Female reproductive decisions and parasite burden in a calopterygid damselfly (Insecta: Odonata)

There is currently a gap in sexual selection theory about how much the environment drives female mating decisions. We present field data that suggest that female sexual behaviour in the damselfly Calopteryx haemorrhoidalis is influenced by parasite burden. Male wing pigmentation in Calopteryx is a sexually selected trait that signals a male's ability to cope with eugregarine parasites (an intestinal parasite that feeds on the adult's ingested food). Because adult C. haemorrhoidalis females also show wing pigmentation, we examined whether this trait is similarly influenced by parasite burden and whether it may signal the female's reproductive value. MaleC. haemorrhoidalis defend riverine substrates that females use for oviposition. After copulation and during oviposition, females are guarded by the copulating male against intruder males. Alternatively, females may avoid mating and ‘steal’ an oviposition site within a male's territory. In the present study, we found that the amount of female wing pigmentation was negatively correlated with the number of eugregarines present. Females with more parasites produced fewer eggs, survived fewer days, spent less time during courtship, ‘inspected’ fewer males before mating, had a lower mating success, were guarded for less time during oviposition and engaged in fewer ‘stealing’ events during oviposition. The reduced egg production and survival of heavily infected females may result from eugregarine depletion of the females' consumed food reserves. Thus, to offset reduced longevity, heavily infected females may accept a mating more rapidly and mate with fewer males. ‘Stealing’ behaviour may be related to the female's differential use of sperm from some males, particularly high-quality males. Interestingly, males that mated with low-pigmented females showed greater variance in wing pigmentation than did males that mated with high-pigmented females. Possibly, female wing pigmentation may signal a female's reproductive value, which provides females with longer mate-guarding episodes and reduced interference from intruder males. This study points out one possible constraint, intestine parasites, that females may face during mating decisions. Because females in bad condition mate with males in both good and bad condition, this constraint may be pervasive enough to weaken the intensity of selection for a male sexually selected trait, wing pigmentation, and help to maintain its variation in phenotypic expression. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

The Role of Wing Pigmentation, UV and Fluorescence as Signals in a Neotropical Damselfly

Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate recognition and mate quality functions in many animal taxa. We investigated the role of wing ultra-violet reflection, fluorescence emission, and pigmentation on age and sexual signals in the damselfly Mnesarete pudica. In this species, wings are sexually dimorphic in colour and exhibit age dependency: males and females show a smoky black colouration when young, turning red in mature males while it turns brown in females. First, we investigated wing UV patterns through reflectance and emission spectra. Second, behavioural experiments were undertaken to show male and female responses to manipulated wing pigmentation and experimentally reduced UV (UV-). Reflectance spectra of the wings of juvenile and mature males and females were used to show the differences between controls and individuals with manipulated colouration used in the behavioural experiment. UV-reduced, females with wings painted red, and control males and females were tethered and presented to conspecific males and females, and their behavioral responses were recorded. The male red wing pigmentation and females with red wings elicited an aggressive response in territorial males and a sexual response in females. Both males and females showed neutral responses towards individuals with reduced UV. Wing signals of juvenile individuals also provoked neutral responses. These results suggest that UV, together with pigmentation, plays a role during mate recognition in males and females. Other than butterflies and spiders, it seems that fluorescence signals and UV reflectance can also be part of communication in odonates.     

A comparative study on the evolution of reversed size dimorphism in monogamous waders

Sexual dimorphism in size is common in birds. Males are usually larger than females, although in some taxa reversed size dimorphism (RSD) predominates. Whilst direct dimorphism is attributed to sexual selection in males giving greater reproductive access to females, the evolutionary causes of RSD are still unclear. Four different hypotheses could explain the evolution of RSD in monogamous birds: (1) The ‘energy storing’ hypothesis suggests that larger females could accumulate more reserves at wintering or refuelling areas to enable an earlier start to egg laying. (2) According to the ‘incubation ability’ hypothesis, RSD has evolved because large females can incubate more efficiently than small ones. (3) The ‘parental role division’ hypothesis suggests that RSD in monogamous waders has evolved in species with parental role division and uniparental male care of the chicks. It is based on the assumption that small male size facilitates food acquisition in terrestrial habitats where chick rearing takes place and that larger females can accumulate more reserves for egg laying in coastal sites. (3) The ‘display agility’ hypothesis suggests that small males perform better in acrobatic displays presumably involved in mate choice and so RSD may have evolved due to female preference for agile males. I tested these hypotheses in monogamous waders using several comparative methods. Given the current knowledge of the phylogeny of this group, the evolutionary history of waders seems only compatible with the hypothesis that RSD has evolved as an adaptation for increasing display performance in males. In addition, the analysis of wing shape showed that males of species with acrobatic flight displays had wings with higher aspect ratio (wing span/²wing area) than non-acrobatic species, which probably increases flight manoeuvrability during acrobatic displays. In species with acrobatic displays males also had a higher aspect ratio than females although no sexual difference was found in non-acrobatic species. These results suggest that acrobatic flight displays could have produced changes in the morphology of some species and suggest the existence of selection favouring higher manoeuvrability in species with acrobatic flight displays. This supports the validity of the mechanisms proposed by the ‘display agility’ hypothesis to explain the evolution of RSD in waders.     

