Micro-Environmental Variation and Plasticity for Body Size Traits: Analyses of Intra- and Inter-Population Variability in Drosophila melanogaster

Abstract

Phenotypic expression is inherently variable, reflecting genetic effects, environmental influences and stochastic developmental processes. Although body size has been extensively studied in Drosophila melanogaster, the genetic basis and phenotypic plasticity of micro-environmental variation remain poorly characterized. We quantified genetic variation, population differentiation, sexual dimorphism, and thermal plasticity of micro-environmental sensitivity, estimated as the coefficient of environmental variation (CV_E), for wing length, face width and thorax length measured in the same individuals. A total of 108 highly inbred lines derived from three natural populations (North Carolina, USA; Lavalle and Uspallata, Argentina) were reared at two developmental temperatures (17°C and 25°C) under controlled conditions. CV_E differed significantly among traits, populations, sexes and temperatures, with face width consistently exhibiting higher micro-environmental sensitivity than wing and thorax length. Thermal plasticity of CV_E was detected for all traits, generally characterized by higher CV_E at lower temperature, and showed marked sexual dimorphism, with females displaying steeper reaction-norm slopes than males. The analyses evaluating CV_E thermal plasticity revealed absence of local adaptation but sexual dimorphism and differences among traits. It should be noted that the pattern of micro-environmental plasticity detected for sexual dimorphism and between traits was similar among the populations analyzed. We also demonstrated that genetic control of micro-environmental variability is shared between traits indicating that the genetic architecture of the environmental sensitivity of the traits analyzed would be similar. Together, our analyses suggest that micro-environmental canalization operates at the organismal rather than trait-specific level.