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

Mixed support for an alignment between phenotypic plasticity and genetic differentiation in damselfly wing shape

The relationship between genetic differentiation and phenotypic plasticity can provide information on whether plasticity generally facilitates or hinders adaptation to environmental change. Here, we studied wing shape variation in a damselfly (Lestes sponsa) across a latitudinal gradient in Europe that differed in time constraints mediated by photoperiod and temperature. We reared damselflies from northern and southern populations in the laboratory using a reciprocal transplant experiment that simulated time-constrained (i.e. northern) and unconstrained (southern) photoperiods and temperatures. After emergence, adult wing shape was analysed using geometric morphometrics. Wings from individuals in the northern and southern populations differed significantly in shape when animals were reared in their respective native environment. Comparing wing shape across environments, we found evidence for phenotypic plasticity in wing shape, and this response differed across populations (i.e. G × E interactions). This interaction was driven by a stronger plastic response by individuals from the northern population and differences in the direction of plastic wing shape changes among populations. The alignment between genetic and plastic responses depended on the specific combination of population and rearing environment. For example, there was an alignment between plasticity and genetic differentiation under time-constrained, but not under non-time-constrained conditions for forewings. We thus find mixed support for the hypothesis that environmental plasticity and genetic population differentiation are aligned. Furthermore, although our laboratory treatments mimicked the natural climatic conditions at northern and southern latitudes, the effects of population differences on wing shape were two to four times stronger than plastic effects. We discuss our results in terms of time constraints and the possibility that natural and sexual selection is acting differently on fore- and hindwings.

Intraspecific variation in wing geometry among Tabanus rubidus (Diptera: Tabanidae) populations in Thailand

Tabanus rubidus (Wiedemann, 1821) (Diptera: Tabanidae) is a hematophagous insect of veterinary and medical importance and is the predominant Tabanus spp. in Thailand. It is a potential mechanical vector of Trypanosoma evansi, which causes surra in domestic and wild animals. Wing geometric morphometrics is widely used as morphological markers for species identification and to assess the insect population structure. Herein, we investigated the intraspecific variation in wing geometry among T. rubidus populations in Thailand using landmark-based geometric morphometric analysis. Tabanus rubidus females were collected from five populations in four geographical regions in Thailand. The left wings of 240 specimens were removed and digitized using 22 landmarks for analysis. While wing size variations were found between some populations, wing shape variations were detected in all. These intraspecific variations in T. rubidus populations indicate an adaptive response to the local environmental conditions.

Seasonal variation in wing size and shape of Drosophila melanogaster reveals rapid adaptation to environmental changes

Populations in seasonal fluctuating environments receive multiple environmental cues and must deal with this heterogenic environment to survive and reproduce. An enlarged literature shows that this situation can be resolved through rapid adaptation in Drosophila melanogaster populations. Long-term monitoring of a population in its natural habitat and quantitative measurement of its responses to seasonal environmental changes are important for understanding the adaptive response of D. melanogaster to temporal variable selection. Here, we use inbred lines of a D. melanogaster population collected at monthly intervals between May to October over a temporal scale spanning three consecutive years to understand the variation in wing size and wing shape over these timepoints. The wing size and shape of this population changed significantly between months and a seasonal cycle of this traits is repeated for three years. Our results suggest that the effects of environmental variables that generated variation in body size between populations such as latitudinal clines, are a selective pressure in a different manner in terms of seasonal variation. Temperature related variable have a significant nonlinear relation to this fluctuating pattern in size and shape, whereas precipitation and humidity have a sex-specific effect which is more significant in males.

Genomics of altitude-associated wing shape in two tropical butterflies

Understanding how organisms adapt to their local environment is central to evolution. With new whole-genome sequencing technologies and the explosion of data, deciphering the genomic basis of complex traits that are ecologically relevant is becoming increasingly feasible. Here, we studied the genomic basis of wing shape in two Neotropical butterflies that inhabit large geographical ranges. Heliconius butterflies at high elevations have been shown to generally have rounder wings than those in the lowlands. We reared over 1,100 butterflies from 71 broods of H. erato and H. melpomene in common-garden conditions and showed that wing aspect ratio, that is, elongatedness, is highly heritable in both species and that elevation-associated wing aspect ratio differences are maintained. Genome-wide associations with a published data set of 666 whole genomes from across a hybrid zone, uncovered a highly polygenic basis to wing aspect ratio variation in the wild. We identified several genes that have roles in wing morphogenesis or wing aspect ratio variation in Drosophila flies, making them promising candidates for future studies. There was little evidence for molecular parallelism in the two species, with only one shared candidate gene, nor for a role of the four known colour pattern loci, except for optix in H. erato. Thus, we present the first insights into the heritability and genomic basis of within-species wing aspect ratio in two Heliconius species, adding to a growing body of evidence that polygenic adaptation may underlie many ecologically relevant traits.

