Wing Spot Size Research Articles

Is body condition of Mexican rubyspot (Odonata:Zygoptera) associated with urbanization?

Urbanized areas can impose selective pressures on insects which can be identified at the individual level based on animal physiological condition. Physiological condition can be measured from variables such as body size, body mass or energetic budget of individuals. We examined whether body mass, wing spot size and energy reserves (proteins, lipids and carbohydrates) were reduced as urbanization increases, using adults of two damselflies, Hetaerina americana and H. vulnerata, in Central Mexico. We used a Habitat Integrity Index to assess the degree of urbanization in our sampled sites, considering biophysical attributes and the impact of anthropogenic activities. We did not find relation of above individual variables with urbanization degree. These results support possible resilience of rubyspot damselflies in the face of radical changes such as urbanization. Our finding echoes other results in damselflies research.Implications for insect conservationOur results highlight the resilience of these damselflies species in the face of urban disturbances. Thus design cities considering not only requirements of humans is essential to promote the presence and conservation of these and other species of insects in cities.Graphical abstract

Thermal plasticity of wing size and wing spot size in Drosophila guttifera

Thermal plasticity of melanin pigmentation patterns in Drosophila species has been studied as a model to investigate developmental mechanisms of phenotypic plasticity. The developmental process of melanin pigmentation patterns on wings of Drosophila is divided into two parts, prepattern specification during the pupal period and wing vein-dependent transportation of melanin precursors after eclosion. Which part can be affected by thermal changes? To address this question, we used polka-dotted melanin spots on wings of Drosophila guttifera, whose spot areas are specified by wingless morphogen. In this research, we reared D. guttifera at different temperatures to test whether wing spots show thermal plasticity. We found that wing size becomes larger at lower temperature and that different spots have different reaction norms. Furthermore, we changed the rearing temperature in the middle of the pupal period and found that the most sensitive developmental periods for wing size and spot size are different. The results suggest that the size control mechanisms for the thermal plasticity of wing size and spot size are independent. We also found that the most sensitive stage for spot size was part of the pupal period including stages at which wingless is expressed in the polka-dotted pattern. Therefore, it is suggested that temperature change might affect the prepattern specification process and might not affect transportation through wing veins.

Territorial males have larger wing spots than non-territorial males in the damselfly Calopteryx splendens (Zygoptera: Calopterygidae)

Males of Calopteryx splendens use two alternative mating tactics, territoriality, and non-territoriality. These different mating tactics are shown to vary between males within the same population and previous studies have shown that territorial males have considerably higher fitness than non-territorial males. In this paper, we tested whether the wing spot size as sexual ornament, wing length, relative wing spot size, asymmetry in wing length, asymmetry in wing spot size, or asymmetry in relative wing spot size differed between the territorial and non-territorial males. We sampled C. splendens males, representing both mating tactics, from a river system in south-west Finland. According to our results, territorial males have larger wing spot than non-territorial males. In contrast, there were no differences in the other tested traits between the territorial and non-territorial males. In conclusion, our data show that the size of pigmented wing spots may predict the alternative mating tactic of C. splendens males.

Drosophila suzukii wing spot size is robust to developmental temperature.

Phenotypic plasticity is an important mechanism allowing adaptation to new environments and as such it has been suggested to facilitate biological invasions. Under this assumption, invasive populations are predicted to exhibit stronger plastic responses than native populations. Drosophila suzukii is an invasive species whose males harbor a spot on the wing tip. In this study, by manipulating developmental temperature, we compare the phenotypic plasticity of wing spot size of two invasive populations with that of a native population. We then compare the results with data obtained from wild‐caught flies from different natural populations. While both wing size and spot size are plastic to temperature, no difference in plasticity was detected between native and invasive populations, rejecting the hypothesis of a role of the wing‐spot plasticity in the invasion success. In contrast, we observed a remarkable stability in the spot‐to‐wing ratio across temperatures, as well as among geographic populations. This stability suggests either that the spot relative size is under stabilizing selection, or that its variation might be constrained by a tight developmental correlation between spot size and wing size. Our data show that this correlation was lost at high temperature, leading to an increased variation in the relative spot size, particularly marked in the two invasive populations. This suggests: (a) that D. suzukii's development is impaired by hot temperatures, in agreement with the cold‐adapted status of this species; (b) that the spot size can be decoupled from wing size, rejecting the hypothesis of an absolute constraint and suggesting that the wing color pattern might be under stabilizing (sexual) selection; and (c) that such sexual selection might be relaxed in the invasive populations. Finally, a subtle but consistent directional asymmetry in spot size was detected in favor of the right side in all populations and temperatures, possibly indicative of a lateralized sexual behavior.

