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Divergence in hormone signaling drives local adaptation and intrinsic reproductive isolation

By Melanie J Wilkinson, Federico Roda, Greg M. Walter, Maddie E. James, Rick Nipper, Jessica Walsh, Scott L Allen, Diana M. Bernal, Henry L. North, Christine Beveridge, Daniel Ortiz-Barrientos

Posted 17 Nov 2019
bioRxiv DOI: 10.1101/845354

Natural selection is a major driver of both adaptation and speciation. Whether or not the processes driving adaptation and speciation share a molecular basis remains largely unknown. Here, we show that divergence in hormone signaling contributed to the evolution of complex adaptations and intrinsic reproductive isolation in an Australian wildflower, Senecio lautus. We provide evidence that differences in the auxin pathway, a hormone signaling pathway required for plant growth and development, has led to the repeated evolution of erect and prostrate forms to contrasting coastal environments. Using multiple hybrid and natural populations, we show that adjacent erect and prostrate populations have repeatedly diverged in auxin-related genes and auxin-dependent phenotypes, such as gravitropism. Analysis of an advanced hybrid population in a multi-year field selection experiment revealed that high fitness families produce offspring with the local gravitropic response. We found that two auxin-related genes explained 45% of the variation in gravitropism in hybrid individuals. Remarkably, crossing hybrid individuals with extreme differences in gravitropism significantly reduces their ability to produce seed, showing gravitropism is genetically correlated with intrinsic reproductive isolation. Together, our results suggest that divergence in hormonal pathways can drive rapid adaptation to contrasting environments and to the origin of new species. ### Competing Interest Statement The authors have declared no competing interest.

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