Mutants Highlight the Modular Control of Butterfly Eyespot Patterns

Evolution & Development. Mar-Apr, 2003  |  Pubmed ID: 12622735

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.

Ancient Wings: Animating the Evolution of Butterfly Wing Patterns

Bio Systems. Oct, 2003  |  Pubmed ID: 14563568

Character optimization methods can be used to reconstruct ancestral states at the internal nodes of phylogenetic trees. However, seldom are these ancestral states visualized collectively. Ancient Wings is a computer program that provides a novel method of visualizing the evolution of several morphological traits simultaneously. It allows users to visualize how the ventral hindwing pattern of 54 butterflies in the genus Bicyclus may have changed over time. By clicking on each of the nodes within the evolutionary tree, the user can see an animation of how wing size, eyespot size, and eyespot position relative the wing margin, have putatively evolved as a collective whole. Ancient Wings may be used as a pedagogical device as well as a research tool for hypothesis-generation in the fields of evolutionary, ecological, and developmental biology.

Germline Transformation of the Butterfly Bicyclus Anynana

Proceedings. Biological Sciences / The Royal Society. Aug, 2004  |  Pubmed ID: 15503989

Ecological and evolutionary theory has frequently been inspired by the diversity of colour patterns on the wings of butterflies. More recently, these varied patterns have also become model systems for studying the evolution of developmental mechanisms. A technique that will facilitate our understanding of butterfly colour-pattern development is germline transformation. Germline transformation permits functional tests of candidate gene products and of cis-regulatory regions, and provides a means of generating new colour-pattern mutants by insertional mutagenesis. We report the successful transformation of the African satyrid butterfly Bicyclus anynana with two different transposable element vectors, Hermes and piggyBac, each carrying EGFP coding sequences driven by the 3XP3 synthetic enhancer that drives gene expression in the eyes. Candidate lines identified by screening for EGFP in adult eyes were later confirmed by PCR amplification of a fragment of the EGFP coding sequence from genomic DNA. Flanking DNA surrounding the insertions was amplified by inverse PCR and sequenced. Transformation rates were 5% for piggyBac and 10.2% for Hermes. Ultimately, the new data generated by these techniques may permit an integrated understanding of the developmental genetics of colour-pattern formation and of the ecological and evolutionary processes in which these patterns play a role.

DaTrypsin, a Novel Clip-domain Serine Proteinase Gene Up-regulated During Winter and Summer Diapauses of the Onion Maggot, Delia Antiqua

Gene. Feb, 2005  |  Pubmed ID: 15715962

Diapause prepares insects and other arthropods to survive in harsh environments. To explore the molecular basis of winter (WD) and summer diapauses (SD), we screened for diapause-specific genes in the onion maggot, Delia antiqua, that diapauses as a pupa in both summer and winter. A diapause-induced transcript, DaTrypsin, was identified through differential display, and examined by Northern blot, quantitative real-time PCR and sequence analyses. The full-length cDNA, 1379 bp long, encodes 384 a.a. with a molecular mass of 43,005 Da. The protein contains a 20-a.a. secretion peptide, followed by an amino-terminal clip domain and a carboxyl-terminal serine proteinase domain. With Ser, His and Asp as catalytic residues and Asp, Gly and Ser as specificity determinants, DaTrypsin is anticipated to be a trypsin-like enzyme. DaTrypsin transcription is up-regulated in both SD and WD pupae with higher mRNA levels during WD than SD. Heat shock further elevated gene transcription in both SD and WD pupae, whereas cold shock reduced DaTrypsin expression in SD pupae and had no significant effect on WD pupae. In SD pupae, DaTrypsin transcripts gradually build up during diapause, and after temperature shocks, whereas in WD pupae DaTrypsin mRNA levels are high at the beginning of diapause and immediately after a temperature shock and then gradually decrease with time. DaTrypsin represents the first serine proteinase gene expressed during diapause as well as the first gene up-regulated in both SD and WD. It may participate in the host's immune defense and/or maintain the developmental status in the diapausing pupae.

