Social Insect Blog

We saw last week how Kin Selection explained the altruism seen in the social insects and in animals that direct their benefits to kin. But even in the social insects there is some room for selfishness. Explain the conflict between queens and workers. Who wins and why? Are there any exceptions?





The ultimate conflict is explained by Trivers and Hare. They state that insects of the group Hymenoptera has a sex determination system that there is a queen who has made one mating flight to store up sperm for the rest of her life. Females have a father and therefor have a double set of chromosomes, whereas a male has only a single set of genes in each body cell and therefore all males in a colony are identical. The relatedness between hymenoptera sisters is 3/4 which is very different from other species in that the relatedness by full sisters is normally 1/2. It means that a hymenoptera female is more closely related to her full sisters than she is to her offspring of either sex. Hamilton realized that this predisposes females to "farm" thier own mothers as a sister making machine, but they must curb her natural tendency to give the 1:1 sex ration of equal sisters and brothers. From the workers point of view, the chance of any brother containing one of her genes is only 1/4, so for the profit of the workers, she cannot produce children in equal ratios. A worker always wants a 3:1 and a queen always wants a 1:1 sex ratio. THe conflict of interest is the queen trying to invest equally in males and females, while the workers try to shift the ratio to a 3 females to every male. Trivers and Hare took 20 species of ants and investigated the sex ratio and found very close to the 3:1 ratio. It turns out that the genes trying to manipulate the world through the queen bodies are outmanuevered by genes manipulating the world through workers bodies.
There are a couple exceptions to this is the slave making species which the queens can disguise male eggs to appear females to the workers. Some queens could mate with multiple males on the mating flight as well and the relatedness would thus decrease.