LB 9-103 - Climate as a driver of divergence in soil-specialist plants

Background/Question/Methods:

The global climate is changing rapidly, and it is important to understand how communities are affected by climate, especially in rare, fragmented habitats. Serpentine soil occurs as fragmented ‘islands’ across California, and provides unique conditions characterized by harsh abiotic stressors for plants. Plants that are found on and off serpentine soils in sympatry are a model system for studying local adaptation via stress-tolerant traits. These adaptive traits help tolerate abiotic stress, which often trades off with competitive ability. One such trait is accelerated phenology, a response to low soil moisture. Phenology can affect gene flow and reproductive isolation between populations. Previous studies have found correlations between precipitation gradients and biogeography of serpentine specialists. Here, I leverage heterogeneous landscapes to study how climate mediates local adaptation in plants within specialized habitats. I predict that certain environmental stressors are more divergent between serpentine and non-serpentine habitats in regions with higher precipitation. As a result, I expect more divergence of traits associated with the drought-competition tradeoff in wetter regions. I predict that nearby serpentine and non-serpentine populations will have more phenological divergence in wetter regions. These results would suggest that climate is a driver of divergence via local adaptation to specialized habitats.

Results/Conclusions:

In a common garden greenhouse experiment, offspring of plants originating from populations with higher regional precipitation flower earlier than those from drier regions. Paired serpentine/ non-serpentine populations from wetter regions are more divergent in days to first flower than pairs from drier regions, but the difference in divergence is not significant. There does appear to be a genetic basis for accelerated flowering in plants that experience more drought stress. Environmental factors that are known to influence phenology, vegetation density and species richness are also more divergent across soil type in areas of higher precipitation. Overall, the effect of precipitation on shifting phenology is stronger than the effect of soil type. This may be due to a predisposition for serpentine-adapted species to inhabit dry, rocky, exposed habitats, regardless of soil parent material. This is important to understanding how soil specialists evolved in the past, how present populations relate to each other, and how climate change will affect different plant communities in the future.