Narrow versus broad: sexual dimorphism in the wing form of western European species of the subgenus Avaritia (Culicoides, Ceratopogonidae)

While wing form is known to differ between males and females of the genus Culicoides, detailed studies of sexual dimorphism are lacking. In this study, we analyze sex-specific differences in the wing form of 5 species of the subgenus Avaritia, using geometric morphometrics and comparative phylogenetic methods. Our results confirm the existence of marked sexual dimorphism in the wing form of the studied species and reveal for the first time that while there is a shared general pattern of sexual shape dimorphism within the subgenus, sexual size dimorphism, and particular features of sexual shape dimorphism differ among species. Sexual shape dimorphism was found to be poorly associated to size and the evolutionary history of the species. The tight association of sexual shape dimorphism with aspect ratio suggests that the shape of the wing is optimized for the type of flight of each sex, that is, dispersal flight in females versus aerobatic flight in males. Moreover, the fact that interspecific shape differences are greater and more strongly associated to aspect ratio in males than in females might be indicating that in males the selective pressures affecting flight performance characteristics are more heterogeneous and/or stronger than in females among the studied species.

Changes in the wing shape and size in Drosophila melanogaster treated with food grade titanium dioxide nanoparticles (E171) - A multigenerational study

Drosophila is among the most commonly used models for toxicity assessment of different types of nanoparticles. This study aims to examine the effects of a constant exposure to the low concentration of human food grade titanium dioxide nanoparticles (TiO₂ E171) on Drosophila melanogaster wing morphology over multiple generations. Subsequently, the Geometric Morphometrics Analysis was employed to examine possible changes in the wing shape and size of the treated flies. The treatment resulted in the diminishment but not a disruption in the sexual dimorphism in wings. Consequently, the female flies were clearly separated from the male flies by the differences in wing morphology as in the control group. A splitting by generations was overly similar within the control and the treatment, but it was slightly more pronounced in the treatment. However, the observed generational differences seemed mostly random between generations, irrespective of the treatment. Specifically, the treated groups displayed slightly higher splitting by generations in females than in males. Regardless of the generation, the results show a clear splitting by the differences in the wing shape between the treated flies and the flies from control. The mean value of centroid size, which refers to the wing size, of both female and male wings was smaller in the treatment when compared to the control. The overall effect of TiO₂ was to induce significant difference in Drosophila wing morphology but it did not alter the general wing morphology pattern. Therefore, the change in the wings occurred only within the normally allowed wing variation.

Altitude and life-history shape the evolution of Heliconius wings

Phenotypic divergence between closely related species has long interested biologists. Taxa that inhabit a range of environments and have diverse natural histories can help understand how selection drives phenotypic divergence. In butterflies, wing color patterns have been extensively studied but diversity in wing shape and size is less well understood. Here, we assess the relative importance of phylogenetic relatedness, natural history, and habitat on shaping wing morphology in a large dataset of over 3500 individuals, representing 13 Heliconius species from across the Neotropics. We find that both larval and adult behavioral ecology correlate with patterns of wing sexual dimorphism and adult size. Species with solitary larvae have larger adult males, in contrast to gregarious Heliconius species, and indeed most Lepidoptera, where females are larger. Species in the pupal-mating clade are smaller than those in the adult-mating clade. Interestingly, we find that high-altitude species tend to have rounder wings and, in one of the two major Heliconius clades, are also bigger than their lowland relatives. Furthermore, within two widespread species, we find that high-altitude populations also have rounder wings. Thus, we reveal novel adaptive wing morphological divergence among Heliconius species beyond that imposed by natural selection on aposematic wing coloration.

Facultative dosage compensation of developmental genes on autosomes in Drosophila and mouse embryonic stem cells

Haploinsufficiency and aneuploidy are two phenomena, where gene dosage alterations cause severe defects ultimately resulting in developmental failures and disease. One remarkable exception is the X chromosome, where copy number differences between sexes are buffered by dosage compensation systems. In Drosophila, the Male-Specific Lethal complex (MSLc) mediates upregulation of the single male X chromosome. The evolutionary origin and conservation of this process orchestrated by MSL2, the only male-specific protein within the fly MSLc, have remained unclear. Here, we report that MSL2, in addition to regulating the X chromosome, targets autosomal genes involved in patterning and morphogenesis. Precise regulation of these genes by MSL2 is required for proper development. This set of dosage-sensitive genes maintains such regulation during evolution, as MSL2 binds and similarly regulates mouse orthologues via Histone H4 lysine 16 acetylation. We propose that this gene-by-gene dosage compensation mechanism was co-opted during evolution for chromosome-wide regulation of the Drosophila male X.

