Mimicry can drive convergence in structural and light transmission features of transparent wings in Lepidoptera

Müllerian mimicry is a positive interspecific interaction, whereby co-occurring defended prey species share a common aposematic signal. In Lepidoptera, aposematic species typically harbour conspicuous opaque wing colour patterns with convergent optical properties among co-mimetic species. Surprisingly, some aposematic mimetic species have partially transparent wings, raising the questions of whether optical properties of transparent patches are also convergent, and of how transparency is achieved. Here, we conducted a comparative study of wing optics, micro and nanostructures in neotropical mimetic clearwing Lepidoptera, using spectrophotometry and microscopy imaging. We show that transparency, as perceived by predators, is convergent among co-mimics in some mimicry rings. Underlying micro- and nanostructures are also sometimes convergent despite a large structural diversity. We reveal that while transparency is primarily produced by microstructure modifications, nanostructures largely influence light transmission, potentially enabling additional fine-tuning in transmission properties. This study shows that transparency might not only enable camouflage but can also be part of aposematic signals.

Cortex cis-regulatory switches establish scale colour identity and pattern diversity in Heliconius

In Heliconius butterflies, wing colour pattern diversity and scale types are controlled by a few genes of large effect that regulate colour pattern switches between morphs and species across a large mimetic radiation. One of these genes, cortex, has been repeatedly associated with colour pattern evolution in butterflies. Here we carried out CRISPR knockouts in multiple Heliconius species and show that cortex is a major determinant of scale cell identity. Chromatin accessibility profiling and introgression scans identified cis-regulatory regions associated with discrete phenotypic switches. CRISPR perturbation of these regions in black hindwing genotypes recreated a yellow bar, revealing their spatially limited activity. In the H. melpomene/timareta lineage, the candidate CRE from yellow-barred phenotype morphs is interrupted by a transposable element, suggesting that cis-regulatory structural variation underlies these mimetic adaptations. Our work shows that cortex functionally controls scale colour fate and that its cis-regulatory regions control a phenotypic switch in a modular and pattern-specific fashion.

Hard to catch: experimental evidence supports evasive mimicry

Most research on aposematism has focused on chemically defended prey, but the signalling difficulty of capture remains poorly explored. Similar to classical Batesian and Müllerian mimicry related to distastefulness, such ‘evasive aposematism' may also lead to convergence in warning colours, known as evasive mimicry. A prime candidate group for evasive mimicry areAdelphabutterflies, which are agile insects and show remarkable colour pattern convergence. We tested the ability of naive blue tits to learn to avoid and generalizeAdelphawing patterns associated with the difficulty of capture and compared their response to that of birds that learned to associate the same wing patterns with distastefulness. Birds learned to avoid all wing patterns tested and generalized their aversion to other prey to some extent, but learning was faster with evasive prey compared to distasteful prey. Our results on generalization agree with longstanding observations of striking convergence in wing colour patterns amongAdelphaspecies, since, in our experiments, perfect mimics of evasive and distasteful models were always protected during generalization and suffered the lowest attack rate. Moreover, generalization on evasive prey was broader compared to that on distasteful prey. Our results suggest that being hard to catch may deter predators at least as effectively as distastefulness. This study provides empirical evidence for evasive mimicry, a potentially widespread but poorly understood form of morphological convergence driven by predator selection.

The evolution and genetics of sexually dimorphic ‘dual’ mimicry in the butterfly Elymnias hypermnestra

Sexual dimorphism is a major component of morphological variation across the tree of life, but the mechanisms underlying phenotypic differences between sexes of a single species are poorly understood. We examined the population genomics and biogeography of the common palmfly Elymnias hypermnestra , a dual mimic in which female wing colour patterns are either dark brown (melanic) or bright orange, mimicking toxic Euploea and Danaus species, respectively. As males always have a melanic wing colour pattern, this makes E. hypermnestra a fascinating model organism in which populations vary in sexual dimorphism. Population structure analysis revealed that there were three genetically distinct E. hypermnestra populations, which we further validated by creating a phylogenomic species tree and inferring historical barriers to gene flow. This species tree demonstrated that multiple lineages with orange females do not form a monophyletic group, and the same is true of clades with melanic females. We identified two single nucleotide polymorphisms (SNPs) near the colour patterning gene WntA that were significantly associated with the female colour pattern polymorphism, suggesting that this gene affects sexual dimorphism. Given WntA 's role in colour patterning across Nymphalidae, E. hypermnestra females demonstrate the repeatability of the evolution of sexual dimorphism.

