Wing Size Variation Research Articles

Sexual dimorphism in Ephedrus persicae (Hymenoptera: Braconidae: Aphidiinae): intraspecific variation in size and shape

AbstractSexual dimorphism in size and shape has been studied in a wide range of organisms, but intraspecific variation in sexual dimorphism remains largely unexplored. In many parasitoid species the diversity of morphological-variation patterns within species is complicated by host effects. It is not known whether the magnitude and direction of sexual size dimorphism can be affected by the developmental environment (i.e., different host species). In this study we explored patterns of sexual dimorphism in size and shape in the aphid parasitoid Ephedrus persicae Froggatt. The analyzed sample consisted of 83 females and 54 males reared from five species of host aphids (Hemiptera: Aphididae) from various areas of the Palaearctic region. The most notable result of the study is that E. persicae displays divergent patterns of sexual dimorphism in body size and wing size: females have larger bodies than males, but males have larger wings. Our analysis of wing size and wing shape also showed significant within species variation in the degree and pattern of sexual dimorphism. Variation in wing shape between the sexes seems to be more conserved than variation in wing size. Variation in wing shape is influenced predominantly by host (biotype) and to a lesser extent by sexual dimorphism within a biotype.

Identification of the species of the Cheilosia variabilis group (Diptera, Syrphidae) from the Balkan Peninsula using wing geometric morphometrics, with the revision of status of C. melanopa redi Vujić, 1996

The present study investigates phenotypic differentiation patterns among four species of the Cheilosia variabilis group (Diptera, Syrphidae) using a landmark-based geometric morphometric approach. Herein, wing geometric morphometrics established species boundaries that confirm C. melanopa and C. redi stat. nov. as evolutionarily independent entities or separate species within the previously described C. melanopa species. Seventeen samples of C. lasiopa, C. variabilis, C. melanopa and C. redi from 11 localities on the Balkan Peninsula were analysed. Based on wing shape and size, both species boundaries and intraspecific divergent units were delineated indicating the possible presence of evolutionarily independent units within the analysed taxa. Significant differences in wing size were obtained among the analysed species and canonical variate analysis showed that wing shape was sufficiently different to allow the correct classification of 99.7% and 100% individuals of males and females, respectively. Considerable wing size variation was detected among males and females of conspecific populations of C. melanopa and males of C. variabilis. Contrary to partial discrimination based on the male wing shape among conspecific populations of C. redi and C. variabilis, clear separation of conspecific populations of C. melanopa (for both sexes) and females of C. redi and C. variabilis was observed. The UPGMA cluster analysis based on squared Mahalanobis distances revealed a close similarity between C. melanopa and C. redi, whereas C. lasiopa was the most divergent species. Results presented in this study utilize wing shape and size as new taxonomic characters in delimitating the closely related species and populations of the Cheilosia variabilis group.

Mapping Regions Within Cosmopolitan Inversion In(3R)Payne Associated With Natural Variation in Body Size in Drosophila melanogaster

Associations between genotypes for inversions and quantitative traits have been reported in several organisms, but little has been done to localize regions within inversions controlling variation in these traits. Here, we use an association mapping technique to identify genomic regions controlling variation in wing size within the cosmopolitan inversion In(3R)Payne in Drosophila melanogaster. Previous studies have shown that this inversion strongly influences variation in wing size, a trait highly correlated with body size. We found three alleles from two separate regions within In(3R)Payne with significant additive effects on wing size after the additional effect of the inversion itself had been taken into account. There were also several alleles with significant genotype-by-inversion interaction effects on wing size. None of the alleles tested had a significant additive effect on development time, suggesting different genes control these traits and that clinal patterns in them have therefore arisen independently. The presence of multiple regions within In(3R)Payne controlling size is consistent with the idea that inversions persist in populations because they contain multiple sets of locally adapted alleles, but more work needs to be done to test if they are indeed coadapted.

Inheritance of Female Flight in <I>Lymantria dispar</I> (Lepidoptera: Lymantriidae)

A clinal female flight polymorphism exists in the gypsy moth, Lymantria dispar L., where female flight diminishes from east to west across Eurasia. A Russian population where females are capable of sustained ascending flight and a North American population with females incapable of flight were crossed: parentals, reciprocal F(1) hybrids, double reciprocal F(2) hybrids, and all possible backcrosses to both the parental lines were compared. Heritabilities were estimated using a threshold model, female offspring on female parent regressions, and joint-scaling analyses. Heritability of female flight capability measured using a free flight test was at least 0.60, and variation in wing size, muscle strength, and flight behaviors contributed to the flight polymorphism. Relative wing size varied continuously and had a heritability of 0.70. Environmental variation accounted for >90% of the variation in female preflight weight and relative flight muscle strength, as estimated by an inverted female's ability to right herself. Preflight walking behavior and early deposition of eggs were each inherited through a single gene with two co-dominant alleles. There was no evidence for sex-linkage or maternal effects in female flight capability or associated traits. Continued vigilance to exclude and eradicate introductions of strains capable of female flight in North America is warranted even in areas where no females fly, because some of the alleles needed for full flight capability may not be present in the North American populations, and some flight capability is maintained in the hybrids that could increase the rate of spread of L. dispar.

