Disease is often known to lead to the performance of risky behaviors. Using the energy budget rule of Risk Sensitivity Theory as a theoretical foundation, this project asks whether such risky behavior stems from the energetic stress incurred from a disease because it is adaptive to be risk-averse when one?s energy budget is positive and be risk-prone when it is negative. Using the honeybee as a model, the project will use a suite of feeding regimes to put individuals at different energy budgets and use an olfactory conditioning assay to test their choice for constant (risk-averse) and variable (risk-prone) reward distributions. The project will also test how an individual monitors its energetic state in order to behave in a risk-sensitive fashion and how this assessment is operative in an individual whose energetic state is tightly tied to that of the colony. Using an enzyme inhibitor to keep an individual artificially starved and thus uncouple its energetic state from that of its colony (which also mimics the energetic stress of a parasitic infection in a host), the project will test if foraging decisions can be dictated by the energetic state of the individual independent of the energetic state of the colony. By integrating potential links between disease ecology, physiology, and behavioral ecology, the proposed research has the potential to provide a mechanistic basis and a novel perspective for the recent worldwide phenomenon of honeybee colony collapse characterized by bees disappearing from their colonies. The project will also involve undergraduate students in science education at local schools and collaboration with local beekeepers to improve honeybee health in general.

Project Report

An individual’s energetic state is a fundamental driver of its behavioral decisions in all animals and one of the ways in which energy is suggested to impact behavior is by regulating one’s sensitivity to risk. This idea proposes that if you are starving, you should prefer a more variable food patch because it allows you the possibility of obtaining a high enough reward that is necessary for survival even though there is an equal chance of getting a low food reward. In contrast, if you are not starving, you should prefer a constant food patch because getting a large food reward is not important and therefore not worth the risk of getting a low food reward in a variable patch. However, empirical support for this idea is not too strong. Using individual honeybees as a model, we first determined the utility (survival value) of different sized food rewards for starving and non-starving animals and confirmed that the utility of a large food reward is indeed higher for starving animals. We then demonstrated that individual bees indeed are risk-prone when they are starving and risk-averse when they are not. We also found that rather than the absolute energetic state of an individual, it is a change in it that is important for dictating risk-sensitive behavior. Since we found that a honeybee individual can make adaptive decisions based on its own individual energetic state, we wanted to investigate how the decision making process works when the individual energetic state is in conflict with the energetic state of the colony that is given by the amount of food stores. Such a situation can arise, for example, when an individual is energetically stressed due to a parasitic infection or another energetic stressor that acts upon the individual without adversely affecting the colony food stores. We therefore uncoupled the energetic state of the individual from that of its colony by feeding bees with sorbose, a sugar they cannot metabolize and which therefore leaves them at a negative energy budget. We found that such bees in a colony with full food stores did not compensate for their hunger by feeding on colony reserves or by taking food from their nestmates but instead by reducing their within-colony activities and eventually by increasing their foraging activity. In summary, our results therefore give insights on how animals adaptively manage risk to deal with changing energy budgets and also provide a possible novel link between disease and risky behavior. They also give insights on how social animals resolve conflicting energetic states and the evolution of social behavior, suggesting that regulatory mechanisms found in solitary animals have not been replaced by entirely new mechanisms in social animals but rather have been co-opted with social regulatory cues. The fact that the energetically stressed bees did not feed on food stores, but reduced their participation in colony tasks can be considered as weakly selfish. A similar response to energetic stress has been found in humans and therefore this may be a universal response due to natural selection acting more strongly on the group level than the individual level. The findings are particularly relevant as they may provide a plausible explanation for why a honeybee forager could leave the hive to forage in an energy depleted state, thus increasing her chances of being unable to return back to the colony, and contribute to the recently observed colony collapse in honeybees.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Michelle M. Elekonich
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Colorado State University-Fort Collins
Fort Collins
United States
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