Molecular Genetics of Pre-Mating Reproductive Isolation in Mimulus

点击翻译按钮获取中文摘要

9616522 Bradshaw In the central Sierra Nevada mountains of California there are two monkeyflower species, Mimulus lewisii and M. cardinalis, which are pollinated by different animals -- M. lewisii is bumblebee-pollinated, while M. cardinalis is pollinated by hummingbirds. The flowers of each Mimulus species differ in color, size, shape, and nectar production to best attract the appropriate pollinator. The two monkeyflower species do not crossbreed in nature because of their different pollinators, but artificial hybrids can be produced easily by hand-pollination. Offspring from the hybrids display a tremendous variety of floral traits, since each offspring has inherited part of its genome from a bee-pollinated ancestor and part from a hummingbird-pollinated ancestor. No two hybrid offspring are exactly alike. More than 200 hybrid offspring will be taken to Yosemite National Park in California, where M. lewisii and M. cardinalis are found together naturally, and the rates of bumblebee and hummingbird visitation measured by direct observation. New genome mapping techniques, originally developed for studying human disease and for plant and animal breeding, will be used to determine which genes in the flowers are responsible for attracting bumblebees and hummingbirds. The working hypothesis is that a few genes, such as those governing flower color and nectar production, will have a large impact on which pollinator chooses to visit a particular flower. Investigating the genetics of speciation -- the process by which one species splits into two or more new species -- is fundamental to understanding the origin of biodiversity. Speciation results from genetic changes that prevent the two species from crossbreeding. Since Darwin, there has been debate about the number and magnitude of genetic changes required for speciation. One view is that reproductive isolation is the cumulative result of many mutations, each with a small effect, over long periods of time. Alternatively, others have suggested that a few genes of large effect play a prominent role, and that speciation could occur rapidly. This issue has not been resolved, largely because detailed genetic studies have been limited to a few organisms, such as fruit flies, which have a long history as experimental models. Improved methods in genome research make it feasible to use wild monkeyflower species to establish a synthesis of modern laboratory molecular biology with ecological studies in the field. This general approach could be used to address many long-standing questions in biology.