DIFFERENTIATION BETWEEN TWO SALT MARSH BEETLE ECOTYPES: EVIDENCE FOR ONGOING SPECIATION

The plausibility of trait divergence under divergent natural selection in the presence of gene flow in natural populations is a contentious issue in evolutionary research. Its importance lies in the fact that this process is thought to be one of the key triggers in ecological speciation in which a species splits into ecologically distinct forms when separate niches are occupied. In this study we demonstrate strong genetic divergence at the IDH1 locus between pond- and canal-inhabiting individuals of the salt marsh beetle Pogonus chalceus from the Guérande salt fields. Moreover, wing size, a trait that has a heritable basis in this species, was significantly larger in the pond populations, which is in concordance with the unstable nature of this habitat. The relationship between IDH1 allele frequencies and wing size variation was consistent with patterns seen across western European populations. By means of neutral allozymes and microsatellites we detected a small but significant degree of sexual isolation between ecotypes. We conclude that speciation is ongoing and that divergence reflects a balance between selection and gene flow.

Parasites hinder monarch butterfly flight: implications for disease spread in migratory hosts

AbstractMonarch butterflies (Danaus plexippus) are parasitized by the protozoanOphryocystis elektroscirrhathroughout their geographical range. Monarchs inhabiting seasonally fluctuating environments migrate annually, and parasite prevalence is lower among migratory relative to non‐migratory populations. One explanation for this pattern is that long‐distance migration weeds out infected animals, thus reducing parasite prevalence and transmission between generations. In this study we experimentally infected monarchs from a migratory population and recorded their long‐distance flight performance using a tethered flight mill. Results showed that parasitized butterflies exhibited shorter flight distances, slower flight speeds, and lost proportionately more body mass per km flown. Differences between parasitized and unparasitized monarchs were generally not explained by individual variation in wing size, shape, or wing loading, suggesting that poorer flight performance among parasitized hosts was not directly caused by morphological constraints. Effects of parasite infection on powered flight support a role for long‐distance migration in dramatically reducing parasite prevalence in this and other host–pathogen systems.

Different cell size and cell number contribution in two newly established and one ancient body size cline of Drosophila subobscura.

Latitudinal genetic clines in body size occur in many ectotherms including Drosophila species. In the wing of D. melanogaster, these clines are generally based on latitudinal variation in cell number. In contrast, differences in wing area that evolve by thermal selection in the laboratory are in general based on cell size. To investigate possible reasons for the different cellular bases of these two types of evolutionary response, we compared the newly established North and South American wing size clines of Drosophila subobscura. The new clines are based on latitudinal variation in cell area in North America and cell number in South America. The ancestral European cline is also based on latitudinal variation in cell number. The difference in the cellular basis of wing size variation in the American clines, which are roughly the same age, together with the similar cellular basis of the new South American cline and the ancient European one, suggest that the antiquity of a cline does not explain its cellular basis. Furthermore, the results indicate that wing size as a whole, rather than its cellular basis, is under selection. The different cellular bases of different size clines are most likely explained either entirely by chance or by different patterns of genetic variance--or its expression--in founding populations.

EXPERIMENTAL ANALYSES OF WING SIZE, FLIGHT, AND SURVIVAL IN THE WESTERN WHITE BUTTERFLY.

Butterflies have distinctively large wings relative to body size, but the functional and fitness consequences of wing size for butterflies are largely unknown. I use natural and experimentally generated variation in wing surface area to examine how decreased wing size affects flight and survival in a population of the western white butterfly, Pontia occidentalis. In the laboratory, experimental reductions in wing area (reduced-wings manipulation) significantly increased wingbeat frequencies of hovering butterflies, whereas a control manipulation had no detectable effects. In contrast, behavioral observations and mark-release-recapture (MRR) studies in the field detected no significant differences in flight activity, initial dispersal rates, or recapture probabilities among treatment groups. Estimated selection coefficients indicated that natural variation in wing size, body mass, and wing loading in the population were not significantly correlated with survival in the two MRR studies. In two mark-recapture studies with manipulated butterflies, survival probabilities were not significantly different for reduced-wings individuals compared with control or unmanipulated individuals. In summary, experimental reductions in wing area significantly altered aspects of flight in the laboratory, but did not detectably alter flight or survival in the field for this population. The large wing size typical of butterflies may reduce the functional and survival consequences of wing size variation within populations.

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 degrees C and 25 degrees 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.

Biometrics and survival rates of Pallid Swifts Apus pallidus in Portugal

A colony of Pallid Swifts Apus pallidus in the Serra da Arrábida (Southern Portugal) was visited regularly during seven consecutive breeding seasons (from 1990 to 1996) in order to study the birds’ biometrics and survival rates through capture and recapture. Wing‐length and weight measurements were taken; wing‐length values corroborate the hypothesis of a west to east clinal variation in wing size within the distribution range of the sub‐species A. p. brehmorum. Annual survival rates varied between 0.75 and 0.86 during the breeding seasons from 1990 to 1995, and a significant correlation was found between survival rates and the rainfall indices from the Sahel region of Africa, where the species winters.

Latitudinal variation in wing size in Drosophila subobscura and its dependence on polygenes of chromosome O

The genetic variability of natural populations of Drosophila subobscura derived from localities situated approximately along a north-to-south diameter through the distribution area of the species was studied. The polygenic and adaptive trait ‘wing size’ shows a continuous clinal reduction from north to south. The comparison between flies homozygous or randomly heterozygous for wild chromosomes showed that heterozygous flies are on an average bigger than homozygous flies and that overdominance exists for increased wing size. The genetic variance proved lower in central than in ecologically marginal populations. From the analysis of left-right asymmetry it could be shown that heterozygous flies are more homeostatic than homozygous flies but no differences appeared between populations. Therefore, lower phenotypic variability in central populations must be due to lower genetic variation. An hypothesis was put forward that normalizing selection eliminates + and-alleles in the central populations; in marginal populations, on the other hand, either + (north) or-(south) alleles are favoured and the genetic variability is augmented.