| Despite an understanding that climate is changing at an unprecedented rate, much remains uncertain about the impacts of these changes on biological systems. In particular, few studies have examined the potential for adaptation to climate change. I investigated aspects of the perennial plant Lupinus perennis that affect its evolutionary responses to predicted increases in drought intensities. I first tested for susceptibility to drought in adults and juveniles. Adults tolerated dry conditions, probably by escaping water stress through tap roots, but reduced water affected juvenile morphology, growth, and physiology. Because juveniles were the sensitive stage, I evaluated the potential for adaptive evolution of traits expressed in young L. perennis plants. In ambient and dry environments, I quantified the nature and magnitude of two components that contribute to an evolutionary response: genetic variation and selection. In both environments, I detected genetic variation in all traits and observed genetic correlations that are likely to facilitate adaptations to drought. However, the magnitude of genetic variation was small, which may limit the rate of an evolutionary response. The opportunity for selection also was greater and phenotypic selection was stronger in dry environments compared to ambient ones. Phenology traits exhibited the largest differences among environments, suggesting that the greatest evolutionary response to increased drought may involve changes in the timing of life history events. These results suggest that adaptation to future drought regimes is possible for L. perennis. Finally, I examined the impact of water and other stresses on a single trait, seed size, that can influence recruitment and hence population dynamics. Mean seed size was not affected by intraspecific competition or water limitation, but individuals growing at higher densities produced more variable seeds. Increasing seed size had strong positive effects on fitness components through the second growing season. Larger seeds mostly provided similar fitness benefits in both dry and ambient conditions, suggesting that the impact of seed size does not vary between environments. Therefore, seed size variation in L. perennis is likely a non-adaptive response to resource limitation, and it is unlikely that future climates will profoundly influence evolutionary changes in seed size. |
