Cost and Evolution of a Facultative Mutualism between Ants and Lycaenid Larvae (Lepidoptera)

Larvae of Arawacus lincoides (Lycaenidae) reared in the lab with ants took 0.68 d longer to complete development than larvae without ants. Pupal weight was independent of whether a larva had been ant-tended. A 0.68 d delay in reaching age of first reproduction represents an estimated 1.0%-2.2% lowered intrinsic rate of increase for this continuously brooded species. I show that mutualism will be favored when then ratio of larval survival with ants to that without ants is greater than exp (dr), where d is the additional larval development time caused by feeding ants and r is the intrinsic rate of increase. Other things being equal, species with higher intrinsic rates of increase will be less likely to be mutualistic than their relatives with lower rates of increase