Evolution of trait modules with climate in California oaks

Camila Dias Barros Medeiros, Aleena Sorfazian and Alayna Mead, Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, Victoria L. Sork, Ecology and Evolutionary Biology; Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, CA, Lawren Sack, Department of Ecology & Evolutionary Biology, University of California Los Angeles, Los Angeles, CA

Background/Question/Methods
Plant species adapt to the environment through the optimization of their functional traits. However, the evolutionary basis for trait coordination has remained little understood due to the multifunctionality of traits and their contributions to multiple functions. We hypothesized that trait evolution during adaptation to climate would result in the emergence of putative structure-function modules, including plant and leaf size-related traits, drought tolerance, resource economics, and nutrient stoichiometry. For common garden-grown adult trees of 15 species from three sections of the genus Quercus in California (Lobatae, Protobalanus and Quercus), we measured 71 functional traits, and tested their associations and with the climatic aridity and soil quality (aridity index, AI, maximum temperature, Tmax, and soil pH, SoilpH). We tested (1) the trait-trait coordination within and across a priori hypothesized structure-function modules and (2) the correlated evolution of traits and structure-function modules with species’ climatic aridity. Further, we built ahistorical and historical trait networks (TNs) to (3) test the influence of species relatedness’ on TN architecture and (4) identify the key traits of the networks, the “hub traits” (i.e., traits with higher degree of connectedness, k) and the “mediator traits” (i.e., most connected to different structure-function modules or higher betweenness, b).
Results/Conclusions
Traits varied strongly among and within species, and on average, traits were more strongly correlated within than across the hypothesized structure-function modules. Traits of the drought module, leaf size and resource economics modules were positively correlated with climatic aridity of species’ native distributions. Including evolutionary history strongly influenced the analysis of trait network architecture. Network analysis indicated that certain traits had special importance as hubs and mediators, including photosynthetic traits and leaf turgor loss point. The evolution of traits within modules highlights the emergence of integrated phenotypes that provide drought tolerance, and points to the necessity of considering the benefits and costs contributed by multiple traits to overall climate adaptation.