Butterfly wings: the evolution of development of colour patterns

The diversity in colour patterns on butterfly wings provides great potential for understanding how developmental mechanisms may be modulated in the evolution of adaptive traits. In particular, we discuss concentric eyespot patterns, which have been shown by surgical experiments to be formed in response to signals from a central focus. Seasonal polyphenism shows how alternate phenotypes can develop through environmental sensitivity mediated by ecdysteroid hormones, whereas artificial selection and single gene mutants demonstrate genetic variation influencing the number, shape, size, position, and colour composition of the eyespots. The expression patterns of the regulatory gene Distal-less reveal that these changes can arise at several different developmental stages, and the phenotypes indicate that some forms of changed pattern may occur much more readily than others. Further study of the genes, of the developmental mechanisms, and of the functions of the patterns will provide novel insights about the evolution of morphological diversity. BioEssays 21:391–401, 1999. © 1999 John Wiley & Sons, Inc.     

Butterfly wing patterns

This paper integrates genetical studies of variation in the wing patterns of Lepidoptera with experimental investigations of developmental mechanisms. Research on the tropical butterfly,Bicyclus anynana, is described. This work includes artificial selection of lines with different patterns of wing eyespots followed by grafting experiments on the lines to examine the phenotypic and genetic differences in terms of developmental mechanisms. The results are used to show how constraints on the evolution of this wing pattern may be related to the developmental organisation. The eyespot pattrn can be envisaged as a set of developmental homologues; a common developmental mechanism is associated with a quantitative genetic system involving high genetic correlations. However, individual genes which influence only subsets of the eyespots, thus uncoupling the interdependence of the eyespots, may be important in evolutionary change. The postulated evolutionary constraints are illustrated with respect to differences in wing pattern found among other species ofBicyclus.     

The genetics and evo-devo of butterfly wing patterns

Understanding how the spectacular diversity of colour patterns on butterfly wings is shaped by natural selection, and how particular pattern elements are generated, has been the focus of both evolutionary and developmental biologists. The growing field of evolutionary developmental biology has now begun to provide a link between genetic variation and the phenotypes that are produced by developmental processes and that are sorted by natural selection. Butterfly wing patterns are set to become one of the few examples of morphological diversity to be studied successfully at many levels of biological organization, and thus to yield a more complete picture of adaptive morphological evolution.     

The conceptual and practical implications of interpreting diet breadth mechanistically in generalist predatory insects

Seasonal polyphenism in animal colour patterns indicates that temporal variation in selection pressures maintains phenotypic plasticity. Spring generation of the polyphenic European map butterfly Araschnia levana has an orange–black fritillary‐like pattern whilst individuals of the summer generation are black with white bands across the wings. What selects for the colour difference is unknown. Because predation is a major selection pressure for insect coloration, we first tested whether map butterfly coloration could have a warning function (i.e. whether the butterflies are unpalatable to birds). In a following field experiment with butterfly dummies we tested whether the spring form is better protected than the summer form from predators in the spring, and vice versa in the summer. The butterflies were palatable to birds (blue tits Cyanistes caeruleus) and in the field the spring and summer form dummies were attacked equally irrespective of season. Therefore, we found no evidence that the map butterfly is warning‐coloured or that seasonal polyphenism is an adaptation to avian predation. Because insect coloration has multiple functions and map butterfly coloration is linked to morphology, life history and development it is likely that the interplay of several selection pressures explains the evolution of colour polyphenism. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Mutants highlight the modular control of butterfly eyespot patterns

SUMMARY The eyespots on butterfly wings are thought to be serially homologous pattern elements. Yet eyespots differ greatly in number, shape, color, and size, within and among species. To what extent do these serially homologues have separate developmental identities, upon which selection acts to create diversity? We examined x‐ray–induced mutations for the eyespots of the nymphalid butterfly Bicyclus anynana that highlight the modular control of these serially homologous wing pattern elements. These mutations reduce or eliminate individual eyespots, or groups of eyespots, with no further effect on the wing color pattern. The collection of mutants highlights a greater potential developmental repertoire than that observed across the genus Bicyclus. We studied in detail one such mutation, of codominant effect, that causes the elimination of two adjacent eyespots on the ventral hindwing. By analyzing the expression of genes known to be involved in eyespot formation, we found an alteration in the differentiation of the “organizing” cells at the eyespot's center. No such cells differentiate in the wing subdivisions lacking the two eyespots in the mutants. We propose several developmental models, based on wing compartmentalization in Drosophila, that provide the first framework for thinking about the molecular evolution of butterfly wing pattern modularity.     

