Hybrid zone origins, species boundaries, and the evolution of wing-pattern diversity in a polytypic species complex of North American admiral butterflies (Nymphalidae: Limenitis)

Hybrid zones present opportunities to study the effects of gene flow, selection, and recombination in natural populations and, thus, provide insights into the genetic and phenotypic changes that occur early in speciation. Here we investigate a hybrid zone between mimetic (Limenitis arthemis astyanax) and nonmimetic (Limenitis arthemis arthemis) populations of admiral butterflies using DNA sequence variation from mtDNA and seven nuclear gene loci. We find three distinct mitochondrial clades within this complex, and observe a strong overall concordance between wing-pattern phenotypes and mitochondrial variation. Nuclear gene genealogies, in contrast, revealed no evidence of exclusivity for either wing-pattern phenotype, suggesting incomplete barriers to gene exchange and/or insufficient time for lineage sorting. Coalescent simulations indicate that gene flow between these two subspecies is highly asymmetric, with the majority of migration occurring from mimetic into nonmimetic populations. Selective sweeps of alleles responsible for mimetic phenotypes may have occurred more than once when mimetic and nonmimetic Limenitis occurred together in the presence of the model (Battus philenor).     

A single origin of Batesian mimicry among hybridizing populations of admiral butterflies (Limenitis arthemis) rejects an evolutionary reversion to the ancestral phenotype

Batesian mimicry is a fundamental example of adaptive phenotypic evolution driven by strong natural selection. Given the potentially dramatic impacts of selection on individual fitness, it is important to understand the conditions under which mimicry is maintained versus lost. Although much empirical and theoretical work has been devoted to the maintenance of Batesian mimicry, there are no conclusive examples of its loss in natural populations. Recently, it has been proposed that non-mimetic populations of the polytypic Limenitis arthemis species complex represent an evolutionary loss of Batesian mimicry, and a reversion to the ancestral phenotype. Here, we evaluate this conclusion using segregating amplified fragment length polymorphism markers to investigate the history and fate of mimicry among forms of the L. arthemis complex and closely related Nearctic Limenitis species. In contrast to the previous finding, our results support a single origin of mimicry within the L. arthemis complex and the retention of the ancestral white-banded form in non-mimetic populations. Our finding is based on a genome-wide sampling approach to phylogeny reconstruction that highlights the challenges associated with inferring the evolutionary relationships among recently diverged species or populations (i.e. incomplete lineage sorting, introgressive hybridization and/or selection).     

Mimicry in North American checkerspot butterflies: Euphydryas phaeton and Chlosyne harrisii (Nymphalidae)

ABSTRACT.

• 1 An examination of the phenetics, ecology and distribution of Chlosyne harrisii suggested that it was a potential mimic of the unpalatable Euphydryas phaeton.
• 2 The wing undersurfaces of the adults are very similar and the larvae are virtually identical. The geographic range of both butterflies is the northeastern United States and both are inhabitants of wet meadow habitats where they may fly together. The life histories of both species are closely synchronized.
• 3 A series of feeding experiments using blue-jays as predators showed first, that C.harrisii is palatable, and second, suggested that the birds could not distinguish between C.harrisii and E.phaeton on the basis of visual cues. Thus, Charrisii seems to be an effective Batesian mimic of E.phaeton.

     

Testing the adaptive hypothesis of Batesian mimicry among hybridizing North American admiral butterflies

Batesian mimicry is characterized by phenotypic convergence between an unpalatable model and a palatable mimic. However, because convergent evolution may arise via alternative evolutionary mechanisms, putative examples of Batesian mimicry must be rigorously tested. Here, we used artificial butterfly facsimiles (N = 4000) to test the prediction that (1) palatable Limenitis lorquini butterflies should experience reduced predation when in sympatry with their putative model, Adelpha californica, (2) protection from predation on L. lorquini should erode outside of the geographical range of the model, and (3) mimetic color pattern traits are more variable in allopatry, consistent with relaxed selection for mimicry. We find support for these predictions, implying that this convergence is the result of selection for Batesian mimicry. Additionally, we conducted mark–recapture studies to examine the effect of mimicry and found that mimics survive significantly longer at sites where the model is abundant. Finally, in contrast to theoretical predictions, we found evidence that the Batesian model (A. californica) is protected from predation outside of its geographic range. We discuss these results considering the ongoing hybridization between L. lorquini and its sister species, L. weidemeyerii, and growing evidence that selection for mimicry predictably leads to a reduction in gene flow between nascent species.     