In Drosophila the Male-Specific Lethal complex (MSLc) mediates upregulation of the single male X chromosome. Here the authors provide evidence that MSL2 also targets autosomal genes required for proper development and that MSL2 binds and similarly regulates mouse orthologues.

Arabidopsis phenotyping through geometric morphometrics

Background

Recently, great technical progress has been achieved in the field of plant phenotyping. High-throughput platforms and the development of improved algorithms for rosette image segmentation make it possible to extract shape and size parameters for genetic, physiological, and environmental studies on a large scale. The development of low-cost phenotyping platforms and freeware resources make it possible to widely expand phenotypic analysis tools for Arabidopsis. However, objective descriptors of shape parameters that could be used independently of the platform and segmentation software used are still lacking, and shape descriptions still rely on ad hoc or even contradictory descriptors, which could make comparisons difficult and perhaps inaccurate. Modern geometric morphometrics is a family of methods in quantitative biology proposed to be the main source of data and analytical tools in the emerging field of phenomics studies. Based on the location of landmarks (corresponding points) over imaged specimens and by combining geometry, multivariate analysis, and powerful statistical techniques, these tools offer the possibility to reproducibly and accurately account for shape variations among groups and measure them in shape distance units.

Results

Here, a particular scheme of landmark placement on Arabidopsis rosette images is proposed to study shape variation in viral infection processes. Shape differences between controls and infected plants are quantified throughout the infectious process and visualized. Quantitative comparisons between two unrelated ssRNA+ viruses are shown, and reproducibility issues are assessed.

Conclusions

Combined with the newest automated platforms and plant segmentation procedures, geometric morphometric tools could boost phenotypic features extraction and processing in an objective, reproducible manner.

A pupal transcriptomic screen identifies Ral as a target of store-operated calcium entry in Drosophila neurons

Transcriptional regulation by Store-operated Calcium Entry (SOCE) is well studied in non-excitable cells. However, the role of SOCE has been poorly documented in neuronal cells with more complicated calcium dynamics. Previous reports demonstrated a requirement for SOCE in neurons that regulate Drosophila flight bouts. We refine this requirement temporally to the early pupal stage and use RNA-sequencing to identify SOCE mediated gene expression changes in the developing Drosophila pupal nervous system. Down regulation of dStim, the endoplasmic reticular calcium sensor and a principal component of SOCE in the nervous system, altered the expression of 131 genes including Ral, a small GTPase. Disruption of Ral function in neurons impaired flight, whereas ectopic expression of Ral in SOCE-compromised neurons restored flight. Through live imaging of calcium transients from cultured pupal neurons, we confirmed that Ral does not participate in SOCE, but acts downstream of it. These results identify neuronal SOCE as a mechanism that regulates expression of specific genes during development of the pupal nervous system and emphasizes the relevance of SOCE-regulated gene expression to flight circuit maturation.

Proteomic analysis of Aedes aegypti midgut during post-embryonic development and of the female mosquitoes fed different diets

In this work we analyzed protein expression in the Aedes aegypti midgut during the larval (fourth instar, L4), pupal, and adult stages [including newly emerged (NE), sugar-fed (SF) and blood-fed (BF) females]. Two-dimensional electrophoresis showed 13 spots in the midgut of larvae, 95 in the midgut of pupae, 90 in the midgut of NE, and 76 in the midgut of SF or BF females. In the larval midguts, high serpin expression was noted, while in the pupae, protein abundance was lower than in the NE, SF, and BF females. The spots related to proteins linked to energy production, protein metabolism, signaling, and transport were highly expressed in the NE stage, while spots related proteins involved in translation were abundant in SF and BF females. The differential abundance of proteins in the midgut of A. aegypti at different developmental stages supports the necessity for midgut development during immature stage followed by the necessity of proteins related to digestion in adults.

A new xyelotomid (Hymenoptera) from the Middle Jurassic of China displaying enigmatic venational asymmetry

BACKGROUND

Pterygota insects typically have symmetric veins in left and right wings. For studying taxonomy and phylogeny of fossil insects, venational patterns are commonly used as diagnostic characters, in conjunction with preserved body characters. Some examples of asymmetrical venation are known among extant insects, but only a few fossil insects with asymmetric wings have been reported, among which a previously described xyelotomid of Hymenoptera, Xyelocerus diaphanous, displays an unusual, small cell of vein Rs in the left forewing, but not in the right.