Differences in biological and behavioural characteristics of Harmonia axyridis (Coleoptera: Coccinellidae) according to colour patterns of elytra

Samples of overwintering populations of Harmonia axyridis were classified into five colour patterns, succinea 1, succinea 2, conspicua, spectabilis and axyridis. Generally, the succinea 1 colour pattern was dominant at six collecting sites in Daejon and Chungnam provinces of Korea and their occurrence proportion was over 50%. Non‐melanic forms such as succinea 1 and 2 were noted in about 90% of collected individuals. On the other hand, conspicua and spectabilis as melanic forms were dominant in the laboratory. One hypothesis is that the difference between field and laboratory populations is related to non‐random mating and environmental conditions. Practically, in mate‐choice experiments, most colour pattern ladybirds seemed to mate with the melanic form, especially the conspicua form. The body size (length) of H. axyridis in colour patterns was slightly different, but in females, there was no significant difference among colour patterns. However, both lengths of males were significantly different among colour patterns. In reproductive ability (fecundity), there was no difference among colour patterns.     

Asymmetry patterns across the distribution range: does the species matter?

An important question in evolutionary ecology is whether different populations across a species range, from core to periphery, experience different levels of stress. The estimation of developmental instability has been proposed as a useful tool for quantifying the degree of environmental and genetic stress that individuals experience during their development. Fluctuating asymmetry, the unsigned difference between the two sides of a bilaterally symmetrical trait, has been suggested to reflect the levels of developmental instability in a population. As such, it has been proposed as a useful tool for estimating changes in developmental instability and in stress response in populations across a range of environmental conditions. Recent studies focusing mostly on birds have detected increasing fluctuating asymmetry from core to periphery across the distribution range, suggesting that peripheral populations may experience higher levels of environmental and/or genetic stress. Most of these comparisons were done for single taxa across a single gradient. However, different species are predicted to respond differently to environmental shifts across the range. We compared asymmetry patterns in wing morphology in populations of two Euchloe butterfly species across their opposing ranges in Israel. Contrary to the patterns observed in birds across the same gradient, bilateral asymmetry did not increase or shift towards the periphery in either of the butterfly species. If fluctuating asymmetry in these traits reflects levels of stress, these results may partly reflect the fact that the range of these two butterfly species is limited by the distribution of their host plant, rather than by abiotic environmental variables. In addition, developing pierids can diapause during harsh seasons and can persist in resource‐rich patches, thus minimizing the environmental stress perceived by developing individuals. We conclude that accounting for differences in species’ life histories and range‐limiting factors is necessary in order to better predict patterns of developmental instability across spatial and environmental gradients. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 313–324.     

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.     

Elements of butterfly wing patterns

The color patterns on the wings of butterflies are unique among animal color patterns in that the elements that make up the overall pattern are individuated. Unlike the spots and stripes of vertebrate color patterns, the elements of butterfly wing patterns have identities that can be traced from species to species, and typically across genera and families. Because of this identity it is possible to recognize homologies among pattern elements and to study their evolution and diversification. Individuated pattern elements evolved from non-individuated precursors by compartmentalization of the wing into areas that became developmentally autonomous with respect to color pattern formation. Developmental compartmentalization led to the evolution of serially repeated elements and the emergence of serial homology. In these compartments, serial homologues were able to acquire site-specific developmental regulation and this, in turn, allowed them to diverge morphologically. Compartmentalization of the wing also reduced the developmental correlation among pattern elements. The release from this developmental constraint, we believe, enabled the great evolutionary radiation of butterfly wing patterns. During pattern evolution, the same set of individual pattern elements is arranged in novel ways to produce species-specific patterns, including such adaptations as mimicry and camouflage.     

A systematic comparison of summary characteristics for quantifying point patterns in ecology

