Aging and demographic plasticity in response to experimental age structures in honeybees (Apis mellifera L)

Abstract

Honeybee colonies are highly integrated functional units characterized by a pronounced division of labor. Division of labor among workers is mainly age-based, with younger individuals focusing on in-hive tasks and older workers performing the more hazardous foraging activities. Thus, experimental disruption of the age composition of the worker hive population is expected to have profound consequences for colony function. Adaptive demography theory predicts that the natural hive age composition represents a colony-level adaptation and thus results in optimal hive performance. Alternatively, the hive age composition may be an epiphenomenon, resulting from individual life history optimization. We addressed these predictions by comparing individual worker longevity and brood production in hives that were composed of a single age cohort, two distinct age cohorts, and hives that had a continuous, natural age distribution. Four experimental replicates showed that colonies with a natural age composition did not consistently have a higher life expectancy and/or brood production than the single cohort or double cohort hives. Instead, a complex interplay of age structure, environmental conditions, colony size, brood production, and individual mortality emerged. A general trade-off between worker life expectancy and colony productivity was apparent, and the transition from in-hive tasks to foraging was the most significant predictor of worker lifespan irrespective of the colony age structure. We conclude that the natural age structure of honeybee hives is not a colony-level adaptation. Furthermore, our results show that honeybees exhibit pronounced demographic plasticity in addition to behavioral plasticity to react to demographic disturbances of their societies.

Reproduction, social behavior, and aging trajectories in honeybee workers

“…The relationship between AFF and flight span was most consistent in the Q+ cohorts, which suggests that colony internal factors in the Q− and Q−B treatments were more important for causing variability among replicates than variable outside foraging conditions (Rueppell et al 2007). The hazard ratios associated with AFF are consistent with previous studies (Rueppell et al 2007(Rueppell et al , 2008) and indicate a similar influence of AFF on worker life expectancy in all treatment and replicate cohorts. In contrast to the AFF effect that indicated a higher mortality in workers Event history charts across all treatments and replicates for the minority of individuals that were observed foraging (a) and workers that were never observed foraging (b).…”

“…In addition to the queen, honeybee colonies typically contain thousands of female but functionally sterile workers that perform all nonreproductive tasks in and outside the hive (Winston 1987). The life expectancy of these workers is influenced by their social environment, such as the age structure (Rueppell et al 2008) and colony size ), the external environment influencing foraging risks (Rueppell et al 2007), and individual physiology and behavior ). Most significantly, worker life span is affected by the timing of their transition from inside tasks to foraging outside of the hive (Rueppell et al 2007).…”

Characterization of Quantitative Trait Loci for the Age of First Foraging in Honey Bee Workers

“…Specifically, the identified QTL do not have explicit ties to female reproductive physiology and may therefore present other components of the genetic architecture of the pollen hoarding syndrome that are not female specific (Rueppell et al 2006b). The timing of the transition from in-hive to forager bees has critical effects on colony energy budget and individual mortality (Rueppell et al , 2008. Thus, it is a central trait for colony fitness and social evolution and a similar age-based division of labor can be found in a variety of social insects.…”

“…This has precluded followup studies on potential candidate genes, and hence the present study was designed to localize the aff QTL. As a benchmark of the age-based division of labor among honey bee workers, the AFF is the central variable in the life history of honey bee workers, determining colony food intake and individual worker mortality (Rueppell et al , 2008. It is an exemplary complex trait determined by an interaction of environmental (Schulz et al 1998), social (Le Conte andHefetz 2008), physiological (Nelson et al 2007), and genetic Robinson 2002) influences.…”

Honey bee colonies provided with natural forage have lower pathogen loads and higher overwinter survival than those fed protein supplements

“…Though we are not certain that the bees fed exclusively on the PS, it probably was the primary protein source. Others have reported no effects of protein stress on soluble protein titers but stressed colonies produced less brood (Schmickl and Crailsheim 2001;Rueppell et al 2008;Willard et al 2011). In our study, brood production did not differ between colonies fed PS or pollen possibly because it occurred in the winter when brood rearing rates are low.…”