Constituents of a mixed-ploidy population of Solidago altissima differ in plasticity and predicted response to selection under simulated climate change.

ABSTRACT

PREMISE OF THE STUDY Polyploids possess unique attributes that influence their environmental tolerance and geographic distribution. It is often unknown, however, whether cytotypes within mixed-ploidy populations are also uniquely adapted and differ in their responses to environmental change. Here, we examine whether diploids and hexaploids from a single mixed-ploidy population of Solidago altissima differ in plasticity and potential response to natural selection under conditions simulating climate change. METHODS: Clonal replicates of diploid and hexaploid genotypes were grown in a randomized split-plot design under two temperature (+1.9°C) and two watering treatments (-13% soil moisture) implemented with open-top passive chambers placed under rainout shelters. Physiological, phenological, morphological traits, and a fitness correlate, reproductive biomass, were measured and compared among treatments. KEY RESULTS: Differences in traits suggest that diploids are currently better adapted to low- water availability than hexaploids. Both ploidy levels had adaptive plastic responses to treatments and are predicted to respond to selection, but often for different traits. Water availability generally had a stronger effect than temperature, but for some traits the effect of water depended on temperature. CONCLUSIONS: Diploid and hexaploid S. altissima may maintain fitness in the short term through adaptive plasticity and evolution depending on which traits are important in a warmer, drier environment. Hexaploids may be at a disadvantage compared to diploids because fewer traits were heritable. Our results underscore the importance of studying combinations of climate variables that are predicted to change simultaneously.