Genetic variation for the positioning of wing veins in Drosophila melanogaster

The Extraordinary Diversity of Merodon avidus Complex (Diptera: Syrphidae)-Adding New Areas, New Species and a New Molecular Marker

In this paper, the Merodon avidus (Diptera, Syrphidae) species complex was revised, whereupon we discovered and described four new species for science: Merodon atroavidus Vujić, Radenković et Likov sp. nov., M. magnus Vujić, Kočiš Tubić et Ačanski sp. nov., M. nigroscutum Vujić, Radenković et Likov sp. nov. and M. pseudomoenium Vujić, Kočiš Tubić et Ačanski sp. nov. An integrative taxonomy approach was used to delimit species boundaries. Two molecular markers (the mitochondrial COI gene and nuclear 28S rRNA gene-newly analysed marker for the complex) and geometric morphometry of the wing shape, together with morphological data and distribution, successfully separated all species from the complex. The morphological variability of the analysed species is described and discussed and an illustrated diagnostic key for typical morpho-forms of species from the M. avidus complex is presented. A distribution map of all investigated species from the complex is provided. The level of endemicity of the M. avidus complex was discussed.

Signs of Urban Evolution? Morpho-Functional Traits Co-variation Along a Nature-Urban Gradient in a Chagas Disease Vector

Environmental change (i.e., urbanization) impacts species in contrasting ways, with some species experiencing benefits given their way of life (i.e., blood-sucking insects). How these species respond to such change is not well understood and for species involved in human diseases, this “how” question is particularly important. Most Triatominae bug species inhabit tropical and subtropical forests where their vertebrate hosts’ temporal abundance depends on climate seasonality. However, in human encroached landscapes, triatomines can benefit from resource stability which may lead to adaptive phenotypic change to track novel hosts. We tested for an association between different landscapes and morpho-functional traits linked to sensory, motion, and feeding functions in Triatoma dimidiata and compared fecundity (i.e., number of eggs) in each landscape as a proxy of fitness. Using geometric and traditional morphometric tools, we predicted a morphological simplification in bugs inhabiting urbanized areas. While wing morphology or proboscis were not influenced by landscape class, the opposite occurred for thorax morphology and number of sensilla. Wing and thorax morphology did not covary under modified landscape scenarios, yet we detected a morpho-functional convergence for thorax size and antennal phenotype in both sexes, with a simplification trend, from nature to urban settings. Given no fecundity differences across landscapes, there is no potential reproductive costs. Moreover, the convergence of thorax size and antennal phenotype suggests differences in flight/locomotion performance and host/environment perception, as a possible adaptive response to relaxed selective pressures of the bug’s native habitat. These results imply that T. dimidiata could be adapting to urbanized areas.

Wing morphometrics for identification of forensically important blowflies (Diptera: Calliphoridae) in Iberian Peninsula

Calliphoridae is a family of Diptera of great forensic interest because some of its species belong to the sarcosaprophagous diptera community, as their larvae are necrophagous or necrophilous. In the Iberian Peninsula there are six species that stand out, as they are the first insects to arrive at carrion: Calliphora vicina, Calliphora vomitoria, Lucilia sericata, Lucilia caesar, Chrysomya albiceps and Chrysomya megacephala. To differentiate among these blowflies, we compared the value of using traditional and geometric morphometrics by performing a morphometric analysis of the wings (shape and size). A total of 600 individuals were considered, segregated by species and sex equally. Seventeen landmarks per wing were recognized, and then centroid size and shape analyses were performed using geometric morphometrics, and size using traditional morphometrics, to identify species and sex. The results showed differences in shape among the species and it was found that landmarks 2 to 11 were the most variable, while the landmarks located at the base of the wings were relatively stable. However, according to both traditional and geometric morphometrics, no significant differences were found among species in wing size (Calliphora vicina, Chrysomya megacephala and Lucilia caesar were indistinguishable), but females were larger than males (except for the two Chrysomya species). Our results indicate that the use of geometric morphometrics to analyze wing configuration (shape) is an easy-to-use tool that helps to distinguish among common blowfly species of forensic importance.

Directional selection reduces developmental canalization against genetic and environmental perturbations in Drosophila wings

Natural selection may enhance or weaken the robustness of phenotypes against genetic or environmental perturbations. However, important aspects of the relationship between adaptive evolution and canalization remain unclear. Recent work showed that the evolution of larger wing size in a high altitude natural population of Drosophila melanogaster was accompanied by decanalized wing development--specifically a loss of robustness to genetic perturbation. But this study did not address environmental robustness, and it compared populations that may have numerous biological differences. Here, we perform artificial selection on this same trait in D. melanogaster (larger wing length) and directly test whether this directional selection resulted in decanalization. We find that in general, size-selected replicates show greater frequencies of wing defects than control replicates both after mutagenesis (genetic perturbation) and when subjected to high temperature stress (environmental perturbation), although the increase in defect frequency varies importantly among replicates. These results support the hypothesis that directional selection may result in the loss of both genetic and environmental robustness-offering a rare window into the relationship between adaptation and canalization.

