Meiotic drive against chromosome fusions in butterfly hybrids.

Species frequently differ in the number and structure of chromosomes they harbor, but individuals that are heterozygous for chromosomal rearrangements may suffer from reduced fitness. Chromosomal rearrangements like fissions and fusions can hence serve as a mechanism for speciation between incipient lineages, but their evolution poses a paradox. How can rearrangements get fixed between populations if heterozygotes have reduced fitness? One solution is that this process predominantly occurs in small and isolated populations, where genetic drift can override natural selection. However, fixation is also more likely if a novel rearrangement is favored by a transmission bias, such as meiotic drive. Here, we investigate chromosomal transmission distortion in hybrids between two wood white (Leptidea sinapis) butterfly populations with extensive karyotype differences. Using data from two different crossing experiments, we uncover that there is a transmission bias favoring the ancestral chromosomal state for derived fusions, a result that shows that chromosome fusions actually can fix in populations despite being counteracted by meiotic drive. This means that meiotic drive not only can promote runaway chromosome number evolution and speciation, but also that it can be a conservative force acting against karyotypic change and the evolution of reproductive isolation. Based on our results, we suggest a mechanistic model for why chromosome fusion mutations may be opposed by meiotic drive and discuss factors contributing to karyotype evolution in Lepidoptera.

Rapid spread of a vertically transmitted symbiont induces drastic shifts in butterfly sex ratio.

The causes and consequences of sex-ratio dynamics constitutes a pivotal subject in evolutionary biology1. Under conditions of evolutionary equilibrium, the male-to-female ratio tends to be approximately 1:1; however, this equilibrium is susceptible to distortion by selfish genetic elements exemplified by driving sex chromosomes and cytoplasmic elements2,3. Although previous studies have documented instances of these genetic elements distorting the sex ratio, studies specifically tracking the process with which these distorters spread within populations, leading to a transition from balanced parity to a skewed, female-biased state, are notably lacking. Herein, we present compelling evidence documenting the rapid spread of the cytoplasmic endosymbiont Wolbachia within a localized population of the pierid butterfly Eurema hecabe (Figure 1A). This spread resulted in a shift in the sex ratio from near parity to an exceedingly skewed state overwhelmingly biased toward females, reaching 93.1% within a remarkably brief period of 4 years.

Bee and butterfly records indicate diversity losses in western and southern North America, but extensive knowledge gaps remain.

Pollinator losses threaten ecosystems and food security, diminishing gene flow and reproductive output for ecological communities and impacting ecosystem services broadly. For four focal families of bees and butterflies, we constructed over 1400 ensemble species distribution models over two time periods for North America. Models indicated disproportionally increased richness in eastern North America over time, with decreases in richness over time in the western US and southern Mexico. To further pinpoint geographic areas of vulnerability, we mapped records of potential pollinator species of conservation concern and found high concentrations of detections in the Great Lakes region, US East Coast, and southern Canada. Finally, we estimated asymptotic diversity indices for genera known to include species that visit flowers and may carry pollen for ecoregions across two time periods. Patterns of generic diversity through time mirrored those of species-level analyses, again indicating a decline in pollinators in the western U.S. Increases in generic diversity were observed in cooler and wetter ecoregions. Overall, changes in pollinator diversity appear to reflect changes in climate, though other factors such as land use change may also explain regional shifts. While statistical methods were employed to account for unequal sampling effort across regions and time, improved monitoring efforts with rigorous sampling designs would provide a deeper understanding of pollinator communities and their responses to ongoing environmental change.

Zygosity-based sex determination in a butterfly drives hypervariability of Masculinizer.

Nature has devised many ways of producing males and females. Here, we report on a previously undescribed mechanism for Lepidoptera that functions without a female-specific gene. The number of alleles or allele heterozygosity in a single Z-linked gene (BaMasc) is the primary sex-determining switch in Bicyclus anynana butterflies. Embryos carrying a single BaMasc allele develop into WZ (or Z0) females, those carrying two distinct alleles develop into ZZ males, while (ZZ) homozygotes initiate female development, have mismatched dosage compensation, and die as embryos. Consequently, selection against homozygotes has favored the evolution of spectacular allelic diversity: 205 different coding sequences of BaMasc were detected in a sample of 246 females. The structural similarity of a hypervariable region (HVR) in BaMasc to the HVR in Apis mellifera csd suggests molecular convergence between deeply diverged insect lineages. Our discovery of this primary switch highlights the fascinating diversity of sex-determining mechanisms and underlying evolutionary drivers.