The Role of Wing Coloration in Sex Recognition and Competitor Recognition in Rubyspot Damselflies (Hetaerina spp.)

The decision rules that animals use for distinguishing between conspecifics of different age and sex classes are relevant for understanding how closely related species interact in sympatry. In rubyspot damselflies (Hetaerina spp.), the red wing coloration of mature males is hypothesized to be a key trait for sex recognition and competitor recognition within species and the proximate trigger for interspecific male–male aggression. We tested this hypothesis by manipulating the wing coloration of tethered conspecific intruders and measuring the responses of territory holders of three species in the field. As predicted, covering the red spots of mature males with black ink nearly eliminated territorial responses, and in some cases, territorial holders clasped the blackened males as if they were females. Adding red spots to female wings triggered territorial responses and nearly eliminated sexual responses. Immature males with artificial red spots were attacked at the same rate as mature male intruders, and much more frequently than were immature male controls. The results varied somewhat by species. In H. titia, the only species of Hetaerina with substantial black wing pigmentation, the effects of blackening the red spots of intruders varied both geographically and seasonally. But even when blackening the red spots of male intruders did not reduce the aggressive response of H. titia territory holders, adding artificial red spots to female wings elicited aggressive responses and nearly eliminated sexual responses. The results of this study further strengthen the evidence that interspecific aggression in Hetaerina results from overlap in territorial signals and that the derived black wing pigmentation of H. titia reduces interspecific aggression.     

Wing pigmentation in Calopteryx damselflies: a role in thermoregulation?

Body melanization may show adaptive variation related to thermoregulation ability, and it is to be expected that the degree of melanization will change among populations or closely related species across environmental gradients of solar radiation and/or environmental temperature. Some melanized secondary sexual traits may also play a role in sexual selection, leading to interpopulation variation, which would not be predicted by thermoregulation pressures alone. We studied the relationships between the interpopulation variation in wing pigmentation level (i.e. melanized secondary sexual trait) of two closely related species of Calopteryx damselfly, and both solar radiation and maximum environmental temperature estimates. Wing pigmentation differs between these species, is gender specific and is used in species' discrimination. Only Calopteryx virgo meridionalis males showed a significant negative partial correlation between wing pigmentation degree and temperature. However, C. virgo meridionalis females showed a positive significant partial correlation between wing pigmentation degree and solar radiation. Wing pigmentation in Calopteryx xanthostoma males was not related to solar radiation or temperature. Thus, thermoregulation pressures poorly explained the observed variations in wing pigmentation between populations, although they might have an adaptive significance at the species' level. As wing pigmentation showed important latitudinal variation, several other selection pressures which might act on melanized traits are briefly discussed. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 36–44.     

Is natural selection promoting sexual dimorphism in the Green-backed Firecrown Hummingbird ( Sephanoides Sephaniodes )?

In many hummingbird species there is an opposite pattern of sexual dimorphism in bill length and other morphometric measures of body size. These differences seem to be closely related with differences in foraging ecology directly associated with a different resource exploitation strategy. The aim of this study was to assess if natural selection is acting on wing length and bill size in hummingbird males and females with different resource exploitation strategies (i.e., territorial males and non-territorial females). If competition for resources promotes sexual dimorphism as a selective pressure, males should be subjected to negative directional selection pressure for wing length and no selection pressure over bill size, while females should undergo positive directional selection pressure for both bill size and wing length. The morphometric data we collected suggests that there is no selection for wing length and bill size in male hummingbirds. In contrast, our females exhibited positive directional selection for both wing length and bill size. Although we cannot reject sexual selection acting on sexually dimorphic traits, this study suggests that natural selection may promote sexual dimorphism in traits that are closely related with hummingbird foraging ecology and resource exploitation strategies.     

