Evolution, 60(2), 2006, pp. 315±327 DO ANTS ENHANCE DIVERSIFICATION IN LYCAENID BUTTERFLIES? PHYLOGEOGRAPHIC EVIDENCE FROM A MODEL MYRMECOPHILE, JALMENUS EVAGORAS ROD EASTWOOD,1,2 NAOMI E. PIERCE,3,4 R. L. KITCHING,1,5 AND JANE M. HUGHES1,6 1Australian School of Environmental Studies, Grif®th University, Nathan 4111, Queensland, Australia 2E-mail: r.eastwood@grif®th.edu.au 3Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138 4E-mail: [email protected] 5E-mail: r.kitching@grif®th.edu.au 6E-mail: jane.hughes@grif®th.edu.au Abstract. The ant-tended Australian butter¯y, Jalmenus evagoras, has been a model system for studying the ecology and evolution of mutualism. A phylogeographic analysis of mitochondrial DNA cytochrome oxidase I sequences from 242 butter¯ies (615 bp) and 66 attendant ants (585 bp) from 22 populations was carried out to explore the relationship between ant association and butter¯y population structure. This analysis revealed 12 closely related butter¯y haplotypes in three distinct clades roughly corresponding to three allopatric subpopulations of the butter¯ies. Minimal genetic diversity and widespread haplotypes within biogeographical regions suggest high levels of matrilineal gene ¯ow. Attendant ants are signi®cantly more diverse than was previously thought, with at least seven well-de®ned clades corresponding to independent morphological determinations, distributed throughout the range of the butter¯ies. Nested analysis of molecular variance showed that biogeography, host plant, and ant associate all contribute signi®cantly in explaining variation in butter¯y genetic diversity, but these variables are not independent of one another. Major in¯uences appear to come from fragmentation due to large-scale biogeographical barriers, and diversi®cation following a shift in habitat preference. A consequence of such a shift could be codiversi®cation of the butter¯y with habitat- adapted ants, resulting in apparent phylogenetic concordance between butter¯ies and ants. The implications of these results are discussed in terms of possible effects of ant attendance on the diversi®cation of Lycaenidae as a whole. Key words. Ant association, biogeography, habitat specialist, Iridomyrmex, mutualism, myrmecophily, obligate. Received July 26, 2005. Accepted November 8, 2005. The butter¯y family Lycaenidae (including the Riodinidae, A second hypothesis suggests that a shift in ant association, often considered a subfamily of the Lycaenidae) contains an particularly a radical shift, may result in an escape-and-ra- estimated 30% of all butter¯y species (Shields 1989; Ackery diation mode of diversi®cation (Pierce et al. 2002). Shifts in et al. 1998) and exhibits a diverse array of life-history strat- attendant ants would be important events for obligately ant- egies (Hinton 1951; Cottrell 1984; Fiedler 1991; Pierce et al. associated lycaenids since most have highly specialized ant 2002). The early stages of about 75% of all lycaenids as- associations (Fiedler 1991; Eastwood and Fraser 1999). The sociate with ants to varying degrees, ranging from casual conservative nature of these associations is highlighted in facultative coexistence to obligate association where the phylogenetic studies by a correlation of discrete ant taxa long-term survival of the butter¯y is dependent on the pres- associating with highly myrmecophilous lycaenids at the spe- ence of its attendant ants. Attendant ants guard the butter¯ies cies and higher clade levels (Maculinea, Thomas et al. 1989; against predators and parasites during their vulnerable period Elmes et al. 1994; Jalmenus, Pierce and Nash 1999; Chry- of larval growth and pupation. The caterpillars, in return, soritis, Rand et al. 2000; Acrodipsas, Eastwood and Hughes reward the ants by providing attractive secretions from spe- 2003a; Arhopala, Megens et al. 2005). However, the ap- cialized glands in the cuticle (Malicky 1969, 1970; Mas- pearance of butter¯y sister taxa associating with different ant chwitz et al. 1975; Pierce and Nash 1999). species may be explained by at least three processes, only The prevalence of caterpillar-ant associations in the spe- one of which would be causative. These mechanisms would cies-rich Lycaenidae is in contrast with other Lepidoptera, exhibit different phylogeographic patterns that could be de- where ant association appears only rarely and in disparate tected in a population of obligately ant-associated lycaenids lineages (Hinton 1951). This has led to the proposal that ant as follows: (1) A shift to an ecologically different ant species association may have accelerated diversi®cation in the group (Pierce 1984; Pierce et al. 2002). At least two mechanisms or to an attendant ant species from another genus or