Geographical and sexual variation of wing size in the monophagous flower-breeding species Drosophila flavopilosa

Flower samples of Cestrum parqui (Solanaceae) containing preadult forms of Drosophila flavopilosa were collected at four localities from the Maipo Valley in the Central zone of Chile (Lat. 33°40'S), one at sea level and the others at 300 m, 780 m and 1365 m of altitude. Only the adults which emerged after 18 days of permanency of the flowers in a chamber at 22°C were employed for wing analysis. Nine different measurements were made in the wings of 100 males and 100 females from each population. In males, a clear tendency of increasing wing length and width according to elevation above sea level was found. Females, however, exhibited a quite different type of variation; the larger and wider wings corresponding to the populations originated in the laces of intermediate elevation. As a result of the different pattern of wing variation in males and females, the sexual dimorphism was found to be significantly different between the studied populations. The results support the idea that males and females react in a different way to selective pressures affecting wing development.     

Adaptive wing asymmetry in males of the speckled wood butterfly (Pararge aegeria)?

We analysed asymmetry in the wings of the speckled wood butterfly (Pararge aegeria)by measuring area, length and width of fore- and hindwings. The type of asymmetry is fluctuating except for fore- and hindwing area, and forewing width in males, where asymmetry is directional. The amount of asymmetry (variance of the left wing minus the right wing) is less in males than in females. Within males asymmetry was directional and less in pale, predominantly territorial males than in melanic, predominantly non-territorial males. Asymmetry was negatively related to growth rate within females, but not within males. Females grew faster than males, but had higher asymmetry, whereas the more asymmetrical melanic males grew more slowly than pale males. The differences in the type and amount of asymmetry between the sexes and colour classes suggest a relationship with sex-specific flight patterns such as the territorial spiralling flight of males. We hypothesize that slightly asymmetrical males turn faster, and therefore are superior in territorial disputes over more symmetrical or extremely asymmetrical males. This implies that sexual selection via male–male competition influences the type and amount of asymmetry. The existence of more extremely asymmetrical individuals in females, and to a lesser extent in non-territorial males, may indicate that there are costs in reducing asymmetry.     

A new species of the chalcid-wasp genus Ericydnus walker (Hymenoptera, Chalcidoidea, Encyrtidae) from West Siberia

A new species, Ericydnus novosibiricus sp. n., is described. The main characters differentiating the new species from the similar E. longicornis Dalman are as follows: female??fore wing noticeably shortened, with almost normally developed veins and rounded apex, marginal vein longer than postmarginal vein, 6th flagellar segment slightly longer than wide, club truncate; male??fore wing noticeably shortened, with almost normally developed veins and pointed apex, flagellar segments subsequently becoming wider toward antennal apex.     

Density‐dependent sex‐biased development of macroptery in a water strider

In wing‐polymorphic insects, wing morphs differ not only in dispersal capability but also in life history traits because of trade‐offs between flight capability and reproduction. When the fitness benefits and costs of producing wings differ between males and females, sex‐specific trade‐offs can result in sex differences in the frequency of long‐winged individuals. Furthermore, the social environment during development affects sex differences in wing development, but few empirical tests of this phenomenon have been performed to date. Here, I used the wing‐dimorphic water strider Tenagogerris euphrosyne to test how rearing density and sex ratio affect the sex‐specific development of long‐winged dispersing morphs (i.e., sex‐specific macroptery). I also used a full‐sib, split‐family breeding design to assess genetic effects on density‐dependent, sex‐specific macroptery. I reared water strider nymphs at either high or low densities and measured their wing development. I found that long‐winged morphs developed more frequently in males than in females when individuals were reared in a high‐density environment. However, the frequency of long‐winged morphs was not biased according to sex when individuals were reared in a low‐density environment. In addition, full‐sib males and females showed similar macroptery incidence rates at low nymphal density, whereas the macroptery incidence rates differed between full‐sib males and females at high nymphal density. Thus complex gene‐by‐environment‐by‐sex interactions may explain the density‐specific levels of sex bias in macroptery, although this interpretation should be treated with some caution. Overall, my study provides empirical evidence for density‐specific, sex‐biased wing development. My findings suggest that social factors as well as abiotic factors can be important in determining sex‐biased wing development in insects.     