Developmental stability, age at onset of foraging and longevity of Africanized honey bees (Apis mellifera L.) under heat stress (Hymenoptera: Apidae)

Beekeeping with the western honey bee (Apis mellifera) is important in tropical regions but scant information is available on the possible consequences of global warming for tropical beekeeping. We evaluated the effect of heat stress on developmental stability, the age at onset of foraging (AOF) and longevity in Africanized honey bees (AHBs) in the Yucatan Peninsula of Mexico, one of the main honey producing areas in the Neotropics, where high temperatures occur in spring and summer. To do so, we reared worker AHB pupae under a fluctuating temperature regime, simulating current tropical heatwaves, with a high temperature peak of 40.0 °C for 1 h daily across six days, and compared them to control pupae reared at stable temperatures of 34.0-35.5 °C. Heat stress did not markedly affect overall body size, though the forewing of heat-stressed bees was slightly shorter than controls. However, bees reared under heat stress showed significantly greater fluctuating asymmetry (FA) in forewing shape. Heat stress also decreased AOF and reduced longevity. Our results show that changes occur in the phenotype and behavior of honey bees under heat stress, with potential consequences for colony fitness.

The role of wing geometric morphometrics in the identification of sandflies within the subgenus Lutzomyia

The Lutzomyia subgenus (Diptera: Psychodidae) includes sibling species with morphologically indistinguishable females. The aims of this study were to analyse variations in the size and shape of wings of species within the Lutzomyia subgenus and to assess whether these analyses might be useful in their identification. Wings (n = 733) of 18 species deposited in Brazilian collections were analysed by geometric morphometrics, using other genera and subgenera as outgroups. Shape variation was summarized in multivariate analyses and differences in wing size among species were tested by analysis of variance. The results showed significant variation in the sizes and shapes of wings of different Lutzomyia species. Two clusters within the Lutzomyia subgenus were distinguished in analyses of both males and females. In Cluster 1 (Lutzomyia ischnacantha, Lutzomyia cavernicola, Lutzomyia almerioi, Lutzomyia forattinii, Lutzomyia renei and Lutzomyia battistinii), scores for correct reclassification were high (females, kappa = 0.91; males, kappa = 0.90), whereas in Cluster 2 (Lutzomyia alencari, Lutzomyia ischyracantha, Lutzomyia cruzi, Lutzomyia longipalpis, Lutzomyia gaminarai and Lutzomyia lichyi), scores for correct reclassification were low (females, kappa = 0.42; males, kappa = 0.48). Wing geometry was useful in the identification of some species of the Lutzomyia subgenus, but did not allow the identification of sibling species such as L. longipalpis and L. cruzi.

Discrimination of Neotropical Anopheles species based on molecular and wing geometric morphometric traits

Morphological similarities among closely related Anopheles species that differ in biological traits and malaria transmission represent a challenge in medical entomology; therefore, new tools are constantly tested to bring solutions. Particularly, in this work, a geometric morphometric analysis of wing geometry variation, based on morphologically and molecularly identified specimens, was applied for the discrimination of fourteen Anopheles species belonging to the Nyssorhynchus, Anopheles and Kerteszia subgenera. DNA barcodes helped to confirm species assignation and the geometric morphometric approach revealed wing form differences not only at the subgenera but also at the species level. Each subgenus presented a particular wing size trend, possibly related to the evolutionary history of these lineages. Wing shape allowed species discrimination, except for some very closely related taxa. The current findings highlight the importance of using complementary approaches involving morphological and molecular data for Anopheles species discrimination.

Network architecture associated with the highly specialized hindlimb of frogs

Network analyses have been increasingly used in the context of comparative vertebrate morphology. The structural units of the vertebrate body are treated as discrete elements (nodes) of a network, whose interactions at their physical contacts (links) determine the phenotypic modules. Here, we use the network approach to study the organization of the locomotor system underlying the hindlimb of frogs. Nodes correspond to fibrous knots, skeletal and muscular units. Edges encode the ligamentous and monoaxial tendinous connections in addition to joints. Our main hypotheses are that: (1) the higher centrality scores (measured as betweenness) are recorded for fibrous elements belonging to the connective system, (2) the organization of the musculoskeletal network belongs to a non-trivial modular architecture and (3) the modules in the hindlimb reflect functional and/or developmental constraints. We confirm all our hypotheses except for the first one, since bones overpass the fibrous knots in terms of centrality. Functionally, there is a correlation between the proximal-to-distal succession of modules and the progressive recruitment of elements involved with the motion of joints during jumping. From a developmental perspective, there is a correspondence between the order of the betweenness scores and the ontogenetic chronology of hindlimbs in tetrapods. Modular architecture seems to be a successful organization, providing of the building blocks on which evolution forges the many different functional specializations that organisms exploit.

