1) The physiological modulation of life history trade-offs
All organisms face trade-offs between investing in reproduction and self-maintenance; how these fitness components are prioritized varies widely among individuals, populations, and species. Hormone levels, particularly the physiological response to a stressor, have been hypothesized to play a central role in modulating life history trade-offs, but little is known about how individual variation in stress responsiveness influences the behaviors that ultimately affect fitness. I am testing the links between hormones, behavior, and fitness in the wild in two model systems: barn swallows (Hirundo rustica) and Galapagos marine iguanas (Amblyrhynchus cristatus) using a combination of observational and experimental approaches.
2) The costs and evolutionary consequences of sexual signaling and signal assessment
The information content of divergent signals:
Populations often show marked phenotypic differentiation in signal traits, but we still know little about what specific information is conveyed by a given signal, how multiple static and dynamic signals are coordinated, and how signal divergence occurs. I am testing these questions using experimental trait manipulations in barn swallows, a recently diverged subspecies complex where different populations use different signals in mate choice. This work, done in collaboration with Rebecca Safran, combines physiological (hormones and oxidative stress), behavioral, morphological, and fitness metrics of breeding birds to examine how signals provide information about their bearer in changing social and ecological contexts.
The cost of mate selectivity:
Females of many species spend significant amounts of time assessing and discriminating among potential mates, but little is known about the energetic cost of these behaviors. Mate choice has often been assumed to carry minimal costs, particularly in species in which females receive no direct benefits from their chosen mate. However, my previous research, which used miniaturized heart rate data loggers to generate fine-scale estimates of oxyen consumption in free-living Galapagos marine iguanas, indicated that females pay high energetic, reproductive, and apparent survival costs to discriminate among potential mates in this lekking system (Vitousek et al. 2007). Females also vary their investment in mate choice according to climate cycles (Vitousek 2009), suggesting that a change in climate could potentially impact the direction or strength of sexual selection. Individual variation in hormone levels prior to and during the reproductive period predicts several aspects of reproductive investment, including the decision whether to reproduce (Vitousek et al. 2010) and the display rate of males (Vitousek et al. 2008). I am currently investigating the physiological predictors of individual variation in mate selectivity.