Sex differences in survival selection in the serin,Serinus serinus

Natural selection is demonstrated in most natural populations which suggests that populations are dispatched from their adaptive peaks as a result of selection on correlated characters, or conflicting selection between the sexes. We analysed patterns of survival selection in a population of serins (Serinus serinus) outside Barcelona over a period of 13 years. There was directional selection for increased wing length in males and females accompanied by strong disruptive selection on both tail and wing length in males and a selection against a positive correlation between the two characters in males. In females there was directional selection for increased bill width but decreased bill depth, which should be contrasted to the stabilizing selection acting on bill depth in males. There were conflicting selection on the characters within a sex and conflicting selection of the same characters between sexes, which constrain the rate of access to the nearest adaptive peak.     

Sexual dimorphism and intraspecific variation in wing size and shape of Tongeia fischeri (Lepidoptera: Lycaenidae)

Wing morphological variations are described here for the lycaenid butterfly Tongeia fischeri. A landmark‐based geometric morphometric approach based on wing venation of 197 male and 187 female butterflies collected in Japan was used to quantify wing size and shape variations between sexes and among populations. Sexual dimorphism in wing size and shape was detected. Females had significantly larger wings than males, while males showed a relatively elongated forewing with a longer apex and narrower wing tornus in comparison to females. Intraspecific variations in wing morphology among populations were revealed for the wing shape, but not wing size. Distinct wing shape differences were found in the vein intersections area around the distal part of the discal cell where median veins originated in the forewing and around the origin of the CU1 vein in the hindwing. In addition, phenotypic relationships inferred from wing shape variations grouped T. fischeri populations into three groups, reflecting the subspecies classification of the species. The spatial variability and phenotypic relationships between conspecific populations of T. fischeri detected here are generally in agreement with the previous molecular study based on mitochondrial and nuclear sequences, suggesting the presence of a phylogenetic signal in the wing shape of T. fischeri, and thus having taxonomic implications.     

Cuckoo Hosts in Southern Africa

There is currently no reliable, affordable method of sexing Mauritius Fodies in their first non-breeding season. Ringed immature fodies from a released population on an offshore island were caught in April and May 2005 and sexed in later breeding seasons. Males had longer wing lengths and tarsi than females, with no overlap in wing length between sexes. Males in their first breeding season could usually be differentiated from older males by the paleness and completeness of their breeding plumage. Two adult females grew red feathers characteristic of breeding males in the winter of 2006. It is possible to sex Mauritius Fodies using wing length and separate immature males from adults using the darkness of the bill in the non-breeding season. It is not possible to separate unringed adult and immature females following the postjuvenile and postbreeding moults using current knowledge.     

Wing shape,wing size,and sexual dimorphism in eye‐span in stalk‐eyed flies (Diopsidae)

The eyes of stalk‐eyed flies (Diopsidae) are positioned at the end of rigid peduncles (‘stalks’) protruding laterally from the head. Eye‐stalk length varies within the family and, in some species, varies between males and females. Larger eye‐stalks in males result from sexual selection for longer stalks, a trait that increases male reproductive success. In the present study, we examined whether an increase in eye‐stalk length results in an adjustment of wing size and shape to deal with the burden of bearing an exaggerated ‘ornament’. We compared wing morphology among ten species of stalk‐eyed flies that differ in eye‐span and the degree of sexual dimorphism. Mass‐specific wing length differed between males and females in seven out of the ten species. Nondimensional wing shape parameters differed between the species (P < 0.001), but mostly did not differ between males and females of the same species. Dimorphism in eye‐span closely correlated with dimorphism in wing length (r = 0.89, P < 0.001) and the correlation remained significant (r = 0.81, P = 0.006) after correcting for phylogenetic relationships. Once corrected for phylogenetic relatedness, the mass‐specific wing length of males (but not females) was weakly correlated with mass‐specific eye‐span (r = 0.66, P = 0.042). We propose that the observed proportional increase in wing length associated with increased eye‐span can facilitate aerial manoeuverability, which would otherwise be handicapped by the elevated moment of inertia imposed by the wider head. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 860–871.     

