Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [28]
Where did the extreme social behavior in these insects, with its self-sacrificial sterility, come from in the first place? The study of the honeybee genome, as well as detailed information on the genes of social and nonsocial species, supports an idea that had been around for a while among entomologists: start with mothers sticking around to feed their young, and go from there, progressing from maternal care to the more generalized care of siblings. Many insects show a more modest amount of social behavior than the ants or honeybees, as I describe in the chapter on parental care; they may guard their eggs, bring food to the developing young, or join forces with other females to rear offspring collectively, and they provide good test cases for this idea. Toth, Robinson, and a group of colleagues used the common paper wasp to see if care of sisters and care of young were governed by the same genes. Although the genome for the wasps has not yet been sequenced, the scientists used an innovative technique to characterize short segments of DNA that were already known to be associated with social behavior in honeybees. Although the bees and wasps last shared a common ancestor 100 to 150 million years ago, the genetic material that was examined turns out to be amazingly unchanged.
Paper wasps do not show the extreme differences among castes seen in ants or honeybees, but the scientists were able to examine DNA from four kinds of individuals. Foundresses are the females that start up a colony in the spring, usually by themselves, which means they forage as well as reproduce. They rear the first generation of daughters, who then become workers, allowing the foundress to become a queen and spend all of her time laying eggs. Finally, gynes are females that mate late in the year, spend the winter in a sheltered place, and then emerge in the spring to become foundresses.
Despite the identical outward appearance of the four types, and the fact that in some cases they are actually the same individuals performing different tasks, the researchers found that the wasp females differed markedly in the expression of genes in their brains. Workers had brains that were more like the foundresses that also cared for young than the queens and gynes that reproduce. Some of the genes that differed in expression were related to the production of insulin, an important component of nutrient regulation in insects, as in humans, which suggests that becoming social involved evolutionary changes in how food is perceived and processed. Toth and Robinson believe that the path from completely solitary to intensely social made use of a kind of molecular toolkit common to the ancestors of both kinds of behavior, modified in small ways as natural selection acted on the components. This differs from earlier ideas that new behaviors needed new genes.
The Collaborative Dictator
RESULTS such as these are leading us to a much better understanding of what it means to have genes control anything, whether that is social behavior or eye color. People often assume the existence of a gene "for" a trait, so that if you have the monogamy gene, for example, you won't cheat on your spouse, but if you lack it, your infidelity is inevitable. Studying genomes shows this is futile. First, genetic material is often redundant, nonfunctional, or just plain disassociated from any obviously useful protein. Second, genes are the great recyclers—all of our genes were modified from preexisting ones, with some new mutations that occurred at random thrown in. The genes associated with parental behavior are related to those that make a bee more likely to feed her sister, which are also associated with myriad other behaviors. This means that no gene can be associated de novo with a single trait