The actin cytoskeleton plays multiple roles in structural colour formation in butterfly wing scales.

Vivid structural colours in butterflies are caused by photonic nanostructures scattering light. Structural colours evolved for numerous biological signalling functions and have important technological applications. Optically, such structures are well understood, however insight into their development in vivo remains scarce. We show that actin is intimately involved in structural colour formation in butterfly wing scales. Using comparisons between iridescent (structurally coloured) and non-iridescent scales in adult and developing H. sara, we show that iridescent scales have more densely packed actin bundles leading to an increased density of reflective ridges. Super-resolution microscopy across three distantly related butterfly species reveals that actin is repeatedly re-arranged during scale development and crucially when the optical nanostructures are forming. Furthermore, actin perturbation experiments at these later developmental stages resulted in near total loss of structural colour in H. sara. Overall, this shows that actin plays a vital and direct templating role during structural colour formation in butterfly scales, providing ridge patterning mechanisms that are likely universal across lepidoptera.

Commensalibacter nepenthis sp. nov. and Commensalibacter oyaizuii sp. nov., from fluid in a Nepenthes pitcher cup and a butterfly (Junonia lemonias) in Thailand.

Two novel Gram-negative, aerobic, rod-shaped, non-motile bacteria, strains TBRC 10068T and TBRC 16381T, were isolated from a fluid sample from a close-pitcher cup (Nepenthes gracilis) and an insect sample (Junonia lemonias), respectively. Comparing the 16S rRNA gene sequences with those found in EzBioCloud's publicly available databases revealed that the two strains exhibited a close genetic relationship with Commensalibacter intestini A911T; the calculated sequence similarities were 98.56 and 97.70  %, respectively. The average nucleotide identity and digital DNA-DNA hybridization values of the two Commensalibacter strains, as well as those of their closely related type strains, were found to be lower than the species demarcation threshold of 95 and 70 %, respectively. The phylogenomic analysis of strains TBRC 10068T and TBRC 16381T showed that they belong to the genus Commensalibacter. However, they formed distinct lineages separate from all other strains of Commensalibacter by use of 81 bacterial core genes. In addition, the comparative genomic analysis revealed that the core orthologues of strains TBRC 10068T and TBRC 16381T, compared to the closely related type strains of Commensalibacter species, had distinct genetic profiles. Strain TBRC 10068T contained 163 unique genes, whereas strain TBRC 16381T contained 83. The three Commensalibacter species possessed Q-9 as the primary isoprenoid quinone homologue. The results of a polyphasic taxonomic investigation indicated that strains TBRC 10068T and TBRC 16381T represent two separate new species within the genus Commensalibacter. The species were designated as Commensalibacter nepenthis sp. nov. with the type strain TBRC 10068T (=KCTC 92798T) and Commensalibacter oyaizuii sp. nov. with the type strain TBRC 16381T (=KCTC 92799T).

Haemolymph transfusions transfer heritable learned novel odour preferences to naive larvae of Bicyclus anynana butterflies.

The mechanisms whereby environmental experiences of parents are transmitted to their offspring to impact their behaviour and fitness are poorly understood. Previously, we showed that naive Bicyclus anynana butterfly larvae, whose parents fed on a normal plant feed but coated with a novel odour, inherited an acquired preference towards that odour, which had initially elicited avoidance in the naive parents. Here, we performed simple haemolymph transfusions from odour-fed and control-fed larvae to naive larval recipients. We found that larvae injected with haemolymph from odour-fed donors stopped avoiding the novel odour, and their naive offspring preferred the odour more, compared to the offspring of larvae injected with control haemolymph. These results indicate that factors in the haemolymph, potentially the odour molecule itself, play an important role in odour learning and preference transmission across generations. Furthermore, this mechanism of odour preference inheritance, mediated by the haemolymph, bypasses the peripheral odour-sensing mechanisms taking place in the antennae, mouthparts or legs, and may mediate food plant switching and diversification in Lepidoptera or more broadly across insects.

Discovery of a peculiar insular race of Ravenna nivea (Nire, 1920) (Lepidoptera: Lycaenidae) endemic to Yinggeling Mountain of Hainan, suggesting heterogeneous geological history of mountain formation of the island.