Sex separation strategies: past experience and new approaches

The success of the sterile insect technique (SIT) and other genetic strategies designed to eliminate large populations of insects relies on the efficient inundative releases of competitive, sterile males into the natural habitat of the target species. As released sterile females do not contribute to the sterility in the field population, systems for the efficient mass production and separation of males from females are needed. For vector species like mosquitoes, in which only females bite and transmit diseases, the thorough removal of females before release while leaving males competent to mate is a stringent prerequisite. Biological, genetic and transgenic approaches have been developed that permit efficient male-female separation for some species considered for SIT. However, most sex separation methods have drawbacks and many of these methods are not directly transferable to mosquitoes. Unlike genetic and transgenic systems, biological methods that rely on sexually dimorphic characters, such as size or development rate, are subject to natural variation, requiring regular adjustment and re-calibration of the sorting systems used. The yield can be improved with the optimization of rearing, but the scale of mass production places practical limits on what is achievable, resulting in a poor rearing to output ratio. High throughput separation is best achieved with scalable genetic or transgenic approaches.     

Sexual dichroism and pigment localization in the wing scales of Pieris rapae butterflies

The beads in the wing scales of pierid butterflies play a crucially important role in wing coloration as shown by spectrophotometry and scanning electron microscopy (SEM). The beads contain pterin pigments, which in Pieris rapae absorb predominantly in the ultraviolet (UV). SEM demonstrates that in the European subspecies Pieris rapae rapae, both males and females have dorsal wing scales with a high concentration of beads. In the Japanese subspecies Pieris rapae crucivora, however, only the males have dorsal wing scales studded with beads, and the dorsal scales of females lack beads. Microspectrophotometry of single scales without beads yields reflectance spectra that increase slightly and monotonically with wavelength. With beads, the reflectance is strongly reduced in the UV and enhanced at the longer wavelengths. By stacking several layers of beaded scales, pierid butterflies achieve strong colour contrasts, which are not realized in the dorsal wings of female P. r. crucivora. Consequently, P. r. crucivora exhibits a strong sexual dichroism that is absent in P. r. rapae.     

Sexual Dimorphism in Sturnira lilium (Chiroptera,Phyllostomidae): Can Pregnancy and Pup Carrying Be Responsible for Differences in Wing Shape?

Competition is one of the most cited mechanisms to explain secondary sexual dimorphism in animals. Nonetheless, it has been proposed that sexual dimorphism in bat wings is also a result of adaptive pressures to compensate additional weight caused by fetus or pup carrying during the reproductive period of females. The main objective of this study is to verify the existence of sexual dimorphism in Sturnira lilium wings. We employed geometric morphometrics techniques using anatomical landmarks superimposition to obtain size (Centroid Size) and shape variables of wings, which were reduced by Linear Discriminant Analysis (LDA). We also employed classical morphometrics using wing length measurements to compare efficiency between these two morphometric approaches and make comparisons using wing area measurements. LDA indicated significant differences between wing shapes of males and females, with 91% (stepwise classification) and 80% (leave-one-out cross validation) of correct classification. However, the size variable obtained did not contribute to such classifications. We have observed larger areas in female wings, but we found no differences in wing length measurements and no allometric effects in wing length, shape and area measurements. Interestingly, our study has provided evidences of morphological differences where classical morphometrics have failed. LDA and area measurements analyses revealed that females have a different area distribution in distinct portions of the wing, with wider dactylopatagia and plagiopatagia, and wingtips more triangular than males. No differences in body length or relative wing length were observed between the sexes, but pregnant females have more body weight than non-pregnant females and males. Our findings suggest that sexual dimorphism in the wing shape of S. lilium is probably related to the increase in flight efficiency of females during reproductive period. It decreases wing loading in specific portions of the wing and reduces energy cost to maintain a faster and maneuverable flight.     