Sexual signals reveal males’ oxidative stress defences: Testing this hypothesis in an invertebrate

Abstract The hypothesis that sexual traits reveal the oxidative stress resistance of their bearers has been widely tested in vertebrates but remains unexplored in invertebrates. Here, Hetaerina americana was used to test whether oxidative stress defences are advertised by male wing spot size and colour (a male sexual trait). To this end, we investigated (1) whether oxidative stress reduced survival, (2) whether wing spot size revealed males’ antioxidant defences and (3) how wing spot size and colour were affected by oxidative stress. We elevated oxidative stress by injecting adult males with paraquat (PQ, a compound that favours the production of free radicals) and then examined how this affected male survival and wing spot size. We then related the expression of wing spot size to indicators of oxidative stress—hydrogen peroxide (H2O2) and total antioxidant capacity (TAC), super oxide dismutase (SOD) and catalase (CAT)—in adult males (whose wing spot is fixed) injected with PQ. In teneral males, whose wing spots are still forming, we compared wing spot size, colour (red and yellow chroma) and brightness in individuals injected with PQ or water as a control. Oxidative stress reduced the survival of adult and teneral males. While the H2O2 and TAC markers of antioxidant defences were positively correlated with wing spot size, there was no correlation with CAT and a negative correlation with SOD. In teneral males, PQ increased the yellow chroma and brightness of wing spots, but did not affect spot size or red chroma. Our results highlight the importance of measuring different markers as indicators of male oxidative stress defences, and that the sexual signals of invertebrates may reveal the oxidative stress status of their bearers. A plain language summary is available for this article.

Body temperature regulation is associated with climatic and geographical variables but not wing pigmentation in two rubyspot damselflies (Odonata: Calopterygidae)

AbstractIt has been proposed that wing pigmented spots function in temperature control in male calopterygids. Using two rubyspot species Hetaerina americana Fabricius and Hetaerina vulnerata Hagen in Selys, the present study investigated whether (i) wing spot size and colour‐modified aspect can predict temperature gain after a cooling event; (ii) wing spot size is related to the temperature needed to fly and how long it takes to initiate flight; and (iii) wing spot size is related to seasonality and altitude. The results obtained do not support any of these relationships. The results also indicate that H. vulnerata can achieve flight at 8 °C less than H. americana. The present study further investigates whether the species differ in their latitudinal and geographical distribution, and respond differently to bioclimatic variables. The results obtained provide support for this particular hypothesis, showing that H. vulnerata inhabits higher altitudes, and is able to tolerate colder environments compared with H. americana. Wing spots in the two Hetaerina species do not help in thermoregulation, although both species show different temperature control abilities. This difference in thermoregulatory ability may enable the species to colonize different environments and reduce interspecific competition.

The genetic architecture of coordinately evolving male wing pigmentation and courtship behavior in Drosophila elegans and Drosophila gunungcola.