Female Bicyclus Anynana Butterflies Choose Males on the Basis of Their Dorsal UV-reflective Eyespot Pupils

Proceedings. Biological Sciences / The Royal Society. Aug, 2005  |  Pubmed ID: 16048768

Sexual and natural selection pressures are thought to shape the characteristic wing patterns of butterfly species. Here we test whether sexual selection by female choice plays a role in the maintenance of the male wing pattern in the butterfly Bicyclus anynana. We perform one of the most extensive series of wing pattern manipulations in butterflies, dissecting every component of the 'bulls-eye' eyespot patterns in both ventral and dorsal wing surfaces of males to test the trait's appeal to females. We conclude that females select males on the basis of the size and brightness of the dorsal eyespot's ultraviolet reflecting pupils. Pupil absence is strongly selected against, as are artificially enlarged pupils. Small to intermediate (normal sized) pupils seem to function equally well. This work contradicts earlier experiments that suggest that the size of dorsal eyespots plays a role in female choice and explains why male dorsal eyespots are very variable in size and often have indistinct rings of coloration, as the only feature under selection by females seems to be the central white pupil. We propose that sexual selection by female choice, rather than predator avoidance, may have been an important selective factor in the early stages of eyespot evolution in ancestral Lepidopteran lineages.

Visualization of Early Embryos of the Butterfly Bicyclus Anynana

Zygote (Cambridge, England). May, 2005  |  Pubmed ID: 16128409

We report on the first attempts, using both light and fluorescence microscopy, to visualize the developing embryo of the butterfly Bicyclus anynana. We developed a new protocol that enabled the clear visualization of the internal egg structures in early embryogenesis (1-24 h after egg laying). Dechorionation was followed by fixation and physical dissection of the external egg structures. Observations of embryonic and extra-embryonic cells were made using a Hoechst nuclear stain that fluoresces in the blue spectrum when bound to DNA and excited with ultraviolet (UV) light under a fluorescence microscope. Preliminary data on the developmental rate of the early embryo are also presented.

The HSP90 Family of Genes in the Human Genome: Insights into Their Divergence and Evolution

Genomics. Dec, 2005  |  Pubmed ID: 16269234

HSP90 proteins are important molecular chaperones. Transcriptome and genome analyses revealed that the human HSP90 family includes 17 genes that fall into four classes. A standardized nomenclature for each of these genes is presented here. Classes HSP90AA, HSP90AB, HSP90B, and TRAP contain 7, 6, 3, and 1 genes, respectively. HSP90AA genes mapped onto chromosomes 1, 3, 4, and 11; HSP90AB genes mapped onto 3, 4, 6, 13 and 15; HSP90B genes mapped onto 1, 12, and 15; and the TRAP1 gene mapped onto 16. Six genes, HSP90AA1, HSP90AA2, HSP90N, HSP90AB1, HSP90B1 and TRAP1, were recognized as functional, and the remaining 11 genes were considered putative pseudogenes. Amino acid polymorphic variants were detected for genes HSP90AA1, HSP90AA2, HSP90AB1, HSP90B1, and TRAP1. The structures of these genes and the functional motifs and polymorphic variants of their proteins were documented and the features and functions of their proteins were discussed. Phylogenetic analyses based on both nucleotide and protein data demonstrated that HSP90(AA+AB+B) formed a monophyletic clade, whereas TRAP is a relatively distant paralogue of this clade.

Comparative Genomics and Evolution of the HSP90 Family of Genes Across All Kingdoms of Organisms

BMC Genomics. 2006  |  Pubmed ID: 16780600

HSP90 proteins are essential molecular chaperones involved in signal transduction, cell cycle control, stress management, and folding, degradation, and transport of proteins. HSP90 proteins have been found in a variety of organisms suggesting that they are ancient and conserved. In this study we investigate the nuclear genomes of 32 species across all kingdoms of organisms, and all sequences available in GenBank, and address the diversity, evolution, gene structure, conservation and nomenclature of the HSP90 family of genes across all organisms.

Comparative Insights into Questions of Lepidopteran Wing Pattern Homology

BMC Developmental Biology. 2006  |  Pubmed ID: 17090321

Butterfly and moth eyespots can share a similar appearance, involving multiple concentric rings of colored scales, but usually occurring in non-homologous positions on the wing. Within the butterflies, on the other hand, spots that share the same homologous position may not share the concentric ring structure; and, in butterfly species that have eyespots with concentric rings, ectopic eyespots with a similar ring structure can be induced by means of a simple epidermal wound. The extent to which all these eyespots, natural or induced, share similar genes and developmental mechanisms is investigated here by means of protein in-situ localizations in selected butterfly and moth species. In addition to looking at some of the transcription factors previously identified as being involved in eyespot formation, we also tested the involvement of candidate genes from the Wingless and TGF-beta signaling pathways as putative morphogens for eyespot development.