Allometry and proximate mechanisms of sexual selection in photinus fireflies, and some other beetles

Ever since Darwin identified it as the force responsible forthe evolution of exaggerated male characters, sexual selectionhas been the focus of research aimed at understanding the mostbizarre and intriguing morphologies and behaviors in Nature.Two congeneric species in the firefly genus Photinus, P. pyralisand P. macdermotti, afford a unique opportunity to examine theinteraction between sexual and countervailing natural selectionthat act to shape the evolution of mating behavior and bodysize in closely related species with very different courtshipstrategies. Photinus pyralis males emit very bright flashesduring their extended patrolling flights and form ‘loveknots’ of competing suitors, while P. macdermotti males,whose courtships seldom exceed two competing males, produceweaker flashes during a shorter patrolling period. Possibly as a consequence of their scramble competition andlong flights, not only is there an extremely wide range of bodysizes in P. pyralis males, but they also exhibit wing allometricslopes greater than one, and lantern allometries less than one.In contrast, P. macdermotti males do not have allometric slopessignificantly different from one. Small males, when tested inan artificial scramble situation move faster than large males,an advantage in the intense competition that ensues once a femaleis located. Females answer several males in alternation andfail to respond to all male flashes, with the evident consequencethat love knots frequently develop around such fickle females.Allometric relationships in two non-luminescent beetle specieswith non-visual courtship protocols are compared. Visual, sexuallyselected characters showed positive allometric slopes, whilenon-visual characters showed isometry or negative slopes. Datapresented here support the existence of distinct patterns inmodality-specific sexual selection.     

Asymmetrical expression of transsexual phenotypes in hummingbirds

I present evidence for asymmetry in the expression of transsexual traits in adult hummingbirds. Among females, individuals with male-like plumage are common and define a continuous range of variation. Among males, individuals with female-like plumage are rare and define discontinuous plumage morphs. Quantitative characters also distinguish transsexuals from other members of their sex, but the characters involved differ for male-like females (bill length) and female-like males (bill, wing and tail length). Gonadal development is correlated with transsexuality only in males; female-like males have significantly smaller testes than male-like males. Both sexes demonstrate a significant negative association between plumage brightness and bill length. This association suggests an ecological basis for transsexuality because differences in plumage and bill morphology are associated with differences in foraging behaviour within and between hummingbird species. Morphological differences between transsexuals and non-transsexuals imply that plumage sexual dimorphism is more likely to evolve through changes in the frequency of female, rather than male, transsexual variants.     

Genetic variation for the positioning of wing veins in Drosophila melanogaster

SUMMARY To define the components of variation for wing shape in Drosophila in relation to what is known about the developmental control of wing patterning, we have characterized shape variation in the wings of 12 randomly chosen highly inbred lines. Despite large differences in wing size between males and females, and between flies reared at 18°C or 25°C, wing shape is remarkably unaffected by these variables and is highly line specific. The shape of each intervein region of the wing appears to be independently regulated at the genetic level, consistent with the role of secreted growth factors in establishing the locations of wing veins. Sex and temperature were found to have different effects on cell number in two intervein regions, with the result that wing shape is to a large extent independent of cell density. Dietary cholesterol was also shown to affect the breadth of the central intervein region, consistent with an effect on the strength of Hedgehog signaling during wing development. We conclude that wing shape is under tighter genetic control than wing size, and hypothesize that this control is achieved in large part by gene activity at the level of wing vein determination and differentiation.     

Lack of morphological coevolution between male forelegs and female wings in Themira (Sepsidae: Diptera: Insecta)

The complex, species-specific foreleg armature in males of the genus Themira (Diptera: Sepsidae) provides an ideal system for testing competing hypotheses for the evolution of sexually dimorphic character divergence. In sepsid flies, the male holds onto the female by clasping her wing base with his modified forelegs. In the present study, we document the male leg and the female wing morphology using scanning electron microscopy and confocal microscopy. We use a phylogenetic tree for Themira to reconstruct male foreleg and female wing evolution and demonstrate that the male legs have evolved elaborate structures with little or no corresponding changes in wing morphology. This lack of interspecific variation in female wings is not in agreement with the hypothesis of a morphological 'evolutionary arms race' between males and females. However, there is also no evidence for sex-specific wing differences in sensory organs on the wing base that may explain how females could assess males according to Eberhard's 'cryptic female choice' hypothesis. Finally, our study reveals the function of several novel morphological clasping structures and documents that the male foreleg characters in Themira are highly homoplastic. Male forelegs in two clades evolve considerably faster than in other species or clades. These two clades include Themira superba and Themira leachi , species that have some of the most dramatically modified forelegs known in Diptera.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 227–238.     

