Plasticity of Drosophila melanogaster wing morphology: effects of sex, temperature and density

In this paper we use an adjusted ellipse to the contour of the wings of Drosophila as an experimental model to study phenotypic plasticity. The geometric properties of the ellipse describe the wing morphology. Size is the geometric mean of its two radii; shape is the ratio between them; and, the positions of the apexes of the longitudinal veins are determined by their angular distances to the major axis of the ellipse. Flies of an inbred laboratory strain of Drosophila melanogaster raised at two temperatures (16.5°C and 25°C) and two densities (10 and 100 larvae per vial) were used. One wing of at least 40 animals of each sex and environmental condition were analyzed (total = 380), a measurement of thorax length was also taken. Wing size variation could be approximately divided into two components: one related to shape variation and the other shape independent. The latter was influenced primarily by temperature, while the former was related to sex and density. A general pattern could be identified for the shape dependent variation: when wings become larger they become longer and the second, fourth and fifth longitudinal veins get closer to the tip of the wing. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of wing morphology and fluctuating asymmetry in interspecific hybrids between Drosophila buzzatii and D. koepferae

In this work we investigate the effect of interspecific hybridization on wing morphology using geometric morphometrics in the cactophilic sibling species D. buzzatii and D. koepferae. Wing morphology in F₁ hybrids exhibited an important degree of phenotypic plasticity and differs significantly from both parental species. However, the pattern of morphological variation between hybrids and the parental strains varied between wing size and wing shape, across rearing media, sexes, and crosses, suggesting a complex genetic architecture underlying divergence in wing morphology. Even though there was significant fluctuating asymmetry for both, wing size and shape in F₁ hybrids and both parental species, there was no evidence of an increased degree of fluctuating asymmetry in hybrids as compared to parental species. These results are interpreted in terms of developmental stability as a function of a balance between levels of heterozygosity and the disruption of coadaptation as an indirect consequence of genomic divergence.     

Outbreeding causes developmental instability in <Emphasis Type="Italic">Drosophila subobscura</Emphasis>

A possible effect of interpopulation hybridization is either outbreeding depression, as a consequence of breakdown of coadapted gene complexes which can increase developmental instability (DI) of the traits, or increased heterozygosity, which can reduce DI. One of the principal methods commonly used to estimate DI is the variability of fluctuating asymmetry (FA). We analysed the effect of interpopulation hybridization in Drosophila subobscura through the variability in the wing size and the FA of wing length and width for both sexes in parental, F1 and F2 generations. The results of the wing size per se in intra- and interpopulation hybrids of D. subobscura do not explicitly reveal the significance of either of the two hypotheses. However, the results of the FA of the wing traits give a different insight. The FA of wing length and width generally increases in interpopulation crosses in F1 with respect to the FA in the parental generation, which suggests the possibility that outbreeding depression occurred in the first generation after the hybridization event. We generally observed that the FA values for the wing length and width of interpopulation hybrids were higher in F1 and F2 generations, compared to intrapopulation hybrids in same generations. These results suggest that the association between coadaptive genes with the same evolutionary history are the most probable mechanism that maintains the developmental homeostasis in Drosophila subobscura populations.     

WITHIN- AND BETWEEN-GENERATION EFFECTS OF TEMPERATURE ON THE MORPHOLOGY AND PHYSIOLOGY OF DROSOPHILA MELANOGASTER

We investigated the effects of developmental and parental temperatures on several physiological and morphological traits of adult Drosophila melanogaster. Flies for the parental generation were raised at either low or moderate temperature (18°C or 25°C) and then mated in the four possible sex-by-parental temperature crosses. Their offspring were raised at either 18°C or 25°C and then scored as adults for morphological (dry body mass, wing size, and abdominal melanization [females only]), physiological (knock-down temperature, and thermal dependence of walking speed), and life history (egg size) traits. The experiment was replicated, and the factorial design allows us to determine whether and how paternal, maternal, and developmental temperatures (as well as offspring sex) influence the various traits. Sex and developmental temperature had major effects on all traits. Females had larger bodies and wings, higher knock-down temperatures, and slower speeds (but similar shaped performance curves) than males. Development at 25°C (versus at 18°C) increased knock-down temperature, increased maximal speed and thermal performance breadth, decreased the optimal temperature for walking, decreased body mass and wing size, reduced abdominal melanization, and reduced egg size. Parental temperatures influenced a few traits, but the effects were generally small relative to those of sex or developmental temperature. Flies whose mother had been raised at 25°C (versus at 18°C) had slightly higher knock-down temperature and smaller body mass. Flies whose father had been raised at 25°C had relatively longer wings. The effects of paternal, maternal, and developmental temperatures sometimes differed in direction. The existence of significant within- and between-generation effects suggests that comparative studies need to standardize thermal environments for at least two generations, that attempts to estimate “field” heritabilities may be unreliable for some traits, and that predictions of short-term evolutionary responses to selection will be difficult.     

