PhD ceremony Mr. M.J.P. Simons: Sexual coloration and aging

PhD ceremony: Mr. M.J.P. Simons

Dissertation: Sexual coloration and aging

Promotor(s): prof. S. Verhulst, prof. A.G.G. Groothuis

Faculty: Mathematics and Natural Sciences

The overlap in the hypothesized costs or reproduction, sexual signaling, and the core causes of aging suggest that by picking one of these aspects, progress can be made in these three research fields together. In his thesis Mirre Simons utilized sexual signaling, manipulations of reproductive effort, and carotenoid supplementation to start to understand these costs. Utilizing meta-analysis, comparative analysis and animal experimentation, Simons finds evidence for immune and oxidative stress costs of carotenoid-dependent signaling. His results also suggest potential alternative or supporting honesty mechanisms, with the most promising candidate being differences in the ability to acquire carotenoids from the environment and context-dependent carotenoid toxicity. Furthermore, Simons experiments suggest that androgens modulate the trade-off between current and future reproduction in stickleback. Moreover, the acceleration in reproductive senescence by sexual stimulation, supports the key prediction of the disposable soma theory. The reduction in sexual signaling induced by experimentally increasing nest building effort suggests phenotypic plasticity to compensate for costs, potentially explaining why costs of reproduction and sexual signals can be elusive. By studying the patterns of senescence and associations with mortality of the zebra finch bill and the stickleback belly, Simons has revealed a potentially general feature of demography of aging: stabilizing selection for pre-senescent expression of traits. This also implies that the information content of a signal may change according to the life-history stage. These results together provide exciting new research questions and substantiate the utility of sexual signals in the study of life-history and aging. Analyzing senescence of trait expression and mortality in synergy and fitting mortality distributions can be used to test basic theory in the biology of ageing, potentially spurring our progress in understanding ageing and death.