"Males typically do not do very much work for their colonies," said O'Donnell. "In some instances males do small amounts of labor inside the nest. But they rarely are allowed outside of the nest and they do not forage for food or building materials, activities that might expose them to disease pathogens.

"If males were exposed to disease we would expect females to avoid, and possibly to attack and kill those males to minimize disease being brought into the colony."

The sick-male theory proposes that female-biased societies, and differences in male and female behavior, may be responses to higher risks of infection to males, he said. The theory also predicts that in some cases males may be segregated or shunned inside the nest, again to reduce the colony ™s potential exposure to disease.

O'Donnell said much research still needs to be done to support the sick-male model and test whether males are less resistant to disease than females.

"We hope our study will inspire scientists to these ideas. Researchers need to challenge different species of social insects with disease pathogens to see whether males and females differ in disease resistance," he said. "Our understanding of the genetic basis of disease resistance is pretty weak, even medically. There actually is little evidence to show how genetic variability at the individual level is effective in fighting off disease, even though this is often assumed to be the case by biologists."

The National Science Foundation funded the research.

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