Temporal and Spatial Control of Transgene Expression Using Laser Induction of the Hsp70 Promoter

BMC Developmental Biology. 2006  |  Pubmed ID: 17116248

Precise temporal and spatial regulation of transgene expression is a critical tool to investigate gene function in developing organisms. The most commonly used technique to achieve tight control of transgene expression, however, requires the use of specific DNA enhancers that are difficult to characterize in non-model organisms. Here, we sought to eliminate the need for this type of sequence-based gene regulation and to open the field of functional genetics to a broader range of organisms.

Cloning and Characterization of the HSP70 Gene, and Its Expression in Response to Diapauses and Thermal Stress in the Onion Maggot, Delia Antiqua

Journal of Biochemistry and Molecular Biology. Nov, 2006  |  Pubmed ID: 17129412

The cytosolic members of the HSP70 family of proteins play key roles in the molecular chaperone machinery of the cell. In the study we cloned and sequenced the fulllength cDNA of Delia antiqua HSP70 gene, which is 2461 bp long and encodes 643 a.a. with a calculated molecular mass of 70,787 Da. We investigated gene copies of cytosolic HSP70 members of 4 insect species with complete genome available, and found that they are quite variable with species. In order to characterize this protein we carried out an alignment and a phylogenetic analysis with 41 complete protein sequences from insects. The analysis divided the cytosolic members of the family into two classes, HSP70 and HSC70, distinguishable on the basis of 15 residues. HSP70 class members were slightly shorter in length and smaller in molecular mass relative to the HSC70 class members, and the conservative and functional regions in these sequences were documented. Mainly, we investigated the expression of Delia antiqua HSP70 gene, in response to diapauses and thermal stresses. Both summer and winter diapauses elevated HSP70 transcript levels. Cold-stress led to increased HSP70 expression levels in summer- and winter-diapausing pupae, but heat-stress elevated the levels only in the winter-diapausing pupae. In all cases, the expression levels, after being elevated, gradually decreased with time. HSP70 expression was low in non-diapausing pupae but was up-regulated following cold- and heatstresses. Heat-stress gradually increased the mRNA level with time whereas cold-stress gradually decreased levels after an initial increase.

The Use of Chemical and Visual Cues in Female Choice in the Butterfly Bicyclus Anynana

Proceedings. Biological Sciences / The Royal Society. Mar, 2007  |  Pubmed ID: 17251116

Investigating the relative importance of multiple cues for mate choice within a species may highlight possible mechanisms that led to the diversification of closely related species in the past. Here, we investigate the importance of close-range pheromones produced by male Bicyclus anynana butterflies and determine the relative importance of these chemical cues versus visual cues in sexual selection by female choice. We first blocked putative androconial organs on the fore- and hindwings of males, while also manipulating the ability of females to perceive chemical signals via their antenna. We found that male chemical signals were emitted by both fore- and hindwing pairs and that they play an important role in female choice. We subsequently tested the relative importance of these chemical cues versus visual cues, previously identified for this species, and found that they play an equally important role in female choice in our laboratory setting. In addition, females will mate with males with only one signal present and blocking both androconial organs on males seems to interfere with male to male recognition. We discuss the possible functions of these signals and how this bimodal system may be used in intra- and interspecific mate evaluation.

The Combined Effect of Two Mutations That Alter Serially Homologous Color Pattern Elements on the Fore and Hindwings of a Butterfly

BMC Genetics. 2007  |  Pubmed ID: 17498305

The ability for serially homologous structures to acquire a separate identity has been primarily investigated for structures dependent on Hox gene input but is still incompletely understood in other systems. The fore and hindwings of butterflies are serially homologous structures as are the serially homologous eyespots that can decorate each of these wings. Eyespots can vary in number between fore and hindwings of the same individual and mutations of large effect can control the total number of eyespots that each of the wings displays. Here we investigate the genetics of a new spontaneous color pattern mutation, Missing, that alters eyespot number in the nymphalid butterfly, Bicyclus anynana. We further test the interaction of Missing with a previously described mutation, Spotty, describe the developmental stage affected by Missing, and test whether Missing is a mutant variant of the gene Distal-less via a linkage association study.