A peculiar population of Ravenna nivea (Nire, 1920) was discovered from the Yinggeling Mountain Mass of central Hainan. Its wing pattern and COI barcode data show considerable distinction from other geographic populations of R. nivea, including that of Bawangling, approximately only 40 km away and also located in Hainan. The p-distance value of the COI barcode between the Yinggeling and Bawangling populations was 1.1%, considerably higher than the value (0.6%) between Bawangling population and populations in eastern China, where the subspecific name howarthi Saigusa, 1993 applies. The population is regarded as a distinct subspecies ngiunmoiae Lo & Hsu, subsp. nov. The distinctness and high degree of COI haplotype diversity of R. nivea found in Hainan and Taiwan suggest continental islands may serve as glacial refugees for the butterfly and other organisms during previous glaciations, and the presence of the relict populations of montane butterflies like R. nivea may provide useful clues towards a better understanding of the geological history of mountain formation within islands.

A working model for the formation of Robertsonian chromosomes.

Robertsonian chromosomes form by fusion of two chromosomes that have centromeres located near their ends, known as acrocentric or telocentric chromosomes. This fusion creates a new metacentric chromosome and is a major mechanism of karyotype evolution and speciation. Robertsonian chromosomes are common in nature and were first described in grasshoppers by the zoologist W. R. B. Robertson more than 100 years ago. They have since been observed in many species, including catfish, sheep, butterflies, bats, bovids, rodents and humans, and are the most common chromosomal change in mammals. Robertsonian translocations are particularly rampant in the house mouse, Mus musculus domesticus, where they exhibit meiotic drive and create reproductive isolation. Recent progress has been made in understanding how Robertsonian chromosomes form in the human genome, highlighting some of the fundamental principles of how and why these types of fusion events occur so frequently. Consequences of these fusions include infertility and Down's syndrome. In this Hypothesis, I postulate that the conditions that allow these fusions to form are threefold: (1) sequence homology on non-homologous chromosomes, often in the form of repetitive DNA; (2) recombination initiation during meiosis; and (3) physical proximity of the homologous sequences in three-dimensional space. This Hypothesis highlights the latest progress in understanding human Robertsonian translocations within the context of the broader literature on Robertsonian chromosomes.

Hybrid speciation driven by multilocus introgression of ecological traits.

Hybridization allows adaptations to be shared among lineages and may trigger the evolution of new species1,2. However, convincing examples of homoploid hybrid speciation remain rare because it is challenging to demonstrate that hybridization was crucial in generating reproductive isolation3. Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies. We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years. This is despite pervasive and ongoing gene flow with one parent, Heliconius pardalinus, which homogenizes 99% of their genomes. The remaining 1% introgressed from the other parent, Heliconius melpomene, and is scattered widely across the H. elevatus genome in islands of divergence from H. pardalinus. These islands contain multiple traits that are under disruptive selection, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Collectively, these traits place H. elevatus on its own adaptive peak and permit coexistence with both parents. Our results show that speciation was driven by introgression of ecological traits, and that speciation with gene flow is possible with a multilocus genetic architecture.

Impacts of fire and prospects for recovery in a tropical peat forest ecosystem.

Uncontrolled fires place considerable burdens on forest ecosystems, compromising our ability to meet conservation and restoration goals. A poor understanding of the impacts of fire on ecosystems and their biodiversity exacerbates this challenge, particularly in tropical regions where few studies have applied consistent analytical techniques to examine a broad range of ecological impacts over multiyear time frames. We compiled 16 y of data on ecosystem properties (17 variables) and biodiversity (21 variables) from a tropical peatland in Indonesia to assess fire impacts and infer the potential for recovery. Burned forest experienced altered structural and microclimatic conditions, resulting in a proliferation of nonforest vegetation and erosion of forest ecosystem properties and biodiversity. Compared to unburned forest, habitat structure, tree density, and canopy cover deteriorated by 58 to 98%, while declines in species diversity and abundance were most pronounced for trees, damselflies, and butterflies, particularly for forest specialist species. Tracking ecosystem property and biodiversity datasets over time revealed most to be sensitive to recurrent high-intensity fires within the wider landscape. These megafires immediately compromised water quality and tree reproductive phenology, crashing commercially valuable fish populations within 3 mo and driving a gradual decline in threatened vertebrates over 9 mo. Burned forest remained structurally compromised long after a burn event, but vegetation showed some signs of recovery over a 12-y period. Our findings demonstrate that, if left uncontrolled, fire may be a pervasive threat to the ecological functioning of tropical forests, underscoring the importance of fire prevention and long-term restoration efforts, as exemplified in Indonesia.