RESULTS

Herein we report a new sawfly of the family Xyelotomidae, Aethotoma aninomorpha gen. et sp. nov., from the late Middle Jurassic of China having a simple Sc in the forewing and Sc with two branches in the hind wing. In additional, the new specimen exhibits an enigmatic venational asymmetry. In the right forewing, crossvein 2r-rs of forms a loop, then forks into 2 long branches reaching Rs, while 2r-rs of the left forewing forks into 2 short branches reaching Rs, in contrast to a linear 2r-rs in typical fossil and extant sawflies.

CONCLUSION

Such rare asymmetrical venation found from fossil sawflies provides a glance at early occurrences of venational variability and instability, or possibly aberrational development, for insects in the late Middle Jurassic.

Natural Genetic Variation and Candidate Genes for Morphological Traits in Drosophila melanogaster

Body size is a complex character associated to several fitness related traits that vary within and between species as a consequence of environmental and genetic factors. Latitudinal and altitudinal clines for different morphological traits have been described in several species of Drosophila and previous work identified genomic regions associated with such variation in D. melanogaster. However, the genetic factors that orchestrate morphological variation have been barely studied. Here, our main objective was to investigate genetic variation for different morphological traits associated to the second chromosome in natural populations of D. melanogaster along latitudinal and altitudinal gradients in Argentina. Our results revealed weak clinal signals and a strong population effect on morphological variation. Moreover, most pairwise comparisons between populations were significant. Our study also showed important within-population genetic variation, which must be associated to the second chromosome, as the lines are otherwise genetically identical. Next, we examined the contribution of different candidate genes to natural variation for these traits. We performed quantitative complementation tests using a battery of lines bearing mutated alleles at candidate genes located in the second chromosome and six second chromosome substitution lines derived from natural populations which exhibited divergent phenotypes. Results of complementation tests revealed that natural variation at all candidate genes studied, invected, Fasciclin 3, toucan, Reticulon-like1, jing and CG14478, affects the studied characters, suggesting that they are Quantitative Trait Genes for morphological traits. Finally, the phenotypic patterns observed suggest that different alleles of each gene might contribute to natural variation for morphological traits. However, non-additive effects cannot be ruled out, as wild-derived strains differ at myriads of second chromosome loci that may interact epistatically with mutant alleles.

Genetic and phenotypic variation in central and northern European populations of Aedes (Aedimorphus) vexans (Meigen, 1830) (Diptera, Culicidae)

The floodwater mosquito Aedes vexans can be a massive nuisance in the flood plain areas of mainland Europe, and is the vector of Tahyna virus and a potential vector of Dirofilaria immitis. This epidemiologically important species forms three subspecies worldwide, of which Aedes vexans arabiensis has a wide distribution in Europe and Africa. We quantified the genetic and phenotypic variation in Ae. vexans arabiensis in populations from Sweden (northern Europe), Hungary, and Serbia (central Europe). A landscape genetics approach (FST , STRUCTURE, BAPS, GENELAND) revealed significant differentiation between northern and southern populations. Similar to genetic data, wing geometric morphometrics revealed two different clusters, one made by Swedish populations, while another included Hungarian and Serbian populations. Moreover, integrated genetic and morphometric data from the spatial analysis suggested groupings of populations into three clusters, one of which was from Swedish and Hungarian populations. Data on spatial analysis regarding an intermediate status of the Hungarian population was supported by observed Isolation-by-Distance patterns. Furthermore, a low proportion of interpopulation vs intrapopulation variance revealed by AMOVA and low-to-moderate FST values on a broader geographical scale indicate a continuous between-population exchange of individuals, including considerable gene flow on the regional scale, are likely to be responsible for the maintenance of the observed population similarity in Aе. vexans. We discussed data considering population structure in the light of vector control strategies of the mosquito from public health importance.

The sex-limited effects of mutations in the EGFR and TGF-β signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing

Much of the morphological diversity in nature-including among sexes within a species-is a direct consequence of variation in size and shape. However, disentangling variation in sexual dimorphism for both shape (SShD), size (SSD), and their relationship with one another remains complex. Understanding how genetic variation influences both size and shape together, and how this in turn influences SSD and SShD, is challenging. In this study, we utilize Drosophila wing size and shape as a model system to investigate how mutations influence size and shape as modulated by sex. Previous work has demonstrated that mutations in epidermal growth factor receptor (EGFR) and transforming growth factor-β (TGF-β) signaling components can influence both wing size and shape. In this study, we re-analyze this data to specifically address how they impact the relationship between size and shape in a sex-specific manner, in turn altering the pattern of sexual dimorphism. While most mutations influence shape overall, only a subset have a genotypic specific effect that influences SShD. Furthermore, while we observe sex-specific patterns of allometric shape variation, the effects of most mutations on allometry tend to be small. We discuss this within the context of using mutational analysis to understand sexual size and shape dimorphism.