Chromosomal evolution of South American frugivorous butterflies in the Satyroid clade (Nymphalidae: Charaxinae, Morphinae and Satyrinae)

We describe the chromosome numbers of a monophyletic group of Satyroid subfamilies of primary fruit-attracted butterflies from South America: Charaxinae, Morphinae (including Brassolini) and Satyrinae. The charaxines do not have a distinct modal number. Their chromosome numbers are in the range n  = 6–50, with n  = 7–9, n  = 12, n  = 16, n  = 19–21, n  = 26, and n  = 28–31 being the most common numbers. Within the Morphinae, the Morphini have a modal n  = 28 and the Brassolini a modal n  = 29, with few exceptions. The Neotropical satyrines, in particular the basal species, have a weak modal n  = 29, which is a strong modal number in Palearctic satyrines. The African satyrines have an equally strong modal n  = 28. Most Neotropical satyrines have, like charaxines, chromosome numbers lower than the weak modal n  = 29, and often half this modal, but there are genera with stable numbers among the satyrines and charaxines. Evidently, the Neotropical satyroids descend from basal Nymphalidae with the typical lepidopteran modal number of n  = 31, which have also given rise to the Heliconiini with modal n  = 31 and 21 and Ithomiinae with modal numbers of n  = 14–15.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 467–481.     

Colour pattern homology and evolution in Vanessa butterflies (Nymphalidae: Nymphalini): eyespot characters

Ocelli are serially repeated colour patterns on the wings of many butterflies. Eyespots are elaborate ocelli that function in predator avoidance and deterrence as well as in mate choice. A phylogenetic approach was used to study ocelli and eyespot evolution in Vanessa butterflies, a genus exhibiting diverse phenotypes among these serial homologs. Forty‐four morphological characters based on eyespot number, arrangement, shape and the number of elements in each eyespot were defined and scored. Ocelli from eight wing cells on the dorsal and ventral surfaces of the forewing and hindwing were evaluated. The evolution of these characters was traced over a phylogeny of Vanessa based on 7750 DNA base pairs from 10 genes. Our reconstruction predicts that the ancestral Vanessa had 5 serially arranged ocelli on all four wing surfaces. The ancestral state on the dorsal forewing and ventral hindwing was ocelli arranged in two heterogeneous groups. On the dorsal hindwing, the ancestral state was either homogenous or ocelli arranged in two heterogeneous groups. On the ventral forewing, we determined that the ancestral state was organized into three heterogeneous groups. In Vanessa, almost all ocelli are individuated and capable of independent evolution relative to other colour patterns except for the ocelli in cells ?1 and 0 on the dorsal and ventral forewings, which appear to be constrained to evolve in parallel. The genus Vanessa is a good model system for the study of serial homology and the interaction of selective forces with developmental architecture to produce diversity in butterfly colour patterns.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

The roles of wing color pattern and geography in the evolution of Neotropical Preponini butterflies

Diversification rates and evolutionary trajectories are known to be influenced by phenotypic traits and the geographic history of the landscapes that organisms inhabit. One of the most conspicuous traits in butterflies is their wing color pattern, which has been shown to be important in speciation. The evolution of many taxa in the Neotropics has also been influenced by major geological events. Using a dated, species‐level molecular phylogenetic hypothesis for Preponini, a colorful Neotropical butterfly tribe, we evaluated whether diversification rates were constant or varied through time, and how they were influenced by color pattern evolution and biogeographical events. We found that Preponini originated approximately 28 million years ago and that diversification has increased through time consistent with major periods of Andean uplift. Even though some clades show evolutionarily rapid transitions in coloration, contrary to our expectations, these shifts were not correlated with shifts in diversification. Involvement in mimicry with other butterfly groups might explain the rapid changes in dorsal color patterns in this tribe, but such changes have not increased species diversification in this group. However, we found evidence for an influence of major Miocene and Pliocene geological events on the tribe''s evolution. Preponini apparently originated within South America, and range evolution has since been dynamic, congruent with Andean geologic activity, closure of the Panama Isthmus, and Miocene climate variability.     

