Effects of Aging on Performance and Oxidative Damage

Abstract

The imbalance between the production of reactive oxygen species (ROS) and the body’s antioxidant defense shortens lifespan and advances aging. ROS, chemical species that contain an unpaired electron in the outer orbit, are unstable and have the potential to oxidize macromolecules, such as lipids, causing damage to cell membranes, resulting in the production of peroxides, which can cause further oxidative damage. Lipid peroxides like malondialdehyde (MDA) are highly reactive, causing a cascade of oxidative reactions that inactivate cellular proteins, impair membrane fluidity and elasticity, and can ultimately lead to cell death. Fruit flies (Drosophila melanogaster) have been used as the insect model organism for aging studies due to its short life cycle, high fecundity, well understood genome, and age‐related diseases that are homologous to that of humans. However, only focusing on a few model organisms ignores the diversity of longevity and the mechanisms involved in aging plasticity. Polyphenic insects can exhibit vast differences in longevity due to environmental and social factors, levels of activity (prolonged flight), and aging intervention, such as diapause, a state of programmed developmental arrest coupled with metabolic suppression. In this study, we begin exploring the effects of diapause on aging by establishing a baseline in the solitary bee, Megachile rotundata,a long‐lived facultative diapauser that experiences intense levels of activity throughout its adult life. We hypothesized that M. rotundata experience age‐related performance declines and increased oxidative damage. We predicted that as bees age, flying and walking performances would decline, and MDA levels would increase. Adult M. rotundata were reared from emergence, and tested at day 0, 7, 14, or 21. For each age group, walking performance was measured using a locomotion activity monitor (LAM), and flight performance was assessed using a cylinder drop assay. Levels of MDA were quantified in whole bees using a thiobarbituric acid reactive substance (TBARS) assay. Walking activity increased two‐fold from day 0 to day 7, and levels of MDA also doubled from day 0 to day 7. However, at day 14 and 21, walking and MDA remained high. In contrast, flight performance decreased with age, with nearly 100% of males and females being able to generate upward lift or slow their descent at day 0, but by day 21 only 34% of females and no males were able to do so. The continual decline in flight performance with age matches previous studies. The decline in flight performance may be attributed to prolonged damage caused by MDA and possible accumulation of other forms oxidative damage, such as protein carbonylation or DNA fragmentation. The plateau of MDA levels beyond the first week may be due to the effectiveness of antioxidant defenses and repair systems. The decline in flight, but not walking, may be explained by the metabolic activity; Insect flight is an intensive activity with a 30‐100 fold increase in oxygen consumption when compared to walking.