Reproduction, social behavior, and aging trajectories in honeybee workers

Abstract

While a negative correlation between reproduction and life span is commonly observed, specialized reproductive individuals outlive their non-reproductive nestmates in all eusocial species, including the honeybee, Apis mellifera (L). The consequences of reproduction for individual life expectancy can be studied directly by comparing reproductive and non-reproductive workers. We quantified the life span consequences of reproduction in honeybee workers by removal of the queen to trigger worker reproduction. Furthermore, we observed the social behavior of large cohorts of workers under experimental and control conditions to test for associations with individual life expectancy. Worker life expectancy was moderately increased by queen removal. Queenless colonies contained a few long-lived workers, and oviposition behavior was associated with a strong reduction in mortality risk, indicating that a reproductive role confers a significant survival advantage. This finding is further substantiated by an association between brood care behavior and worker longevity that depends on the social environment. In contrast, other in-hive activities, such as fanning, trophallaxis, and allogrooming did not consistently affect worker life expectancy. The influence of foraging varied among replicates. An earlier age of transitioning from in-hive tasks to outside foraging was always associated with shorter life spans, in accordance with previous studies. In sum, our studies quantify how individual mortality is affected by particular social roles and colony environments and demonstrate interactions between the two. The exceptional, positive association between reproduction and longevity in honeybees extends to within-caste plasticity, which may be exploited for mechanistic studies.

Early life stress affects mortality rate more than social behavior, gene expression or oxidative damage in honey bee workers

“…Newly emerged workers were individually marked with colored plastic tags (Dixon et al, 2014; Rueppell et al, 2007). Marked workers were introduced within 24 hours of emergence into a four-frame observation hive that had been established two weeks prior with a queen, 3000 workers of mixed ages, one frame of brood, and pollen and nectar resources.…”

“…Daily behavioral observations over 10 hours each day followed a previously established scan-sampling protocol (Dixon et al, 2014) with 24 defined behaviors that were consolidated in subsequent analyses to 14 behavioral categories (Table 1). Individuals were recorded as dead one day after their last observation because honey bee workers return to their hives as long as they live.…”

Ties between ageing plasticity and reproductive physiology in honey bees (Apis mellifera) reveal a positive relation between fecundity and longevity as consequence of advanced social evolution

“…Honey bee workers display a wide range of life expectancies, dependent on the rate of their behavioural ontogeny, which in turn is influenced by social environment, such as colony age composition [17] and size [18], and external environment, such as season [19,20]. Recent life expectancy estimates of honey bee workers can vary from 18 to 30 days in one experiment [21], but earlier studies report higher life expectancies, ranging from 20 to 50 days [9] or even 28 to 154 days across multiple seasons [20]. Low food reserves and other forms of stress can accelerate the behavioural progression towards foraging through physiological control circuits (see below), and pheromone signals emitted by brood [22] and the queen [23] also influence the onset of foraging.…”

“…This usually happens whenever the queen is lost and cannot be replaced (Bourke 1988). Reproductive workers experience lower mortality rates [21], although they do not to live the degree of queens, and functional genomic studies suggest that the differences between normal and reproductive workers are much smaller than between workers and queens [28]. Rarely worker reproduction can be observed in the presence of the queen, which is known as the ‘anarchic syndrome’ [29].…”

The possible role of ritualized aggression in the vibration signal of the honeybee, Apis mellifera

“…We used the presence and maturity of forming oocytes to classify the left and right ovary of each worker as reproductively 'active' (individual oocytes clearly present and deforming the shape of the ovariole) or 'inactive' (oocytes absent or not exceeding the width of the ovariole) (Dixon et al, 2014). If the left and right ovaries of an individual bee differed in development, we classified the worker according to its greatest level of activation.…”