Geometric morphometric analysis of the effect of temperature on wing size and shape in Aedes albopictus

Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperature has a well‐known effect on insect metric properties. Can such effects blur the taxonomic signal embedded in the wing? Two strains of Aedes albopictus (laboratory and field strain) were examined under three different rearing temperatures (26, 30 and 33 °C) using landmark‐ and outline‐based morphometric approaches. The wings of each experimental line were compared with Aedes aegypti. Both approaches indicated similar associations between wing size and temperature. For the laboratory strain, the wing size significantly decreased as the temperature increased. For the field strain, the largest wings were observed at the intermediate temperature. The two morphometric approaches describing shape showed different sensibilities to temperature. For both strains and sexes, the landmark‐based approach disclosed significant wing shape changes with temperature changes. The outline‐based approach showed lesser effects, detecting significant changes only in laboratory females and in field males. Despite the size and shape changes induced by temperature, the two strains of Ae. albopictus were always distinguished from Ae. aegypti. The present study confirms the lability of size. However, it also suggests that, despite environmentally‐induced variation, the architecture of the wing still provides a strong taxonomic signal.     

The genetics of phenotypic plasticity. III. Genetic correlations and fluctuating asymmetries

We examined the relationship of three aspects of development, phenotypic plasticity, genetic correlations among traits, and developmental noise, for thorax length, wing length, and number of sternopleural bristles in Drosophila melanogaster. We used 14 lines which had previously been selected on either thorax length or plasticity of thorax length in response to temperature. A half-sib mating design was used and offspring were raised at 19° C or 25° C. We found that genetic correlations were stable across temperatures despite the large levels of plasticity of these traits. Plasticities were correlated among developmentally related traits, thorax and wing length, but not among unrelated traits, lengths and bristle counts. Amount of developmental noise, measured as fluctuating asymmetry and within-environmental variation, was positively correlated with amount of plasticity only for some traits, thorax length and bristle number, and only at one temperature, 25° C.     

Phenotypic plasticity across 50 MY of evolution: Drosophila wing size and temperature

We studied the response in wing size to rearing at different temperatures of nine strains of Drosophila representing six species. The species varied in their natural habitats from tropical to temperate and one cosmopolitan. The evolutionary divergence of the species spans 50 million years. While some quantitative differences were found, all species responded to temperature very similarly: females increased an average of ∼11% and males ∼14% when reared at 19 °C compared to 25 °C. The phenotypic plasticity in wing size in response to temperature appears to be a fixed trait in Drosophila across long evolutionary time and diverse ecological settings. This likely reflects the close relationship between wing area (and thus wing loading) and insect body mass that is a crucial factor for flight regardless of ecology and is, thus, maintained across long evolutionary time.     

Effect of different larval rearing temperatures on the productivity (Ro) and morphology of the malaria vector Anopheles superpictus Grassi (Diptera: Culicidae) using geometric morphometrics

Temperature affects both the biology and morphology of mosquito vectors. Geometric morphometrics is a useful new tool for capturing and analyzing differences in shape and size in many morphological parameters, including wings. We have used this technique for capturing the differences in the wings of the malaria vector Anopheles superpictus, using cohorts reared at six different constant temperatures (15°, 20°, 25°, 27°, 30°, and 35° C) and also searched for potential correlations with the life tables of the species. We studied wing shape in both male and female adults, using 22 landmarks on the wing in relation to ecological parameters, including the development rate. The ecological zero was calculated as 9.93° C and the thermal constant as 296.34 day‐degrees. The rearing temperature affects egg, larval, and pupal development and also the total time from egg to adult. As rearing temperatures increased, longevity decreased in both sexes. In An. superpictus, R_o value and productivity correlated with the statistically significant gradual deformations in the wing shape related to size in both sexes. These deformations directly linked to differences in immature rearing temperatures. Analysis using PCA and UPGMA phenograms showed that although wings of females became narrower dorsoventrally as the temperature increased, they became broader in males. Comparisons of the wing landmarks indicated the medial part of the wing was most affected by larval rearing temperatures, showing relatively more deformations. Algorithmic values of the life tables were determined in correlation with the results of geometric morphometrics. Comparisons of centroid sizes in the cohorts showed that overall wing size became smaller in both sexes in response to higher rearing temperatures.     