Many adaptive phenotypes consist of combinations of simpler traits that act synergistically, such as morphological traits and the behaviors that use those traits. Genetic correlations between components of such combinatorial traits, in the form of pleiotropic or tightly linked genes, can in principle promote the evolution and maintenance of these traits. In the Oriental Drosophila melanogaster species group, male wing pigmentation shows phylogenetic correlations with male courtship behavior; species with male-specific apical wing melanin spots also exhibit male visual wing displays, whereas species lacking these spots generally lack the displays. In this study, we investigated the quantitative genetic basis of divergence in male wing spots and displays between D. elegans, which possesses both traits, and its sibling species D. gunungcola, which lacks them. We found that divergence in wing spot size is determined by at least three quantitative trait loci (QTL) and divergence in courtship score is determined by at least four QTL. On the autosomes, QTL locations for pigmentation and behavior were generally separate, but on the X chromosome two clusters of QTL were found affecting both wing pigmentation and courtship behavior. We also examined the genetic basis of divergence in three components of male courtship, wing display, circling, and body shaking. Each of these showed a distinct genetic architecture, with some QTL mapping to similar positions as QTL for overall courtship score. Pairwise tests for interactions between marker loci revealed evidence of epistasis between putative QTL for wing pigmentation but not those for courtship behavior. The clustering of X-linked QTL for male pigmentation and behavior is consistent with the concerted evolution of these traits and motivates fine-scale mapping studies to elucidate the nature of the contributing genetic factors in these intervals.

Male wing shape differs between condition-dependent alternative reproductive tactics in territorial damselflies

Territorial contests between males without weaponry are based on costly displays and can result in condition-dependent alternative reproductive tactics that maximize male fitness. Physiological and morphological traits such as fat content, body size or the expression of secondary sexual traits have been shown to contribute to male territory-holding potential. When territorial contests are based on flight displays, wing morphology is expected to contribute to the territory-holding potential of a male through its effects on flight performance. We explored whether wing shape contributed to the territory-holding potential of males of three species of Calopteryx damselflies. Males of these species show two distinct, condition-dependent behavioural tactics: territorial and nonterritorial. Previous studies have shown that territorial males have higher fitness than nonterritorial males. We used mark–recapture to determine male tactics within the populations and compared wing shape, size and wing coloured spot size (a secondary sexual trait) between tactics. Territorial males of all three species had shorter and slightly broader hindwings than nonterritorial males. In two species, forewings of territorial males were longer and broader than forewings of nonterritorial males. Wing size and wing spot size did not differ between tactics. We suggest that the wing shape of territorial males might confer better flight manoeuvrability, which would be advantageous for territorial contests. Therefore, wing shape is likely to be an important trait contributing to territory-holding potential in condition-dependent alternative reproductive tactics based on flight displays.

Allometry of secondary, primary, and nonsexual traits in the beautiful demoiselle (Calopteryx virgo meridionalis)

The static allometry between the size of a trait and the body size results from the net selection forces acting on the evolution of both the trait and the body size. An increased knowledge of the functional significance of traits is necessary to understand observed allometric patterns. We studied several traits of males of the beautiful demoiselle ( Calopteryx virgo meridionalis Sélys, 1873), for which there is a good functional knowledge of the genitalic traits and ornaments. We found positive allometry for the wing spot size (considered a secondary sexual trait) and for the distal width (but not length) of the anal appendages, which are used for grasping the female prior to copulation. Regarding the male secondary genitalia, the length but not the width of the big horns of the aedeagus showed an isometric pattern. The aedeagus shaft length showed a negative allometric pattern, while its distal width did not show a significant regression. The slopes of the regressions were higher when using wing length than when using body length as estimators of body size, with the exception of wing spot length. Results are discussed based on the functional significance of the study traits, as well as the pre- and post-copulatory selective pressures acting on them.

Selection on size and secondary sexual characters of the damselfly Calopteryx splendens when sympatric with the congener Calopteryx virgo

