THE ROLE OF TEMPERATURE AND ADAPTIVE PHENOTYPIC PLASTICITY IN THE EVOLUTION OF DROSOPHILA MELANOGASTER MORPHOLOGICAL CLINES

Variation in morphology results in variation in ecologically relevant performances, which ultimately results in variation in fitness allowing for adaptive evolution. Task performances, such as flight ability, result from the proper scaling of and functional integration of numerous component traits. Morphological variation underlying ecologically relevant task performances can experience strong environmental effects in their expression, or phenotypic plasticity. Historically, the role phenotypic plasticity in adaptive evolution has been controversial, although it has garnered increased support in recent decades. Drosophila spp. are globally distributed and exhibit convergent morphological clines in flight morphology, and importantly, they also exhibit patterns of phenotypic plasticity consistent with these geographic patterns. In the work presented here, I examine if existing patterns of D. melanogaster flight morphology are adaptive regarding flight performance and fitness under the prediction of phenotype-environment matching, wherein the phenotype expressed in an environment enhances fitness in the predicted environment. In the work presented here, I demonstrate (i) phenotypic plasticity in D. melanogaster exhibits a pattern of adaptive phenotype-environment matching in which an induced phenotype is best-suited for flight at the temperature of development, (ii) the pattern of thermally-induced phenotypic plasticity facilitates the evolution of upwind flight performance at Cool and Warm flight temperatures, (iii) adaptive evolution by genetic accommodation is a dynamic process and the contribution of traits responding to selection vary and change over time, and finally, (iv) the adaptive pattern of phenotype-environment matching regarding flight performance is only partially realized as an increase to fitness, measured as survival in presence of predators. My dissertation work importantly demonstrates existing patterns of phenotype-environment matching in D. melanogaster, and demonstrates how this pattern facilitates adaptive evolution by genetic accommodation in a complex phenotype that exhibits natural, continuous variation.