Evolution of the male genitalia: morphological variation of the aedeagi in a natural population of <Emphasis Type="Italic">Drosophila mediopunctata</Emphasis>

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.     

Adaptation to different climates results in divergent phenotypic plasticity of wing size and shape in an invasive drosophilid

The phenotypic plasticity of wing size and wing shape of Zaprionus indianus was investigated in relation to growth temperature (17°C to 31°C) in two natural populations living under different climates, equatorial and subtropical. The two populations were clearly distinguished not only by their wing size (the populations from the colder climate being bigger in size), but also by the shape of the response curves to growth temperature i.e., their reaction norms. In this respect, the temperature at which the size of the wing was maximum was about 3°C higher in the equatorial population. Such a difference in size plasticity is already found in two other nonclosely related species, might be a general evolutionary pattern in drosophilids. Wing shape was investigated by calculating an ellipse included into the wing blade, then by considering the ratio of the two axes, and also by analysing the angular position of 10 wing-vein landmarks. For an overall shape index (ratio of the two axes of the ellipse), a regular and almost linear increase was observed with increasing temperature i.e., a more round shape at high temperatures. Wing shape was also analysed by considering the variations of the various angles according to temperature. A diversity of response curves was observed, revealing either a monotonous increase or decrease with increasing temperature, and sometimes a bell shape curve. An interesting conclusion is that, in most cases, a significant difference was observed between the two populations, and the difference was more pronounced at low temperatures. These angular variations are difficult to interpret in an evolutionary context. More comparative studies should be undertaken before reaching some general conclusions.     

Flies evolved small bodies and cells at high or fluctuating temperatures

Recent theory predicts that the sizes of cells will evolve according to fluctuations in body temperature. Smaller cells speed metabolism during periods of warming but require more energy to maintain and repair. To evaluate this theory, we studied the evolution of cell size in populations of Drosophila melanogaster held at either a constant temperature (16°C or 25°C) or fluctuating temperatures (16 and 25°C). Populations that evolved at fluctuating temperatures or a constant 25°C developed smaller thoraxes, wings, and cells than did flies exposed to a constant 16°C. The cells of flies from fluctuating environments were intermediate in size to those of flies from constant environments. Most genetic variation in cell size was independent of variation in wing size, suggesting that cell size was a target of selection. These evolutionary patterns accord with patterns of developmental plasticity documented previously. Future studies should focus on the mechanisms that underlie the selective advantage of small cells at high or fluctuating temperatures.     

Heat stress and age induced maternal effects on wing size and shape in parthenogenetic Drosophila mercatorum

Maternal effects on progeny wing size and shape in a homozygous parthenogenetic strain of Drosophila mercatorum were investigated. The impact of external maternal factors (heat stress) and the impact of internal maternal factors (different maternal and grand maternal age) were studied. The offspring developed under identical environmental conditions, and due to lack of genetic variation any phenotypic difference among offspring could be ascribed to maternal effects. Wing size was estimated by centroid size, shape was analysed with the Procrustes geometric morphometric method and variation in landmark displacement was visualized by principal component analysis. Both kinds of maternal effects had a significant impact on progeny wing size and shape. Maternal heat stress led to the same pattern of response in size and shape among the progeny, with increased difference between the control group and progeny from heat stressed flies in both size and shape with increased maternal heat stress temperature. The effects of maternal age, however, led to different responses in size and shape between the different progeny groups. The observed variation in landmark displacements was similar, and in both cases mainly associated with shape differences of the posterior part of the wing. Finally, our results suggest that maternal effect has some evolutionary implications by altering the genetic correlations among traits, which can affect the response to selective pressures.     

Morphological and histological examination of polyphenic wing formation in the pea aphid <Emphasis Type="Italic">Acyrthosiphon pisum</Emphasis> (Hemiptera,Hexapoda)