Colonization of and radiation in South America by butterflies in the subtribe Phyciodina (Lepidoptera: Nymphalidae)

The historical biogeography of insects in South America is largely unknown, as dated phylogenies have not been available for most groups. We have studied the phylogenetic relationships and historical biogeography of a subtribe of butterflies, Phyciodina in the family Nymphalidae, based on one mitochondrial gene (COI) and two nuclear gene regions (EF-1alpha and wingless). The subtribe comprises 89 species mainly found in tropical South America, with a few species in North America and the Greater Antilles. We find that the enigmatic genus Antillea is sister to the rest of Phyciodina, and suggest that it should be included in the subtribe. Several genera are found to be polyphyletic or nested within another genus, and are proposed to be synonymised. These are Dagon, Castilia, Telenassa and Janatella, which we propose should be synonymised with Eresia. Brazilian "Ortilia" form an independent lineage and require a new genus name. The diversification of Phyciodina has probably taken place over the past about 34 MYA. The ancestral phyciodine colonised South America from North America through a possible landspan that connected the Greater Antilles to South America about 34MYA. A vicariance event left the ancestral Antillea on the Greater Antilles, while the ancestral 0e on South America colonised the Guyanan Shield and soon after the Brazilian Shield. We hypothesise that the Brazilian Shield was an important area for the diversification of Phyciodina. From there, the ancestor of Anthanassa, Eresia and Tegosa colonised NW South America, where especially Eresia diversified in concert with the rising of the Andes beginning about 20 MYA. Central America was colonised from NW South America about 15 MYA by the ancestors of Anthanassa and Phyciodes. Our study is the first to use a dated phylogeny to study the historical biogeography of a group of South American species of butterflies.     

Phylogenetic relationships of the New World Troidini swallowtails (Lepidoptera: Papilionidae) based on COI, COII, and EF-1α genes

A phylogeny of the Neotropical members of the Tribe Troidini (Lepidoptera: Papilionidae) was obtained with sequences of three protein-coding genes: two mitochondrial (COI and COII), and one nuclear (EF-1α). Parsimony and Bayesian analyses of 33 taxa resulted in very similar trees regardless of method used with the 27 troidines always forming a monophyletic clade. Within Troidini, the genus Battus is sister group to the remaining troidines, followed by a clade formed by the Paleotropical taxa (here represented by three exemplars). The genus Euryades is the next branch, and sister group of Parides. The genus Parides is monophyletic, and is divided into four main groups by Maximum Parsimony analysis, with the most basal group composed of tailed species restricted to SE Brazil. Character optimization of ecological and morphological traits over the phylogeny proposed for troidines indicated that the use of several species of Aristolochia is ancestral over the use of few or a single host-plant. For the other three characters, the ancestral states were the absence of long tails, forest as the primary habitat and oviposition solitary or in loose group of several eggs.     

Phylogenetics and differentiation among the western taxa of the Erebia tyndarus group (Lepidoptera: Nymphalidae)

The phylogenetic relationships among six members of the 'tyndarus' group in the Erebia genus of Satyrid butterflies, i.e. E. tyndarus, E. cassioides, E. nivalis, E. calcaria, E. hispania and E. ottomana were analysed using data from 19 presumptive enzyme loci, as well as 440 and 429 bp, respectively, from the mitochondrial large ribosomal subunit (16S) and subunit 1 from the NADH dehydrogenase (ND1) genes. The two types of molecular data (allozymes and mtDNA) yielded largely congruent tree topologies. The two basal, independent lineages formed by E. ottomana and E. hispania are contrasted by a group of Genétically closely related taxa, suggestive of a recent radiation associated with allopatric speciation, and competitive exclusion. The time of divergence for the radiation event is similar for both allozymes and mtDNA with an estimation of 440000 years ago. The lineages involved in this radiation do not comply with all the criteria necessary to assign to each of them full species rank, but they can no more be included in one single species unit. Such situations involving more than two alio- or parapatric lineages may explain why polytomies are so often met in phylogenetic reconstructions, after the lineages have reached full species rank. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 319–332.     

Phylogenetic relationships among genera of danaine butterflies (Lepidoptera: Nymphalidae) as implied by morphology and DNA sequences

Cladistic relationships among genera and subtribes of Danaini (the milkweed butterflies) were inferred by analysis of data combined from five sources: morphology of adults and immature stages, and DNA sequences from three gene regions. The results corroborate and greatly increase support for prior hypotheses based on morphology alone. A new index summarizing incongruence among data partitions, the Partition Congruence Proportion (PCP), is introduced. The significance of the inferred pattern of phylogenetic relationships for comparative chemical ecology of milkweed butterflies is briefly discussed.     

