SYMP 1-1 - Using landscape genomics and resurrection studies to understand whether rapid evolution can forestall range contractions

Climate change is a leading threat to biodiversity. In theory, rapid adaptation can rescue populations that are driven into decline by the direct or indirect effects of climatic stress. Despite a growing body of evidence that rapid adaptation often happens on contemporary timescales, it remains unclear whether rapid adaptation is sufficient for evolutionary rescue, whereby adaptation recovers demographic stability. Instead, rapid adaptation might simply slow rates of demographic decline. Moreover, evolutionary potential is likely to vary across a species range due to differences in life history and demographic history that shape levels of standing genetic variation and responses to selection. Determining when and where rapid adaptation can yield evolutionary rescue will lead to more accurate assessments of range shifts, extinction risks, and needs for interventions such as assisted gene flow.

In this talk I will discuss a case study of the scarlet monkeyflower that assesses the potential for rapid adaptation and evolutionary rescue by linking a demographic time series with landscape genomics and resurrection studies. This range-wide study encompasses a broad latitudinal gradient in temperature and precipitation along which the species displays an associated cline in life history. Annual demographic surveys spanning more than a decade document population crashes and recovery during a period of historically unprecedented drought. Whole-genome sequencing identifies allelic variation at several hundred loci associated with climatic heterogeneity over space. Allele frequencies at climate-associated genetic loci changed non-randomly over the time course of unprecedented drought, compared to a matched set of non-climate-associated loci. Concomitantly, traits associated with drought avoidance and drought tolerance such as leaf anatomy and reproductive phenology evolved over six years, resulting in significant trait differences between pre-drought ancestors and peak-drought descendants in a common garden. Populations were inferred to differ in genomic vulnerability to the drought based on starting allele frequencies at climate-associated loci (“genetic offsets”). Nonetheless, higher genomic vulnerability did not predict higher demographic vulnerability: populations with higher genetic offset values did not have faster demographic crashes under drought.

These results suggest that rapid adaptation was insufficient for evolutionary rescue, and that in this case genetic offsets are not a robust predictor of demographic vulnerability during the sorts of extreme climatic events that are projected to increase into the future.