Male mating success is often determined by body size or secondary sexual characters because of female mate choice or competition for females. In addition to intraspecific interactions, interspecific interactions may interfere with intraspecific selection. In this study, we investigated sexual selection on size and sexual characters of male banded demoiselle ( Calopteryx splendens (Harris, 1780)) in wild populations sympatric with the beautiful demoiselle ( Calopteryx virgo (L., 1758)). As secondary sexual characters, male C. splendens have pigmented wing spots whose size appears to be under positive selection. Male C. virgo resemble male C. splendens that have the largest wing spots, leading to interspecific male–male aggression and possibly also to heterospecific matings via mistaken species recognition. If interspecific interactions interfere with intraspecific sexual selection on wing-spot size of C. splendens, their effects should increase with the increasing relative abundance of C. virgo. Our results did not show the expected positive selection on wing-spot size in C. splendens, suggesting that interspecific interactions might interfere with sexual selection. Also, we observed no relationship between the strength of interspecific sexual selection and the relative abundance of C. virgo. However, there was a positive intraspecific density-dependent sexual selection for larger size. Although the present results are tentative, we suggest that interspecific interactions should be considered along with intraspecific selection when studies of sexual selection are performed in the wild.

Sympatric shift in a male sexual ornament in the damselfly Calopteryx splendens

Character displacement is a process by which interactions between two species that exhibit similar traits, results in geographical patterns of trait divergence in one or both species. These traits evolve to reduce costs of interspecific interactions in sympatry and thus differ from their condition in allopatry. In male damselflies Calopteryx splendens, large wing spots are sexually selected. However, in sympatric populations with Calopteryx virgo, wing spot size decreases as C.virgo abundance increases. The stability of this pattern is unclear, because previous studies have focused on sympatric populations with potentially fluctuating relative abundances. We studied the wing spot sizes of C.splendens in both sympatric and allopatric populations. Our data show that male C.splendens' wing spots are larger in allopatry than in sympatry with C.virgo. We suggest that both interspecific aggression and avoidance of interspecific reproductive interactions may result in this pattern, although their relative importance remains unclear.

Predation selects for increased immune function in male damselflies, Calopteryx splendens.

Predation selects for numerous traits in many animal species, with sick or parasitized prey often being at high risk. When challenged by parasites and pathogens, prey with poor immune functions are thus likely to be at a selective disadvantage. We tested the hypothesis that predation by birds selects for increased immune function in a wild population of male damselflies Calopteryx splendens, while controlling for a trait known to be under selection by bird predation, dark wing-spots. We found that selection on both immune function and wing-spot size was significantly positive, and that selection on either trait was independent of selection on the other. We found no evidence of nonlinear quadratic or correlational selection. In contrast to previous studies, we found no phenotypic correlation between immune function and wing-spot size. There was also no difference in immune response between territorial and non-territorial males. Our study suggests that predation may be an important agent of selection on the immune systems of prey, and because the selection we detected was directional, has the potential to cause phenotypic change in populations.

Genetic diversity, population structure and taxonomy of Calopteryx splendens (Odonata: Calopterygidae): An AFLP analysis

Calopteryx splendens is a widely distributed palaearctic damselfly with a remarkably uniform morphology. Variation in the size and shape of the pigmented spot on the wing is the main diagnostic character used to discriminate subspecies across its huge geographic range. Here, AFLP analysis was used to assess the genetic structure and diversity of nine populations representing 3 putative subspecies and evaluate the pigment spot as a taxonomic marker. Genetic diversity was high, with the number of polymorphic loci per population ranging from 141 to 280 out of a total of 333 variable sites (42.3-84.1%) and Nei's gene diversity from 0.160 to 0.283 (overall 0.299). Overall population genetic differentiation (FST = 0.2766) suggests limited gene flow and adaptation to local environments. Restricted gene flow and genetic differentiation among populations are supported by significant FST estimates. High levels of gene flow (Nm >1) were only recorded among three Asian populations (Russia - Kazakhstan - Turkey). The patterns of genotypic diversity suggest that a given wing spot size and shape may arise from the hybridization of a limited number, possibly not more than four, ancestral gene pools in different ways and at different times. Clearly, the sample analyzed was not sufficient to capture all of the complex history of C. splendens, but sufficient to indicate the taxa ancilla, waterstoni, and orientalis possibly represent three of the four ancestral gene pools, and originated in western Asia. The origin of the fourth, xanthostoma, is the western Mediterranean.

