Differences in phosphorus use between ancient and extant Daphnia genotypes alters algal stoichiometry and abundance

Abstract

Understanding the ecological relevance of intraspecific variation and evolutionary change in traits is a central frontier in contemporary ecology. Ecological stoichiometry uses variation in the content and kinetics of elements among species to predict key ecological functions such as nutrient recycling. Although much work has focused on interspecific variation, little is known about the ecological consequences of intraspecific variation and evolutionary change in the processing of ecologically relevant elements such as phosphorus (P). We tested whether physiological evolution can alter somatic P content of Daphnia and algal stoichiometry and abundance as predicted by stoichiometric models of consumer-driven nutrient recycling. We used genotypes of Daphnia pulicaria hatched from resting eggs in lake sediments separated by several hundreds of years of evolution in the wild. Although no significant differences were observed in somatic P content of genotypes from different sediment layers, radiotracer (33P) assays in 2 P–supply conditions (HiP and LoP) revealed considerable differences in P incorporation, particularly under HiP conditions. Further, algae co-occurring with the modern, P-inefficient Daphnia genotypes contained more 33P and exhibited faster population growth compared to counterparts co-occurring with ancient, P-efficient genotypes, with differences more prominent under HiP conditions. This study highlights the potential for intraspecific variation in P-use physiology in affecting trophic interactions via consumer-driven nutrient recycling. Melding ecological stoichiometry and resurrection ecology should elucidate the evolutionary sources and ecological consequences of such variation.