The role of range edges in determining adaptive climate responses in the cut-leaved monkeyflower (Mimulus laciniatus)

Populations occupying opposing climates of a species range have the potential to evolve climatically adapted, phenotypic extremes.  If connectivity among populations exists, these climate-edge populations may be important during rapid environmental shifts (e.g. human-caused global warming) by contributing genes that enhance climate tolerance.  Nevertheless, such gene flow may be constrained by spatial or temporal isolation.  This may be particularly true in plants from mountain systems with steep gradients, where migration from lower, warmer-adapted populations is limited by steep landscapes (seed barriers) and/or non-overlapping temporal windows among elevations (pollen barriers).  Thus, differential rates of gene flow among different climatic selection regimes may strongly influence adaptive climate responses.  Preliminary survival and fitness data on Mimulus laciniatus, an annual plant endemic to the Sierra Nevada with a limited, well-defined climate range, show evidence for adaptive climate structuring among eight populations grown at middle and low elevations. The degree to which this structuring extends to range edges is being explored.  Microsatellite markers are being used to estimate gene flow among and across elevational strata, making this a promising system to estimate the interaction and contributions of gene flow and quantitative trait variation in enabling species to potentially tolerate, and adapt to, climate change.