Rapid Evolution of Host Repertoire and Geographic Range in a Young and Diverse Genus of Montane Butterflies.

Evolutionary changes in geographic distribution and larval host plants may promote the rapid diversification of montane insects, but this scenario has been rarely investigated. We studied rapid radiation of the butterfly genus Colias, which has diversified in mountain ecosystems in Eurasia, Africa, and the Americas. Based on a dataset of 150 nuclear protein-coding genetic loci and mitochondrial genomes, we constructed a time-calibrated phylogenetic tree of Colias species with broad taxon sampling. We then inferred their ancestral geographic ranges, historical diversification rates, and the evolution of host use. We found that the most recent common ancestor of Colias was likely geographically widespread and originated ~3.5 Ma. The group subsequently diversified in different regions across the world, often in tandem with geographic expansion events. No aspect of elevation was found to have a direct effect on diversification. The genus underwent a burst of diversification soon after the divergence of the Neotropical lineage, followed by an exponential decline in diversification rate toward the present. The ancestral host repertoire included the legume genera Astragalus and Trifolium but later expanded to include a wide range of Fabaceae genera and plants in more distantly related families, punctuated with periods of host range expansion and contraction. We suggest that the widespread distribution of the ancestor of all extant Colias lineages set the stage for diversification by isolation of populations that locally adapted to the various different environments they encountered, including different host plants. In this scenario, elevation is not the main driver but might have accelerated diversification by isolating populations.

Testing hypotheses of a coevolutionary key innovation reveals a complex suite of traits involved in defusing the mustard oil bomb.

Coevolutionary interactions are responsible for much of the Earth's biodiversity, with key innovations driving speciation bursts on both sides of the interaction. One persistent question is whether macroevolutionary traits identified as key innovations accurately predict functional performance and selection dynamics within species, as this necessitates characterizing their function, investigating their fitness consequences, and exploring the selection dynamics acting upon them. Here, we used CRISPR-Cas9 mediating nonhomologous end joining (NHEJ) in the butterfly species Pieris brassicae to knock out and directly assess the function and fitness impacts of nitrile specifier protein (NSP) and major allergen (MA). These are two closely related genes that facilitate glucosinolate (GSL) detoxification capacity, which is a key innovation in mustard feeding Pierinae butterflies. We find NSP and MA are both required for survival on plants containing GSLs, with expression differences arising in response to variable GSL profiles, concordant with detoxification performance. Importantly, this concordance was only observed when using natural host plants, likely reflecting the complexity of how these enzymes interact with natural plant variation in GSLs and myrosinases. Finally, signatures of positive selection for NSP and MA were detected across Pieris species, consistent with these genes' importance in recent coevolutionary interactions. Thus, the war between these butterflies and their host plants involves more than the mere presence of chemical defenses and detoxification mechanisms, as their regulation and activation represent key components of complex interactions. We find that inclusion of these dynamics, in ecologically relevant assays, is necessary for coevolutionary insights in this system and likely others.

A genetic switch for male UV iridescence in an incipient species pair of sulphur butterflies.

Mating cues evolve rapidly and can contribute to species formation and maintenance. However, little is known about how sexual signals diverge and how this variation integrates with other barrier loci to shape the genomic landscape of reproductive isolation. Here, we elucidate the genetic basis of ultraviolet (UV) iridescence, a courtship signal that differentiates the males of Colias eurytheme butterflies from a sister species, allowing females to avoid costly heterospecific matings. Anthropogenic range expansion of the two incipient species established a large zone of secondary contact across the eastern United States with strong signatures of genomic admixtures spanning all autosomes. In contrast, Z chromosomes are highly differentiated between the two species, supporting a disproportionate role of sex chromosomes in speciation known as the large-X (or large-Z) effect. Within this chromosome-wide reproductive barrier, linkage mapping indicates that cis-regulatory variation of bric a brac (bab) underlies the male UV-iridescence polymorphism between the two species. Bab is expressed in all non-UV scales, and butterflies of either species or sex acquire widespread ectopic iridescence following its CRISPR knockout, demonstrating that Bab functions as a suppressor of UV-scale differentiation that potentiates mating cue divergence. These results highlight how a genetic switch can regulate a premating signal and integrate with other reproductive barriers during intermediate phases of speciation.

