Just saw the news about an article in PLoS Biology by Nancy Moran and colleagues. In their paper, which studied bacterial symbionts of aphids, they show that mutations in the gene encoding a heat shock protien in the symbiont influence the heat tolerance of the aphid hosts. Inturn this means that these mutations influence aphid geographical range and ecology. It is a relly cool story (Nancy Moran seems to publish a cool story like this every other week -- I feel lucky to have worked with her on one symbiont project which I have written about here).
To read more about the Moran work, go to the article, which anyone can read since it is in PLoS Biology. Or go to the press releases such as here.
Dunbar, H., Wilson, A., Ferguson, N., & Moran, N. (2007). Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts PLoS Biology, 5 (5) DOI: 10.1371/journal.pbio.0050096