The nurse's load: early-life exposure to brood-rearing affects behavior and lifespan in honey bees (Apis mellifera)

Abstract

Long-lived honey bees (Apis mellifera) develop in fall. This pattern may be explained by reduced nurse loads. When the amount of brood in colonies declines as a function of adverse foraging conditions, adult bees build up surplus nutrient stores that include vitellogenin, a behavioral affector protein that also can increase lifespan. Although the seasonal reduction in exposure to nursing tasks predictably results in vitellogenin accumulation, the assumption that long-lived adults thereby develop is confounded by a concomitant decline in foraging effort. Foraging activity reduces lifespan, and is influenced by colony resource consumption, brood pheromones, availability of nectar and pollen, and weather. Here, we perform the first controlled experiment where the nursing environment of pre-foraging sister bees was set to vary, while their foraging environment later was set to be the same. We measure vitellogenin, age at foraging onset and lifespan. We establish that reduced brood-rearing increases vitellogenin levels, and delays foraging onset and death. Longevity is largely explained by the effect of nursing on the onset of foraging behavior, but is also influenced by the level of brood-rearing independent of behavioral change. Our findings are consistent with the roles of vitellogenin in regulation of honey bee behavior and lifespan.

Fig. 1

Vitellogenin protein level (relative quantity, RQ) in worker bees from two randomly chosen colony pairs. In both replicates, the No Brood treatment resulted in increased vitellogenin titers compared to the High brood treatment. Bars are means with standard errors.

Fig. 2

Foraging onset shown as the cumulative proportion of bees that has not yet foraged. Reduced brood-rearing (No Brood) resulted in delayed foraging onset. The panels show data from all tagged workers that were observed to forage at least twice.

Fig. 3

Worker longevity shown as the cumulative proportion of marked bees that is still alive. Reduced brood-rearing (No Brood) extended the lifespan of workers. The panels show data from all tagged workers that were observed alive during the study.