Senior Research Specialist Arizona State University Tempe, Arizona
Aging theory suggests that animals should reproduce early at a cost to longevity, leading to a fecundity-longevity trade-off. Social insects with long-lived reproductive queens and short-lived helper workers are a notable exception to this pattern, primarily attributed to increased extrinsic mortality of workers performing risky tasks outside the safe nest environment. By creating different age groups of non-reproductive workers in the ant Harpegnathos saltator where workers can replace reproductive queens, we investigated the effect of age on reproductive and parenting abilities and the impact of help on lifespan. We show that isolated workers could become reproductive and raise offspring to adulthood despite being twice the median age of non-reproductive worker ants and the high extrinsic mortality assumption. The experimentally selected old workers converged with workers half the median age to a common lifespan maximum of about 600 days in the absence of worker help. However, most reproductive workers surviving beyond this point were associated with at least one helper worker and showed an increase in lifespan up to 2.5 times above the lifespan convergence point. To test the hypothesis that helpers increase the longevity of reproductives, we compared the longevity of isolated single reproductive workers with the same type of worker but that received help. We found a significant increase in longevity with helper aid. Helper presence may thus be a primary reason for the longevity differences between reproductive and non-reproductive individuals in social insects similar to cooperatively breeding birds and mammals.