Phenoloxidase activity and melanization do not always covary with sexual trait expression in Hetaerina damselflies (Insecta: Calopterygidae)

Sexual selection theory indicates that males use sexual traits to signal immune ability, a hypothesis known as the immunocompetence principle. A positive relationship between sexual traits and immune ability is not always present. Here we illustrate this pattern by using five damselfly species in the genus Hetaerina. Previous studies have documented a positive correlation between sexual trait expression (wing spot size) and immune ability in members of this genus. These studies have also documented that there are fitness and energetic costs of producing and bearing wing pigmentation. First we used five Hetaerina species to investigate the correlation between spot size and phenoloxidase (PO) activity (a key insect immune component) in two contrasting seasons. Second, we experimentally challenged males of two Hetaerina species and correlated spot size with PO activity and melanization ability. Results indicate either a positive relationship, a negative relationship or, more commonly, no relationship at all between immune components and wing pigmentation. Season did not predict any of these relationships or expression of spot size and PO activity. These results, although limited to two immune components, indicate that the relationship between sexual trait expression and immunity is not always consistent.

Seasonal variation in ornament expression, body size, energetic reserves, immune response, and survival in males of a territorial insect

Abstract 1. Seasonal variation in immune response has rarely been investigated in invertebrates and, therefore, we have studied this using territorial adult males of the damselfly, Hetaerina americana (Fabricius), in several generations, for a year and a half.2. We investigated and related seasonal variation in red pigmented wing spot size (an ornamental trait) and body size to fat reserves using four immunity components – melanisation ability, phenoloxidase (PO) and nitric oxide (NO) activity, and haemolymph protein concentration – and survival ability after a bacterial immune challenge.3. There was seasonal variation in spot expression, being more intense in the non‐winter months and less intense in winter months, and, to some extent, a similar pattern was found for NO. Although there was also variation in melanisation, PO activity, protein concentration and fat reserves, this was not consistently related to variation in spot size. Survival was lower in the winter than in non‐winter months.4. Animals with larger spot and body size had greater values of melanisation, PO and NO activity, and protein concentration. The relation of spot and body size with fat reserves is still not clear.5. Unlike other studies, ornament was not similarly correlated with all typical immune components (at best, mainly NO).6. Similar to what occurs in vertebrates, survival is lower during the winter months. In the case of vertebrate studies, however, the same individual suffers these changes. In the American rubyspot, distinct cohorts demonstrated seasonal differences.

Spatial and temporal population differences in male density and condition in the American rubyspot,Hetaerina americana(Insecta: Calopterygidae)

AbstractIncreased resource availability should favor higher animal density. It may also affect sex ratio, the male condition, and mating competition over access to females, although the direction of these variables is not straightforward to predict. Using a non‐experimental approach, we carried out preliminary research using the territorial American rubyspot (Hetaerina americana) by comparing two spatially separated populations and the same population in two different seasons (each comparison with varying population densities). We first compared the sex ratio by counting males (using two categories, territorial and non‐territorial) and females; relative foraging time (as an indicator of how much feeding resources each site provides); wing spot size (a sexual ornament), body size and immune melanization response (these two variables were used to assess male condition); and fighting time and contest number (to assess competition). For the seasonal comparison we used a third population in which we only compared male spot size and two indicators of condition and immune response, phenoloxidase (PO) and nitric oxide (NO) activity. The high‐density population had higher values of non‐territorial males (but similar sex ratio), relative foraging time, contest time and number, wing spot (but similar body size) and melanization response than the low‐density population. According to season, at high density, males had higher values of wing spots, PO, and NO. Our results suggest that in a population where animals have more dietary resources, males reach a better condition despite the competition being more intense.

