GENETIC-MAPPING OF FLORAL TRAITS ASSOCIATED WITH REPRODUCTIVE ISOLATION IN MONKEYFLOWERS (MIMULUS)

SPECIATION is the process whereby populations acquire sufficient genet ic differences to become reproductively isolated(1). Since Darwin it h as been recognized that the tempo and mode of speciation are greatly i nfluenced by the number and magnitude of genetic changes required for reproductive isolation(2-6), but detailed genetic studies have been li mited to a few taxa such as Drosophila(7). Genome mapping techniques n ow widely adopted in plant(8,9) and animal(10,11) breeding make it pos sible to investigate the genetic basis of reproductive isolating mecha nisms in natural populations. Here we use this approach to map eight f loral traits in two sympatric monkeyflower species that are reproducti vely isolated owing to pollinator preference by bumblebees or hummingb irds. For each trait we found at least one quantitative trait locus ac counting for more than 25% of the phenotypic variance. This suggests t hat genes of large effect can contribute to speciation.