Growing Up Too Fast May Mean Dying Young In Honey Bees

Reactive oxygen species (ROS) occur as a by-product of aerobic metabolism and impair cellular function by damaging proteins, nucleotides and lipids. Organisms possess a variety of anti-oxidant mechanisms to mitigate the effects of ROS, and the oxidative stress model of aging and senescence suggests that physiological performance declines with age due to lifetime accrual of ROS-induced damage and progressively limited anti-oxidant capacity. Hence, the onset, pace and duration of energetically-intense behaviors should affect lifetime kinetics of ROS-induced damage, anti-oxidant responses, physiological capacity and longevity.

A new study examines how these traits in honey bees are affected by age and behavioral intensity (factors which can be experimentally decoupled via manipulation of colony demographics), and is the first to use such an approach to test the oxidative stress model of aging in a free-living organism.

Background

Behavioral development in adult honeybees involves a stereotypical transition from energetically-inexpensive hive work to energetically-expensive foraging behavior at approximately 3 weeks of age. Each day after this transition, a foraging bee (which weighs only 80 mg, or roughly equivalent to a breath mint) will on average fly 8 km (5 miles), contract their wing muscles approximately 4,000,000 times, and reduce approximately 60 ml of pure oxygen in its thorax (the body segment housing the flight muscles). Age and foraging behavior should have strong affects on cellular oxidative stress and antioxidant mechanisms, especially in flight muscle, as well as functional senescence.

In this study the researchers used single-cohort colonies to experimentally manipulate the onset of foraging and compare markers of oxidative damage and antioxidant mechanisms among different tissues (head vs. thorax), age-matched behavioral groups (hive bees vs. foragers) and periods of the day (morning vs. afternoon), with the prediction that such markers are prevalent in high-intensity tissues, behaviors and day-time periods.

The study was conducted by Stephen P. Roberts, Michelle M. Elekonich and Jason B. Williams, all of the School of Life Sciences, University of Nevada Las Vegas. Their study was funded in part by the National Science Foundation (NSF) and the National Institutes of Health (NIH) and is entitled Oxidative stress and antioxidant mechanisms at the transition to an aerobically intensive lifestyle in honey bees. Dr. Roberts is presenting the team's preliminary findings at the 2008 American Physiological Society Intersociety Meeting The Integrative Biology of Exercise V.

Study Summary

Honey bees were reared in single-cohort colonies to enable sampling and comparisons of (a) same-aged bees performing different behaviors and (b) different-aged bees performing the same behaviors. Comparison groups were 8-10 day-old (precocious) foragers, 8-10 day-old (typical) hive bees, 30-32 day-old (typical) foragers and 30-32 day-old (over-aged) hive bees. Antioxidant proteins Hsp70 and catalase were measured in head and thorax tissues using western blot.

Total antioxidant capacity of the tissues was measured as the ability of homogenate to inhibit the oxidation of ABTS® (2,20-azino-di-[3-ethylbenzthiazolinesulphonate]) to ABTS+® relative to trolox standards. Protein carbonylation, aconitase Vmax inhibition and mitochondrial H₂O₂ production were measured as markers of oxidative damage.

Preliminary Study Results

The research team found that:

• Foragers upregulate Hsp70, catalase and total antioxidant capacity in their flight muscles over the course of a day. However, these changes did not occur or were muted in forager head tissues and hive bee flight muscles and head tissues.
• The diurnal upregulation of antioxidants and antioxidation capacity in flight muscle disappeared with age, which may explain the impairment of flight muscle mitochondrial function (elevated H2O2 production and reduced aconitase Vmax) and flight capacity observed in foragers.

Conclusions

According to Dr. Roberts, the study's first author, "These data show that transitions to aerobically-expensive behaviors in organisms living free in nature can have important consequences affecting the pace of aging and senescence. The results support a live-fast-and-die-young view of aging, but so many questions remain about how this aging model works in natural populations, especially for species like honey bees whose social complexity rivals our own."