Aphids display divergent adult phenotypes, depending on environmental conditions experienced during their embyonic and nymphal stages in their complex life cycles. The plastic developmental mode is an extreme case of phenotypic plasticity, so-called “polyphenism”, in which discrete multiple phenotypes are produced based on a single genome. For example, winged and wingless adult females are derived from a single genotype. However, the developmental mechanisms producing these polyphenic traits according to the extrinsic stimuli, such as density conditions, still remain unknown. In this study, to analyze the developmental processes underlying the wing polyphenism, we extensively observed and compared wing development in the winged and wingless individuals in parthenogenetic generations of the aphid Acyrthosiphon pisum (Harris), using scanning electron microscopy and histological sectioning. At the first-instar stage, the wing primordia were observed both in the future winged (W) and wingless (WL) nymphs. Developmental differences can be seen from the second-instar stage, when wing primordia degenerate in the WL nymphs, while they develop and become more thickened in the W nymphs, suggesting that the developmental programs should be launched prior to this stage. Furthermore, during the third- to fifth-instar stages, wing buds and flight muscles were well developed in the W nymphs, while wing primordia completely disappeared in the WL ones. In addition, the observation on the detailed developmental process of wing primordia during the third-instar W nymphs showed that the wing buds become swollen especially at the basal part, even during the intermolt period. This was caused by the development of wing epithelia under the cuticle of this instar nymph. Actually on the surface of the cuticle of wing-bud bases, there were numerous furrows, which gradually expand during the intermolt period. The similar situation was also observed at the forth-instar nymphs, in which the wings are formed in the complicated manner inside the wing pads. Furthermore, the developmental process of flight muscles was also described in detail. These dynamic developmental differences between the wing morphs should be regulated under the gene expression cascades that switch according to environmental stimuli.     

Heritability of wing development and body size in a carabid beetle,Pogonus chalceus MARSHAM,and its evolutionary significance

Summary The wing-polymorphic ground beetle Pogonus chalceus MARSHAM was subjected to crossbreeding experiments under different laboratory conditions in order to estimate the genetic and environmental contributions to the total phenotypic variance in different morphological traits related to relative wing development and body size. Heritability of relative wing development appears to be strong. Beetle size also seems genetically determined in some cases, but separation of male and female parent contribution invariably shows a maternal effect. These results are tested in a breeding experiment with a high number of progeny from one parental pair, reared at two temperatures and at two levels of food supply. Relative wing development is not influenced by these environmental conditions, as expected, but different temperatures add significant variance to the body size values. The experimental results are used to explain interdemic variation in these morphological traits, as observed in three isolated field populations. The reproductive effort under optimum breeding conditions is higher in macropterous beetles than in beetles with reduced wings, but this could result from their larger body size. Migtion seems to be the most plausible underlying evolutionary mechanism for the observed wing reduction in older populations.     

Genetic differences and phenotypic plasticity in body size between high- and low-altitude populations of the ground beetle Carabus tosanus

The body size of a univoltine carabid beetle Carabus tosanus on Shikoku Island, Japan, was clearly smaller in higher‐altitude populations (subspecies), which possibly represents incipient speciation. To explore the determinants of altitudinal differences in body size in this species, we studied the degree of phenotypic plasticity by conducting rearing experiments at two constant temperatures and examined genetic differences through interpopulation crosses. At 15 °C, C. tosanus had a longer developmental period and a shorter adult body than at 20 °C. Nevertheless, variation in body size due to temperature effects (phenotypic plasticity) was small compared to the interpopulation differences, which suggests substantial genetic differences between populations (subspecies) at different altitudes. In F₁ offspring from crosses between a low‐altitude (subspecies tosanus) and a high‐altitude population (subspecies ishizuchianus), adult body length was affected by the genotypes of both parents, with an interaction effect of parental genotype and offspring sex. Further analyses revealed that adult body length was affected by sex‐linked factors in addition to autosomal factors. These genetic differences in body size may have resulted from adaptations to different altitudes and may be important for the process of incipient speciation because body size differences could contribute to premating reproductive isolation.     

Nonlinear effects of temperature on body form and developmental canalization in the threespine stickleback

Theoretical models predict that nonlinear environmental effects on the phenotype also affect developmental canalization, which in turn can influence the tempo and course of organismal evolution. Here, we used an oceanic population of threespine stickleback (Gasterosteus aculeatus) to investigate temperature‐induced phenotypic plasticity of body size and shape using a paternal half‐sibling, split‐clutch experimental design and rearing offspring under three different temperature regimes (13, 17 and 21 °C). Body size and shape of 466 stickleback individuals were assessed by a set of 53 landmarks and analysed using geometric morphometric methods. At approximately 100 days, individuals differed significantly in both size and shape across the temperature groups. However, the temperature‐induced differences between 13 and 17 °C (mainly comprising relative head and eye size) deviated considerably from those between 17 and 21 °C (involving the relative size of the ectocoracoid, the operculum and the ventral process of the pelvic girdle). Body size was largest at 17 °C. For both size and shape, phenotypic variance was significantly smaller at 17 °C than at 13 and 21 °C, indicating that development is most stable at the intermediate temperature matching the conditions encountered in the wild. Higher additive genetic variance at 13 and 21 °C indicates that the plastic response to temperature had a heritable basis. Understanding nonlinear effects of temperature on development and the underlying genetics are important for modelling evolution and for predicting outcomes of global warming, which can lead not only to shifts in average morphology but also to destabilization of development.     