Many functional summary characteristics such as Ripley's K function have been used in ecology to describe the spatial structure of point patterns to aid understanding of the underlying processes. However, their use is poorly guided in ecology because little is understood how well single summary characteristics, or a combination of them, capture the spatial structure of real world patterns. Here, we systematically tested the performance of combinations of eight summary characteristics [i.e. pair correlation function g(r), K‐function K(r), the proportion E(r) of points with no neighbor at distance r, the nearest neighbor distribution function D(r), the spherical contact distribution H_s(r), the kth nearest‐neighbor distribution functions D_k(r), the mean distance nn(k) to the kth neighbor, and the intensity function λ( x )]. To this end we used point pattern data covering a wide range of spatial structures including simulated (stationary) as well as real, possibly non‐stationary, patterns on tree species in a tropical forest in Panamá. To measure the information contained in a given combination of summary characteristics we used simulated annealing to reconstruct the observed patterns based only on the limited information provided by this combination and assessed how well other characteristics of the observed pattern were recovered. We found that the number of summary characteristics required to capture the spatial structure of stationary patterns varied between one (for patterns with near random structures) and three (for patterns with complex cluster and superposition structures), but with a robust ranking g(r), D_k(r), and H_s(r) that was largely independent on pattern idiosyncrasies. Stationary summary characteristics [with ranking g(r), D_k(r), H_s(r), E(r)] captured small‐ to intermediate scale properties of non‐stationary patterns, but for describing large‐scale spatial structures the intensity function was required. Our finding revealed that the current practice in ecology of using only one or two summary characteristics bears danger that essential characteristics of more complex patterns would not be detected. The technique of pattern reconstruction presented here has wide applications in ecology.     

Genetic heterogeneity and selection signature at the KIT gene in pigs showing different coat colours and patterns

Mutations in the porcine KIT gene (Dominant white locus) have been shown to affect coat colours and colour distribution in pigs. We analysed this gene in several pig breeds and populations (Sicilian black, completely black or with white patches; Cinta Senese; grey local population; Large White; Duroc; Hampshire; Pietrain; wild boar; Meishan) with different coat colours and patterns, genotyping a few polymorphisms. The 21 exons and parts of the intronic regions were sequenced in these pigs and 69 polymorphisms were identified. The grey-roan coat colour observed in a local grey population was completely associated with a 4-bp deletion of intron 18 in a single copy KIT gene, providing evidence that this mutation characterizes the I^d allele described in the early genetic literature. The white patches observed in black Sicilian pigs were not completely associated with the presence of a duplicated KIT allele (I^p), suggesting that genetic heterogeneity is a possible cause of different coat colours in this breed. Selection signature was evident at the KIT gene in two different belted pig breeds, Hampshire and Cinta Senese. The same mutation(s) may cause the belted phenotype in these breeds that originated in the 18th–19th centuries from English pigs (Hampshire) and in Tuscany (Italy) in the 14th century (Cinta Senese). Phylogenetic relationships of 28 inferred KIT haplotypes indicated two clades: one of Asian origin that included Meishan and a few Sicilian black haplotypes and another of European origin.     

Butterflies in the spotlight

Recent advances in our understanding of developmental phenomena has come from highly interdisciplinary studies where molecular biology, ecology and evolution converge to elucidate fundamental mechanisms, how they change through time, and what function they actually have in the context of the niche of the organism. A recent study on butterfly eyespots⁽¹⁾ pinpoints the surprisingly simple regulatory cascade controlling such an apparently complex phenotype. The implications go beyond the elucidation of a fascinating developmental pathway, into the mechanisms and tempo of speciation and macroevolution.     

Lepidopteran wing patterns and the evolution of satyric mimicry

The hypothesis of satyric mimicry postulates that the colour patterns of an animal may make its identity ambiguous, and this ambiguity interferes with the process of perception in vertebrate predators for a sufficient time to allow the potential prey to take evasive action. It has now been found that eyespots and other designs on the wings of many insect species are often coupled with other wing patterns and designs. These composite images often closely resemble heads and bodies of vertebrates (including birds and reptiles) and of various invertebrates. Such images can be perceived in living insects, although only rarely in set specimens because of displacement of the components. Visual processing by non‐mammalian vertebrates generally involves attention to detail, suggesting that, at least initially, and unlike humans, they perceive embedded images on insect wings and bodies and ignore the whole or Gestalt. They are therefore likely to be confused by the ambiguity of the potential prey. It can be calculated that a delay of the order of only tenths of a second in the attack on a stationary insect by a predator could result in failure of capture. It is proposed in the present review that the concept of satyric mimicry be extended to include complex imagery of other organisms. Such iconic images, which often represent toxic or dangerous animals, are particularly common amongst saturniid moths and nymphalid and danaid butterflies (including the Monarch butterfly, Danaus plexippus). © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 203–214.     

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability. The hybrids do not have meristic counts intermediate to the counts of the parental species. The hybrids usually have counts as high as the species with the higher count for those characters that differ between the parental species and often have higher counts for those characters that do not differ between the parental species. We suggest that the tendency for interspecific hybrids to have high meristic counts may be related to differences between the species in the length and timing of the developmental periods during which the counts of the characters are determined.     

