Two ways to be a myrmecophilous butterfly: Natural history and comparative immature-stage morphology of two species of Theope (Lepidoptera: Riodinidae)

Abstract

Symbiotic interactions between butterfly larvae and ants, termed myrmecophily, require a range of behavioural and morphological adaptations (ant-organs). Here, using light and scanning electron microscopy, we describe the complete life cycle of two species of Theope (Lepidoptera: Riodinidae) that have contrasting ways of life. Theope thestias larvae are facultatively tended by several ant species, whereas Theope pieridoides have obligate symbiotic interactions with Azteca ants that inhabit a myrmecophytic tree. Morphological differences associated with their different degrees of intimacy with tending ants are visible from hatching. In T.thestias, the untended first-instar larva has elongated bifurcated setae and a few tiny perforated cupola organs (PCOs), whereas in T.pieridoides, the ant-tended first instar has short dendritic setae, larger and more numerous PCOs, and functional tentacle nectary organs (TNOs). Throughout ontogeny, T.pieridoides always shows more conspicuous ant-organs than T.thestias, with the exception of balloon setae, which are larger and more numerous in T.thestias. In addition, mature T.pieridoides larvae have an anterior set of ant-organs, including a new type, here described and termed anterior glandular openings (AGOs). Based on the behavioural responses of ants in contact with these structures, a new interpretation for the mechanism whereby Theope larvae can manipulate the behaviour of their tending ants is proposed. Until now, three ecological syndromes can be defined among Theope species: (1) oligophagous larvae with facultative myrmecophily; (2) monophagous larvae with obligate myrmecophily; and (3) polyphagous larvae with obligate myrmecophily. These results suggest that differences in the degree of specificity in the ant-plant interactions may have an important role in the evolution of host-plant use in Theope. © 2013 The Linnean Society of London.