Transgenic Approaches to Study Wing Color Pattern Development in Lepidoptera

Molecular BioSystems. Aug, 2007  |  Pubmed ID: 17639127

The extremely diverse lepidopteran wing patterns make useful models to study the evolution of development and the molecular changes that enable it. Until now, the implication of candidate genes in the differentiation of color patterns has relied primarily on correlational evidence, i.e., gene expression patterns in a developing wing mapping closely to the adult color pattern. The use of transgenic techniques in the Lepidoptera, including the manipulation of gene expression, will finally allow researchers to test hypotheses of gene function at various levels of the patterning hierarchy, from signaling ligands and transcription factors to pigment enzymes. Here we present an overview of transgenic techniques employed in lepidopteran systems and highlight areas where current and future research will provide exciting opportunities to deepen our understanding of the mechanisms of morphological evolution.

In Vivo Electroporation of DNA into the Wing Epidermis of the Butterfly, Bicyclus Anynana

Journal of Insect Science (Online). 2007  |  Pubmed ID: 20337557

The direct transfer of genes into differentiated insect tissues is a useful method of determining gene function because it circumvents the need to perform germ line transformations and of having information on tissue-specific gene promoters. Here in vivo gene delivery is achieved through electroporation of a reporter gene into the pupal forewing of the butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae). Plasmids containing the coding sequence for enhanced green fluorescent protein (EGFP), driven by the Drosophila heat-shock promoter hsp70, were successfully expressed in epidermal cells after plasmid injection followed by electroporation and heat shock. EGFP expression was restricted to the vicinity of the injection and electroporation site, but the number of transformed cells varied from a few to over 5000 cells. Electroporation parameters were optimized in order to maximize the number of transformed cells while minimizing the extent of damage to the adult wing. While certain electrical parameters were well tolerated by the wing tissue, the physical damage caused by the insertion of the tungsten electrodes led to frequent disruptions of the adult wing pattern around the puncture sites. While this technique can be useful to test the correct expression of marker genes (such as EGFP) in newly build plasmids immediately following their injection, its potential use in testing the function of candidate genes in wing pattern formation is limited.

Alternative Models for the Evolution of Eyespots and of Serial Homology on Lepidopteran Wings

BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology. Apr, 2008  |  Pubmed ID: 18348192

Serial homology is widespread in organismal design, but the origin and individuation of these repeated structures appears to differ with the different types of serial homologues, and remains an intriguing and exciting topic of research. Here I focus on the evolution of the serially repeated eyespots that decorate the margin of the wings of nymphalid butterflies. In this system, unresolved questions relate to the evolutionary steps that lead to the appearance of these serial homologues and how their separate identities evolved. I present and discuss two alternative hypotheses. The first proposes that eyespots first appeared as a row of undifferentiated repeated modules, one per wing compartment, that later become individuated. This individuation allowed eyespots to appear and disappear from specific wing compartments and also allowed eyespots to acquire different morphologies. The second hypothesis proposes that eyespots first appeared as individuated single units, or groups of units, that over evolutionary time were co-opted into new compartments on the wing. I discuss the merits of each of these alternate hypotheses by finding analogies to other systems and propose research avenues for addressing these issues in the future.

Are We There Yet? Tracking the Development of New Model Systems

Trends in Genetics : TIG. Jul, 2008  |  Pubmed ID: 18514356

It is increasingly clear that additional 'model' systems are needed to elucidate the genetic and developmental basis of organismal diversity. Whereas model system development previously required enormous investment, recent advances including the decreasing cost of DNA sequencing and the power of reverse genetics to study gene function are greatly facilitating the process. In this review, we consider two aspects of the development of new genetic model systems: first, the types of questions being advanced using these new models; and second, the essential characteristics and molecular tools for new models, depending on the research focus. We hope that researchers will be inspired to explore this array of emerging models and even consider developing new molecular tools for their own favorite organism.

Automatic Recognition and Measurement of Butterfly Eyespot Patterns

Bio Systems. Feb, 2009  |  Pubmed ID: 18955106

A favorite wing pattern element in butterflies that has been the focus of intense study in evolutionary and developmental biology, as well as in behavioral ecology, is the eyespot. Because the pace of research on these bull's eye patterns is accelerating we sought to develop a tool to automatically detect and measure butterfly eyespot patterns in digital images of the wings. We used a machine learning algorithm with features based on circularity and symmetry to detect eyespots on the images. The algorithm is first trained with examples from a database of images with two different labels (eyespot and non-eyespot), and subsequently is able to provide classification for a new image. After an eyespot is detected the radius measurements of its color rings are performed by a 1D Hough Transform which corresponds to histogramming. We trained software to recognize eyespot patterns of the nymphalid butterfly Bicyclus anynana but eyespots of other butterfly species were also successfully detected by the software.

