title: Lazy workers are necessary for long-term sustainability in insect societies.
abstract: Optimality theory predicts the maximization of productivity in social insect colonies, but many inactive workers are found in ant colonies. Indeed, the low short-term productivity of ant colonies is often the consequence of high variation among workers in the threshold to respond to task-related stimuli. Why is such an inefficient strategy among colonies maintained by natural selection? Here, we show that inactive workers are necessary for the long-term sustainability of a colony. Our simulation shows that colonies with variable thresholds persist longer than those with invariable thresholds because inactive workers perform the critical function of replacing active workers when they become fatigued. Evidence of the replacement of active workers by inactive workers has been found in ant colonies. Thus, the presence of inactive workers increases the long-term persistence of the colony at the expense of decreasing short-term productivity. Inactive workers may represent a bet-hedging strategy in response to environmental stochasticity.
authors.affiliation: Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Eisuke
authors.initials: E
authors.lastname: Hasegawa
authors.affiliation: Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Ishii
authors.affiliation: Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Tada
authors.affiliation: Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Science and Technology and Department of Mathematical and Systems Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan.|Marine Biosystems Research Center, Chiba University, Uchiura, Kamogawa, Chiba 299-5502, Japan.|Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY13210 USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Yoshimura
mesh_terms: D000818:Animals; D001000:Ants; D001522:Behavior, Animal; D003198:Computer Simulation; D007313:Insecta; D008962:Models, Theoretical; D012641:Selection, Genetic