The mechanism underlying the regulation of work-related behaviors in the monomorphic ant, Myrmica kotokui

The mechanism underlying the regulation of the work performed by the members of a colony is a crucial factor in the colonial life of eusocial organisms. If the response thresholds of the workers vary, greater-than-chance variation in the prevalence of work-related behaviors (i.e., in the working degree) is expected, and the distribution of these behaviors should be reestablished after demographic changes. We show that greater-than-chance variation in the working degree is restored after a demographic change in the ant Myrmica kotokui. The working degree varied markedly among workers, and the degree of variation could not be explained by chance alone. Moreover, the degree of variation could not be attributed to intrinsic factors such as reproductive potential or age. After a demographic change, some previously inactive workers started to work, whereas some previously active workers became inactive. These shifts resulted in the restoration of a substantial amount of variation in the working degree. These observations all support the hypothesis that variance in the response threshold is the basis of the regulation of work-related behaviors in this ant.