The histone demethylase dKDM5/LID interacts with the SIN3 histone deacetylase complex and shares functional similarities with SIN3

Background

Regulation of gene expression by histone-modifying enzymes is essential to control cell fate decisions and developmental processes. Two histone-modifying enzymes, RPD3, a deacetylase, and dKDM5/LID, a demethylase, are present in a single complex, coordinated through the SIN3 scaffold protein. While the SIN3 complex has been demonstrated to have functional histone deacetylase activity, the role of the demethylase dKDM5/LID as part of the complex has not been investigated.

Results

Here, we analyzed the developmental and transcriptional activities of dKDM5/LID in relation to SIN3. Knockdown of either Sin3A or lid resulted in decreased cell proliferation in S2 cells and wing imaginal discs. Conditional knockdown of either Sin3A or lid resulted in flies that displayed wing developmental defects. Interestingly, overexpression of dKDM5/LID rescued the wing developmental defect due to reduced levels of SIN3 in female flies, indicating a major role for dKDM5/LID in cooperation with SIN3 during development. Together, these observed phenotypes strongly suggest that dKDM5/LID as part of the SIN3 complex can impact previously uncharacterized transcriptional networks. Transcriptome analysis revealed that SIN3 and dKDM5/LID regulate many common genes. While several genes implicated in cell cycle and wing developmental pathways were affected upon altering the level of these chromatin factors, a significant affect was also observed on genes required to mount an effective stress response. Further, under conditions of induced oxidative stress, reduction of SIN3 and/or dKDM5/LID altered the expression of a greater number of genes involved in cell cycle-related processes relative to normal conditions. This highlights an important role for SIN3 and dKDM5/LID proteins to maintain proper progression through the cell cycle in environments of cellular stress. Further, we find that target genes are bound by both SIN3 and dKDM5/LID, however, histone acetylation, not methylation, plays a predominant role in gene regulation by the SIN3 complex.

Conclusions

We have provided genetic evidence to demonstrate functional cooperation between the histone demethylase dKDM5/LID and SIN3. Biochemical and transcriptome data further support functional links between these proteins. Together, the data provide a solid framework for analyzing the gene regulatory pathways through which SIN3 and dKDM5/LID control diverse biological processes in the organism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0053-9) contains supplementary material, which is available to authorized users.

A new approach for investigating venom function applied to venom calreticulin in a parasitoid wasp

A new method is developed to investigate functions of venom components, using venom gene RNA interference knockdown in the venomous animal coupled with RNA sequencing in the envenomated host animal. The vRNAi/eRNA-Seq approach is applied to the venom calreticulin component (v-crc) of the parasitoid wasp Nasonia vitripennis. Parasitoids are common, venomous animals that inject venom proteins into host insects, where they modulate physiology and metabolism to produce a better food resource for the parasitoid larvae. vRNAi/eRNA-Seq indicates that v-crc acts to suppress expression of innate immune cell response, enhance expression of clotting genes in the host, and up-regulate cuticle genes. V-crc KD also results in an increased melanization reaction immediately following envenomation. We propose that v-crc inhibits innate immune response to parasitoid venom and reduces host bleeding during adult and larval parasitoid feeding. Experiments do not support the hypothesis that v-crc is required for the developmental arrest phenotype observed in envenomated hosts. We propose that an important role for some venom components is to reduce (modulate) the exaggerated effects of other venom components on target host gene expression, physiology, and survival, and term this venom mitigation. A model is developed that uses vRNAi/eRNA-Seq to quantify the contribution of individual venom components to total venom phenotypes, and to define different categories of mitigation by individual venoms on host gene expression. Mitigating functions likely contribute to the diversity of venom proteins in parasitoids and other venomous organisms.

