As organisms get older, they often lose their ability to move and reproduce, and some may struggle to think clearly. This usually results from damage to the nervous and muscular systems, which are vulnerable to the side effects of high energy demands. Cells using oxygen for energy produce harmful byproducts that can damage fat tissue and alter the structure and function of proteins and DNA. Aging theories suggest that when these toxins exceed the body's defences, damage accumulates, affecting movement and shortening lifespan. In humans, antioxidants like vitamins C and E help combat this damage, but some still occurs and defences weaken with age. That said, this theory is not true for all organisms. For instance, sea urchins and some insects do not show the expected buildup of toxins or decrease in antioxidants with age. To study the effects of aging on cell damage and behaviour, researchers Jacob Pithan, Kendra Greenlee and Giancarlo López-Martínez from North Dakota State University, USA, and Joseph P. Rinehart from USDA-ARS, USA, chose the solitary leafcutting bee Megachile rotundata. These bees, known for their varied lifespans and high activity levels, produce their own antioxidants to manage cell damage. The researchers wondered whether aging would impair the bees’ abilities to walk and fly due to the buildup of damage over time.
The team began by studying how aging affects the leafcutting bees’ abilities to walk and fly. On average, the insects live for 17 days, with life spans ranging from 3 to 31 days. They live alone without worker bees to help, so they are super-active, caring for their young and building nests. To test how well the bees could fly as they aged, the researchers dropped the insects from a height into a cylinder and considered the bees successful if they managed to slow their descent and began flying upwards. All newly emerged bees passed the test on their first attempt with flying colours, but their performance declined with age. The success rate of 14 day old bees taking to the wing after recovering from a fall dropped by 27%. By day 21, only 32% of the bees could fly successfully on their first try, with many needing multiple attempts. In contrast, the amount that the bees walked doubled by the age of 7 days, but then began decreasing slightly. This suggests that while the bees kept up their enthusiasm for walking, they lost their high-energy flying abilities as they aged.
To assess the amount of cell damage suffered by the bees as they aged, which would reflect the levels of oxygen-based toxins in their bodies, the scientists measured compounds known as biomarkers, which indicate damage to lipids in fat tissue and proteins. They discovered that newly emerged bees had low levels of malondialdehyde (from fat tissue damage) and carbonyls (from protein damage), increasing up to the age of 7 days. However, after that, the levels of both types of damage remained fairly steady, even though you would expect them to increase as the insects aged. Interestingly, the researchers found that although the insects’ antioxidant production increased up to 7 days, it also remained relatively stable throughout the rest of their lives. Overall, the insects did not exhibit the expected increase in cell damage, associated with an increase in toxic oxygen by-products, or decrease in antioxidants that the researchers had expected to see as the insects aged.
Pithan and colleagues have shown that the stable levels of toxins and antioxidants experienced by the bees as they aged challenge prevailing aging theories. The aged insects are clearly losing some of their youthful abilities as their flight performance fails, but they do not show the symptoms of cellular aging that usually underlie this decline in performance. However, increasing activity levels during the insects’ early days did increase cell damage and cause the insects to raise their antioxidant levels to combat the damaging effects of the toxic oxygen by-products produced by the activity. Have leafcutting bees found part of the elixir of life? That isn't clear, but Pithan and colleagues highlight the need for a deeper understanding of how various factors impact aging and performance across different organisms.
