Geographic variation in climate as a proxy for climate change: Forecasting evolutionary trajectories from species differentiation and genetic correlations

AJB Advance Article published on January 7, 2016, as 10.3732/ajb.1500108. The latest version is at http://www.amjbot.org/cgi/doi/10.3732/ajb.1500108 RESEARCH ARTICLE A M E R I C A N J O U R N A L O F B O TA N Y I N V I T E D PA P E R For the Special Issue: Evolutionary Insights from Studies of Geographic Variation Geographic variation in climate as a proxy for climate change: Forecasting evolutionary trajectories from species diff erentiation and genetic correlations 1 Heather E. Schneider 2 and Susan J. Mazer PREMISE OF THE STUDY: Climate change models for California predict a warmer, drier future, potentially resulting in shorter growing seasons. If phenotypic diff erences between closely related species currently distributed across a moisture and temperature gradient represent adaptations to their abiotic envi- ronment, then as conditions become warmer and drier, populations presently adapted to cooler and wetter conditions may evolve to become more simi- lar to those adapted to warmer and drier conditions. Two sister species, Clarkia unguiculata and C. exilis , are distributed across a moisture and temperature gradient in the southern Sierra Nevada, providing an opportunity to predict how this process may occur. METHODS: In a greenhouse experiment using wild-collected seeds from 11 populations in the southern Sierra Nevada, we examined relationships among elevation, climatic conditions, and population means for each trait, then evaluated bivariate relationships among maternal family means, using raw values and controlling for population and seed mass eff ects on phenotype. KEY RESULTS: Clarkia exilis occupied warmer, drier conditions, typically at lower elevations, than C. unguiculata did and fl owered earlier and faster, produc- ing smaller fl owers with lower herkogamy. In C. unguiculata , petal area, herkogamy, and the rate of fl ower production were positively correlated with days to fi rst fl ower. CONCLUSIONS: If selection favors earlier fl owering, smaller petals, or faster fl ower production in C. unguiculata , then the genetic correlations among these traits should reinforce their joint evolution. Moreover, the correlations between these traits and herkogamy may promote the evolution of self-fertilization as an indirect response to selection, a previously unrecognized potential outcome of climate change. KEY WORDS Clarkia ; climate change; correlated evolution; geographic variation; life history; Onagraceae; self-fertilization Climate change is altering natural systems across the globe ( Parmesan and Yohe, 2003 ; Pereira et al., 2010 ; IPCC, 2014 ). Understanding the responses of plant populations to climate change is imperative for predicting its long-term eff ects on wild species. In a changing climate, plant populations may respond in several ways, including migration or dispersal to more suitable habitats; alteration of life history and other traits through phenotypic plasticity; adaptive evolution; and local extirpation or large-scale extinction. Many studies have focused on the eff ects of climate change on migration and/or dispersal ( Huntley, 1991 ; Davis and Shaw, 2001 ; Ackerly, 2003 ; Parmesan and Yohe, 2003 ; Neilson et al., 2005 ; Grace et al., 2002 ; Chen et al., 2011 ; Zhu et al., 2014 ), phenology ( Parmesan and Manuscript received 19 March 2015; revision accepted 6 October 2015. Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93106 USA Author for correspondence (e-mail: heather.schneider@lifesci.ucsb.edu) doi:10.3732/ajb.1500108 Yohe, 2003 ; Parmesan, 2006 ; Springer and Ward, 2007 ; Anderson et al., 2012 ; Mazer et al., 2013 ; Wolkovich et al., 2013 ; CaraDonna et al., 2014 ) and extinction ( Midgley et al., 2002 ; Fordham et al., 2012 ; Sax et al., 2013 ). Migration and plastic responses to local changes in climatic conditions may allow many genotypes and populations to persist, but for those that can neither disperse to more hospitable locations nor exhibit plastic responses that al- low local persistence, evolutionary adaptation may be required. The potential for plants to adapt (through natural selection) to climate change has received less attention than dispersal and plasticity (but see Etterson and Shaw, 2001 ; Davis et al., 2005 ; Jump and Panuelas, 2005 ; Franks and Weis, 2007 ; Aitken et al., 2008 ; Franks and Weis, 2008 ; Salamin et al., 2010 ; Hoffmann and Sgro, 2011 ), but will play a crucial role in determining fu- ture community composition, species distributions, and the mean phenotypes of populations for ecologically important traits. While individual traits can evolve by natural selection in A M E R I C A N J O U R N A L O F B OTA N Y 103 ( 1 ): 1 – 13 , 2016 ; http://www.amjbot.org/ © 2016 Botanical Society of America • 1 Copyright 2016 by the Botanical Society of America