The impacts of drought are expanding worldwide as a consequence of climate change. However, there is still little knowledge of how species respond to long-term selection in seasonally dry ecosystems. In this study, we used QST-FST comparisons to investigate (i) the role of natural selection on population genetic differentiation for a set of functional traits related to drought resistance in the seasonally dry tropical oak Quercus oleoides and (ii) the influence of water availability at the site of population origin and in experimental treatments on patterns of trait divergence. We conducted a thorough phenotypic characterization of 1912 seedlings from ten populations growing in field and greenhouse common gardens under replicated watering treatments. We also genotyped 218 individuals from the same set of populations using eleven nuclear microsatellites. QST distributions for leaf lamina area, specific leaf area, leaf thickness and stomatal pore index were higher than FST distribution. Results were consistent across growth environments. Genetic differentiation among populations for these functional traits was associated with the index of moisture at the origin of the populations. Together, our results suggest that drought is an important selective agent for Q. oleoides and that differences in length and severity of the dry season have driven the evolution of genetic differences in functional traits.
Bibliographical noteFunding Information:
National Science Foundation, Grant/Award Number: IOS 0843665; Severo Ochoa excellence programme
The authors wish to acknowledge the lifetime career of Dr. George Pilz, his facilitation of and contribution to this research and his dedication to teaching and mentoring generations of students at the University of Zamorano, who helped maintain the common gardens in Honduras. We thank Marileth de los Angeles Briceño for seed collection in Costa Rica and for facilitating the permit process to bring acorns. Antonio González-Rodríguez and colleagues collected and transported seeds in La Vigueta Mexican population. We gratefully acknowledge Esau M. Zúniga for permit assistance, seed collection, field management, technical assistance and help with physiological measurements. We would also like to thank Rubén Ramírez, Chris Park, Beth Fallon, Steven Brewer, Xiaojing Wei, Matthew Kaproth, Sydney Schiffner Natalie McMann, Tatiana Dimugno, Nolan Radziej and all Zamorano undergraduate students who participated in field and laboratory help. We also thank the Plant Growth Facilities staff, particularly Roger Meissner and Pamela Warnke for their technical support during the development of the greenhouse experiment. The project was funded by the National Science Foundation IOS 0843665 to JC-B, JRE and JS. JAR-V was also supported by a postdoctoral fellowship from the Severo Ochoa excellence programme.
- adaptive evolution
- ecotypic divergence
- local adaptation
- specific leaf area