Making quantitative morphological variation from basic developmental processes: Where are we? The case of the Drosophila wing

One of the aims of evolutionary developmental biology is to discover the developmental origins of morphological variation. The discipline has mainly focused on qualitative morphological differences (e.g., presence or absence of a structure) between species. Studies addressing subtle, quantitative variation are less common. The Drosophila wing is a model for the study of development and evolution, making it suitable to investigate the developmental mechanisms underlying the subtle quantitative morphological variation observed in nature. Previous reviews have focused on the processes involved in wing differentiation, patterning and growth. Here, we investigate what is known about how the wing achieves its final shape, and what variation in development is capable of generating the variation in wing shape observed in nature. Three major developmental stages need to be considered: larval development, pupariation, and pupal development. The major cellular processes involved in the determination of tissue size and shape are cell proliferation, cell death, oriented cell division and oriented cell intercalation. We review how variation in temporal and spatial distribution of growth and transcription factors affects these cellular mechanisms, which in turn affects wing shape. We then discuss which aspects of the wing morphological variation are predictable on the basis of these mechanisms. Developmental Dynamics 244:1058-1073, 2015. © 2015 Wiley Periodicals, Inc.

Constraints, independence, and evolution of thermal plasticity: probing genetic architecture of long- and short-term thermal acclimation

Seasonal and daily thermal variation can limit species distributions because of physiological tolerances. Low temperatures are particularly challenging for ectotherms, which use both basal thermotolerance and acclimation, an adaptive plastic response, to mitigate thermal stress. Both basal thermotolerance and acclimation are thought to be important for local adaptation and persistence in the face of climate change. However, the evolutionary independence of basal and plastic tolerances remains unclear. Acclimation can occur over longer (seasonal) or shorter (hours to days) time scales, and the degree of mechanistic overlap is unresolved. Using a midlatitude population of Drosophila melanogaster, we show substantial heritable variation in both short- and long-term acclimation. Rapid cold hardening (short-term plasticity) and developmental acclimation (long-term plasticity) are positively correlated, suggesting shared mechanisms. However, there are independent components of these traits, because developmentally acclimated flies respond positively to short-term acclimation. A strong negative correlation between basal cold tolerance and developmental acclimation suggests that basal cold tolerance may constrain developmental acclimation, whereas a weaker negative correlation between basal cold tolerance and short-term acclimation suggests less constraint. Using genome-wide association mapping, we show the genetic architecture of rapid cold hardening and developmental acclimation responses are nonoverlapping at the SNP and corresponding gene level. However, genes associated with each trait share functional similarities, including genes involved in apoptosis and autophagy, cytoskeletal and membrane structural components, and ion binding and transport. These results indicate substantial opportunity for short-term and long-term acclimation responses to evolve separately from each other and for short-term acclimation to evolve separately from basal thermotolerance.

Genetic and morphological variation in sexual and asexual parasitoids of the genus Lysiphlebus - an apparent link between wing shape and reproductive mode

Background

Morphological divergence often increases with phylogenetic distance, thus making morphology taxonomically informative. However, transitions to asexual reproduction may complicate this relationship because asexual lineages capture and freeze parts of the phenotypic variation of the sexual populations from which they derive. Parasitoid wasps belonging to the genus Lysiphlebus Foerster (Hymenoptera: Braconidae: Aphidiinae) are composed of over 20 species that exploit over a hundred species of aphid hosts, including many important agricultural pests. Within Lysiphlebus, two genetically and morphologically well-defined species groups are recognised: the “fabarum” and the “testaceipes” groups. Yet within each group, sexual as well as asexual lineages occur, and in L. fabarum different morphs of unknown origin and status have been recognised. In this study, we selected a broad sample of specimens from the genus Lysiphlebus to explore the relationship between genetic divergence, reproductive mode and morphological variation in wing size and shape (quantified by geometric morphometrics).

Results

The analyses of mitochondrial and nuclear gene sequences revealed a clear separation between the “testaceipes” and “fabarum” groups of Lysiphlebus, as well as three well-defined phylogenetic lineages within the “fabarum” species group and two lineages within the “testaceipes” group. Divergence in wing shape was concordant with the deep split between the “testaceipes” and “fabarum” species groups, but within groups no clear association between genetic divergence and wing shape variation was observed. On the other hand, we found significant and consistent differences in the shape of the wing between sexual and asexual lineages, even when they were closely related.

Conclusions

Mapping wing shape data onto an independently derived molecular phylogeny of Lysiphlebus revealed an association between genetic and morphological divergence only for the deepest phylogenetic split. In more recently diverged taxa, much of the variation in wing shape was explained by differences between sexual and asexual lineages, suggesting a mechanistic link between wing shape and reproductive mode in these parasitoid wasps.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0293-5) contains supplementary material, which is available to authorized users.

