Adaptive divergence in shoot gravitropism creates hybrid sterility in an Australian wildflower
Melanie J. Wilkinson, Federico Roda, Greg M. Walter, Maddie E. James, Rick Nipper, Jessica Walsh, Scott L. Allen, Henry L. North, Christine A. Beveridge, Daniel Ortíz-Barrientos
Abstract
We find that shoot gravitropism has evolved multiple times in association with plant height between adjacent populations inhabiting contrasting environments, suggesting that these traits have evolved by natural selection. We directly tested this prediction using a hybrid population subjected to eight rounds of recombination and three rounds of selection in the field. Our experiments revealed that shoot gravitropism responds to natural selection in the expected direction of the locally adapted population. Using the advanced hybrid population, we discovered that individuals with extreme differences in gravitropism had more sterile crosses than individuals with similar gravitropic responses, which were largely fertile, indicating that this adaptive trait is genetically correlated with hybrid sterility. Our results suggest that natural selection can drive the evolution of locally adaptive traits that also create hybrid sterility, thus revealing an evolutionary connection between local adaptation and the origin of new species.