Pursuit of Heterospecific Targets by Territorial Amberwing Dragonflies (Perithemis tenera Say): A Case of Mistaken Identity

Although they are defending mating territories, territory residents of a wide variety of insect species have been observed to pursue heterospecifics in addition to the conspecifics that intrude on their territories. One species that has such heterospecific pursuits is the Eastern amberwing dragonfly (Perithemis tenera Say) (Anisoptera: Libellulidae). In this study, we tested five alternative hypotheses for the function of heterospecific pursuits in amberwings: competition for resources, prevention of interference while mating, predator deterrence, foraging, and mistaken identity. Resident males pursued both male and female conspecifics, as well as a species of horse fly (Tabanus spp.) and butterfly (Ancyloxypha numitor). Other intruding odonates, including Epitheca princeps, Erythemis simplicicollis, Libellula luctuosa, Pachydiplax longipennis, and Plathemis lydia, were relatively ignored. Because the horse fly and butterfly were similar to amberwings in body size, color, and flight height, and because they are not predators or prey of amberwings, we concluded that the pursuit of these heterospecifics was due to mistaken identity. The characteristics of the horsefly and butterfly likely correspond to the cues that the male amberwings use to identify conspecifics, and the relative rarity of intrusions by these two species (as well as by female amberwings) probably made it more costly to discriminate and pursue only conspecifics than to make some mistaken pursuits.     

Seasonal butterfly design: morphological plasticity among three developmental pathways relative to sex,flight and thermoregulation

The temperate‐zone butterfly Pararge aegeria can use three developmental pathways corresponding to different seasonal cohorts: (1) development with a pupal winter diapause resulting in early spring adults; (2) development with a larval winter diapause resulting in late‐spring adults and (3) direct development resulting in summer or second generation adults. In order to test adaptive predictions, we compared variation in flight‐ and thermoregulation‐related morphology among adult males and females from the three pathways using both field data (i.e. wild‐caught butterflies) and experimental breeding data (i.e. reared under different photoperiod regimes). Morphological patterns among the pathways were largely similar in the field and rearing data. Seasonal patterns differed between the sexes for most traits, including (relative) size measures and wing colour. Our results suggest sex‐related, adaptive seasonal plasticity for morphological traits related to flight behaviour in a multivoltine insect.     

Rearing the pale grass blue Zizeeria maha (Lepidoptera,Lycaenidae): Toward the establishment of a lycaenid model system for butterfly physiology and genetics

Although some nymphalid butterflies have been intensively used to study mechanisms of the colour pattern formation on butterfly wings, lycaenid butterflies are equally attractive, having easily identifiable distinct spot patterns and highly diverse colour patterns among species. To establish a lycaenid model system for physiological and genetic experiments, we here describe a series of methods for rearing the Japanese pale grass blue Zizeeria maha (Kollar) (Lepidoptera, Lycaenidae) in a small laboratory space with an artificial diet for generations. Adult individuals readily mated and oviposited in a small cage with sufficient light, flowers, and host plants. Eggs were harvested in the cage, and larvae were successfully reared to normal adults with an artificial diet made from fresh leaves (AD‐F), although they were smaller than those reared with a natural diet. Feeding an artificial diet made from dried leaves (AD‐D) frequently produced adult individuals with aberrant wing colour patterns. Using our rearing methods, it is now possible to rear this species in a laboratory and to establish specific strains for physiological and genetic experiments on the wing colour pattern development, diversity, and evolution.     

Molecular and morphological divergence in the butterfly genus Lycaeides (Lepidoptera: Lycaenidae) in North America: evidence of recent speciation

Male genital morphology, allozyme allele frequencies and mtDNA sequence variation were surveyed in the butterfly species Lycaeides idas and L. melissa from across much of their range in North America. Despite clear differences in male genital morphology, wing colour patterns and habitat characteristics, genetic variation was not taxonomically or geographically structured and the species were not identifiable by either genetic data set. Genetic distances (Nei's D=0.002–0.078, calculated from allozyme data) between all populations of both species were within the range commonly observed for conspecific populations of other butterflies. The most frequent mtDNA haplotype was present in individuals of both species in populations from southern California to Wisconsin. We conclude that speciation has probably happened recently and the lack of genetic differentiation between the species is the product of either (1) recent or ongoing gene flow at neutral loci, and/or (2) an insufficiency of time for lineage sorting. The evolution of male genital morphology, wing colour patterns and ecological characteristics has proceeded more rapidly than allozyme or mtDNA evolution.