Ecological consequences of different kinds and degrees of ant-butterfly symbioses

Author(s): Schär S, Pierce NE, Vila R, Nash DR

Summary:

Lycaenid butterflies show a wide continuum of symbiotic associations with ants, ranging from no to obligate interactions. Mutualistic caterpillars generally feed their ant symbionts with honeydew from their dorsal nectary organ, and in return receive protection from predators and parasitoids. At the other end of the virulence spectrum are species that exploit ants as inquiline social parasites or brood predators, often drastically reducing the fitness of the host ant colony. Here I will report on a project exploring the population level genetic consequences of this variety of lifestyles among lycaenids, using worldwide sample collections and a range of species. The focus is on how kind and degree of interactions with ants affect dispersal (transmission) and population size of the butterflies. Evolutionary theory suggests that virulent parasitic organisms have higher rates of transmission than mutualistic ones (with negative virulence). At the same time, virulence of the butterflies is expected to be negatively correlated with population size, allowing sustainable recovery of the host ant populations. Finally, the challenge of expanding classical population genetic studies beyond the level of congeneric populations will be addressed.