Little effect of HSP90 inhibition on the quantitative wing traits variation in Drosophila melanogaster

Drosophila wings have been a model system to study the effect of HSP90 on quantitative trait variation. The effect of HSP90 inhibition on environmental buffering of wing morphology varies among studies while the genetic buffering effect of it was examined in only one study and was not detected. Variable results so far might show that the genetic background influences the environmental and genetic buffering effect of HSP90. In the previous studies, the number of the genetic backgrounds used is limited. To examine the effect of HSP90 inhibition with a larger number of genetic backgrounds than the previous studies, 20 wild-type strains of Drosophila melanogaster were used in this study. Here I investigated the effect of HSP90 inhibition on the environmental buffering of wing shape and size by assessing within-individual and among-individual variations, and as a result, I found little or very weak effects on environmental and genetic buffering. The current results suggest that the role of HSP90 as a global regulator of environmental and genetic buffering is limited at least in quantitative traits.

An image database of Drosophila melanogaster wings for phenomic and biometric analysis

BACKGROUND

Extracting important descriptors and features from images of biological specimens is an ongoing challenge. Features are often defined using landmarks and semi-landmarks that are determined a priori based on criteria such as homology or some other measure of biological significance. An alternative, widely used strategy uses computational pattern recognition, in which features are acquired from the image de novo. Subsets of these features are then selected based on objective criteria. Computational pattern recognition has been extensively developed primarily for the classification of samples into groups, whereas landmark methods have been broadly applied to biological inference.

RESULTS

To compare these approaches and to provide a general community resource, we have constructed an image database of Drosophila melanogaster wings - individually identifiable and organized by sex, genotype and replicate imaging system - for the development and testing of measurement and classification tools for biological images. We have used this database to evaluate the relative performance of current classification strategies. Several supervised parametric and nonparametric machine learning algorithms were used on principal components extracted from geometric morphometric shape data (landmarks and semi-landmarks). For comparison, we also classified phenotypes based on de novo features extracted from wing images using several computer vision and pattern recognition methods as implemented in the Bioimage Classification and Annotation Tool (BioCAT).

CONCLUSIONS

Because we were able to thoroughly evaluate these strategies using the publicly available Drosophila wing database, we believe that this resource will facilitate the development and testing of new tools for the measurement and classification of complex biological phenotypes.

Geometric morphometric analysis of Colombian Anopheles albimanus (Diptera: Culicidae) reveals significant effect of environmental factors on wing traits and presence of a metapopulation

Anopheles albimanus is a major malaria mosquito vector in Colombia. In the present study, wing variability (size and shape) in An. albimanus populations from Colombian Maracaibo and Chocó bio-geographical eco-regions and the relationship of these phenotypic traits with environmental factors were evaluated. Microsatellite and morphometric data facilitated a comparison of the genetic and phenetic structure of this species. Wing size was influenced by elevation and relative humidity, whereas wing shape was affected by these two variables and also by rainfall, latitude, temperature and eco-region. Significant differences in mean shape between populations and eco-regions were detected, but they were smaller than those at the intra-population level. Correct assignment based on wing shape was low at the population level (<58%) and only slightly higher (>70%) at the eco-regional level, supporting the low population structure inferred from microsatellite data. Wing size was similar among populations with no significant differences between eco-regions. Population relationships in the genetic tree did not agree with those from the morphometric data; however, both datasets consistently reinforced a panmictic population of An. albimanus. Overall, site-specific population differentiation is not strongly supported by wing traits or genotypic data. We hypothesize that the metapopulation structure of An. albimanus throughout these Colombian eco-regions is favoring plasticity in wing traits, a relevant characteristic of species living under variable environmental conditions and colonizing new habitats.

The Drosophila insulin-degrading enzyme restricts growth by modulating the PI3K pathway in a cell-autonomous manner

The Drosophila insulin-degrading enzyme (dIDE) is a negative modulator of the PI3K pathway that restrains tissue growth in an autonomous manner. Larvae reared in high sucrose exhibit reduced growth and delayed developmental timing due to insulin resistance; dIDE loss of function exacerbates these phenotypes.

Mammalian insulin-degrading enzyme (IDE) cleaves insulin, among other peptidic substrates, but its function in insulin signaling is elusive. We use the Drosophila system to define the function of IDE in the regulation of growth and metabolism. We find that either loss or gain of function of Drosophila IDE (dIDE) can restrict growth in a cell-autonomous manner by affecting both cell size and cell number. dIDE can modulate Drosophila insulin-like peptide 2 levels, thereby restricting activation of the phosphatidylinositol-3-phosphate kinase pathway and promoting activation of Drosophila forkhead box, subgroup O transcription factor. Larvae reared in high sucrose exhibit delayed developmental timing due to insulin resistance. We find that dIDE loss of function exacerbates this phenotype and that mutants display increased levels of circulating sugar, along with augmented expression of a lipid biosynthesis marker. We propose that dIDE is a modulator of insulin signaling and that its loss of function favors insulin resistance, a hallmark of diabetes mellitus type II.

