Should Environmental Caste Determination Be Assumed for Termites?

A defining feature of social insects is the differentiation of colony members into either royal or worker castes. It is widely believed that caste is determined by environmental factors, with genotype playing little or no role. Social insects are thus considered key examples of polyphenism. In termites, various data support environmental caste determination (ECD) in two of the seven families; however, the evidence is less clear-cut for the other five. An alternative to ECD is genetically influenced caste determination (GCD), in which genotype has a significant influence over caste. We have recently discovered the first case of GCD of royals and workers in a termite. Here we examine previous colony composition studies of various termite species, and we find a number of results that are suggestive of GCD. On the basis of these results, we suggest that ECD should not necessarily be assumed for most termite families, and we outline methods for testing between ECD and GCD.