Climate drives variation in intraspecific flowering phenology in a native CA wildflower

Elena Suglia, Megan Bontrager, Johanna Schmitt and Jennifer R. Gremer, Evolution and Ecology, University of California, Davis, Davis, CA, Elena Suglia, Population Biology Graduate Group, University of California, Davis, Davis, CA, Megan Bontrager, Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada, Megan Bontrager, Johanna Schmitt and Jennifer R. Gremer, Center for Population Biology, University of California, Davis, Davis, CA

Background/Question/Methods

In the face of ongoing rapid climate change, a crucial question in evolutionary ecology is how species will respond to environmental changes and resulting novel combinations of abiotic conditions. Flowering phenology is an important plant trait that affects individual fitness and population success. Therefore, phenological traits often evolve to match local conditions and may reflect local adaptation, creating intraspecific variation in phenology across environmental clines. Such phenological differentiation across the landscape can subsequently affect gene flow and landscape genetic structure. While it is well understood that phenological traits vary along environmental clines, less is known about how life history responses to cues like temperature and precipitation align to drive overall population differences in phenological traits. For example, many populations use a combination of temperature and precipitation cues to time germination and winter chilling followed by spring warming to time flowering. Understanding how climate shapes phenological traits and the consequences for individual and population success has important implications for predicting future response to changing climate.
Here, we examine intraspecific flowering phenology variation in Streptanthus tortuosus, which experiences variable environments across its range. To determine how climate shapes intraspecific divergence in phenological traits, we conducted a common garden study comparing 10 populations of S. tortuosus across an elevational and climatic gradient using plants derived from both wild-collected seed and within-population crosses.
Results/Conclusions
Preliminary results suggest that climate drives intraspecific phenological variation across S. tortuosus’ range and that flowering time responses are cued by temperature, precipitation, and summer drought conditions. This variation was maintained in a common garden, suggesting a genetic basis for these traits. We compared pairwise phenological trait differences against pairwise climatic distances among populations using Mantel tests, and found that in all cases, phenological traits correlate strongly and significantly with climate. Climate explained the most variation in the timing of cessation of flowering, followed by peak flowering, then onset in flowering and flowering duration. Phenology varied most strongly along a precipitation gradient, with individuals from environments with higher precipitation flowering later and for a shorter duration. Future analyses will test whether genetic isolation by environment is stronger than isolation by distance and whether phenological traits are adaptively diverged using Qst-Fst and Qpc. This study provides insights into how phenology varies along environmental clines, the importance of climate for driving phenological patterns, and which phenological traits vary most with climate to influence overall flowering phenology.