A time course analysis through diapause reveals dynamic temporal patterns of microRNAs associated with endocrine regulation in the butterfly Pieris napi.

Organisms inhabiting highly seasonal environments must cope with a wide range of environmentally induced challenges. Many seasonal challenges require extensive physiological modification to survive. In winter, to survive extreme cold and limited resources, insects commonly enter diapause, which is an endogenously derived dormant state associated with minimized cellular processes and low energetic expenditure. Due to the high degree of complexity involved in diapause, substantial cellular regulation is required, of which our understanding primarily derives from the transcriptome via messenger RNA expression dynamics. Here we aim to advance our understanding of diapause by investigating microRNA (miRNA) expression in diapausing and direct developing pupae of the butterfly Pieris napi. We identified coordinated patterns of miRNA expression throughout diapause in both head and abdomen tissues of pupae, and via miRNA target identification, found several expression patterns to be enriched for relevant diapause-related physiological processes. We also identified two candidate miRNAs, miR-14-5p and miR-2a-3p, that are likely involved in diapause progression through their activity in the ecdysone pathway, a critical regulator of diapause termination. miR-14-5p targets phantom, a gene in the ecdysone synthesis pathway, and is upregulated early in diapause. miR-2a-3p has been found to be expressed in response to ecdysone, and is upregulated during diapause termination. Together, the expression patterns of these two miRNAs match our current understanding of the timing of hormonal regulation of diapause in P. napi and provide interesting candidates to further explore the mechanistic role of microRNAs in diapause regulation.

Plasticity for the win: Flexible transcriptional response to host plant switches in the comma butterfly (Polygonia c-album).

Generalist plant-feeding insects are characterised by a broad host repertoire that can comprise several families or even different orders of plants. The genetic and physiological mechanisms underlying the use of such a wide host range are still not fully understood. Earlier studies indicate that the consumption of different host plants is associated with host-specific gene expression profiles. It remained, however, unclear if and how larvae can alter these profiles in the case of a changing host environment. Using the polyphagous comma butterfly (Polygonia c-album) we show that larvae can adjust their transcriptional profiles in response to a new host plant. The switch to some of the host plants, however, resulted in a larger transcriptional response and, thus, seems to be more challenging. At a physiological level, no correspondence for these patterns could be found in larval performance. This suggests that a high transcriptional but also phenotypic flexibility are essential for the use of a broad and diverse host range. We furthermore propose that host switch tests in the laboratory followed by transcriptomic investigations can be a valuable tool to examine not only plasticity in host use but also subtle and/or transient trade-offs in the evolution of host plant repertoires.

Genetic constraints in genes exhibiting splicing plasticity in facultative diapause.

Phenotypic plasticity is produced and maintained by processes regulating the transcriptome. While differential gene expression is among the most important of these processes, relatively little is known about other sources of transcriptional variation. Previous work suggests that alternative splicing plays an extensive and functionally unique role in transcriptional plasticity, though plastically spliced genes may be more constrained than the remainder of expressed genes. In this study, we explore the relationship between expression and splicing plasticity, along with the genetic diversity in those genes, in an ecologically consequential polyphenism: facultative diapause. Using 96 samples spread over two tissues and 10 timepoints, we compare the extent of differential splicing and expression between diapausing and direct developing pupae of the butterfly Pieris napi. Splicing differs strongly between diapausing and direct developing trajectories but alters a smaller and functionally unique set of genes compared to differential expression. We further test the hypothesis that among these expressed loci, plastically spliced genes are likely to experience the strongest purifying selection to maintain seasonally plastic phenotypes. Genes with unique transcriptional changes through diapause consistently had the lowest nucleotide diversity, and this effect was consistently stronger among genes that were differentially spliced compared to those with just differential expression through diapause. Further, the strength of negative selection was higher in the population expressing diapause every generation. Our results suggest that maintenance of the molecular mechanisms involved in diapause progression, including post-transcriptional modifications, are highly conserved and likely to experience genetic constraints, especially in northern populations of P. napi.

The genetic basis of wing spots in Pieris canidia butterflies.

