Geographic variation in reaction norms of phenological traits in the greater duckweed, Spirodela polyrhiza

Abstract

Variability is a ubiquitous feature of natural environments. Organisms can adapt through several methods such as adaptive phenotypic plasticity, changes in phenotype in response to reliable cues predicting fitness outcomes across environments, and bet hedging, the maximization of geometric mean fitness. The greater duckweed Spirodela polyrhiza is an ideal system to study the evolution of these strategies. Phenology of production of overwintering structures called turions, a phenotypically plastic trait that can prevent reproductive failure, is vital to fitness. Here I use S. polyrhiza populations collected from a latitudinal gradient to study how life-history traits evolve in response to variable environments. I hypothesized that reaction norms in turion formation differ across latitudes due to differences in season length and environmental predictability. I found support for the first hypothesis, showing that reaction norms in turion phenology do differ with earlier turion production at higher latitudes under warm, but cold experimental treatments.