Collaborative Research: The role of compensation in the evolution of ornaments

College Of Charleston, Charleston SC

Investigators

Abstract

Evolution is responsible for many bizarre and showy physical characteristics (i.e. ornaments) in males, but how they remain reliable indicators of male quality remains controversial. Current hypotheses indicate that ornaments are costly to their bearers, however studies testing for decreased locomotor performance or decreased survival or reproductive success (i.e. Darwinian fitness) as a result of ornaments have been inconclusive. For large ornaments, selection should favor evolution of traits and behavior that offset costs of ornaments, thus concealing their true costs. Stalk-eyed flies provide an ideal model system to test for costs and tradeoffs related to male ornamentation due to their exaggerated head morphology, with eyes displaced at the end of long stalks. These flies exhibit considerable variation in muscle and wing size, compensatory traits that may offset the inertial effects of eye stalks on flight performance. This research incorporates biomechanical and flight performance experiments to characterize compensatory ability in relation to ornament size, and determine how the interaction of ornaments and compensatory traits impact flies' ability to evade predators and reproduce. The proposed research has the potential to significantly revise our understanding of how exaggerated traits evolve and also improve our understanding of biomechanical compensation for ornaments and inform bio-inspired engineering efforts such as miniature drones. This research will provide technical training and professional development to a post-doctoral scholar, a technician and graduate and undergraduate students. Outreach efforts at both campuses will provide STEM education to elementary students and training to K-12 educators. This research employs a novel theoretical and empirical approach to assess the costs of ornaments by considering how compensatory ability in relation to relative ornament size affects the interaction between viability and fecundity. Three distinct avenues of research will be integrated to achieve this goal. First, using species of stalk-eye flies within the family Diopsidae, patterns of correlated evolution between eye stalks and compensatory traits will reveal the macroevolutionary consequences of selection and test the hypothesis that relative ornament size will be positively correlated with the relative size of compensatory traits within and across species. Second, a series of flight performance, maneuverability and predator-avoidance experiments will test the hypothesis that relative compensatory ability predicts viability costs. Finally, a series of mesocosm experiments, where predation and competition interact, will test whether investment in ornamentation versus investment in compensatory traits offers different means to the same fitness end in stalk-eyed flies; the mesocosm experiments will assess the reproductive consequences of viability costs associated with under-compensating for large ornamentation compared to the viability advantages associated with over-compensating for small ornamentation.