蛱蝶翅鳞片的超微结构观察

对我国东北地区典型常见蛱蝶科15属20种蝴蝶翅鳞片的超微结构进行了扫描电镜观察。结果显示：蛱蝶翅鳞片形态上可分为窄叶形、阔叶形和圆叶形3种,鳞片长65～135 μm,宽35～85 μm,间距48～112 μm。蛱蝶翅鳞片的超微结构可分为拱桥形、棋盘形和筛孔形3 种。拱桥形结构和棋盘形结构比较接近,二者与筛孔形结构差异较明显。在已观察的种类中,线蛱蝶属红线蛱蝶翅鳞片上的纵肋突起最小（200 nm×300 nm）,闪蛱蝶属柳紫闪蛱蝶翅鳞片上的纵肋突起最大（590 nm×560 nm）。鳞片具有相似的形状、结构和排列,尤其是同属蝴蝶翅鳞片超微结构的形状和尺寸差异较小,表明它们之间的亲缘关系接近。     

Molecular evolution of a long wavelength-sensitive opsin in mimetic Heliconius butterflies (Lepidoptera: Nymphalidae)

This study examines the pattern of opsin nucleotide and amino acid substitution among mimetic species 'rings' of Heliconius butterflies that are characterized by divergent wing colour patterns. A long wavelength opsin gene, OPS1 , was sequenced from each of seven species of Heliconius and one species of Dryas (Lepidoptera: Nymphalidae). A parsimony analysis of OPS1 nucleotide and amino acid sequences resulted in a phylogeny that was consistent with that presented by Brower & Egan in 1997, which was based on mitochondrial cytochrome oxidase I and II as well as nuclear wingless genes. Nodes in the OPS1 phylogeny were well supported by bootstrap analysis and decay indices. An analysis of specific sites within the gene indicates that the accumulation of amino acid substitutions has occurred independently of the morphological diversification of Heliconius wing colour patterns. Amino acid substitutions were examined with respect to their location within the opsin protein and their possible interactions with the chromophore and the G-protein. Of the 15 amino acid substitutions identified among the eight species, one nonconservative replacement (A226Q) was identified in a position that may be involved in binding with the G-protein.     

Phylogeny of the Neotropical moth tribe Josiini (Notodontidae: Dioptinae): a hidden case of Miillerian mimicry

The Neotropical moth tribe Josiini (Notodontidae: Dioptinae) contains over 100 described species in 11 genera. All are diurnal, with brightly-coloured, presumably aposematic wing patterns. Larval hostplants are exclusively in the genus Passiflora (Passifloraceae) except for two new records, reported here, from Tumera (Turneraceae). A comparative morphological study of 26 representative josiine species yielded 86 characters from adults, larvae and pupae, all of which are figured and discussed. Phylogenetic analysis of these data produced a single most-parsimonious cladogram. According to the phylogenetic results: (1) monophyly of the Josiini is strongly supported; (2) the currently accepted generic classification is in disarray; (3) morphological character variation is extensive, and adult traits reflect phylogeny more effectively than do those of immature stages; (4) wing pattern types have undergone convergent evolution. A rare phenotype, longitudinal wing stripes, appears in two widely divergent clades, suggesting the evolution of Miillerian mimicry within the Josiini.     

Biogeography of milkweed butterflies (Nymphalidae: Danainae) and mimetic patterns on tropical Paciflc archipelagos

Distributions of danaine butterfly species and associated mimetic patterns were compared among fifteen archipelagos of the tropical Pacific Ocean, and within five major archipelagos (the Bismarcks, Fiji, East and West Solomon Islands, and Vanuatu). Using both simple and stepwise linear regression analysis, variation in the total number of danaine species and number of mimetic patterns was assessed with respect to island size, isolation and elevation. Relative to interarchipelago distributions, the distribution of danaine species and number of mimetic patterns on islands within archipelagos exhibited less dependence upon interisland distance and island area. Geographical features influencing the number of mimetic patterns were similar to those of danaines as a whole. Analysis of residuals from stepwise linear regression suggested that factors influencing danaine distributions were different from those for non-danaine butterflies. This result is consistent with the hypothesis of enhancement of danaine species establishment through Müllerian mimicry, although other factors such as host plant availability and similar habitat use may also be important.     