Wing geometry as a tool for discrimination of Obsoletus group (Diptera: Ceratopogonidae: Culicoides) in France

In Europe, Culicoides chiopterus, Culicoides dewulfi, Culicoides obsoletus and Culicoides scoticus, which belongs to the subgenus Avaritia and Obsoletus group are the most proficient Bluetongue and Schmallenberg vectors. Within this group, correct identification based on morphological traits is difficult but essential to assess disease transmission risk. The development of new tools has revolutionized taxonomy (i.e. geometric morphometrics and molecular biology). Wing morphology is of primary importance to entomologists interested in systematics. Here, we report phenotypic differentiation patterns among the species above mentioned using a landmark-based geometric morphometric approach that efficiently identified C. chiopterus and C. dewulfi. Wing shape of the C. scoticus sample exhibited large specific variability. Based on landmarks and phylogenetic analyses (Maximum Parsimony), we suggest that Obsoletus group in Europe includes only C. obsoletus and C. scoticus. C. dewulfi and C. chiopterus are clearly excluded. Their shape seems closer to C. obsoletus that is why we suggest that only these two species should be grouped in the Obsoletus group. In addition, the concordance between phenetic clusters and phylogenies inferred from molecular data based on a fragment of the mtDNA COI gene and rDNA 28S suggests the existence of a strong signal in wing shape. These findings encourage us to use this powerful tool in taxonomic studies.

Gene-by-temperature interactions and candidate plasticity genes for morphological traits in Drosophila melanogaster

Understanding the genetic architecture of any quantitative trait requires identifying the genes involved in its expression in different environmental conditions. This goal can be achieved by mutagenesis screens in genetically tractable model organisms such as Drosophila melanogaster. Temperature during ontogenesis is an important environmental factor affecting development and phenotypic variation in holometabolous insects. In spite of the importance of phenotypic plasticity and genotype by environment interaction (GEI) for fitness related traits, its genetic basis has remained elusive. In this context, we analyzed five different adult morphological traits (face width, head width, thorax length, wing size and wing shape) in 42 co-isogenic single P-element insertional lines of Drosophila melanogaster raised at 17°C and 25°C. Our analyses showed that all lines differed from the control for at least one trait in males or females at either temperature. However, no line showed those differences for all traits in both sexes and temperatures simultaneously. In this sense, the most pleiotropic candidate genes were CG34460, Lsd-2 and Spn. Our analyses also revealed extensive genetic variation for all the characters mostly indicated by strong GEIs. Further, our results indicate that GEIs were predominantly explained by changes in ranking order in all cases suggesting that a moderate number of genes are involved in the expression of each character at both temperatures. Most lines displayed a plastic response for at least one trait in either sex. In this regard, P-element insertions affecting plasticity of a large number of traits were associated to the candidate genes Btk29A, CG43340, Drak and jim. Further studies will help to elucidate the relevance of these genes on the morphogenesis of different body structures in natural populations of D. melanogaster.

Identification of novel loci regulating interspecific variation in root morphology and cellular development in tomato

While the Arabidopsis (Arabidopsis thaliana) root has been elegantly characterized with respect to specification of cell identity, its development is missing a number of cellular features present in other species. We have characterized the root development of a wild and a domesticated tomato species, Solanum pennellii and Solanum lycopersicum 'M82.' We found extensive differences between these species for root morphology and cellular development including root length, a novel gravity set point angle, differences in cortical cell layer patterning, stem cell niche structure, and radial cell division. Using an introgression line population between these two species, we identified numerous loci that regulate these distinct aspects of development. Specifically we comprehensively identified loci that regulate (1) root length by distinct mechanisms including regulation of cell production within the meristem and the balance between cell division and expansion, (2) the gravity set point angle, and (3) radial cell division or expansion either in specific cell types or generally across multiple cell types. Our findings provide a novel perspective on the regulation of root growth and development between species. These loci have exciting implications with respect to regulation of drought resistance or salinity tolerance and regulation of root development in a family that has undergone domestication.