Fly wing vein patterns have spatial reproducibility of a single cell

Developmental processes in multicellular organisms occur in fluctuating environments and are prone to noise, yet they produce complex patterns with astonishing reproducibility. We measure the left-right and inter-individual precision of bilaterally symmetric fly wings across the natural range of genetic and environmental conditions and find that wing vein patterns are specified with identical spatial precision and are reproducible to within a single-cell width. The early fly embryo operates at a similar degree of reproducibility, suggesting that the overall spatial precision of morphogenesis in Drosophila performs at the single-cell level. Could development be operating at the physical limit of what a biological system can achieve?

Host alkaloids differentially affect developmental stability and wing vein canalization in cactophilic Drosophila buzzatii

Host shifts cause drastic consequences on fitness in cactophilic species of Drosophila. It has been argued that changes in the nutritional values accompanying host shifts may elicit these fitness responses, but they may also reflect the presence of potentially toxic secondary compounds that affect resource quality. Recent studies reported that alkaloids extracted from the columnar cactus Trichocereus terscheckii are toxic for the developing larvae of Drosophila buzzatii. In this study, we tested the effect of artificial diets including increasing doses of host alkaloids on developmental stability and wing morphology in D. buzzatii. We found that alkaloids disrupt normal wing venation patterning and affect viability, wing size and fluctuating asymmetry, suggesting the involvement of stress-response mechanisms. Theoretical implications are discussed in the context of developmental stability, stress, fitness and their relationship with robustness, canalization and phenotypic plasticity.

Wing geometry of Culex coronator (Diptera: Culicidae) from South and Southeast Brazil

BACKGROUND

The Coronator Group encompasses Culex coronator Dyar & Knab, Culex camposi Dyar, Culex covagarciai Forattini, Culex ousqua Dyar, Culex usquatissimus Dyar, Culex usquatus Dyar and Culex yojoae Strickman. Culex coronator has the largest geographic distribution, occurring in North, Central and South America. Moreover, it is a potential vector-borne mosquito species because females have been found naturally infected with several arboviruses, i.e., Saint Louis Encephalitis Virus, Venezuelan Equine Encephalitis Virus and West Nile Virus. Considering the epidemiological importance of Cx. coronator, we investigated the wing shape diversity of Cx. coronator from South and Southeast Brazil, a method to preliminarily estimate population diversity.

METHODS

Field-collected immature stages of seven populations from a large geographical area in Brazil were maintained in the laboratory to obtain both females and males linked with pupal and/or larval exuviae. For each individual female, 18 landmarks of left wings were marked and digitalized. After Procrustes superimposition, discriminant analysis of shape was employed to quantify wing shape variation among populations. The isometric estimator centroid size was calculated to assess the overall wing size and allometry.

RESULTS

Wing shape was polymorphic among populations of Cx. coronator. However, dissimilarities among populations were higher than those observed within each population, suggesting populational differentiation in Cx. coronator. Morphological distances between populations were not correlated to geographical distances, indicating that other factors may act on wing shape and thus, determining microevolutionary patterns in Cx. coronator. Despite the population differentiation, intrapopulational wing shape variability was equivalent among all seven populations.

CONCLUSION

The wing variability found in Cx. coronator populations brings to light a new biological problem to be investigated: the population genetics of Cx. coronator. Because of differences in the male genitalia, we also transferred Cx. yojoae to the Apicinus Subgroup.

The ontogeny and evolution of sex-biased gene expression in Drosophila melanogaster

Sexually dimorphic phenotypes are thought to largely result from sex differences in gene expression, and genes with sex-biased expression have been well characterized in adults of many species. Although most sexual dimorphisms manifest in adults, many result from sex-specific developmental trajectories, implying that juveniles may exhibit significant levels of sex-biased expression. However, it is unclear how much sex-biased expression occurs before reproductive maturity and whether preadult sex-biased genes should exhibit the same evolutionary dynamics observed for adult sex-biased genes. In order to understand the continuity, or lack thereof, and evolutionary dynamics of sex-biased expression throughout the life cycle, we examined sex-biased genes in pre-gonad tissue of two preadult stages and compared them with the adult gonad of Drosophila melanogaster. We found that the majority of the genome is sex-biased at some point in the life cycle, with some genes exhibiting conserved sex-biased expression and others displaying stage-specific sex bias. Our results also reveal a far more complex pattern of evolution for sex-biased genes throughout development. The most rapid evolutionary divergence occurred in genes expressed only in larvae within each sex, compared with continuously expressed genes. In females—but not males—this pattern appeared to be due to relaxed purifying selection in larva-limited genes. Furthermore, genes that retained male bias throughout life evolved more rapidly than stage-specific male-biased genes, due to stronger purifying selection in stage-specific genes. However, female-biased genes that were specific to larvae evolved most rapidly, a pattern that could not be definitively attributed to differences in adaptive evolution or purifying selection, suggesting that pleiotropic constraints on protein-coding sequences can arise when genes are broadly expressed across developmental stages. These results indicate that the signature of sex-specific selection can be detected well before reproductive maturity and is strongest during development.

