DIFFERENTIATION IN PHENOTYPIC PLASTICITY TO CLIMATE AMONG ERIOGONUM FASCICULATUM SUBSP. FOLIOLOSUM (POLYGONACEAE) POPULATIONS IN CALIFORNIA

Abstract

California, a hotspot of plant biodiversity, is projected to experience a significant increase in average temperature by the end of the century, from +1.5°C under low emissions to +4°C under medium-high emissions models. This warming could severely affect unique, endemic ecosystems like the chaparral. Phenotypic plasticity, the capacity of organisms to express different phenotypes in response to environmental cues, may be an important means by which plants adjust to climate change. Here, we examine differentiation in two traits related to climate adaptation, leaf length and trichome density, previously observed to differ qualitatively between coastal and inland populations of Eriogonum fasciculatum subsp. foliolosum (Nutt.) S.Stokes. We quantitatively verify these leaf trait differences, assess whether they are plastic to temperature, and also assess whether coastal and inland populations express this plasticity differently. We performed field collections, established a novel procedure for vegetative propagation of woody cuttings, and grew cuttings and germinated seeds in temperature treatments simulating current conditions and those projected by future climate models. Our results revealed that leaf traits of both populations respond plastically to temperature, and we also found differentiation for the plasticity expressed by the two populations. Population genetic analyses detected limited genetic differentiation and high gene flow between these two populations, indicating that the observed differentiation in plasticity may be locally adaptive. Together, these findings suggest that this system may exemplify genetic accommodation, in which the evolution of plasticity mediates adaptation, and imply that variation in plasticity is relevant to conservation strategies for this plant and other California native chaparral shrubs in the face of climate change.