Wing geometric morphometrics and molecular assessment of members in the Albitarsis Complex from Colombia

Malaria parasites are transmitted to humans by female mosquitoes of the genus Anopheles. The Albitarsis Complex harbours at least eight species not readily differentiable by morphology. This complicates the determination of those species involved in malaria transmission and the implementation of targeted and effective vector control strategies. In Colombia, there is little information about the identity and distribution of the Albitarsis Complex members. In this work, COI DNA barcoding was used to assign specimens Anopheles albitarsis s.l. to any of the previously designated species of the Albitarsis Complex. Two molecular operational taxonomic units (MOTUs), differentially distributed in Colombia, were detected, A. albitarsis I in the NW and NE, and A. albitarsis F, E and NE Colombia. In contrast, nuclear white gene and ITS2 sequence analyses did not allow differentiating between the MOTUs. Wing landmark-based geometric morphometrics applied to explore intertaxa phenotypic heterogeneity showed a subtle but significant difference in size, while shape did not allow the separation of the MOTUs. In general, the multiple marker analysis was not supportive of the existence in Colombia of more than one species of the Albitarsis Complex.

Wing shape as a potential discriminator of morphologically similar pest taxa within the Bactrocera dorsalis species complex (Diptera: Tephritidae)

Four morphologically cryptic species of the Bactrocera dorsalis fruit fly complex (B. dorsalis s.s., B. papayae, B. carambolae and B. philippinensis) are serious agricultural pests. As they are difficult to diagnose using traditional taxonomic techniques, we examined the potential for geometric morphometric analysis of wing size and shape to discriminate between them. Fifteen wing landmarks generated size and shape data for 245 specimens for subsequent comparisons among three geographically distinct samples of each species. Intraspecific wing size was significantly different within samples of B. carambolae and B. dorsalis s.s. but not within samples of B. papayae or B. philippinensis. Although B. papayae had the smallest wings (average centroid size=6.002 mm±0.061 SE) and B. dorsalis s.s. the largest (6.349 mm±0.066 SE), interspecific wing size comparisons were generally non-informative and incapable of discriminating species. Contrary to the wing size data, canonical variate analysis based on wing shape data discriminated all species with a relatively high degree of accuracy; individuals were correctly reassigned to their respective species on average 93.27% of the time. A single sample group of B. carambolae from locality 'TN Malaysia' was the only sample to be considerably different from its conspecific groups with regards to both wing size and wing shape. This sample was subsequently deemed to have been originally misidentified and likely represents an undescribed species. We demonstrate that geometric morphometric techniques analysing wing shape represent a promising approach for discriminating between morphologically cryptic taxa of the B. dorsalis species complex.

Dpp signaling activity requires Pentagone to scale with tissue size in the growing Drosophila wing imaginal disc

The activity of the Dpp morphogen adapts to tissue size in the growing Drosophila wing imaginal disc, and Pentagone, an important secreted feedback regulator of the Dpp pathway, is required for this adaptation.

The wing of the fruit fly, Drosophila melanogaster, with its simple, two-dimensional structure, is a model organ well suited for a systems biology approach. The wing arises from an epithelial sac referred to as the wing imaginal disc, which undergoes a phase of massive growth and concomitant patterning during larval stages. The Decapentaplegic (Dpp) morphogen plays a central role in wing formation with its ability to co-coordinately regulate patterning and growth. Here, we asked whether the Dpp signaling activity scales, i.e. expands proportionally, with the growing wing imaginal disc. Using new methods for spatial and temporal quantification of Dpp activity and its scaling properties, we found that the Dpp response scales with the size of the growing tissue. Notably, scaling is not perfect at all positions in the field and the scaling of target gene domains is ensured specifically where they define vein positions. We also found that the target gene domains are not defined at constant concentration thresholds of the downstream Dpp activity gradients P-Mad and Brinker. Most interestingly, Pentagone, an important secreted feedback regulator of the pathway, plays a central role in scaling and acts as an expander of the Dpp gradient during disc growth.

Scaling, the fitting of pattern to size, manifests itself in numerous examples around us. During development, individual body parts scale up to fit the overall body size. Starved animals form smaller adults with proportionally smaller parts, and amphibian embryos can form normally proportioned adults after extreme surgical operations. How scaling is achieved is not well understood. Here, we establish the Drosophila wing imaginal disc, the precursor tissue of the adult wing, as a model to study scaling quantitatively during growth. In this model, we define scaling as the preservation of proportions of gene expression domains with tissue size during disc growth. The Decapentaplegic (Dpp) morphogen is known to play a central role in Drosophila wing formation and co-coordinately regulates growth and patterning. We found that as the disc grows, the Dpp response expands and scales with the tissue size. Interestingly, scaling is not perfect at all positions in the field. The scaling of the target gene domains is best where they have a function; Spalt, for example, scales best at the position in the anterior compartment where it helps to form one of the anterior veins of the wing. Analysis of mutants for pentagone, a transcriptional target of Dpp that encodes a secreted feedback regulator of the pathway, indicates that Pentagone plays a key role in scaling the Dpp gradient activity.

