Age-resistant worker reproductive potential and effect of helpers on prolonged lifespan in an ant.

Abstract

Background: 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 notable exceptions, primarily attributed to selection on queen lifespan in the protected nest and increased extrinsic mortality of workers performing risky outside tasks. By creating different age groups of non-reproductive workers in an ant where workers can replace reproductive queens and by isolating single workers with and without helpers, we investigated the effect of age on reproductive and parenting abilities and the impact of help on reproductive worker lifespan.

Results: Isolated workers could become reproductive and raise offspring to adulthood despite commencing reproduction at ages twice the median lifespan of non-reproductive worker ants. 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 a marked lifespan increase. In a separate test, helper presence increased the median life-span at least 2.6-fold in single, isolated workers compared to helperless workers.

Conclusions: Helper presence may be a primary reason for the longevity differences between reproductive and non-reproductive individuals in social insects similar to cooperatively breeding birds and mammals while mechanisms associated with selection on queen lifespan have evolved secondarily. Contrary to many ant species with high extrinsic mortality, some with sexual reproduction invest in reproductive capacities until advanced age.