Spots in pierid butterflies and eyespots in nymphalid butterflies are likely non-homologous wing colour pattern elements, yet they share a few features in common. Both develop black scales that depend on the function of the gene spalt, and both might have central signalling cells. This suggests that both pattern elements may be sharing common genetic circuitry. Hundreds of genes have already been associated with the development of nymphalid butterfly eyespot patterns, but the genetic basis of the simpler spot patterns on the wings of pierid butterflies has not been investigated. To facilitate studies of pierid wing patterns, we report a high-quality draft genome assembly for Pieris canidia, the Indian cabbage white. We then conducted transcriptomic analyses of pupal wing tissues sampled from the spot and non-spot regions of P. canidia at 3-6 h post-pupation. A total of 1352 genes were differentially regulated between wing tissues with and without the black spot, including spalt, Krüppel-like factor 10, genes from the Toll, Notch, TGF-ß, and FGFR signalling pathways, and several genes involved in the melanin biosynthetic pathway. We identified 14 genes that are up-regulated in both pierid spots and nymphalid eyespots and propose that spots and eyespots share regulatory modules despite their likely independent origins.

Drosophila Evolution over Space and Time (DEST): A New Population Genomics Resource.

Drosophila melanogaster is a leading model in population genetics and genomics, and a growing number of whole-genome data sets from natural populations of this species have been published over the last years. A major challenge is the integration of disparate data sets, often generated using different sequencing technologies and bioinformatic pipelines, which hampers our ability to address questions about the evolution of this species. Here we address these issues by developing a bioinformatics pipeline that maps pooled sequencing (Pool-Seq) reads from D. melanogaster to a hologenome consisting of fly and symbiont genomes and estimates allele frequencies using either a heuristic (PoolSNP) or a probabilistic variant caller (SNAPE-pooled). We use this pipeline to generate the largest data repository of genomic data available for D. melanogaster to date, encompassing 271 previously published and unpublished population samples from over 100 locations in >20 countries on four continents. Several of these locations have been sampled at different seasons across multiple years. This data set, which we call Drosophila Evolution over Space and Time (DEST), is coupled with sampling and environmental metadata. A web-based genome browser and web portal provide easy access to the SNP data set. We further provide guidelines on how to use Pool-Seq data for model-based demographic inference. Our aim is to provide this scalable platform as a community resource which can be easily extended via future efforts for an even more extensive cosmopolitan data set. Our resource will enable population geneticists to analyze spatiotemporal genetic patterns and evolutionary dynamics of D. melanogaster populations in unprecedented detail.

Intrapopulation variance in ecophysiological responses to water limitation in a butterfly metapopulation suggests adaptive resilience to environmental variability.

How organisms that are part of the same trophic network respond to environmental variability over small spatial scales has been studied in a multitude of systems. Prevailing theory suggests a large role for plasticity in key traits among interacting species that allows matching of life cycles or life-history traits across environmental gradients, for instance insects tracking host-plant phenology across variable environments (Posledovich et al. 2018). A key aspect that remains understudied is the extent of intrapopulation variability in plasticity and whether stressful conditions canalize plasticity to an optimal level, or alternatively if variation in plasticity indeed could increase fitness in itself via alternative strategies. In a From the Cover article in this issue of Molecular Ecology, Kahilainen et al. (2022) investigate this issue in a classical insect study system, the metapopulation of the Glanville fritillary butterfly (Melitea cinxia) in the Åland archipelago of Finland. The authors first establish how a key host plant responds to water limitation, then quantify among-family variation in larval growth and development across control and water-limited host plants. Finally, they use RNA sequencing to gain mechanistic insights into some of these among-family differences in larval performance in response to host-plant variation, finding results suggesting the existence of heritable, intrapopulation variability in ecologically relevant plasticity. This final step represents a critically important and often overlooked component of efforts to predict sensitivity of biological systems to changing environmental conditions, since it provides a key metric of adaptive resilience present in the system.

Local adaptation of life cycles in a butterfly is associated with variation in several circadian clock genes.

Many insects exhibit geographical variation in voltinism, the number of generations produced per year. This includes high-latitude species in previously glaciated areas, meaning that divergent selection on life cycle traits has taken place during or shortly after recent colonization. Here, we use a population genomics approach to compare a set of nine Scandinavian populations of the butterfly Pararge aegeria that differ in life cycle traits (diapause thresholds and voltinism) along both north-south and east-west clines. Using a de novo-assembled genome, we reconstruct colonization histories and demographic relationships. Based on the inferred population structure, we then scan the genome for candidate loci showing signs of divergent selection potentially associated with population differences in life cycle traits. The identified candidate genes include a number of components of the insect circadian clock (timeless, timeless2, period, cryptochrome and clockwork orange). Most notably, the gene timeless, which has previously been experimentally linked to life cycle regulation in P. aegeria, is here found to contain a novel 97-amino acid deletion unique to, and fixed in, a single population. These results add to a growing body of research framing circadian gene variation as a potential mechanism for generating local adaptation of life cycles.

