59.6 Saturday, Jan. 5 Genetic, developmental, and ecological determinants of resource allocation tradeoffs in the horned beetle, Onthophagus taurus SCHWAB, D.B.*; KIJIMOTO, T.; MOCZEK, A.P.; Indiana University - Bloomington; Indiana University - Bloomington; Indiana University - Bloomington email@example.com
During ontogeny, growing structures may compete for a shared pool of limited resources to sustain their development. Such interactions may lead to tradeoffs, where the elaboration of one structure must come at the expense of another. Tradeoffs have the potential to constrain the production of phenotypic variation and to bias evolutionary trajectories. In Onthophagus beetles, large males produce extravagant horns used to secure matings. Previous studies suggest tradeoffs between horns and both proximally- (i.e. antennae, eyes, wings) and distally-located (i.e. genitalia) structures; however, the developmental mechanisms underlying these interactions and their evolutionary significance are unknown. Here we explore the nature of tradeoffs between head horns and eyes in the horned beetle O. taurus. We investigate (a) relative investment into horns and eyes among discrete populations and find that tradeoffs are absent in established populations, but may be present in populations at the edge of an invasion front. Using common garden rearing, we show that (b) relative investment into horns and eyes changes under laboratory conditions. We then (c) contrast exotic populations that have diverged heritably in horn investment. We find that reduced horn investment results in reduced investment into horns, opposite to predictions based on tradeoffs. Lastly, we (d) altered horn investment via RNAi of the somatic sex-determination gene doublesex, which results in greatly reduced horns in males. Again, we find that horn reduction also results in reduced investment into eyes. These results suggest that resource allocation tradeoffs between developing structures may depend greatly on genetic, developmental, and environmental contexts. This context-dependency may therefore limit the degree to which tradeoffs can be detected in natural populations or constrain their evolutionary trajectories.