COS 278-1 - It’s all about timing: Variation in responses to germination timing reveal vulnerability to climate change in a clade of native wildflowers

Abstract: The timing of germination not only influences conditions that seedlings experience, but also determines exposure to environmental cues and conditions experienced throughout the growing season and the life cycle. As such, germination timing can strongly influence life history timing (phenology) and fitness, with implications for selection, population dynamics, and species distribution across environmental gradients. Shifting conditions with climate change are affecting germination timing, through shifting timing of germination-triggering rain events, as well as subsequent growing season conditions. While there is a vast literature on shifts in flowering phenology with climate, much less is known about on germination timing and its fitness consequences under climate change. Further, the effects of germination timing on phenology and fitness may vary among closely-related species, revealing processes shaping evolution of the seasonal niche as well as identifying vulnerability or resilience to change. To investigate variation in phenology and fitness in response to the timing of germination and subsequent seasonal conditions, we experimentally manipulated the timing of the onset of the rainy season for 11 species in the Streptanthus (s.l.) clade in a common garden environment. For all but two species, the probability of flowering was significantly reduced with later germination timing. For those that did flower, reproductive phenology was delayed in later cohorts. Further, results indicate that later germination generally reduced first year fitness, as evaluated by biomass and seed production, but that species varied in their sensitivity to the timing of germination rains. For example, desert-dwelling species had lower sensitivity than more northern ones. Future analyses will distinguish direct effects of germination timing versus those mediated by effects on flowering phenology, as well as evaluating phylogenetic signal in responses. Together, our results indicate that shifting precipitation timing associated with climate change may negatively affect fitness and population dynamics, particularly for species from less xeric climates.