Extensive transcriptomic profiling of pupal diapause in a butterfly reveals a dynamic phenotype.

Diapause is a common adaptation for overwintering in insects that is characterized by arrested development and increased tolerance to stress and cold. While the expression of specific candidate genes during diapause have been investigated, there is no general understanding of the dynamics of the transcriptional landscape as a whole during the extended diapause phenotype. Such a detailed temporal insight is important as diapause is a vital aspect of life cycle timing. Here, we performed a time-course experiment using RNA-Seq on the head and abdomen in the butterfly Pieris napi. In both body parts, comparing diapausing and nondiapausing siblings, differentially expressed genes are detected from the first day of pupal development and onwards, varying dramatically across these formative stages. During diapause there are strong gene expression dynamics present, revealing a preprogrammed transcriptional landscape that is active during the winter. Different biological processes appear to be active in the two body parts. Finally, adults emerging from either the direct or diapause pathways do not show large transcriptomic differences, suggesting the adult phenotype is strongly canalized.

Structural complexity and molecular heterogeneity of a butterfly ejaculate reflect a complex history of selection.

Male ejaculates are often structurally complex, and this complexity is likely to influence key reproductive interactions between males and females. However, despite its potential evolutionary significance, the molecular underpinnings of ejaculate structural complexity have received little empirical attention. To address this knowledge gap, we sought to understand the biochemical and functional properties of the structurally complex ejaculates of Pieris rapae butterflies. Males in this species produce large ejaculates called spermatophores composed of an outer envelope, an inner matrix, and a bolus of sperm. Females are thought to benefit from the nutrition contained in the soluble inner matrix through increases in longevity and fecundity. However, the indigestible outer envelope of the spermatophore delays female remating, allowing males to monopolize paternity for longer. Here, we show that these two nonsperm-containing spermatophore regions, the inner matrix and the outer envelope, differ in their protein composition and functional properties. We also reveal how these divergent protein mixtures are separately stored in the male reproductive tract and sequentially transferred to the female reproductive tract during spermatophore assembly. Intriguingly, we discovered large quantities of female-derived proteases in both spermatophore regions shortly after mating, which may contribute to spermatophore digestion and hence, female control over remating rate. Finally, we report evidence of past selection on these spermatophore proteins and female proteases, indicating a complex evolutionary history. Our findings illustrate how structural complexity of ejaculates may allow functionally and/or spatially associated suites of proteins to respond rapidly to divergent selective pressures, such as sexual conflict or reproductive cooperation.

Effects of adult temperature on gene expression in a butterfly: identifying pathways associated with thermal acclimation.

BACKGROUND: Phenotypic plasticity is a pervasive property of all organisms and considered to be of key importance for dealing with environmental variation. Plastic responses to temperature, which is one of the most important ecological factors, have received much attention over recent decades. A recurrent pattern of temperature-induced adaptive plasticity includes increased heat tolerance after exposure to warmer temperatures and increased cold tolerance after exposure to cooler temperatures. However, the mechanisms underlying these plastic responses are hitherto not well understood. Therefore, we here investigate effects of adult acclimation on gene expression in the tropical butterfly Bicyclus anynana, using an RNAseq approach. RESULTS: We show that several antioxidant markers (e.g. peroxidase, cytochrome P450) were up-regulated at a higher temperature compared with a lower adult temperature, which might play an important role in the acclamatory responses subsequently providing increased heat tolerance. Furthermore, several metabolic pathways were up-regulated at the higher temperature, likely reflecting increased metabolic rates. In contrast, we found no evidence for a decisive role of the heat shock response. CONCLUSIONS: Although the important role of antioxidant defence mechanisms in alleviating detrimental effects of oxidative stress is firmly established, we speculate that its potentially important role in mediating heat tolerance and survival under stress has been underestimated thus far and thus deserves more attention.

Local adaptation of photoperiodic plasticity maintains life cycle variation within latitudes in a butterfly.

