Genetic architecture of wing morphology in Drosophila simulans and an analysis of temperature effects on genetic parameter estimates

Wing plastic response to temperature variation in two distantly related Neotropical Drosophila species (Diptera, Drosophilidae)

Phenotypic plasticity has been described for morphological and life-history traits in many organisms. In Drosophila, temperature drives phenotypic change in several traits, but few Neotropical species have been studied and whether the phenotypic variation associated with plasticity is adaptive remains unclear. Here, we studied the phenotypic response to temperature variation in the distantly related Neotropical species Drosophila mercatorum Patterson and Wheeler, 1942 and Drosophila willistoni Sturtevant, 1916. We evaluate if wing shape variation follows that observed in the Neotropical species Drosophila cardini Sturtevant, 1916: round wings at lower temperatures and narrower wings at higher temperatures. The variation in egg–adult development time and in wing size, shape, and allometry was described using reaction norms and geometric morphometrics. In both species, development time and wing size decreased with increasing temperature and wing allometry showed that size explained ≈10% of the shape variation. Wing shape, however, exhibited contrasting responses. At higher temperatures, D. mercatorum developed slightly slender wings, following the pattern previously found for D. cardini, whereas D. willistoni developed plumper and shorter wings, supporting previous studies on Drosophila melanogaster Meigen, 1830. We conclude that all traits studied here were influenced by temperature, and that wing shape seems also to be influenced by phylogeny.

Quantitative genetics of wing morphology in the parasitoid wasp Nasonia vitripennis: hosts increase sibling similarity

The central aim of evolutionary biology is to understand patterns of genetic variation between species and within populations. To quantify the genetic variation underlying intraspecific differences, estimating quantitative genetic parameters of traits is essential. In Pterygota, wing morphology is an important trait affecting flight ability. Moreover, gregarious parasitoids such as Nasonia vitripennis oviposit multiple eggs in the same host, and siblings thus share a common environment during their development. Here we estimate the genetic parameters of wing morphology in the outbred HVRx population of N. vitripennis, using a sire-dam model adapted to haplodiploids and disentangled additive genetic and host effects. The results show that the wing-size traits have low heritability (h² ~ 0.1), while most wing-shape traits have roughly twice the heritability compared with wing-size traits. However, the estimates increased to h² ~ 0.6 for wing-size traits when omitting the host effect from the statistical model, while no meaningful increases were observed for wing-shape traits. Overall, host effects contributed to ~50% of the variation in wing-size traits. This indicates that hosts have a large effect on wing-size traits, about fivefold more than genetics. Moreover, bivariate analyses were conducted to derive the genetic relationships among traits. Overall, we demonstrate the evolutionary potential for morphological traits in the N. vitripennis HVRx-outbred population, and report the host effects on wing morphology. Our findings can contribute to a further dissection of the genetics underlying wing morphology in N. vitripennis, with relevance for gregarious parasitoids and possibly other insects as well.

Distribution and predictors of wing shape and size variability in three sister species of solitary bees

Morphological traits can be highly variable over time in a particular geographical area. Different selective pressures shape those traits, which is crucial in evolutionary biology. Among these traits, insect wing morphometry has already been widely used to describe phenotypic variability at the inter-specific level. On the contrary, fewer studies have focused on intra-specific wing morphometric variability. Yet, such investigations are relevant to study potential convergences of variation that could highlight micro-evolutionary processes. The recent sampling and sequencing of three solitary bees of the genus Melitta across their entire species range provides an excellent opportunity to jointly analyse genetic and morphometric variability. In the present study, we first aim to analyse the spatial distribution of the wing shape and centroid size (used as a proxy for body size) variability. Secondly, we aim to test different potential predictors of this variability at both the intra- and inter-population levels, which includes genetic variability, but also geographic locations and distances, elevation, annual mean temperature and precipitation. The comparison of spatial distribution of intra-population morphometric diversity does not reveal any convergent pattern between species, thus undermining the assumption of a potential local and selective adaptation at the population level. Regarding intra-specific wing shape differentiation, our results reveal that some tested predictors, such as geographic and genetic distances, are associated with a significant correlation for some species. However, none of these predictors are systematically identified for the three species as an important factor that could explain the intra-specific morphometric variability. As a conclusion, for the three solitary bee species and at the scale of this study, our results clearly tend to discard the assumption of the existence of a common pattern of intra-specific signal/structure within the intra-specific wing shape and body size variability.

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.

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.

