Morph-specific life-history correlations in a wing-dimorphic water strider

Life-history theory predicts a negative correlation between reproduction and survival because individuals differ in their investment in early reproduction at the expense of survival. However, life-history trade-offs can be masked when individual differences in resource allocation are smaller than those in resource acquisition. In polymorphic species, as distinct morphs exhibit differences in intrinsic physiology, the relative effects of resource acquisition and allocation on life-history traits will differ between morphs, contributing to morph-specific life-history correlations. Here, in the wing-dimorphic water strider Aquarius paludum, we found that wing morphs differed in within-morph individual-level life-history correlations. Longer-lived flight-capable long-winged females produced fewer eggs per day and matured later, whereas life-history trade-offs were not observed in short-winged flightless females. The survival–reproduction trade-off observed in long-winged females may be a result of individual differences in the timing of wing muscle histolysis. Individuals that underwent wing histolysis early would have increased reproduction at the expense of a shorter life, whereas individuals with late wing histolysis would have reduced reproduction but a longer life. Short-winged females, who never develop wings, effectively have more resources to allocate to both survival and reproduction, masking any life-history trade-offs. Thus, we suggest that morph-specific effects of resource allocation trade-offs can shape the morph-specific extent of individual variation in life-history strategies, which may contribute to the evolution and maintenance of within-species polymorphism.