Molecular phylogenetics of the neotropical butterfly subtribe Oleriina (Nymphalidae: Danainae: Ithomiini)

Abstract

The Oleriina is one of the most speciose subtribes of the neotropical nymphalid butterfly tribe Ithomiini. They are widely distributed across the Andes and Amazonian lowlands and like other ithomiines they are involved in complex mimicry rings. This subtribe is of particular interest because it contains the most diverse ithomiine genus, Oleria, as well as two genera, Megoleria and Hyposcada, that feed on hostplants not utilized elsewhere in the tribe. Here we present the first comprehensive species-level phylogeny for the Oleriina, representing 83% of recognised species in the group, and based on 6698 bp from eight mitochondrial (mt) and nuclear (nc) genes. Topologies are largely congruent for ncDNA and the concatenated dataset and the genera Oleria, Hyposcada and Megoleria are recovered and well-supported, although strongly discordant genealogy between mtDNA and ncDNA suggest possible introgression among Hyposcada and Megoleria. A fourth clade containing the type species of Ollantaya is consistently recovered, and this recently synonymized name is resurrected. Clear subdivisions within Oleria separate the genus into four species groups, onega, amalda, makrena and aegle, which also correspond to differing biogeographic and elevation range characteristics.

Unlike other ithomiine genera, the Oleriina show homogeneity in mimetic wing pattern, in sharp contrast to the emerging paradigm that mimetic shifts have enhanced diversification in the tribe. Our results show a potentially more important role for geographic isolation in the diversification of the Oleriina compared to other Ithomiini studied to date and provide a framework for more detailed biogeographical studies, in addition to a rare opportunity for comparative analyses with other neotropical groups.

Introduction

The nymphalid butterfly tribe Ithomiini form a diverse and widespread neotropical group of approximately 370 species and over 1500 geographical races (Lamas, 2004, Willmott and Freitas, 2006). They are dominant members of complex mimicry rings that involve ithomiine, heliconiine, nymphaline and riodinid butterflies, notodontid day-flying moths and other insects (Beccaloni, 1997a). Adults of all Ithomiini use dehydropyrrolizidine alkaloids as defensive compounds, in the synthesis of pheromones to attract mates (Brown, 1987) and in the formation of aggregations of butterflies in ithomiine ‘pockets’ (Haber, 1978, Pinheiro et al., 2008). Most Ithomiini larvae feed on Solanaceae and the use of this family as a hostplant is seen as a key to the diversification of the butterfly group (Brown, 1987, Willmott and Freitas, 2006).

Knowledge of their systematics, biology and distribution is relatively advanced and the tribe has provided excellent models in studies on mimicry (Beccaloni, 1997a, Beccaloni, 1997b, Joron et al., 2001, Willmott and Mallet, 2004), biogeography (Elias et al., 2009), evolution (Whinnett et al., 2005a, Whinnett et al., 2005b, Jiggins et al., 2006, Elias et al., 2007, Elias et al., 2008) and chemical ecology (Brown, 1987, Schultz et al., 2004). However, species-level molecular phylogenies have yet to be elucidated and currently only two out of 50 genera (Mallarino et al., 2005, Elias et al., 2009) have been completed.

Ten Ithomiini subtribes (one unnamed) are currently recognised based on morphological characteristics (Lamas, 2004, Willmott and Freitas, 2006) and molecular data (Brower et al., 2006). The subtribe Oleriina contains 63 species and is of particular interest because one of its three constituent genera, Oleria, is the most speciose ithomiine genus (52 species) (Lamas, 2004). In contrast, the other two genera are relatively depauperate, with nine species of Hyposcada (Willmott and Lamas, unpublished data) and two species of Megoleria (Willmott and Lamas, 2008) currently recognised. The biogeography of this group is also of interest. Oleria and Hyposcada are both widely distributed, occurring from Mexico to Brazil at varying altitudes from sea level to 3000 m, with the former genus diverse in both lowland and montane habitats. Conversely, Megoleria is restricted to the high Andes of Colombia, Ecuador and Peru at altitudes ranging from 1200 to 2700 m.

Elucidating the systematics of the Ithomiini has proved particularly problematic because of their involvement in complex mimicry rings and geographical polymorphism. Additionally, association of the sexes in Oleria is sometimes complicated by sexual dimorphism in mimicry pattern (Willmott and Mallet, 2004).

Fox (1956) first proposed the subtribe Oleriina (then considered a tribe called Oleriini) including Hyposcada, Oleria, Aeria and an undescribed genus, but Harvey (1991) revised the constituent genera to include Hyposcada, Oleria and two new undescribed genera later named Ollantaya (Brown and Freitas, 1994) and Megoleria (Constantino, 1999). The genus Ollantaya was synonymized with the Oleria (Lamas, 2004), although recent morphological work suggests Ollantaya should be resurrected to include O. canilla, O. aegineta, H. olerioides and a fourth undescribed species from the Peruvian Andes (Willmott and Freitas, 2006).

Recent higher-level systematics of the Ithomiini using morphological characters confirmed Oleriina as monophyletic and sister to the Napeogenina and Ithomiina (Brown and Freitas, 1994, Willmott and Freitas, 2006). The monophyly of this group is corroborated from molecular data (Brower et al., 2006), based on 2335 bp of the mitochondrial (mtDNA) cytochrome oxidase subunits I and II (COI–COII) and the nuclear (ncDNA) genes, wingless and elongation factor 1-alpha (EF-1α). These data provide conflicting signal regarding the relationships of Megoleria to other oleriines, with morphological characters suggesting that Megoleria is sister to Hyposcada (Willmott and Freitas, 2006), while molecular data place Megoleria as sister to all other Oleriina (Brower et al., 2006). With the exception of Megoleria, there are few clear morphological synapomorphies supporting the remaining genera, and molecular data thus offer a promising solution to resolve relationships within this group.

The first molecular phylogenetic study of the Oleriina included 41 species (103 samples) based on 1619 bp of the mtDNA COI–COII and the ncDNA genes, wingless and EF-1α (Whinnett, 2005), and recovered the four genera, Oleria, Hyposcada, Megoleria and Ollantaya. Analyses using neighbour-joining (NJ) and maximum parsimony (MP) recovered Hyposcada as sister to all other Oleriina (Whinnett, 2005), whereas Bayesian inference (BI) of the concatenated data identified Megoleria as sister to all other Oleriina as in Brower et al. (2006).

Here we present one of the first comprehensive molecular phylogenetic analyses for any diverse butterfly tribe. Our sampling includes 52 of the 63 known Oleriina species, based on six gene regions comprising three mtDNA and five ncDNA genes for multiple individuals from the whole of the Oleriina subtribe. Our phylogenetic hypotheses allow revision of the generic classification of the tribe as a basis for generic revisions currently in preparation. In addition, this study forms part of a collaborative effort to generate species-level molecular phylogenetic hypotheses for the whole of the Ithomiini (Mallarino et al., 2005, Elias et al., 2009). As a result, we are also able to further assess the general importance of biogeographic processes identified as critical in the evolution of the few other tropical Andean butterfly genera studied to date (e.g., Willmott et al., 2001, Hall, 2005, Jiggins et al., 2006, Elias et al., 2009).