When males outlive females: Sex-specific effects of temperature on lifespan in a cyclic parthenogen.

Lifespans of males and females frequently differ as a consequence of different life history strategies adopted to maximize fitness. It is well visible in cyclic parthenogens, such as water fleas of the genus , where males appear in the population usually only for periods when receptive females are available. Moreover, even within one sex, different life history strategies and mechanisms regulating lifespan may exist. Previous studies suggested that males may regulate their lifespan by staying in colder waters than females. We hypothesize that such behavioral mechanism should be associated with stronger reaction to low temperature-that is greater lifespan extension in males than in females. In this study, we monitored survivorship of females and males of three clonal lines cultured at 16 or 20°C. The results did not provide a species-level corroboration of our hypothesis; instead, they revealed very strong intraspecific differences in the responses of male and female lifespan to temperature change. They further suggest the existence of parallel life history strategies, hypothesis whose tests would bring new insights into the ecology of males in cyclic parthenogens.