What is the main driver of ageing in long-lived winter honeybees : antioxidant enzymes, innate immunity, or vitellogenin?

Abstract

Senescence or ageing in invertebrates is only partly unscrambled. Up to now five different theories deal with explaining the biology of ageing. Most likely physiology, genetic predestination and the impact of the environment form the image of ageing in individuals and groups. Social insects, especially the honeybee Apis mellifera, present the best model system to study developmentally related ageing, because high phenotypic plasticity makes the worker caste useful to dissolve remaining questions. Here, we used long-lived winter honeybee workers and measured transcriptional changes of 14 antioxidative enzymes, immunity and ageing-related (Insulin/insulin-like growth factor signalling-pathway) genes at two time points during hibernation. Additionally, the bees received a bacterial infection to see ageing and infection associated immunity changes. Gene expression levels for each group of target genes revealed that ageing had a much higher impact than the bacterial infections, notably for immunity related genes. Antimicrobial peptide and antioxidative enzyme genes were significantly up-regulated in aged worker honeybees independent of bacterial infections. Vitellogenin and IlP-1, known ageing markers, were contrary regulated with increasing vitellogenin levels during ageing. The increased antioxidative enzyme and antimicrobial peptide gene expression may have a positive and also protective effect during ageing in hibernating worker honeybees.