Reproductive decision-making in the termite, Cryptotermes secundus (Kalotermitidae), under variable food conditions

Abstract

Relatedness concepts have dominated the discussion on the evolution and maintenance of eusociality in social insects. In the diploid termites, explanations based on relatedness asymmetries have been less relevant than in the Hymenoptera; ecological factors have been claimed to be paramount. Yet, relevant quantitative studies investigating the role of ecological factors are lacking. We examined the influence of ecological factors on reproductive tactics in the drywood termite, Cryptotermes secundus. In this species, caste development is very flexible, with individuals having the option to remain at the natal nest as helpers/workers or to develop into dispersing reproductives (sexuals). An important ecological factor expected to influence this “decision” is food availability; C. secundus nests in a piece of wood that serves as food and shelter, with individuals never leaving the nest to forage. Thus, a reduction in the amount of food parallels a reduction in the nests' longevity. Therefore, we tested the influence of food availability on caste-developmental decisions in natural colonies, as well as in two experiments in which we simulated a gradual and a sudden decline in the amount of available food. In all trials dispersing sexuals occurred more often in colonies with diminished food resources than in colonies with abundant suitable food. Thus, regardless of how food declines, individuals seem to switch their tactic from being a helper to becoming a dispersing reproductive if nest conditions deteriorate and the nests's longevity decline.