Convergent morphology and divergent phenology: unravelling the coexistence of mimetic Morpho butterfly species

The emergence and persistence of closely-related species in sympatry is puzzling because the potential gene flow and the common local selective pressures may lead to either merging or competitive exclusion. Some species of Morpho butterflies occurring in sympatry display highly similar wing colour patterns. Associated with erratic flight abilities, their bright colouration may limit predator success and discourage future attacks. The evolution of similar colouration in sympatric species is thus likely under local selection by predators (i.e. escape mimicry). Such phenotypic similarity may promote interspecific territoriality and/or reproductive interference, questioning how closely-related co-mimetic species become sexually isolated and coexist in sympatry. We performed a series of field experiments using flying Morpho dummies placed in a natural habitat where wild males commonly patrol. Analysing the interactions of wild Morpho with different dummies, we show that similarity in wing colour pattern leads to interspecific territoriality and courtship among sympatric species. Using genomic data, we then showed that sympatric Morpho species are surprisingly strictly isolated despite their close relatedness and the observed heterospecific interactions. Finally, using a mark-recapture experiment, we discovered a strong temporal segregation in patrolling activity of males from two co-mimetic sister species. Such divergence in phenology may favour sympatry between closely-related species, despite behavioural interferences induced by the local convergence in colour pattern. Altogether, our findings show that temporal segregation may facilitate the co-existence of closely-related species sharing the same ecological niche, suggesting that phenological shifts may represent an overlooked factor of sympatric speciation. Our study therefore highlights how the evolution of multiple traits may favour species diversification in sympatry by partitioning niche in different dimensions.

Perfect mimicry between Heliconius butterflies is constrained by genetics and development

Müllerian mimicry strongly exemplifies the power of natural selection. However, the exact measure of such adaptive phenotypic convergence and the possible causes of its imperfection often remain unidentified. Here, we first quantify wing colour pattern differences in the forewing region of 14 co-mimetic colour pattern morphs of the butterfly species Heliconius erato and Heliconius melpomene and measure the extent to which mimicking colour pattern morphs are not perfectly identical. Next, using gene-editing CRISPR/Cas9 KO experiments of the gene WntA , which has been mapped to colour pattern diversity in these butterflies, we explore the exact areas of the wings in which WntA affects colour pattern formation differently in H. erato and H. melpomene. We find that, while the relative size of the forewing pattern is generally nearly identical between co-mimics, the CRISPR/Cas9 KO results highlight divergent boundaries in the wing that prevent the co-mimics from achieving perfect mimicry. We suggest that this mismatch may be explained by divergence in the gene regulatory network that defines wing colour patterning in both species, thus constraining morphological evolution even between closely related species.

Two new species of the genus Curranosia Paterson, 1957 (Diptera: Muscidae) from the Afrotropical Region

Curranosia vanemdeni spec. nov. is described from Kenya. The species is characterized by features such as protruding mouthparts, slender proboscis and an anterior seta on mid tibia, which were not previously known to occur in this genus. Curranosia wyatti spec. nov., collected in The Gambia differs from other Curranosia species by wing colour, absence of white dusted markings on the presutural mesonotum, and differences in the numbers of large setae of the body, characters that are more common for the differentiation of species of the genus. Taxonomic acts Curranosia vanemdeni spec. nov. – urn:lsid:zoobank.org:act:192F65AF-3E14-4DDE-921C-DB840B8A06B4Curranosia wyatti spec. nov. – urn:lsid:zoobank.org:act:971D4E89-CCE4-471D-BAF2-6703B1766324

Chemical signals act as the main reproductive barrier between sister and mimetic Heliconius butterflies

Colour pattern is the main trait that drives mate recognition between Heliconius species that are phylogenetically close. However, when this cue is compromised such as in cases of mimetic, sympatric and closely related species, alternative mating signals must evolve to ensure reproductive isolation and species integrity. The closely related species Heliconius melpomene malleti and H. timareta florencia occur in the same geographical region, and despite being co-mimics, they display strong reproductive isolation. In order to test which cues differ between species, and potentially contribute to reproductive isolation, we quantified differences in the wing phenotype and the male chemical profile. As expected, the wing colour pattern was indistinguishable between the two species, while the chemical profile of the androconial and genital males' extracts showed marked differences. We then conducted behavioural experiments to study the importance of these signals in mate recognition by females. In agreement with our previous results, we found that chemical blends and not wing colour pattern drive the preference of females for conspecific males . Also, experiments with hybrid males and females suggested an important genetic component for both chemical production and preference. Altogether, these results suggest that chemicals are the major reproductive barrier opposing gene flow between these two sister and co-mimic species.