The seasonal cycle varies geographically and organisms are under selection to express life cycles that optimally exploit their spatiotemporal habitats. In insects, this often means producing an annual number of generations (voltinism) appropriate to the local season length. Variation in voltinism may arise from variation in environmental factors (e.g., temperature or photoperiod) acting on a single reaction norm shared across populations, but it may also result from local adaptation of reaction norms. However, such local adaptation is poorly explored at short geographic distances, especially within latitudes. Using a combination of common-garden rearing and life cycle modeling, we have investigated the causal factors behind voltinism variation in Swedish populations of the butterfly Pararge aegeria, focusing on a set of populations that lie within a single degree of latitude but nonetheless differ in season length and voltinism. Despite considerable differences in ambient temperature between populations, modeling suggested that the key determinant of local voltinism was in fact interpopulation differences in photoperiodic response. These include differences in the induction thresholds for winter diapause, as well as differences in photoperiodic regulation of larval development, a widespread but poorly studied phenomenon. Our results demonstrate previously neglected ways that photoperiodism may mediate insect phenological responses to temperature, and emphasize the importance of local adaptation in shaping phenological patterns in general, as well as for predicting the responses of populations to changes in climate.

Genetic variation underlying local adaptation of diapause induction along a cline in a butterfly.

Diapause is a life history strategy allowing individuals to arrest development until favourable conditions return, and it is commonly induced by shortened day length that is latitude specific for local populations. Although understanding the evolutionary dynamics of a threshold trait like diapause induction provides insights into the adaptive process and adaptive potential of populations, the genetic mechanism of variation in photoperiodic induction of diapause is not well understood. Here, we investigate genetic variation underlying latitudinal variation in diapause induction and the selection dynamics acting upon it. Using a genomewide scan for divergent regions between two populations of the butterfly Pararge aegeria that differ strongly in their induction thresholds, we identified and investigated the patterns of variation in those regions. We then tested the association of these regions with diapause induction using between-population crosses, finding significant SNP associations in four genes present in two chromosomal regions, one with the gene period, and the other with the genes kinesin, carnitine O-acetyltransferase and timeless. Patterns of allele frequencies in these two regions in population samples along a latitudinal cline suggest strong selection against heterozygotes at two genes within these loci (period, timeless). Evidence for additional loci modifying the diapause decision was found in patterns of allelic change in relation to induction thresholds over the cline, as well as in backcross analyses. Taken together, population-specific adaptations of diapause induction appear to be due to a combination of alleles of larger and smaller effect size, consistent with an exponential distribution of effect sizes involved in local adaption.

Microevolutionary selection dynamics acting on immune genes of the green-veined white butterfly, Pieris napi.

Insects rely on their innate immune system to successfully mediate complex interactions with their microbiota, as well as the microbes present in the environment. Previous work has shown that components of the canonical immune gene repertoire evolve rapidly and have evolutionary characteristics originating from interactions with fast-evolving microorganisms. Although these interactions are likely to vary among populations, there is a poor understanding of the microevolutionary dynamics of immune genes, especially in non-Dipteran insects. Here, we use the full set of canonical insect immune genes to investigate microevolutionary dynamics acting on these genes between and among populations by comparing three allopatric populations of the green-veined white butterfly, Pieris napi (Linné; Lepidoptera, Pieridae). Immune genes showed increased genetic diversity compared to genes from the rest of the genome and various functional categories exhibited different types of signatures of selection, at different evolutionary scales, presenting a complex pattern of selection dynamics. Signatures of balancing selection were identified in 10 genes, and 17 genes appear to be under positive selection. Genes involved with the cellular arm of the immune response as well as the Toll pathway appear to be enriched among our outlier loci, regardless of functional category. This suggests that the targets of selection might focus upon an entire pathway, rather than functional subsets across pathways. Our microevolutionary results are similar to previously observed macroevolutionary patterns from diverse taxa, suggesting that either the immune system is robust to dramatic differences in life history and microbial communities, or that diverse microbes exert similar selection pressures.

Metabolome dynamics of diapause in the butterfly Pieris napi: distinguishing maintenance, termination and post-diapause phases.