The genetics of phenotypic plasticity. IV. Chromosomal localization

The contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanogaster were measured. A composite stock was created from lines previously subjected to selection on thorax size or plasticity of thorax size. A chromosome extraction was performed against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, chromosome I and the balancer stock showed no plasticity, the composite stock showed the greatest plasticity, and chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19° C and 25° C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. Chromosome III showed significant genetic variation for both thorax size and plasticity. We tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25° C, in agreement with earlier work. A negative correlation was found at 19° C for chromosome II, contrary to earlier work.     

Genetic variation for an aphid wing polyphenism is genetically linked to a naturally occurring wing polymorphism

Many polyphenisms are examples of adaptive phenotypic plasticity where a single genotype produces distinct phenotypes in response to environmental cues. Such alternative phenotypes occur as winged and wingless parthenogenetic females in the pea aphid (Acyrthosiphon pisum). However, the proportion of winged females produced in response to a given environmental cue varies between clonal genotypes. Winged and wingless phenotypes also occur in males of the sexual generation. In contrast to parthenogenetic females, wing production in males is environmentally insensitive and controlled by the sex-linked, biallelic locus, aphicarus (api). Hence, environmental or genetic cues induce development of winged and wingless phenotypes at different stages of the pea aphid life cycle. We have tested whether allelic variation at the api locus explains genetic variation in the propensity to produce winged females. We assayed clones from an F2 cross that were heterozygous or homozygous for alternative api alleles for their propensity to produce winged offspring. We found that clones with different api genotypes differed in their propensity to produce winged offspring. The results indicate genetic linkage of factors controlling the female wing polyphenism and male wing polymorphism. This finding is consistent with the hypothesis that genotype by environment interaction at the api locus explains genetic variation in the environmentally cued wing polyphenism.     

Effects of parental radiation exposure on developmental instability in grasshoppers

Mutagenic and epigenetic effects of environmental stressors and their transgenerational consequences are of interest to evolutionary biologists because they can amplify natural genetic variation. We studied the effect of parental exposure to radioactive contamination on offspring development in lesser marsh grasshopper Chorthippus albomarginatus. We used a geometric morphometric approach to measure fluctuating asymmetry (FA), wing shape and wing size. We measured time to sexual maturity to check whether parental exposure to radiation influenced offspring developmental trajectory and tested effects of radiation on hatching success and parental fecundity. Wings were larger in early maturing individuals born to parents from high radiation sites compared to early maturing individuals from low radiation sites. As time to sexual maturity increased, wing size decreased but more sharply in individuals from high radiation sites. Radiation exposure did not significantly affect FA or shape in wings nor did it significantly affect hatching success and fecundity. Overall, parental radiation exposure can adversely affect offspring development and fitness depending on developmental trajectories although the cause of this effect remains unclear. We suggest more direct measures of fitness and the inclusion of replication in future studies to help further our understanding of the relationship between developmental instability, fitness and environmental stress.     

A fusant of Sphingomonas sp. GY2B and Pseudomonas sp. GP3A with high capacity of degrading phenanthrene

A fusant strain F14 with high biodegradation capability of phenanthrene was obtained by protoplast fusion between Sphingomonas sp. GY2B (GenBank DQ139343) and Pseudomonas sp. GP3A (GenBank EU233280). F14 was screened and identified from 39 random fusants by antibiotic tests, scanning electron microscope (SEM) and randomly amplified polymorphic DNA (RAPD). The result of SEM analysis demonstrated that the cell shape of fusant F14 different from parental strains. RAPD analysis of 5 primers generated a total of 70 bands. The genetic similarity indices between F14 and parental strains GY2B and GP3A were 27.9 and 34.6 %, respectively. F14 could rapidly degrade phenanthrene within 24 h, and the degradation efficiency was much better than GY2B and GP3A. GC–MS analysis of metabolites of phenanthrene degradation indicated F14 had a different degradation pathway from GY2B. Furthermore, the fusant strain F14 had a wider adaptation of temperatures (25–36 °C) and pH values (6.5–9.0) than GY2B. The present study indicated that fusant strain F14 could be an effective and environment-friendly bacterial strain for PAHs bioremediation.