A pair of scientists has proposed a new model for behavioral development among social insects, suggesting that a higher male susceptibility to disease has helped shape the evolution of the insects' behavior.
What might be called the "sick-male" theory has been proposed by animal behaviorists Sean O'Donnell of the University of Washington and Samuel Beshers of the University of Illinois at Urbana-Champaign, and appears in the current issue of Proceedings Biological Sciences, published by the Royal Society of London.
Among behaviors possibly affected are the division of labor between males and females and the relative social isolation experienced by males in many social insect colonies.
The researchers looked at Hymenoptera, an order of insects, including bees, ants and wasps, some of which have highly complicated societies and an unusual genetic makeup. These insects are called haplodiploids because males and females have a different number of sets of chromosomes. The females, like most animals, including humans, are diploid and have two sets of chromosomes, one from each parent. Hymenopteran males, however, hatch from unfertilized eggs and are haploids with just one set of chromosomes.
"Disease and infections are a very powerful and ongoing force in natural selection, and natural selection should favor individuals that possess forms of genes, or alleles, that make them more resistant to infection," said O'Donnell, a UW associate professor of psychology. "In some cases, an individual that has more than one form of a gene can ward off more parasites. In humans, for example, there are different forms of a blood gene that can help ward off malaria parasites. People with two different alleles for this gene are more resistant to malaria."
Because they are haploid, Hymenopteran males can't have alternate forms of any genes, or in other words, individual males have no genetic variability. This, O'Donnell and Beshers contend, puts males at a higher susceptibility to disease.
The researchers, who are trying to understand the basis of social behavior in these creatures, suggest that this male vulnerability has shaped certain behaviors in social insect colonies. These behaviors, they say, are designed to minimize the risk of disease transmission in a colony.
Division of labor is a prime example. While colonies vary widely in the total number of individuals, females vastly outnumber males and seem to do most of the work.