physiological responses to abiotic conditions could influence the fitness and spatial distribution of hybrids and parental species. This study compared gas exchange physiology of Ipomopsis aggregata, I. tenuituba, and their natural hybrids in situ and assessed whether physiological differences were consistent with their native environmental conditions. We also produced reciprocal F2s in a greenhouse study to test for cytonuclear effects on water-use efficiency (WUE). The relative performance of natural hybrids and parentals was consistent with their native habitats: I. aggregata at the coolest, wettest locations had the lowest WUE, while hybrids from the most xeric sites had the highest WUE. In hybrids, the mechanism by which both natural and experimental hybrids achieved this high WUE depended on cytotype: those with I. tenuituba cytoplasm had reduced transpiration, while those with I. aggregata cytoplasm had an increased photosynthetic rate, consistent with patterns in the cytoplasmic parent. The high WUE in hybrids may contribute to their high survival in the dry center of the natural hybrid zone, consistent with environment-dependent models of hybrid zone dynamics.