Homologies in the colour patterns of the genus Charaxes (Lepidoptera: Nymphalidae)

The phylogenetically and morphologically diverse patterns of Charaxes can be reduced to a simple set of pattern elements which can be homologized throughout the genus. At least five types of correspondence (homologies) exist among pattern elements: those between (1) species, (2) forewing and hindwing, (3) dorsal and ventral wing surface, (4) serial wing-cells, and (5) individual pattern elements within a single wing-cell. Differences in Charaxes colour patterns result from the distortion, elaboration, enlargement, reduction or loss of individual pattern elements. Further variation is often the result of dislocation of pattern elements from their serial homologues in neighbouring wing-cells, and fusion of individual pattern elements to create larger areas of colour. The type of analysis presented in this paper should be broadly applicable within the Lepidoptera and may prove useful in studying the systematics of colour patterns and the evolution of the developmental system that gives rise to them.     

Vertical stratification of ithomiine butterfly (Nymphalidae: Ithomiinae) mimicry complexes: the relationship between adult flight height and larval host-plant height

Data are presented which confirm previous findings that sympatric mimicry complexes dominated by unpalatable Neotropical ithomiine butterflies (Nymphalidae: Ithomiinae) are vertically stratified by height of flight. Flight height of ithomiine species is positively correlated with the height of their larval host-plants. Thus members of a mimicry complex utilize host-plants of similar heights. Non-mimetic British woodland butterflies also show a positive relationship between flight height and host-plant height, which suggests that the relationship is independent of mimicry. I propose that female butterflies fly at heights which maximize the probability of encountering their larval host-plants, and that males fly at similar heights to females in order to maximize the probability of encountering potential mates. Female butterflies probably encounter plants of similar heights to their larval hosts more frequently than they encounter plants of other heights. I suggest that butterfly species may therefore be more likely to make host shifts to plant species of a similar height to their current host-plants. Finally, I discuss how the relationship between flight height and height of larval host-plants, coupled with microhabitat-dependent selection on colour pattern, could lead to the evolution in sympatry of vertically stratified mimicry complexes.     

The phylogenetics and biochemistry of host-plant specialization in Melitaeine butterflies (Lepidoptera: Nymphalidae)

Butterflies in the tribe Melitaeini (Lepidoptera: Nymphalidae) are known to utilize host plants belonging to 16 families, although most host-plant records are from four families. Of the 16 host-plant families, 12 produce secondary plant metabolites called iridoids. Earlier studies have shown that larvae of several melitaeine species use iridoids as feeding stimulants and sequester these compounds for larval defense. I investigate the evolutionary history of host-plant use in the tribe Melitaeini by testing a recent phylogenetic hypothesis of 65 species representing the four major species groups of the tribe. By simple character optimization of host-plant families and presence/absence of iridoids in the host plants, I find that plant chemistry is a more conservative trait than plant taxonomy. The ancestral host plant(s) of the entire tribe most likely contained iridoids and were likely to be in the plant family Plantaginaceae. A major host shift from plants containing iridoids to plants not containing iridoids has happened three times independently. The results show that the evolution of host-plant use in melitaeines has been (and still is) a dynamic process when considering plant taxonomy, but is relatively stable when considering host-plant chemistry.     

Plastidic trnFUUC pseudogenes in North American genus Boechera (Brassicaceae): mechanistic aspects of evolution

The origin and maintenance of a plastidic tandem repeat next to the TRNF (UUC) gene were analyzed in the genus BOECHERA in a phylogenetic context and were compared to published analogous examples that emerged in parallel in the Asteraceae and Juncaceae, respectively. Although we identified some features common to these taxonomic groups with respect to structure and origin of the region, obvious differences were encountered, which argue against a specific mechanism or evolutionary principle underlying the parallel origin and maintenance of the TRNF-tandem repeats in those families. In contrast to the situation in the Asteraceae, no reciprocal recombinant repeat types have been observed in the Brassicaceae. Forty copy types, classified into three groups, were isolated from 103 chloroplast haplotypes of BOECHERA and it was demonstrated that they are composed of four subregions of various origins. We discuss various mutation mechanisms such as DNA replication slippage, and inter- and intrachromosomal recombination which were reported to mediate variation in copy numbers and other types of observed sequence length polymorphism. It is shown that the observed molecular structure of the tandem repeat region did not fully fit the particular patterns expected under a scenario of evolution including any of the known mechanisms. Nevertheless, it appeared that intermolecular unequal crossing-over is most likely the driving force in the evolution of this tandem repeat. However, it remains to be explained, why no reciprocal recombinant copy types have been observed. The reconstructed phylogenetic relationships among copies reflected different evolutionary scenarios as follows: (1) A single and ancient origin of copies pre-dates the radiation of BOECHERA. (2) Parallel expansion and shortening of the tandem repeat within different BOECHERA lineages. (3) Conservation of the first copy, as it was the only one present in all chloroplast haplotypes.