Experimental test for adaptive differentiation of ginseng populations reveals complex response to temperature.

Abstract

Local climatic adaptation can influence species' response to climate change. If populations within a species are adapted to local climate, directional change away from mean climatic conditions may negatively affect fitness of populations throughout the species' range. Adaptive differentiation to temperature was tested for in American ginseng (Panax quinquefolius) by reciprocally transplanting individuals from two populations, originating at different elevations, among temperature treatments in a controlled growth chamber environment. Fitness-related traits were measured in order to test for a population × temperature treatment interaction, and key physiological and phenological traits were measured to explain population differences in response to temperature. Response to temperature treatments differed between populations, suggesting genetic differentiation of populations. However, the pattern of response of fitness-related variables generally did not suggest 'home temperature' advantage, as would be expected if populations were locally adapted to temperature alone. Failure consistently to detect a 'home temperature' advantage response suggests that adaptation to temperature is complex, and environmental and biotic factors that naturally covary with temperature in the field may be critical to understanding the nature of adaptation to temperature.