What one genus of showy moths can say about migration, adaptation, and wing pattern.

The Ornate Moth, Utetheisa ornatrix, has served as a model species in chemical ecology studies for decades. Like in the widely publicized stories of the Monarch and other milkweed butterflies, the Ornate Moth and its relatives are tropical insects colonizing whole continents assisted by their chemical defenses. With the recent advances in genomic techniques and evo-devo research, it is becoming a model for studies in other areas, from wing pattern development to phylogeography, from toxicology to epigenetics. We used a genomic approach to learn about Utetheisa's evolution, detoxification, dispersal abilities, and wing pattern diversity. We present an evolutionary genomic analysis of the worldwide genus Utetheisa, then focusing on U. ornatrix. Our reference genome of U. ornatrix reveals gene duplications in the regions possibly associated with detoxification abilities, which allows them to feed on toxic food plants. Finally, comparative genomic analysis of over 100 U. ornatrix specimens from the museum with apparent differences in wing patterns suggest the potential roles of cortex and lim3 genes in wing pattern formation of Lepidoptera and the utility of museum-preserved collection specimens for wing pattern research.

The quantitative genetic basis of variation in sexual versus non-sexual butterfly wing colouration: autosomal, Z-linked, and maternal effects.

Viability indicator traits are expected to be integrated extensively across the genome yet sex-limited to ensure that any benefits are sexually concordant. Understanding how such expectations are accommodated requires elucidating the quantitative genetic architecture of candidate traits in and across the sexes. Here we applied an animal modelling approach to partition the autosomal, allosomal, and direct maternal bases of variation in sexual versus non-sexual dorsal wing colouration in the butterfly Eurema hecabe. The sexual colour trait-coherently scattered ultraviolet that is under strong directional selection due to female choice-is brighter and more expansive in males, and overlays non-sexual pigmentary yellow markings that otherwise dominate both wing surfaces in each sex. Our modelling estimated high and sexually equivalent autosomal variances for ultraviolet reflectance (furnishing h2 ~ 0.58 overall and ~0.75 in males), accompanied by smaller but generally significant Z-linked and maternal components. By contrast, variation in non-sexual yellow was largely attributed to Z-linked sources. Intersexual genetic correlations based upon the major source of variation in each trait were high and not different from 1.0, implying regulation by a pool of genes common to each sex. An expansive autosomal basis for ultraviolet is consistent with its hypothesized role as a genome-wide viability indicator and ensures that both sons and daughters will inherit their father's attractiveness.

A macroevolutionary role for chromosomal fusion and fission in Erebia butterflies.

The impact of large-scale chromosomal rearrangements, such as fusions and fissions, on speciation is a long-standing conundrum. We assessed whether bursts of change in chromosome numbers resulting from chromosomal fusion or fission are related to increased speciation rates in Erebia, one of the most species-rich and karyotypically variable butterfly groups. We established a genome-based phylogeny and used state-dependent birth-death models to infer trajectories of karyotype evolution. We demonstrated that rates of anagenetic chromosomal changes (i.e., along phylogenetic branches) exceed cladogenetic changes (i.e., at speciation events), but, when cladogenetic changes occur, they are mostly associated with chromosomal fissions rather than fusions. We found that the relative importance of fusion and fission differs among Erebia clades of different ages and that especially in younger, more karyotypically diverse clades, speciation is more frequently associated with cladogenetic chromosomal changes. Overall, our results imply that chromosomal fusions and fissions have contrasting macroevolutionary roles and that large-scale chromosomal rearrangements are associated with bursts of species diversification.

RNAi efficiency is enhanced through knockdown of double-stranded RNA-degrading enzymes in butterfly Papilio xuthus.

