Antipredator Defence and the Evolution of Senescence in Lepidoptera

Senescence, defined as a reduction in physiological function, fecundity or survivorship with age, is a nearly ubiquitous phenomenon which nonetheless presents an apparent evolutionary paradox, since individuals that did not senesce would seemingly have a selective advantage over those that do. This paradox is resolved by evolutionary theory in terms of life history trade-offs, since selection is expected to favour benefits early in life even if they are associated with costs late in life. In this research project, I explored one of the fundamental predictions of the evolutionary theory of senescence: that increased predation should select for increased rates of senescence and therefore reduced longevity. In particular, I tested the prediction that aposematism (conspicuous coloration paired with chemical defence) should be associated with lower predation rates than other strategies such as crypsis (or camouflage), and this should lead to lower senescence rates and higher longevity in aposematic species. My research program addressed two broad questions: first, are there differences in predation-related mortality between cryptic and aposematic prey, and second, what are the implications of these differences (or lack thereof) for the evolution of senescence? Predation rates were compared using field experiments with artificial prey and wild predators, and included a test of a specific theory of post-reproductive senescence based on kin selection. My results indicated that there was little support for the kin selection mechanism of post-reproductive senescence, however there was some support for the more general mechanism of differential predation rates between aposematic and cryptic prey. The relationship between defence and senescence was explored in two ways: by fitting senescence models to demographic data from Lepidoptera, and by building a simulated population which evolved longevity in the presence of predation.