Developmental stability: a major role for cyclin G in drosophila melanogaster

Morphological consistency in metazoans is remarkable given the pervasive occurrence of genetic variation, environmental effects, and developmental noise. Developmental stability, the ability to reduce developmental noise, is a fundamental property of multicellular organisms, yet its genetic bases remains elusive. Imperfect bilateral symmetry, or fluctuating asymmetry, is commonly used to estimate developmental stability. We observed that Drosophila melanogaster overexpressing Cyclin G (CycG) exhibit wing asymmetry clearly detectable by sight. Quantification of wing size and shape using geometric morphometrics reveals that this asymmetry is a genuine-but extreme-fluctuating asymmetry. Overexpression of CycG indeed leads to a 40-fold increase of wing fluctuating asymmetry, which is an unprecedented effect, for any organ and in any animal model, either in wild populations or mutants. This asymmetry effect is not restricted to wings, since femur length is affected as well. Inactivating CycG by RNAi also induces fluctuating asymmetry but to a lesser extent. Investigating the cellular bases of the phenotypic effects of CycG deregulation, we found that misregulation of cell size is predominant in asymmetric flies. In particular, the tight negative correlation between cell size and cell number observed in wild-type flies is impaired when CycG is upregulated. Our results highlight the role of CycG in the control of developmental stability in D. melanogaster. Furthermore, they show that wing developmental stability is normally ensured via compensatory processes between cell growth and cell proliferation. We discuss the possible role of CycG as a hub in a genetic network that controls developmental stability.

Genetic basis of wing morphogenesis in Drosophila: sexual dimorphism and non-allometric effects of shape variation

BACKGROUND

The Drosophila wing represents a particularly appropriate model to investigate the developmental control of phenotypic variation. Previous studies which aimed to identify candidate genes for wing morphology demonstrated that the genetic basis of wing shape variation in D. melanogaster is composed of numerous genetic factors causing small, additive effects. In this study, we analyzed wing shape in males and females from 191 lines of D. melanogaster, homozygous for a single P-element insertion, using geometric morphometrics techniques. The analysis allowed us to identify known and novel candidate genes that may contribute to the expression of wing shape in each sex separately and to compare them to candidate genes affecting wing size which have been identified previously using the same lines.

RESULTS

Our results indicate that more than 63% of induced mutations affected wing shape in one or both sexes, although only 33% showed significant differences in both males and females. The joint analysis of wing size and shape revealed that only 19% of the P-element insertions caused coincident effects on both components of wing form in one or both sexes. Further morphometrical analyses revealed that the intersection between veins showed the smallest displacements in the proximal region of the wing. Finally, we observed that mutations causing general deformations were more common than expected in both sexes whereas the opposite occurred with those generating local changes. For most of the 94 candidate genes identified, this seems to be the first record relating them with wing shape variation.

CONCLUSIONS

Our results support the idea that the genetic architecture of wing shape is complex with many different genes contributing to the trait in a sexually dimorphic manner. This polygenic basis, which is relatively independent from that of wing size, is composed of genes generally involved in development and/or metabolic functions, especially related to the regulation of different cellular processes such as motility, adhesion, communication and signal transduction. This study suggests that understanding the genetic basis of wing shape requires merging the regulation of vein patterning by signalling pathways with processes that occur during wing development at the cellular level.

Temporal patterns of genetic and phenotypic variation in the epidemiologically important drone fly, Eristalis tenax

Eristalis tenax L. (Diptera: Syrphidae) is commonly known as the drone fly (adult) or rat-tailed maggot (immature). Both adults and immature stages are identified as potential mechanical vectors of mycobacterial pathogens, and early-stage maggots cause accidental myiasis. We compared four samples from Mount Fruška Gora, Serbia, with the aim of obtaining insights into the temporal variations and sexual dimorphism in the species. This integrative approach was based on allozyme loci, morphometric wing parameters (shape and size) and abdominal colour patterns. Consistent sexual dimorphism was observed, indicating that male specimens had lighter abdomens and smaller and narrower wings than females. The distribution of genetic diversity at polymorphic loci indicated genetic divergence among collection dates. Landmark-based geometric morphometrics revealed, contrary to the lack of divergence in wing size, significant wing shape variation throughout the year. In addition, temporal changes in the frequencies of the abdominal patterns observed are likely to relate to the biology of the species and ecological factors in the locality. Hence, the present study expands our knowledge of the genetic diversity and phenotypic plasticity of E. tenax. The quantification of such variability represents a step towards the evaluation of the adaptive potential of this species of medical and epidemiological importance.