Wings, Horns, and Butterfly Eyespots: How Do Complex Traits Evolve?

PLoS Biology. Feb, 2009  |  Pubmed ID: 19243218

Accommodating Natural and Sexual Selection in Butterfly Wing Pattern Evolution

Proceedings. Biological Sciences / The Royal Society. Jul, 2009  |  Pubmed ID: 19364741

Visual patterns in animals may serve different functions, such as attracting mates and deceiving predators. If a signal is used for multiple functions, the opportunity arises for conflict among the different functions, preventing optimization for any one visual signal. Here we investigate the hypothesis that spatial separation of different visual signal functions has occurred in Bicyclus butterflies. Using phylogenetic reconstructions of character evolution and comparisons of evolutionary rates, we found dorsal surface characters to evolve at higher rates than ventral characters. Dorsal characters also displayed sex-based differences in evolutionary rates more often than did ventral characters. Thus, dorsal characters corresponded to our predictions of mate signalling while ventral characters appear to play an important role in predator avoidance. Forewing characters also fit a model of mate signalling, and displayed higher rates of evolution than hindwing characters. Our results, as well as the behavioural and developmental data from previous studies of Bicyclus species, support the hypothesis that spatial separation of visual signal functions has occurred in Bicyclus butterflies. This study is the first to demonstrate, in a phylogenetic framework, that spatial separation of signals used for mate signalling and those used for predator avoidance is a viable strategy to accommodate multiple signal functions. This signalling strategy has important ramifications on the developmental evolution of wing pattern elements and diversification of butterfly species.

The Genetic, Morphological, and Physiological Characterization of a Dark Larval Cuticle Mutation in the Butterfly, Bicyclus Anynana

PloS One. 2010  |  Pubmed ID: 20644735

Studies on insect melanism have greatly contributed to our understanding of natural selection and the ultimate factors influencing the evolution of darkly pigmented phenotypes. Research on several species of melanic lepidopteran larvae have found that low levels of circulating juvenile hormone (JH) titers are associated with a melanic phenotype, suggesting that genetic changes in the JH biosynthetic pathway give rise to increased deposition of melanin granules in the cuticle in this group. But does melanism arise through different molecular mechanisms in different species? The present study reports on a Bicyclus anynana (Lepidoptera: Nymphalidae) dark larvae single locus mutation, in which larvae exhibit a darker cuticle relative to wild type. Unlike other lepidopteran melanic larvae mutations, this one is autosomal recessive and does not appear to involve a deficiency in JH titers. Unlike JH deficiency mutants, dark larvae mutants display similar growth rates and sexual behaviors as wild type, and topical application of a JH analogue failed to rescue the wild type cuticular coloration. Finally, transmission electron microscopy showed that sclerotization or deposition of diffuse melanin, rather than deposition of melanin granules, produces the dark coloration found in the cuticle of this species. We conclude that different molecular mechanisms underlie larval melanism in different species of Lepidoptera.

RNA Interference in Lepidoptera: an Overview of Successful and Unsuccessful Studies and Implications for Experimental Design

Journal of Insect Physiology. Feb, 2011  |  Pubmed ID: 21078327

Gene silencing through RNA interference (RNAi) has revolutionized the study of gene function, particularly in non-model insects. However, in Lepidoptera (moths and butterflies) RNAi has many times proven to be difficult to achieve. Most of the negative results have been anecdotal and the positive experiments have not been collected in such a way that they are possible to analyze. In this review, we have collected detailed data from more than 150 experiments including all to date published and many unpublished experiments. Despite a large variation in the data, trends that are found are that RNAi is particularly successful in the family Saturniidae and in genes involved in immunity. On the contrary, gene expression in epidermal tissues seems to be most difficult to silence. In addition, gene silencing by feeding dsRNA requires high concentrations for success. Possible causes for the variability of success in RNAi experiments in Lepidoptera are discussed. The review also points to a need to further investigate the mechanism of RNAi in lepidopteran insects and its possible connection to the innate immune response. Our general understanding of RNAi in Lepidoptera will be further aided in the future as our public database at http://insectacentral.org/RNAi will continue to gather information on RNAi experiments.

