SIGNALING IN A MUTUALISTIC INTERACTION

The costs and benefits for partners in interspecific, mutualistic rela tionships can vary from one interaction to the next, or change with ti me during an interaction, which might influence the mutualistic contri butions. Such flexible behavioural responses could be important in reg ulating the interaction. Partners could also have special adaptations for the purpose of influencing each other. An individual might, for in stance, signal its need for the services provided by the partner. In i nteractions between lycaenid butterfly larvae and ants, the larvae del iver nutritious droplets from a specialized gland and, in return, are protected from enemy attacks by the ants. Lycaenid larvae have several ant-related adaptations, one being a pair of eversible tentacular org ans. In this study, the relationships between tentacle display, the de livery of droplets and ant attendance were investigated in a number of experiments, where the interaction between larvae of Polyommatus icar us and either Lasius niger or L. flavus ants was manipulated. High rat es of both droplet delivery and tentacle display were found at the fir st contact with ants, after an interruption in attendance and, for low levels of attendance, after a simulated enemy attack. Under steady st ate conditions, displays were most frequent at low levels of attendanc e, but droplet delivery had a maximum at intermediate levels. Manipula tion of a larva's ability to use its tentacles also showed that ants r espond to tentacle display by increasing their attendance. Larval beha viour was interpreted as aimed at regulating the, number of attending ants. (C) 1996 The Association for the Study of Animal Behaviour