Chromosomal and environmental determinants of morphometric variation in natural populations of the malaria vector Anopheles funestus in Cameroon

Anopheles funestus is one of the most proficient malaria vectors in the world, mainly because of its remarkable ability to populate a wide range of ecological settings across Africa. Its formidable environmental plasticity has been primarily associated to high amounts of genetic and inversion polymorphisms. However, very little is known about the morphological changes that this ecological adaptation entails. Here, we report on wing morphometric variations in karyotyped specimens of this species collected throughout a wide range of eco-geographical conditions in Cameroon (Central Africa). Our results revealed strong selection on mosquito wing traits. Variation of wing size was dependent on temperature and elevation (p < 0.001), while wing shape did not exhibit a specific environmental pattern. On the other hand, we observed a significant correlation of wing shape variation (p < 0.001), but not size (p > 0.05), with regard to karyotype. This pattern was maintained across different environmental conditions. In conclusion, our findings cast strong evidence that change in morphometric traits are under natural selection and contribute to local adaptation in A. funestus populations. Furthermore, the robust relation between chromosome polymorphisms and wing shape suggests new evolutionary hypotheses about the effect of chromosomal inversions on phenotypic variation in this malaria vector.

Geometric morphometrics of the wing in the subgenus Culicoides (Diptera: Ceratopogonidae): from practical implications to evolutionary interpretations

Biting midges of the genus Culicoides Latreille have been incriminated in transmission of bluetongue. Since 1998, the disease has spread across Europe provoking the largest epidemic ever recorded with important economic loses. Some species of the subgenus Avaritia and Culicoides have been described as candidate vectors involved in these epizootics. Both subgenera contain groups of cryptic species that could differ in their vectorial capacity. For this reason, the correct identification of vector species is considered an essential issue in epidemiological programs. In the current study, the usefulness of wing form in differentiating morphologically similar species of the subgenus Culicoides by means of geometric morphometric techniques is assessed in specimens previously identified through molecular analyses based on cytochrome oxidase subunit I gene sequences. Significant differences between species were detected in the two components of form, i.e., size and shape. Although wing size was affected by temperature, wing shape showed a more stable specific variation, allowing the proper classification of a high percentage of specimens. In addition, the concordance between phylogenies inferred from molecular data and phenetic clusters suggests the existence of a phylogenetic signal in wing shape. These findings enhance the use of this complex phenotypic trait not only to infer genetic relationships among species of the subgenus Culicoides but also as apotentially powerful tool to differentiate cryptic species within the genus.

The effects of weak genetic perturbations on the transcriptome of the wing imaginal disc and its association with wing shape in Drosophila melanogaster

A major objective of genomics is to elucidate the mapping between genotypic and phenotypic space as a step toward understanding how small changes in gene function can lead to elaborate phenotypic changes. One approach that has been utilized is to examine overall patterns of covariation between phenotypic variables of interest, such as morphology, physiology, and behavior, and underlying aspects of gene activity, in particular transcript abundance on a genome-wide scale. Numerous studies have demonstrated that such patterns of covariation occur, although these are often between samples with large numbers of unknown genetic differences (different strains or even species) or perturbations of large effect (sexual dimorphism or strong loss-of-function mutations) that may represent physiological changes outside of the normal experiences of the organism. We used weak mutational perturbations in genes affecting wing development in Drosophila melanogaster that influence wing shape relative to a co-isogenic wild type. We profiled transcription of 1150 genes expressed during wing development in 27 heterozygous mutants, as well as their co-isogenic wild type and one additional wild-type strain. Despite finding clear evidence of expression differences between mutants and wild type, transcriptional profiles did not covary strongly with shape, suggesting that information from transcriptional profiling may not generally be predictive of final phenotype. We discuss these results in the light of possible attractor states of gene expression and how this would affect interpretation of covariation between transcriptional profiles and other phenotypes.

Morphometric integration and modularity in configurations of landmarks: tools for evaluating a priori hypotheses

Identifying the modular components of a configuration of landmarks is an important task of morphometric analyses in evolutionary developmental biology. Modules are integrated internally by many interactions among their component parts, but are linked to one another only by few or weak interactions. Accordingly, traits within modules are tightly correlated with each other, but relatively independent of traits in other modules. Hypotheses concerning the boundaries of modules in a landmark configuration can therefore be tested by comparing the strength of covariation among alternative partitions of the configuration into subsets of landmarks. If a subdivision coincides with the true boundaries between modules, the correlations among subsets should be minimal. This article introduces Escoufier's RV coefficient and the multi-set RV coefficient as measures of the correlation between two or more subsets of landmarks. These measures can be compared between alternative partitions of the configuration into subsets. Because developmental interactions are tissue bound, it is sensible to require that modules should be spatially contiguous. I propose a criterion for spatial contiguity for sets of landmarks using an adjacency graph. The new methods are demonstrated with data on shape of the wing in Drosophila melanogaster and the mandible of the house mouse.

