Abstract
BackgroundThe performance and fitness of social societies mainly depends on the efficiency of interactions between reproductive individuals and helpers. Helpers need to react to the group’s requirements and to adjust their tasks accordingly, while the reproductive individual has to adjust its reproductive rate. Social insects provide a good system to study the interrelations between individual and group characteristics. In general, sterile workers focus on brood care and foraging while the queen lays eggs. Reproductive division of labor is determined by caste and not interchangeable as, e.g., in social mammals or birds. Hence, changing social and environmental conditions require a flexible response by each caste. In the ant Cardiocondyla obscurior, worker task allocation is based on age polyethism, with young workers focusing on brood care and old workers on foraging. Here, we examine how group age demography affects colony performance and fitness in colonies consisting of only old or young workers and a single old or young queen. We hypothesized that both groups will be fully functional, but that the forced task shift affects the individuals’ performance. Moreover, we expected reduced worker longevity in groups with only young workers due to precocious foraging but no effect on queen longevity depending on group composition.ResultsNeither the performance of queens nor that of workers declined strongly with time per se, but offspring number and weight were influenced by queen age and the interaction between queen and worker age. Individual residual life expectancy strongly depended on colony demography instead of physiological age. While worker age affected queen longevity only slightly, exposing old workers to the conditions of colony founding increased their life spans by up to 50% relative to workers that had emerged shortly before colony set-up.ConclusionsThe social environment strongly affected the tempo of aging and senescence in C. obscurior, highlighting the plasticity of life expectancy in social insects. Furthermore, colonies obtained the highest reproductive output when consisting of same-aged queens and workers independent of their physiological age. However, workers appeared to be able to adjust their behavior to the colony’s needs and not to suffer from age-dependent restrictions.
Highlights
The performance and fitness of social societies mainly depends on the efficiency of interactions between reproductive individuals and helpers
While task allocation among workers may be influenced by their experience, morphology, genetic background, and social interactions [10,11,12,13], in many species the chronological age of workers plays a major role: Giehr et al BMC Evolutionary Biology (2017) 17:173 younger individuals preferentially engage in brood care in the nest, while older individuals focus on foraging outside and nest defense [14,15,16,17,18]
They initially laid more eggs after colony set-up than young queens, Fig. 4 Distance [cm] covered by C. obscurior workers of different age during 10 min but the latter caught up with time. Both old and young workers were able to perform all necessary tasks, and colonies produced similar numbers of offspring independent of worker age. This supports the view that task allocation in manipulated colonies of C. obscurior is not strictly age-based but relatively plastic [33], which is consistent with the repertoire expansion model [18]
Summary
The performance and fitness of social societies mainly depends on the efficiency of interactions between reproductive individuals and helpers. We examine how group age demography affects colony performance and fitness in colonies consisting of only old or young workers and a single old or young queen. Insect societies are characterized by reproductive division of labor between queens (in termites kings) and sterile helpers (workers). While task allocation among workers may be influenced by their experience, morphology, genetic background, and social interactions [10,11,12,13], in many species the chronological age of workers plays a major role: Giehr et al BMC Evolutionary Biology (2017) 17:173 younger individuals preferentially engage in brood care in the nest, while older individuals focus on foraging outside and nest defense [14,15,16,17,18]
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