Longevity cost of remaining unmated under dietary restriction

Abstract

Summary 1. Increases in longevity from dietary restriction (DR) have been linked to the evolution of physiological strategies for maintaining lifetime reproductive output despite periods of nutritional deficiency. If this is the case, then reproductive life history and mating status should determine whether or not dietary restriction increases longevity. 2. We investigate the effects of DR and mating status (mated or unmated) on longevity and lifetime reproductive output and explore mechanisms underlying these patterns by measuring resting energetic rates and changes in mass over time. We study iteroparous female Australian redback spiders (Latrodectus hasselti), which are known to tolerate periods of starvation (ecologically relevant DR) in nature. 3. Mated DR females had the highest longevity of any experimental group, in strong contrast to results for semelparous males of this species [M.M. Kasumovic, M.C.B. Andrade & R.C. Brooks (2009), Biology Letters,5, 636]. Most strikingly, mated females (whether DR or not) had higher longevity than unmated females. 4. Mated females rapidly decreased their resting energetic rates and stopped egg production under DR. Once feeding returned to normal, resting energetic rates of mated females increased immediately, egg sac production continued and there was no net decrease in lifetime reproductive output relative to mated females without DR. 5. This shows DR increases longevity for mated females, but there is a longevity cost of remaining unmated, which may arise because unmated females (regardless of diet) maintained high energetic rates. This may be an evolved pattern of physiological support for reproductive readiness which exerts a fitness cost when mating is delayed. Taken together, these results suggest positive effects of DR on longevity critically depend on reproductive life history (iteroparity or semelparity) and individual mating status.