Getting real with real-time qPCR: a case study of reference gene selection for morphological variation in Drosophila melanogaster wings

Accurate estimation of gene expression differences during development requires sensitive techniques combined with gold-standard normalization procedures. This is particularly true in the case of quantitative traits, where expression changes might be small. Nevertheless, systematic selection and validation of reference genes has been overlooked, even in Drosophila studies. Here, we tested the stability of six traditional reference genes across samples of imaginal wing disks from morphologically divergent strains of Drosophila melanogaster, in a two-class comparison: quantitative or qualitative variation in wing morphology. Overall, we identified and validated a pair of genes (RpL32 and Tbp) as being stably expressed in both experimental comparisons. These genes might be considered as a bona fide pair of reference genes for gene expression analyses of morphological divergence in D. melanogaster wings. They might also be taken as good candidates for experimental identification of stable reference genes in other morphological comparisons using Drosophila or other insect species. Besides, we found that some genes traditionally used as reference in qPCR experiments were not stably expressed in wing disks from the different fly strains. In fact, a significant bias was observed when the expression of three genes of interest, which are involved in the regulation of growth and patterning during imaginal wing development, was normalized with such putative reference genes. Our results demonstrate how inaccurate findings and opposite conclusions might be drawn if traditional reference genes are arbitrarily used for internal normalization without proper validation in the given experimental condition, a practice still common in qPCR experiments.

Effects of genetic factors and infection status on wing morphology of Triatoma dimidiata species complex in the Yucatán peninsula, Mexico

Triatoma dimidiata is one of the main vectors of Chagas disease, and it has been shown to be a species complex. In the Yucatán peninsula, Mexico, vector populations are non-domiciliated, and the transmission of Trypanosoma cruzi thus critically relies on vector dispersal. This leads us to study the morphologic variations in T. dimidiata wings with respect to genetic factors (sex and genotype at the ITS-2 locus), geographic location, and T. cruzi-infection status. Females were found to have larger and more symmetrical wings than males. Wing shape was influenced by ITS-2 genotypes, although differences are unlikely sufficient to allow taxonomic discrimination of the sibling species. Hybrids were shown to have similar fluctuating asymmetries in wing size and shape as parental species, but the level of asymmetry in shape varied slightly between villages. The two later findings are consistent with a high level of gene flow between parental species, and the high dispersal potential of these non-domiciliated vectors. More surprisingly, individuals infected with T. cruzi were found to have larger wings than non-infected ones. This effect, which was consistently observed across sexes, genotypes and villages, is likely to be due to a direct impact of T. cruzi on insect development. Sex and infection status are thus likely to be key factors influencing vector dispersal with important impacts on disease transmission, since dispersal directly controls the domestic abundance of these vectors. These aspects should be investigated further to fully capture the ecology and evolution of Chagas disease transmission by non-domiciliated vectors.

Evolution of the male genitalia: morphological variation of the aedeagi in a natural population of Drosophila mediopunctata

To investigate the size and shape of the aedeagus of Drosophila mediopunctata, we used basic statistics and geometric morphometrics. We estimated the level of phenotypic variation, natural and laboratory heritability as well as the phenotypic correlations between aedeagus and wing measures. The wing was used as an indicator for both body size and shape. Positive significant correlation was obtained for centroid size of aedeagus and wing for field parents and their offspring reared in the laboratory. Many positive significant phenotypic correlations were found among linear measures of both organs. The phenotypic correlations were few for aedeagus and wing shape. Coefficients of variation of the measures were on average larger in the aedeagus than in the wing for offspring reared in laboratory, but not for flies coming from the field. Significant "natural" heritabilities were found for five linear measures of the aedeagus and only one for the wing. Few significant heritabilities were found for aedeagus and wing shape, mostly ones concerning the uniform components. In an exploratory analysis, we found that inversion DS-PC0 is associated with both uniform and nonuniform components of shape, respectively, in the wing and aedeagus. Our results do not support the lock-and-key hypothesis for the male genitalia evolution, but cannot refute the sexual selection and pleiotropy hypotheses.

Evolutionary Genetics of Drosophila Mediopunctata

Drosophila mediopunctata belongs to the tripunctata group, which is the second largest Neotropical group of Drosophila with 64 species described. Here I review the work done with this forest dwelling species, and some applications of the methods developed using it as a model organism, to other species. Specifically I look at: the phylogenetic status of the tripunctata group and its relation with other groups in the Hirtodrosophila-immigrans radiation; D. mediopunctata's chromosome inversion polymorphism (altitudinal cline of frequencies and evidences of selection); the morphological variation of the wing and the development and applications of the ellipse method to describe the morphology of the wing; the variation on the number of aristal branches; the genetic basis of the polychromatism present in D. mediopunctata and its association with chromosome inversions; the sex-ratio trait and its use in the demonstration of Fisher's principle; and, finally, the finding of the transposable P-element in this species.

Variability of Wing Size and Shape in Three Populations of a Recent Brazilian Invader, Zaprionus indianus (Diptera: Drosophilidae), from Different Habitats

Zaprionus indianus (Diptera: Drosophilidae) is an African species that was introduced in Brazil near the end of the 1990's decade. To evaluate the adaptive potential of morphological traits in natural populations of this recently introduced species, we have investigated wing size and shape variation at Rio de Janeiro populations only two years after the first record of Z. indianus in Brazil. Significant genetic differences among populations from three distinct ecological habitats were detected. The heritability and evolvability estimates show that, even with the population bottleneck that should have occurred during the invasion event, an appreciable amount of additive genetic variation for wing size and shape was retained. Our results also indicated a greater influence of environmental variation on wing size than on wing shape. The importance of quantitative genetic variability and plasticity in the successful establishment and dispersal of Z. indianus in the Brazilian territory is then discussed.