Unique drought resistance strategies occur among monkeyflower populations spanning an aridity gradient.

Abstract

Annual plants often exhibit drought-escape and avoidance strategies to cope with limited water availability. Determining the extent of variation and factors underlying the evolution of divergent strategies is necessary for determining population responses to more frequent and severe droughts. We leveraged five Mimulus guttatus populations collected across an aridity gradient within manipulative drought and quantitative genetics experiments to examine constitutive and terminal-drought induced responses in drought resistance traits. Populations varied considerably in drought-escape- and drought-avoidance-associated traits. The most mesic population demonstrated a unique resource conservative strategy. Xeric populations exhibited extreme plasticity when exposed to terminal drought that included flowering earlier at shorter heights, increasing water-use efficiency, and shifting C:N ratios. However, plasticity responses also differed between populations, with two populations slowing growth rates and flowering at earlier nodes and another population increasing growth rate. While nearly all traits were heritable, phenotypic correlations differed substantially between treatments and often, populations. Our results suggest drought resistance strategies of populations may be finely adapted to local patterns of water availability. Substantial plastic responses suggest that xeric populations can already acclimate to drought through plasticity, but populations not frequently exposed to drought may be more vulnerable.