Ant association facilitates the evolution of diet breadth in a lycaenid butterfly

Abstract

The role of mutualistic interactions in adaptive diversification has not been thoroughly examined. Lycaenid butterflies provide excellent systems for exploring mutualistic interactions, as more than half of this family is known to use ants as a resource in interactions that range from parasitism to mutualism. We investigate the hypothesis that protection from predators offered to caterpillars by ants might facilitate host-range evolution. Specifically, experiments with the butterfly Lycaeides melissa investigated the role of ant association in the use of a novel host, alfalfa, Medicago sativa, which is a sub-optimal host for larval development. Survival on alfalfa is increased by the presence of ants, thus supporting the hypothesis that interaction with ants might be important for host-range evolution. Using a demographic model to explore ecological conditions associated with host-range expansion in L. melissa, we conclude that the presence of ants might be an essential component for populations persisting on the novel, sub-optimal host.

Temporal and geographic variation in parasitoid attack with no evidence for ant protection of the Melissa blue butterfly, Lycaeides melissa

“…Savignano () found that the presence of ants did not reduce parasitism but did reduce predation in Lycaeides samuelis (formerly L. melissa samuelis ; Forister et al , ). Combined with the results from Savignano () and a previous study from one of our focal sites (Forister et al , ), it seems likely that the presence of ants reduces predation, but not parasitism in L. melissa .…”

“…Lycaeides melissa caterpillars are facultatively myrmecophilous, providing secretions rich in sugars and amino acids that attract the attention of ants that tend and presumably protect caterpillars. Forister et al () found that the presence of ants reduced rates of attack by generalist predators of L. melissa on the novel host alfalfa, but not on the native host A. canadensis . Other studies have shown that ants can also protect lycaenids from parasitoids (Pierce & Mead, ; Pierce & Easteal, ; Weeks, ).…”

Admixture and the organization of genetic diversity in a butterfly species complex revealed through common and rare genetic variants

“…; Forister et al . ), with limited dispersal among localities (i.e. dispersal beyond 500 m is rare; U.S.…”

Use of Exotic Hosts by Lepidoptera: Widespread Species Colonize More Novel Hosts

“…In a few well‐studied examples, hosts shifts involving exotic plants have resulted in speciation (e.g., Rhagoletis flies shifting from hawthorn to apple trees; Feder 1998; Feder and Forbes 2008), the evolution of feeding morphology (e.g., Leptocoris bugs adapting to introduced hosts in the Sapindaceae; Carroll 2008; Carroll et al 2005a), and shifts in oviposition behavior (e.g., Euphydryas butterflies and exotic Plantago hosts; Singer et al 1993, 2008). A shift to an exotic host has also been associated with an escape from natural enemies ( Papilio machaon aliaska caterpillars on novel Asteraceae hosts; Murphy 2004), as well as an increased reliance on a protection mutualism ( Lycaeides melissa caterpillars with ants on alfalfa; Forister et al 2011). Outside these detailed studies, we have much to learn about the frequency with which native insects use exotic plants, the potential for host shifts, and the conditions which either constrain or promote the colonization of exotic hosts (Thompson 1998; Strauss et al 2006).…”