Phenological Variation and Evolution Across Space and Time in Erythranthe Cardinalis

Committee Members

• Dr. Lluvia Flores-Renteria, Chair (Biology) 
• Dr. Nicholas Barber (Biology)
• Dr. Fernando De Sales (Geography)
• Dr. Seema Sheth (North Carolina State University, Biology)

Abstract

Climate change poses an existential threat to global biodiversity, especially in the California Floristic Province, where many latitudinally distributed species face different selective pressures at opposite edges of their range. Populations at lower latitudes face extreme heat and drought stress, but may also be older and more likely to harbor alleles adapted to these conditions. On the other hand, poleward populations were likely established more recently and face a rapidly changing climate. Quantifying intraspecific variation in traits across latitudinal gradients is vital for predicting evolutionary responses to climate change. Flowering phenology, the seasonal timing and intensity of plant reproduction, varies across a species’ range and is closely tied to plant strategies for dealing with drought.

In this study, we combine a resurrection study and common garden experiment at the southern edge of the scarlet monkeyflower’s (Erythranthe cardinalis) range to investigate how its flowering phenology and life history have evolved in response to recent climate change. We grew seeds from populations at the northern, southern, and central edges of its range, collected once in 2010 and again in 2017, before and after a pronounced drought in California. We measured height at first flower, rhizome production, and recorded counts of individuals in flower every 4 days from June to September. We then analyzed how breeding values for vegetative and phenological traits vary across populations, collection years, and half-sibling seed families, providing estimates for additive genetic variance and heritability. Southern populations were generally the largest and flowered later in the season, although they flowered shorter and earlier post-drought. Northern populations produced substantially more rhizomes and flowered the earliest at the smallest size but showed some evidence of later and larger flowering post-drought.

Our preliminary findings suggest northern and southern populations represent opposite phenotypic extremes, but both are shifting toward a median phenotype comparable to central populations. This suggests E. cardinalis may be experiencing stabilizing selection across its range, as opposed to directional selection, which is commonly expected from climate change-induced evolution.