Wing morphology and fluctuating asymmetry depend on the host plant in cactophilic Drosophila

As in most insect groups, host plant shifts in cactophilic Drosophila represent environmental challenges as flies must adjust their developmental programme to the presence of different chemical compounds and/or to a microflora that may differ in the diversity and abundance of yeasts and bacteria. In this context, wing morphology provides an excellent opportunity to investigate the factors that may induce changes during development. In this work, we investigated phenotypic plasticity and developmental instability of wing morphology in flies on the cactophilic Drosophila buzzatii and Drosophila koepferae raised on alternative breeding substrates. We detected significant differences in wing size between and within species, and between flies reared on different cactus hosts. However, differences in wing shape between flies emerged from different cactus hosts were not significant either in D. buzzatii or in D. koepferae. Our results also showed that morphological responses involved the entire organ, as variation in size and shape correlated between different portions of the wing. Finally, we studied the effect of the rearing cactus host on developmental instability as measured by the degree of fluctuating asymmetry (FA). Levels of FA in wing size were significantly greater in flies of both species reared in non-preferred when compared with those reared in preferred host cacti. Our results are discussed in the framework of an integrative view aimed at investigating the relevance of host plant shifts in the evolution of the guild of cactophilic Drosophila species that diversified in South America.

Developmental constraints vs. variational properties: How pattern formation can help to understand evolution and development

This article suggests that apparent disagreements between the concept of developmental constraints and neo-Darwinian views on morphological evolution can disappear by using a different conceptualization of the interplay between development and selection. A theoretical framework based on current evolutionary and developmental biology and the concepts of variational properties, developmental patterns and developmental mechanisms is presented. In contrast with existing paradigms, the approach in this article is specifically developed to compare developmental mechanisms by the morphological variation they produce and the way in which their functioning can change due to genetic variation. A developmental mechanism is a gene network, which is able to produce patterns in space though the regulation of some cell behaviour (like signalling, mitosis, apoptosis, adhesion, etc.). The variational properties of a developmental mechanism are all the pattern transformations produced under different initial and environmental conditions or IS-mutations. IS-mutations are DNA changes that affect how two genes in a network interact, while T-mutations are mutations that affect the topology of the network itself. This article explains how this new framework allows predictions not only about how pattern formation affects variation, and thus phenotypic evolution, but also about how development evolves by replacement between pattern formation mechanisms. This article presents testable inferences about the evolution of the structure of development and the phenotype under different selective pressures. That is what kind of pattern formation mechanisms, in which relative temporal order, and which kind of phenotypic changes, are expected to be found in development.

Epidermal growth factor receptor and transforming growth factor-beta signaling contributes to variation for wing shape in Drosophila melanogaster

Wing development in Drosophila is a common model system for the dissection of genetic networks and their roles during development. In particular, the RTK and TGF-beta regulatory networks appear to be involved with numerous aspects of wing development, including patterning, cell determination, growth, proliferation, and survival in the developing imaginal wing disc. However, little is known as to how subtle changes in the function of these genes may contribute to quantitative variation for wing shape, per se. In this study 50 insertional mutations, representing 43 loci in the RTK, Hedgehog, TGF-beta pathways, and their genetically interacting factors were used to study the role of these networks on wing shape. To concurrently examine how genetic background modulates the effects of the mutation, each insertion was introgressed into two wild-type genetic backgrounds. Using geometric morphometric methods, it is shown that the majority of these mutations have profound effects on shape but not size of the wing when measured as heterozygotes. To examine the relationships between how each mutation affects wing shape hierarchical clustering was used. Unlike previous observations of environmental canalization, these mutations did not generally increase within-line variation relative to their wild-type counterparts. These results provide an entry point into the genetics of wing shape and are discussed within the framework of the dissection of complex phenotypes.

Tests for the replication of an association between Egfr and natural variation in Drosophila melanogaster wing morphology

Background

Quantitative differences between individuals stem from a combination of genetic and environmental factors, with the heritable variation being shaped by evolutionary forces. Drosophila wing shape has emerged as an attractive system for genetic dissection of multi-dimensional traits. We utilize several experimental genetic methods to validation of the contribution of several polymorphisms in the Epidermal growth factor receptor (Egfr) gene to wing shape and size, that were previously mapped in populations of Drosophila melanogaster from North Carolina (NC) and California (CA). This re-evaluation utilized different genetic testcrosses to generate heterozygous individuals with a variety of genetic backgrounds as well as sampling of new alleles from Kenyan stocks.

Results

Only one variant, in the Egfr promoter, had replicable effects in all new experiments. However, expanded genotyping of the initial sample of inbred lines rendered the association non-significant in the CA population, while it persisted in the NC sample, suggesting population specific modification of the quantitative trait nucleotide QTN effect.

Conclusion

Dissection of quantitative trait variation to the nucleotide level can identify sites with replicable effects as small as one percent of the segregating genetic variation. However, the testcross approach to validate QTNs is both labor intensive and time-consuming, and is probably less useful than resampling of large independent sets of outbred individuals.