subfamily have been proposed: ®rst, the stringent requirements of both could result in ecological diversi®cation with the novel ant. suitable host plants and appropriate attendant ant species may If this were to occur, it should be detectable at the population have resulted in smaller population sizes and population frag- level as genetic breaks in butter¯y subpopulations coinciding mentation of ant-associated lycaenids (Pierce 1984; Costa et with radically different ant associates, particularly if the dif- al. 1996). This would increase the likelihood of isolation, ferent associations were to occur in sympatry or parapatry. leading to allopatric speciation (Mayr 1942). At the popu- (2) Butter¯y sister species associating with different ant spe- lation level, a signal of such fragmentation could be detect- cies could be observed coincidentally in a phylogeny if frag- able as high levels of genetic differentiation and signi®cant mentation of an oligomyrmecophilous butter¯y population levels of isolation by distance among butter¯y subpopula- (associating with several closely related species of ants across tions. its range) coincided with a geographically restricted or locally 315 q 2006 The Society for the Study of Evolution. All rights reserved. 316 ROD EASTWOOD ET AL. preferred ant partner. This could be detected at the population tains to Binjour (see Fig. 1) where there may be a stepped level if an isolated butter¯y subpopulation, associating with cline or intermediate populations (Braby 2000). In general, the local ant, was genetically divergent from the remaining nominotypical specimens from eastern Queensland are paler butter¯y population. (3) Butter¯y sister taxa associating with than their southern counterparts, and the very pale subspecies ant sister taxa (parallel cladogenesis) could occur if a butter¯y J. e. eubulus is regarded as the morphological extreme. population tended by a single ant species across its range Female J. evagoras eclose with a large complement of underwent fragmentation together with its attendant ant. In mature eggs (Hill and Pierce 1989) and are often mated upon time, this could result in cospeciation of the two partners. eclosion, before they have even expanded their wings (Pierce Evidence at the population level would be seen if a frag- and Nash 1999). They exhibit high levels of site ®delity and mented subgroup of butter¯ies showed genetic differences in preferentially deposit eggs on suitable Acacia host plants in parallel with a subgroup of its attendant ant. or around their natal colony (Elgar and Pierce 1988). Larvae An earlier attempt at unraveling the relationships between feed gregariously and are recorded as having an obligate ants and butter¯ies at the population level found little evi- mutualistic relationship with Iridomyrmex ants (Dolichod- dence in favor of ant-associated effects on population size erinae), primarily I. anceps and I. rufoniger (Eastwood and and structure (Costa et al. 1996). Estimates of Wright's FST Fraser 1999; Pierce and Nash 1999). Attendant ants protect using multilocus allozyme data from 1052 specimens of Jal- the caterpillars from predators and parasitoids and act as an menus evagoras sampled from 15 geographically separated important stimulus for female J. evagoras to deposit their sites in an area of about 150 km2 revealed low amounts of eggs on the host plant (Pierce and Elgar 1985; Pierce et al. genetic structure at the level of geographic subpopulation, 1987; Pierce and Nash 1999; Fraser et al. 2002). and no evidence of population differentiation corresponding to the two species of ant associate common to these sites. Specimens However, this study was conducted at a small spatial scale The 242 J. evagoras specimens used in this analysis were relative to the overall species range of J. evagoras, and did collected from 22 sites across the range of both subspecies not consider the degree of differentiation of the associated extending from Wallan in southern Victoria to Taroom in ants. Moreover, subsequent behavioral observations showing central Queensland (Appendix 1). Where possible, at each that J. evagoras females preferentially deposit eggs on plants site, adults, larvae, or pupae were collected from different containing their locally predominant attendant ant species, trees to maximize the potential for sampling genetic diversity. even when the butter¯ies are reared in the absence of ants Latitude and longitude coordinates were determined for all (Fraser et al. 2002), further raised the question of whether sites, and place names shown in Figure 1 are the nearest town this behavior might be re¯ected in the population structure to the sampling site. Specimens at all life stages were pre- of the butter¯ies.