Phenotypic variation of the housefly, Musca domestica: amounts and patterns of wing shape asymmetry in wild populations and laboratory colonies

Musca domestica L. (Diptera: Muscidae) is a vector of a range variety of pathogens infecting humans and animals. During a year, housefly experiences serial population bottlenecks resulted in reduction of genetic diversity. Population structure has also been subjected to different selection regimes created by insect control programs and pest management. Both environmental and genetic disturbances can affect developmental stability, which is often reflected in morphological traits as asymmetry. Since developmental stability is of great adaptive importance, the aim of this study was to examine fluctuating asymmetry (FA), as a measure of developmental instability, in both wild populations and laboratory colonies of M. domestica. The amount and pattern of wing shape FA was compared among samples within each of two groups (laboratory and wild) and between groups. Firstly, the amount of FA does not differ significantly among samples within the group and neither does it differ between groups. Regarding the mean shape of FA, contrary to non-significant difference within the wild population group and among some colonies, the significant difference between groups was found. These results suggest that the laboratory colonies and wild samples differ in buffering mechanisms to perturbations during development. Hence, inbreeding and stochastic processes, mechanisms dominating in the laboratory-bred samples contributed to significant changes in FA of wing shape. Secondly, general patterns of left-right displacements of landmarks across both studied sample groups are consistent. Observed consistent direction of FA implies high degrees of wing integration. Thus, our findings shed light on developmental buffering processes important for population persistence in the environmental change and genetic stress influence on M. domestica.

FijiWings: an open source toolkit for semiautomated morphometric analysis of insect wings

Development requires coordination between cell proliferation and cell growth to pattern the proper size of tissues, organs, and whole organisms. The Drosophila wing has landmark features, such as the location of veins patterned by cell groups and trichome structures produced by individual cells, that are useful to examine the genetic contributions to both tissue and cell size. Wing size and trichome density have been measured manually, which is tedious and error prone, and although image processing and pattern-recognition software can quantify features in micrographs, this approach has not been applied to insect wings. Here we present FijiWings, a set of macros designed to perform semiautomated morphophometric analysis of a wing photomicrograph. FijiWings uses plug-ins installed in the Fiji version of ImageJ to detect and count trichomes and measure wing area either to calculate trichome density of a defined region selected by the user or generate a heat map of overall trichome densities. For high-throughput screens we have developed a macro that directs a trainable segmentation plug-in to detect wing vein locations either to measure trichome density in specific intervein regions or produce a heat map of relative intervein areas. We use wing GAL4 drivers and UAS-regulated transgenes to confirm the ability of these tools to detect changes in overall tissue growth and individual cell size. FijiWings is freely available and will be of interest to a broad community of fly geneticists studying both the effect of gene function on wing patterning and the evolution of wing morphology.

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.

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.

Identification of genetic suppressors of the Sin3A knockdown wing phenotype

The role of the Sin3A transcriptional corepressor in regulating the cell cycle is established in various metazoans. Little is known, however, about the signaling pathways that trigger or are triggered by Sin3A function. To discover genes that work in similar or opposing pathways to Sin3A during development, we have performed an unbiased screen of deficiencies of the Drosophila third chromosome. Additionally, we have performed a targeted loss of function screen to identify cell cycle genes that genetically interact with Sin3A. We have identified genes that encode proteins involved in regulation of gene expression, signaling pathways and cell cycle that can suppress the curved wing phenotype caused by the knockdown of Sin3A. These data indicate that Sin3A function is quite diverse and impacts a wide variety of cellular processes.

A critical assessment of storytelling: gene ontology categories and the importance of validating genomic scans

In the age of whole-genome population genetics, so-called genomic scan studies often conclude with a long list of putatively selected loci. These lists are then further scrutinized to annotate these regions by gene function, corresponding biological processes, expression levels, or gene networks. Such annotations are often used to assess and/or verify the validity of the genome scan and the statistical methods that have been used to perform the analyses. Furthermore, these results are frequently considered to validate "true-positives" if the identified regions make biological sense a posteriori. Here, we show that this approach can be potentially misleading. By simulating neutral evolutionary histories, we demonstrate that it is possible not only to obtain an extremely high false-positive rate but also to make biological sense out of the false-positives and construct a sensible biological narrative. Results are compared with a recent polymorphism data set from Drosophila melanogaster.