Constraints on the evolution of plasticity in Drosophila melanogaster. Brandon S. Cooper¹, Loubna A. Hammad², Kristi L. Montooth¹. 1) Department of Biology, Indiana University, Bloomington, IN; 2) METACyt Biochemical Analysis Center, Department of Chemistry, Indiana University, Bloomington, IN.

   When environments vary greatly, alleles that enable the matching of the phenotype to the current environment should be favored by selection. Antagonistic pleiotropy and mutation accumulation, however, can create negative genetic correlations in fitness across environments leading to decreased performance of generalist relative to specialist genotypes. Our previous work has shown that an increased degree of cellular plasticity evolves in an experimentally variable environment, consistent with the selective advantage of an environmentally sensitive allele(s) with associated costs in constant environments. This evolution of increased cellular plasticity enables specialization within generations in environments that vary among generations. Here, we extend this work to natural populations by evaluating the evolution of cellular generalization and specialization in populations of Drosophila melanogaster from Vermont, Indiana, and North Carolina. To evaluate the evolution of cellular generalization, we quantified plasticity in two measures of cell membrane lipid composition: (1) change in the ratio of phosphatidylethanolamine to phosphatidylcholine and (2) change in lipid saturation in cool (16ºC) relative to warm (26ºC) developmental conditions. Within each developmental environment we also evaluated the evolution of cellular specialization in environments that differ in mean temperature. We will discuss these data in the context of (1) measures of genetic correlations between developmental and reversible plasticity of the cell membrane, and (2) our data from experimentally evolved populations that support the selective advantage of environmentally sensitive alleles that modify plastic responses of the cell in variable environments. While these alleles increase reproductive fitness, they also decrease tolerance to certain environments, resulting in antagonistic pleiotropy that may constrain the evolution of cellular plasticity in nature.