Ergatoid reproductives in Nasutitermes columbicus (Isoptera,Termitidae)

Numerous functional ergatoid replacement reproductives were found in one colony of Nasutitermes columbicus in Panama. Their morphology was mainly workerlike, although several imaginal characters such as the compound eyes and variable wing buds were more or less developed. The sex organs were fully mature and the fat body of the females, not of the males, was of the “royal” type. The development of the eyes was not accompanied by the differentiation of the optic lobes of the brain, nor was the presence of wing buds correlated with a development of the wing muscles.     

LIFETIME REPRODUCTIVE SUCCESS,SELECTION, AND THE OPPORTUNITY FOR SELECTION IN THE WHITE-TAILED SKIMMER PLATHEMIS LYDIA (ODONATA: LIBELLULIDAE)

We present estimates of lifetime reproductive success in Plathemis lydia, a territorial dragonfly. We partition the opportunity for selection into multiplicative episodes using the techniques of Arnold and Wade (1984a, 1984b) and measure selection on several morphological and behavioral characters. For both sexes, variance in survivorship was the largest contribution to variance in lifetime reproductive success. Covariance effects are also strong for both sexes, suggesting considerable non-independence of episodes. Opportunity for selection calculated on a daily basis did not approximate analogous values determined from lifetime reproductive success. Phenotypic characters for which we investigated selection included body mass, hind wing length, first date of reproduction, and (for males) an index of territorial aggressiveness. We failed to find any significant direct targets of selection in either males or females. However, the combined effects of direct and indirect selection on early reproduction were significant for males, acting primarily through increased survivorship and increased time per day spent at the pond. Similarly, females present earlier in the season had shorter interclutch intervals. Partitioning of selection acting on male hind wing length and on aggressiveness reveals relationships between selective episodes, possibly indicative of phenotypic trade-offs between natural and sexual selection through male-male competition for females. Division of selection into episodes is a useful technique for identifying the source of selection. However, ordering effects can bias results, except when episodes occur in strictly chronological sequence. We present a method for circumventing this difficulty.     

Recapture of male and female dragonflies in relation to parasitism by mites, time of season, wing length and wing cell symmetry

For aquatic mites parasitic on dragonflies, completion of their life cycle depends on their being returned to appropriate water bodies by their hosts, after completion of engorgement. We examined whether differences among hosts in timing of emergence or phenotypic attributes might affect their probability of return to an emergence pond, and hence success of mites. Parasitized males and females of the dragonfly Sympetrum obtrusum (Hagen) did not differ in overall recapture rates. Females that had wing cell symmetry and emerged early were more likely to be recaptured than females that emerged later or had wing cell asymmetry, but there were no consistent relations between these variables and parasitism by mites. No such relations between wing cell asymmetry, emergence date, and recapture likelihood were found for males. Using randomization tests, we found that mean intensities of Arrenurus planus (Marshall) mites at host emergence were the same for recaptured females and females not recaptured; however, males that were recaptured had lower mean intensities of mites at emergence than males not recaptured. Further, mature females carried more mites than mature males, and the latter had fewer mites than newly emerged males not recaptured. Biases in detachment of engorging mites do not explain the differences in parasitism between mature males and females, nor the differences in mite numbers between mature males and newly emerged males that were not recaptured. Rather, heavily parasitized males appear to disperse or die and are not recaptured, which should have implications for dispersal of mites and fitness of male hosts.     

A male fitness advantage to wing reduction in the oriental chinch bug,Cavelerius saccharivorus okajima (heteroptera: Lygaeidae)

A male fitness advantage to wing reduction was investigated for the oriental chinch bug, Cavelerius saccharivorus, which is wing dimorphic. Field surveys for the frequency of matings between wing morphs showed that the mating probability was much higher in brachypterous males than in macropterous males in the early breeding season. Brachypterous males copulated with not only brachypterous females but also macropterous females in this season. This led to a considerable rate (30%) of insemination of macropterous females just before emigration even in the early breeding season. A rearing experiment for the pre-reproductive period of females revealed that females mated with brachypterous males copulated and oviposited earlier than females mated with macropterous males. These results indicate that there is a fitness advantage to wing reduction in the males of C. saccharivorus in terms of the earlier sexual maturation.