Genetic population structure of buckeye butterflies (Junonia) from Argentina

Abstract

There are nine named species of buckeye butterflies (genus Junonia Hübner) in the Western Hemisphere. There is considerable geographic variation within Junonia species, and possible ongoing hybridization between species, suggesting that Junonia may be a ring species, but also making this a very difficult group to define taxonomically. We tried to determine whether two forms of Junonia from Argentina – conventionally referred to as Junonia genoveva hilaris C. & R. Felder, the light buckeye butterfly, and Junonia evarete flirtea (Fabricius), the dark buckeye butterfly – were genetically distinct species or simply colour forms of a single species using morphological characters, mitochondrial cytochrome oxidase I (COI) DNA barcodes, nuclear wingless (wg) locus DNA sequences, and anonymous nuclear Randomly Amplified Fingerprints (RAF). Phylogenetic analysis of COI identified two distinct mitochondrial haplotypes that differ by about 4% sequence divergence; one confined to light‐coloured Junonia specimens and one shared between some light‐coloured Junonia and all of dark‐coloured Junonia specimens. Analysis of nuclear wingless sequences revealed 32 alleles among 22 Junonia specimens and showed significant genetic differentiation between light‐coloured and dark‐coloured Junonia. Analysis of RAF genotypes suggests that there are actually three genetically distinct Junonia populations in Argentina: two with light wing coloration, and one with dark wing coloration. Genetic evidence of recent hybridization among these populations was also observed, consistent with the ring species hypothesis. Careful comparisons of morphological characters between Argentinian Junonia and Junonia species from elsewhere in South America suggests that the two light‐coloured populations correspond to J. genoveva and either a genetically disparate population of the same species or an undescribed cryptic Junonia species, The dark‐coloured population may correspond to J. wahlbergi Brévignon. Our data suggest that COI DNA barcodes by themselves are not very useful for studying Junonia taxonomy, population structure or evolution.

Molecular Population Structure ofJunoniaButterflies from French Guiana, Guadeloupe, and Martinique

“…More recent studies of the molecular phylogeny of New World Junonia [23,54,55], which have better taxon sampling, have focused entirely on the mitochondrial cytochrome oxidase I (COI) locus, which is widely used as a barcoding locus for animal taxa [56,57]. Based on mitochondrial haplotype sequences, the relationships among many New World Junonia species are ambiguous and most species are not reciprocally monophyletic [23,24,54]. The degree to which recent divergences, retained polymorphisms, and/or hybridization events contribute to these patterns in Junonia is unknown because only mitochondrial markers were considered.…”

“…The degree to which recent divergences, retained polymorphisms, and/or hybridization events contribute to these patterns in Junonia is unknown because only mitochondrial markers were considered. What is apparent is that there are two very divergent COI haplotype groups (4% sequence divergence between them) present in New World Junonia: Group A, which predominates in South America and is also present in the Caribbean, and Group B, which predominates in North and Central America but which also occurs in the Caribbean and South America [24,54]. Sequences belonging to each of these haplotype groups can occur in different individuals of the same species at the same locality [24].…”

“…In the current study, we extend the genetic tools that were employed by Borchers and Marcus [24] to Junonia populations from French Guiana and the French Antilles in order to study the distinctiveness of the named taxa within and between these two localities. This will allow an explicit test of the 7-species taxonomic hypothesis (2 species in the French Antilles plus 5 species in French Guiana) of L. Brévignon and C. Brévignon [23] and also detect possible hybridization events between named forms.…”

“…Borchers and Marcus [24] used DNA sequences from the nuclear wingless gene and anonymous nuclear loci identified by Randomly Amplified Fingerprinting (RAF) (a technique used to assess genetic diversity within populations [58][59][60] and gene flow between populations [61]) in addition to sequences from the mitochondrial COI gene. They identified 3 distinct populations of Junonia from Buenos Aires: one population with dark-coloured wings referred to as J. evarete flirtea [62] which Borchers and Marcus [24] suggested may correspond to J. wahlbergi and 2 light-coloured populations that correspond to J. genoveva hilaris and either a genetically disparate population of J. genoveva hilaris or an undescribed cryptic Junonia species. However, the relationship of these Argentinian forms with J. evarete and J. genoveva from Suriname and French Guiana is not known, so we refer to them as J.…”

“…In the Western Hemisphere, forms of Junonia occur from southern Canada to Tierra del Fuego [22][23][24] and have a complicated taxonomic history. In 1775, Cramer [25] identified and described two similar species of Junonia, J. evarete and J. genoveva, from Suriname, a Dutch colony on the north coast of South America.…”