Evolutionary divergence of potential drought adaptations between two subspecies of an annual plant: Are trait combinations facilitated, independent, or constrained?

Premise Whether drought-adaptation mechanisms tend to evolve together, independently, or constrained by genetic architecture is incompletely resolved, particularly for water-relations traits besides gas exchange. We addressed this issue in two subspecies of Clarkia xantiana (Onagraceae), California winter annuals that separated approximately 65,000 years ago and are adapted, partly differences flowering time, native ranges differing precipitation. Methods In these recombinant inbred lines (RILs) from a cross between them, we scored related drought adaptation (timing seed germination flowering, succulence, pressure–volume curve variables) common environments. Results The more arid environments (parviflora) exhibited slower saturated conditions, earlier greater likely indicating superior avoidance, escape, dehydration resistance via water storage. other (xantiana) had lower osmotic potential at full turgor loss, implying tolerance. Genetic correlations among RILs suggest facilitated evolution some trait combinations independence others. Where exist, fell along with the exception succulence loss point. case, difference overcame correlations, possibly reflecting strong selection and/or antagonistic traits. Conclusions subspecies’ differ multiple adaptation. generally does not seem have mechanisms, it may combinations.