Research highlights

Monkeyflower adaptation mechanism

Chromosomal inversions are thought to contribute to adaptation and speciation, as they can lead to hybrid sterility. Now, David Lowry and John Willis report an adaptive inversion polymorphism in the yellow monkeyflower Mimulus guttatus (PLoS Biol. 8, e1000500, 2010). They initially observed suppression of recombination at a large effect, pleiotropic quantitative trait locus in crosses between inland-annual and coastal-perennial populations. In-depth genotyping of more crosses between geographically distinct inland-annual and coastal-perennial populations showed evidence for a chromosomal inversion linked to ecotype. This inversion contributes to adaptive flowering time differences between annual and perennial populations. To test if this inversion polymorphism affects adaptation in the wild, the authors introgressed alternative inversion arrangements into outbred annual and perennial backgrounds and performed reciprocal transplant experiments. Fitness was measured as survival to flowering and number of flowers produced per plant, and the effect of the inversion was significant. For example, at the inland field site, survival to flowering in plants with the coastal genetic background and the inland annual inversion was eight times greater than that of coastal plants with the coastal perennial inversion. The authors suggest that this inversion may directly contribute to reproductive isolation between annual and perennial ecotypes, consistent with the theory that local adaptation can facilitate the maintenance of chromosomal rearrangements and promote speciation. PC