Diapause is a deep resting stage facilitating temporal avoidance of unfavourable environmental conditions, and is used by many insects to adapt their life cycle to seasonal variation. Although considerable work has been invested in trying to understand each of the major diapause stages (induction, maintenance and termination), we know very little about the transitions between stages, especially diapause termination. Understanding diapause termination is crucial for modelling and predicting spring emergence and winter physiology of insects, including many pest insects. In order to gain these insights, we investigated metabolome dynamics across diapause development in pupae of the butterfly Pieris napi, which exhibits adaptive latitudinal variation in the length of endogenous diapause that is uniquely well characterized. By employing a time-series experiment, we show that the whole-body metabolome is highly dynamic throughout diapause and differs between pupae kept at a diapause-terminating (low) temperature and those kept at a diapause-maintaining (high) temperature. We show major physiological transitions through diapause, separate temperature-dependent from temperature-independent processes and identify significant patterns of metabolite accumulation and degradation. Together, the data show that although the general diapause phenotype (suppressed metabolism, increased cold tolerance) is established in a temperature-independent fashion, diapause termination is temperature dependent and requires a cold signal. This revealed several metabolites that are only accumulated under diapause-terminating conditions and degraded in a temperature-unrelated fashion during diapause termination. In conclusion, our findings indicate that some metabolites, in addition to functioning as cryoprotectants, for example, are candidates for having regulatory roles as metabolic clocks or time-keepers during diapause.

The butterfly plant arms-race escalated by gene and genome duplications.

Coevolutionary interactions are thought to have spurred the evolution of key innovations and driven the diversification of much of life on Earth. However, the genetic and evolutionary basis of the innovations that facilitate such interactions remains poorly understood. We examined the coevolutionary interactions between plants (Brassicales) and butterflies (Pieridae), and uncovered evidence for an escalating evolutionary arms-race. Although gradual changes in trait complexity appear to have been facilitated by allelic turnover, key innovations are associated with gene and genome duplications. Furthermore, we show that the origins of both chemical defenses and of molecular counter adaptations were associated with shifts in diversification rates during the arms-race. These findings provide an important connection between the origins of biodiversity, coevolution, and the role of gene and genome duplications as a substrate for novel traits.

Female fecundity variation affects reproducibility of experiments on host plant preference and acceptance in a phytophagous insect.

Reproducibility is a scientific cornerstone. Many recent studies, however, describe a reproducibility crisis and call for assessments of reproducibility across scientific domains. Here, we explore the reproducibility of a classic ecological experiment-that of assessing female host plant preference and acceptance in phytophagous insects, a group in which host specialization is a key driver of diversification. We exposed multiple cohorts of Pieris napi butterflies from the same population to traditional host acceptance and preference tests on three Brassicaceae host species. Whereas the host plant rank order was highly reproducible, the propensity to oviposit on low-ranked hosts varied significantly even among cohorts exposed to similar conditions. Much variation could be attributed to among-cohort variation in female fecundity, a trait strongly correlated both to female size and to the size of the nuptial gift a female receives during mating. Small males provide small spermatophores, and in our experiment small females that mated with small males had a disproportionally low propensity to oviposit on low-ranked hosts. Hence, our results provide empirical support to the theoretical prediction that female host utilization is strongly affected by non-genetic, environmental variation, and that such variation can affect the reproducibility of ecological experiments even under seemingly identical conditions.

Investigating the genomic basis of discrete phenotypes using a Pool-Seq-only approach: New insights into the genetics underlying colour variation in diverse taxa.

While large-scale genomic approaches are increasingly revealing the genetic basis of polymorphic phenotypes such as colour morphs, such approaches are almost exclusively conducted in species with high-quality genomes and annotations. Here, we use Pool-Seq data for both genome assembly and SNP frequency estimation, followed by scanning for FST outliers to identify divergent genomic regions. Using paired-end, short-read sequencing data from two groups of individuals expressing divergent phenotypes, we generate a de novo rough-draft genome, identify SNPs and calculate genomewide FST differences between phenotypic groups. As genomes generated by Pool-Seq data are highly fragmented, we also present an approach for super-scaffolding contigs using existing protein-coding data sets. Using this approach, we reanalysed genomic data from two recent studies of birds and butterflies investigating colour pattern variation and replicated their core findings, demonstrating the accuracy and power of a Pool-Seq-only approach. Additionally, we discovered new regions of high divergence and new annotations that together suggest novel parallels between birds and butterflies in the origins of their colour pattern variation.