On the Origins of Sexual Dimorphism in Butterflies

Proceedings. Biological Sciences / The Royal Society. Jul, 2011  |  Pubmed ID: 21123259

The processes governing the evolution of sexual dimorphism provided a foundation for sexual selection theory. Two alternative processes, originally proposed by Darwin and Wallace, differ primarily in the timing of events creating the dimorphism. In the process advocated by Darwin, a novel ornament arises in a single sex, with no temporal separation in the origin and sex-limitation of the novel trait. By contrast, Wallace proposed a process where novel ornaments appear simultaneously in both sexes, but are then converted into sex-limited expression by natural selection acting against showy coloration in one sex. Here, we investigate these alternative modes of sexual dimorphism evolution in a phylogenetic framework and demonstrate that both processes contribute to dimorphic wing patterns in the butterfly genera Bicyclus and Junonia. In some lineages, eyespots and bands arise in a single sex, whereas in other lineages they appear in both sexes but are then lost in one of the sexes. In addition, lineages displaying sexual dimorphism were more likely to become sexually monomorphic than they were to remain dimorphic. This derived monomorphism was either owing to a loss of the ornament ('drab monomorphism') or owing to a gain of the same ornament by the opposite sex ('mutual ornamentation'). Our results demonstrate the necessity of a plurality in theories explaining the evolution of sexual dimorphism within and across taxa. The origins and evolutionary fate of sexual dimorphism are probably influenced by underlying genetic architecture responsible for sex-limited expression and the degree of intralocus sexual conflict. Future comparative and developmental work on sexual dimorphism within and among taxa will provide a better understanding of the biases and constraints governing the evolution of animal sexual dimorphism.

Developmental Plasticity in Sexual Roles of Butterfly Species Drives Mutual Sexual Ornamentation

Science (New York, N.Y.). Jan, 2011  |  Pubmed ID: 21212355

Current explanations for why sexual ornaments are found in both sexes include genetic correlation, same sex competition, and mutual mate choice. In this study, we report developmental plasticity in mating behavior as induced by temperature during development in the butterfly Bicyclus anynana. Males and females reciprocally change their sexual roles depending on their larval rearing temperatures. This switch is correlated with a change in mating benefits to females and costs to males. The discrete seasonal environments, wet season and dry season, are known to produce the two developmental forms and as a consequence impose alternating, symmetrical patterns of sexual selection, one season on male ornaments, the following season on female ornaments. Thus, reciprocal selection through time may result in mutual sexual ornamentation.

Pogostick: a New Versatile PiggyBac Vector for Inducible Gene Over-expression and Down-regulation in Emerging Model Systems

PloS One. 2011  |  Pubmed ID: 21533190

Non-traditional model systems need new tools that will enable them to enter the field of functional genetics. These tools should enable the exploration of gene function, via knock-downs of endogenous genes, as well as over-expression and ectopic expression of transgenes.

Evolutionary Reduction of the First Thoracic Limb in Butterflies

Journal of Insect Science (Online). 2011  |  Pubmed ID: 21867433

Members of the diverse butterfly families Nymphalidae (brush-footed butterflies) and Riodinidae (metalmarks) have reduced first thoracic limbs and only use two pairs of legs for walking. In order to address questions about the detailed morphology and evolutionary origins of these reduced limbs, the three thoracic limbs of 13 species of butterflies representing all six butterfly families were examined and measured, and ancestral limb sizes were reconstructed for males and females separately. Differences in limb size across butterflies involve changes in limb segment size rather than number of limb segments. Reduction of the first limb in both nymphalids and riodinids appears particularly extensive in the femur, but the evolution of these reduced limbs is suggested to be a convergent evolutionary event. Possible developmental differences as well as ecological factors driving the evolution of reduced limbs are discussed.

Gene Regulatory Networks Reused to Build Novel Traits: Co-option of an Eye-related Gene Regulatory Network in Eye-like Organs and Red Wing Patches on Insect Wings is Suggested by Optix Expression

BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology. Mar, 2012  |  Pubmed ID: 22223407

Co-option of the eye developmental gene regulatory network may have led to the appearance of novel functional traits on the wings of flies and butterflies. The first trait is a recently described wing organ in a species of extinct midge resembling the outer layers of the midge's own compound eye. The second trait is red pigment patches on Heliconius butterfly wings connected to the expression of an eye selector gene, optix. These examples, as well as others, are discussed regarding the type of empirical evidence and burden of proof that have been used to infer gene network co-option underlying the origin of novel traits. A conceptual framework describing increasing confidence in inference of network co-option is proposed. Novel research directions to facilitate inference of network co-option are also highlighted, especially in cases where the pre-existent and novel traits do not resemble each other.