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Honey bee workers perform a variety of functions in the colony at different ages. We call this age polyethism. Young workers, staying in the hive, and older ones, acting as foragers, are two important periods in the life of bee workers. A very interesting aspect of this age-related phenotypic plasticity has been recently discovered. It is behavioural reversion – the transition from the forager bee back to the nurse bee and the resumption of normal functions typical of this stage of development. It has been proved that the reversion is associated with higher levels of metabolic activity, development of ovaries, better-developed ovarioles, restoration of the function of the hypopharyngeal gland, which retrogrades with aging, an increase in haemolymph vitellogenin, and a decrease in the level of the juvenile hormone, which rises with age. The reversion is a very interesting phenomenon, as it consists in delaying or even reversing the physiological process of aging. This is confirmed by the fact that reversant bees live several times longer. Thus, the honey bee becomes a valuable animal model in gerontological research.
The article provides a review of research on evolution, ecology and physiology of aging and longevity, and focuses on results gained from the studies of a facultatively sexual crustacean, Daphnia. Despite its clonality and indeterminate growth, evidence for its senescence has been collected. Differences in the dynamics of age- specific parameters were seen between both environmentally developed phenotypes within a genotype and between genotypes, including between sister species. The lifespan of the animals varies depending on the habitat of origin and predation pressure experienced therein, and on environmental conditions - showing a hormetic response, or revealing trade-offs in the life history. Extreme differences in lifespan can be found in closely related lineages and within a single habitat, providing opportunities to study the underlying mechanism. This all makes Daphnia a so-far underscored, but already emerging model in the study of ecology and evolution of aging, and its molecular mechanisms.
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