Jason B. Williams, Stephen P. Roberts, and Michelle M. Elekonich. Biological Sciences, University of Nevada Las Vegas, 4505 Maryland Parkway, Biology 454004, Las Vegas, NV 89154-4004
As honey bees age they switch from in-colony tasks, such as nursing, to foraging for nectar or pollen outside the colony. Nurses rarely fly, have a relatively low metabolic rate, and experience a homogeneous environment. By contrast, foragers have the highest measured mass specific metabolic rates and produce high thoracic temperatures during their frequent foraging trips (thoraces average 36ºC compared to 29ºC in heads). Consequently, foragers have a six-fold higher concentration of the stress protein Hsp70 in their thoraces than their heads, as well as two-fold and six-fold higher Hsp70 levels than nurse thoraces and heads. Hsp70 is a chaperone that stabilizes other proteins during stress, especially from high temperatures. However, temperature does not induce Hsp70 expression in forager thoraces at typical flight temperatures or even after exposure to 50ºC for 1h, a temperature bees are unlikely to experience in nature. In this ongoing study, we used the metabolic differences between nurse and foragers to test the hypothesis that oxidative stress, rather than temperature, induces Hsp70 expression in forager thoraces. We measured carbonyl content (a measure of protein oxidative damage), total antioxidant activity, and expression of Hsp70 and several antioxidant enzymes, superoxide dismutase, catalase and glutathione-s-transferase, in thoraces and heads of 9 to11 day-old foragers and nurses collected as foraging activity begins, at mid-day, or at end of the foraging day. To determine the effect of a single foraging flight on tissue oxidative damage and Hsp70 expression, we examined the above stress measures on thoraces and heads of foragers that were collected from bees just leaving for, or returning from a foraging flight at each collection period. To assess the effect of age on accrued oxidative damage and Hsp70 expression we repeated the above experiments on old foragers and nurses aged 30 to 32 days.
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