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Every species occupies a restricted geographic distribution, but it is unclear why natural selection at the range margin fails to increase tolerance to limiting environmental variables and thereby allow continual range expansion. Models indicate that the interplay of demographic asymmetries, dispersal, divergent natural selection, and adaptive trade-offs across spatially varying environments can give rise to stable range limits. Here we examine sister species of the monkeyflowers Mimulus cardinalis and M. lewisii to identify traits that might contribute to the evolution of the species' ranges and to ask whether adaptive trade-offs between environments can limit their geographic distribution. In the Sierra Nevada Mountains of California, M. cardinalis is found from low to mid elevation and M. lewisii is found from mid to high elevation. We transplanted segregating populations of interspecific hybrids to low and high elevation and cross-pollinated those that survived to flowering to create selected populations that evolved at low or high elevation. When grown in a common environment, the progeny of hybrids selected at high elevation flowered earlier compared to a greenhouse control population, whereas hybrids selected at low elevation displayed increased warm-temperature photosynthetic capacity. If adaptation to one environment entails a cost to adaptation in other environments, then selected hybrid populations should display reduced fitness, relative to an unselected control population, when grown in an environment in which they were not selected. Two such trade-offs were observed in this study, where hybrids selected at high elevation displayed reduced biomass when grown in temperatures characteristic of low elevation and hybrids selected at low elevation showed reduced resistance to freezing. These results identify traits under selection for range expansion and suggest that adaptive trade-offs can contribute to limiting the geographic distribution of species. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the nature of reproductive isolation between Mimulus lewisii and M. cardinalis, sister species of monkeyflowers. Review of related literature; Data and methods used; Results and discussion.

Presents quantitative trait loci (QTL) for commercially important traits (stem growth and form) and an adaptive trait (spring leaf flush) in a Populus F2 generation derived from a cross between interspecific F1 hybrids. Trait distributions; Stem growth QTLs; Marker heterozygosity as a predictor of growth; Stem form QTL; Spring leaf phenology.

Presents a study which discussed the affects of differences in floral morphology between two species of monkeyflower (mimulus) by quantitative trait loci (QTL). Exploration of the genetic control of 12 morphological differences between flowers of Mimulus lewisii and Mimulus cardinalis; What the genetic basis of adaptation depends upon; Results obtained from study.

The genetic and developmental basis of many ecologically important floral traits (e.g., carotenoid pigmentation, corolla tube structure, nectar volume, pistil and stamen length) remains poorly understood. Here we analyze a chemically induced floral mutant of Mimulus lewisii through bulk segregant analysis and transgenic experiments and identify a MIXTA-like R2R3 MYB gene that controls nectar guide formation in M. lewisii flowers, which involves epidermal cell development and carotenoid pigmentation. [ABSTRACT FROM AUTHOR]

Prezygotic barriers play a major role in the evolution of reproductive isolation, which is a prerequisite for speciation. However, despite considerable progress in identifying genes and mutations responsible for postzygotic isolation, little is known about the genetic and molecular basis underlying prezygotic barriers. The bumblebee-pollinated and the hummingbird- Mimulus lewisii pollinated represent a classic example of pollinator-mediated prezygotic isolation between two sister species in sympatry. M. cardinalis Flower color differences resulting from both carotenoid and anthocyanin pigments contribute to pollinator discrimination between the two species in nature. Through fine-scale genetic mapping, site-directed mutagenesis, and transgenic experiments, we demonstrate that a single-repeat R3 MYB repressor, ROSE INTENSITY1 (ROI1), is the causal gene underlying a major quantitative trait locus (QTL) with the largest effect on anthocyanin concentration and that cis-regulatory change rather than coding DNA mutations cause the allelic difference between M. lewisii and M. cardinalis. Together with the genomic resources and stable transgenic tools developed here, these results suggest that is an excellent platform for studying the genetics of pollinator-mediated reproductive isolation and Mimulus the molecular basis of morphological evolution at the most fundamental level--gene by gene, mutation by mutation. [ABSTRACT FROM AUTHOR]