Genetics of divergence in male wing pigmentation and courtship behavior between Drosophila elegans and D. gunungcola

Many sex-specific traits involved in mating consist of functionally coordinated morphologies and behaviors. How the components of these complex traits evolve and become coordinated during evolution is unknown. In order to understand how such trait complexes evolve and diversify, we must decipher the genetic underpinnings of their components. In this study, we begin to elucidate the genetic architecture underlying differences in functionally related male pigmentation and behavior between two Asian Drosophila melanogaster group species, D. elegans and D. gunungcola. D. elegans possesses a male-specific wing melanin spot and a stereotypical wing display element in male courtship, whereas D. gunungcola lacks both of these traits. Using reciprocal F1 male hybrids, we demonstrate that the X-chromosome contains a major locus or loci required for wing spot formation and that autosomal loci largely determine the male courtship display. Using phenotypic and genetic analysis of backcross progeny, we further demonstrate that both the wing spot and courtship differences between the two species are polygenic and both depend at least in small part on genetic factors on both the X and the autosomes. Finally, we find that male wing spot size and courtship wing display are highly correlated in backcross progeny, suggesting that linkage or pleiotropy may have been involved in their coordinated evolution.

Interspecific territoriality in Calopteryx damselflies: the role of secondary sexual characters

Interspecific territoriality is usually interpreted to result from interspecific interference competition, although it may also originate from mistaken species recognition. In the latter case, it may be based on similarity of secondary sexual characters. In the damselfly Calopteryx splendens , males have pigmented wing spots as a sexual character, and males with the largest spots resemble males of another species, Calopteryx virgo . Probably because of this resemblance, C. virgo males are more aggressive towards large- than small-spotted C. splendens males. We examined whether wing spot size of C. splendens males affects territorial interactions between the species. In a removal experiment, the number of territorial C. splendens increased after C. virgo males were removed. However, interspecific territoriality was incomplete since before the removal the territories of the species partially overlapped. Wing spot size of C. splendens seemed to affect interspecific territoriality: before the removal territorial and nonterritorial C. splendens males had similar spot sizes and the distance to the nearest C. virgo territory increased with wing spot size of C. splendens . In addition, after the removal of C. virgo , the relation between wing spot size and the distance to the nearest old C. virgo territory disappeared. Our results suggest that mistaken species recognition may account for the interspecific territorial behaviour in the two species. Furthermore, interspecific territoriality may cause negative selection on wing spot size and thus may explain character displacement in wing spot size of C. splendens males.

INTERSPECIFIC AGGRESSION CAUSES NEGATIVE SELECTION ON SEXUAL CHARACTERS

Interspecific aggression originating from mistaken species recognition may cause selection on secondary sexual characters, but this hypothesis has remained untested. Here we report a field experiment designed to test directly whether interspecific aggression causes selection on secondary sexual characters, wing spots, in wild damselfly populations. Males of Calopteryx virgo are more aggressive toward males of C. splendens with large than with small wing spots. This differential interspecific aggression may cause negative selection on wing spot size. Indeed, our results show that directional survival selection on wing spot size of C. splendens males was changed by experimental removal of C. virgo males. Without removal, directional selection went from positive to negative with increasing relative abundance of C. virgo males. In populations where C. virgo males were removed, this relationship disappeared. These results verify that interspecific aggression can cause negative selection on sexual characters. Thus, interspecific aggression has the potential to cause divergence on these characters between two species offering an alternative explanation for reinforcement for generating character displacement in secondary sexual characters.

INTERSPECIFIC AGGRESSION CAUSES NEGATIVE SELECTION ON SEXUAL CHARACTERS

Interspecific aggression originating from mistaken species recognition may cause selection on secondary sexual characters, but this hypothesis has remained untested. Here we report a field experiment designed to test directly whether interspecific aggression causes selection on secondary sexual characters, wing spots, in wild damselfly populations. Males of Calopteryx virgo are more aggressive toward males of C. splendens with large than with small wing spots. This differential interspecific aggression may cause negative selection on wing spot size. Indeed, our results show that directional survival selection on wing spot size of C. splendens males was changed by experimental removal of C. virgo males. Without removal, directional selection went from positive to negative with increasing relative abundance of C. virgo males. In populations where C. virgo males were removed, this relationship disappeared. These results verify that interspecific aggression can cause negative selection on sexual characters. Thus, interspecific aggression has the potential to cause divergence on these characters between two species offering an alternative explanation for reinforcement for generating character displacement in secondary sexual characters.