The efficiency of RNA interference (RNAi) has always limited the research on the phenotype innovation of Lepidoptera insects. Previous studies have found that double-stranded RNA-degrading enzyme (dsRNase) is an important factor in RNAi efficiency, but there have been no relevant reports in butterflies (Papilionoidea). Papilio xuthus is one of the important models in butterflies with an extensive experimental application value. To explore the effect of dsRNase in the RNAi efficiency on butterflies, six dsRNase genes (PxdsRNase 1-6) were identified in P. xuthus genome, and their dsRNA-degrading activities were subsequently detected by ex vivo assays. The result shows that the dsRNA-degrading ability of gut content (<1 h) was higher than hemolymph content (>12 h). We then investigated the expression patterns of these PxdsRNase genes during different tissues and developmental stages, and related RNAi experiments were carried out. Our results show that different PxdsRNase genes had different expression levels at different developmental stages and tissues. The expression of PxdsRNase2, PxdsRNase3, and PxdsRNase6 were upregulated significantly through dsGFP injection, and PxdsRNase genes can be silenced effectively by injecting their corresponding dsRNA. RNAi-of-RNAi studies with PxEbony, which acts as a reporter gene, observed that silencing PxdsRNase genes can increase RNAi efficiency significantly. These results confirm that silencing dsRNase genes can improve RNAi efficiency in P. xuthus significantly, providing a reference for the functional study of insects such as butterflies with low RNAi efficiency.

Testing of arctic insect hemolymph as a secondary agent in applied cryopreservation.

BACKGROUND: Cold hardiness of insects from extremely cold regions is based on a principle of natural cryoprotection, which is associated with physiological mechanisms provided by cryoprotectants. OBJECTIVE: Since arctic cold-hardy insects are producers of highly effective cryoprotectants, in this study, the hemolymph of Aporia crataegi L. and Upis ceramboides L. from an extremely cold area (Yakutia) was tested as a secondary component of cryoprotective agents (CPA) for cryopreservation (-80 degree C) of human peripheral blood lymphocytes and skin fibroblasts. MATERIALS AND METHODS: Lymphocytes and skin fibroblasts were treated with various combinations of DMSO and hemolymph extract and step-wise cooled to -80 degree C. Post-cryopreservation cell viability was assessed by vital staining and morphological appearance. RESULTS: Viability was higher when cells were frozen with a mixture containing DMSO and Upis ceramboides hemolymph compared to the cells frozen in DMSO, while cells frozen with DMSO and Aporia crataegi hemolymph did not survive. The fact that hemolymph of not every cold-resistant insect can be used as a secondary agent along with DMSO indicates that only a unique combination of hemolymph components and its compatibility with cells might result in a positive effect. CONCLUSION: Although the use of insect hemolymph as a complementary agent in applied cryopreservation is a problem in terms of practical application, such studies could initiate new trends in the search for the most successful hemolymph-like cryoprotectant systems. https://doi.org/10.54680/fr24210110712.

Blind measurements did not confirm effects of forest fragmentation on fluctuating asymmetry of a tropical butterfly Morpho helenor.

Re-evaluation of photographs of the tropical butterfly Morpho helenor from a previous study (Pignataro et al. 2023) revealed that its conclusion regarding increased wing fluctuating asymmetry in forest edge habitats compared to forest interior habitats could not be replicated. This discrepancy likely arises from (i) original measurements not being conducted blindly, (ii) insufficient photograph quality hindering accurate landmark selection, and (iii) a lack of detailed description of the measurement protocol. The likelihood of false positive discoveries within the published data concerning the impacts of environmental stress on the fluctuating asymmetry of plants and animals is probably higher than previously assumed.

A genetic atlas for the butterflies of continental Canada and United States.

Multi-locus genetic data for phylogeographic studies is generally limited in geographic and taxonomic scope as most studies only examine a few related species. The strong adoption of DNA barcoding has generated large datasets of mtDNA COI sequences. This work examines the butterfly fauna of Canada and United States based on 13,236 COI barcode records derived from 619 species. It compiles i) geographic maps depicting the spatial distribution of haplotypes, ii) haplotype networks (minimum spanning trees), and iii) standard indices of genetic diversity such as nucleotide diversity (π), haplotype richness (H), and a measure of spatial genetic structure (GST). High intraspecific genetic diversity and marked spatial structure were observed in the northwestern and southern North America, as well as in proximity to mountain chains. While species generally displayed concordance between genetic diversity and spatial structure, some revealed incongruence between these two metrics. Interestingly, most species falling in this category shared their barcode sequences with one at least other species. Aside from revealing large-scale phylogeographic patterns and shedding light on the processes underlying these patterns, this work also exposed cases of potential synonymy and hybridization.