Allometry of a sexual trait in relation to diet experience and alternative mating tactics in two rubyspot damselflies (Calopterygidae: Hetaerina)

Several arguments have been put forward to explain how sexual selection drives the evolution of sexual trait allometry, especially hyperallometry. The ‘positive allometry theory’ suggests that hyperallometry is a rule in all‐secondary sexual traits, whereas the ‘display hypothesis’ suggests that only males in good condition will exhibit hyperallometric sexual display traits. In the present study, we investigated: (1) the condition‐dependence nature (by using two diet treatments that varied in the amount of food provided to the larvae) of a sexually selected trait (wing pigmentation; WP) in recently‐emerged adults of the American rubyspot damselfly, Hetaerina americana, and (2) the scaling relationship between WP and body size (wing and body length) in the rubyspot damselflies H. americana and Hetaerina vulnerata, according to alternative reproductive tactics (ARTs; territorial and nonterritorial males). First, we found support that indicated that diet positively affected WP length, although there was no significant WP allometric pattern in relation to diet regimes. Second, WP was hyperallometric in both Hetaerina species. WP size was similar between ARTs and, in H. americana (but not H. vulnerata), nonterritorial males showed steeper slopes than territorial males when wing length was used. The results obtained support the notion that sexual traits are hyperallometric, although there is no clear pattern in relation to ARTs. © 2013 The Linnean Society of London     

Do individuals in better condition survive for longer? Field survival estimates according to male alternative reproductive tactics and sex

There is a gap in terms of the supposed survival differences recorded in the field according to individual condition. This is partly due to our inability to assess survival in the wild. Here we applied modern statistical techniques to field‐gathered data in two damselfly species whose males practice alternative reproductive tactics (ARTs) and whose indicators of condition in both sexes are known. In Paraphlebia zoe, there are two ART: a larger black‐winged (BW) male which defends mating territories and a smaller hyaline‐winged (HW) male that usually acts as a satellite. In this species, condition in both morphs is correlated with body size. In Calopteryx haemorrhoidalis, males follow tactics according to their condition with males in better condition practicing a territorial ART. In addition, in this species, condition correlates positively with wing pigmentation in both sexes. Our prediction for both species was that males practicing the territorial tactic will survive less longer than males using a nonterritorial tactic, and larger or more pigmented animals will survive for longer. In P. zoe, BW males survived less than females but did not differ from HW males, and not necessarily larger individuals survived for longer. In fact, size affected survival but only when group identity was analysed, showing a positive relationship in females and a slightly negative relationship in both male morphs. For C. haemorrhoidalis, survival was larger for more pigmented males and females, but size was not a good survival predictor. Our results partially confirm assumptions based on the maintenance of ARTs. Our results also indicate that female pigmentation, correlates with a fitness component – survival – as proposed by recent sexual selection ideas applied to females.     

Assessing the intensity of sexual selection on male body mass and antler length in roe deer Capreolus capreolus: is bigger better in a weakly dimorphic species?

Little is known about traits under sexual selection in territorial mammals with low sexual size dimorphism. We examined the potential for sexual selection on male body mass and antler length in the European roe deer Capreolus capreolus, a territorial ungulate in which males are less than 10% heavier than females. Independently, both body mass and antler length (irrespective of age) had a positive effect on male yearly breeding success. However, when corrected for body mass, antler length at a given mass only had a slight effect on male breeding success. This suggests that: (1) ‘bigger is better’ and (2) sexual selection is responsible for at least part of the observed variation in body mass and antler length in roe deer. High body mass and large antlers may be advantageous to males for two reasons: (1) they enhance fighting ability and dominance, so allowing males to defend better their territory and hence access mates, and (2) they attract females because they are honest signals of male phenotypic quality. This suggests that, even in weakly dimorphic ungulate species, sexual selection may lead to a marked influence of body mass on male breeding success, as long as body mass is also strongly selected in females.     

Hind Wing Shape Evolves Faster than Front Wing Shape in Calopteryx Damselflies

Wing shape has been shown in a variety of species to be influenced by natural and sexual selection. In damselflies, front- and hind wings can beat independently, and functional differentiation may occur. Males of Calopteryx damselflies show species-specific nuptial flights that differ in colour signalling with the hind wings. Therefore, hind wing shape and colour may evolve in concert to improve colour display, independent of the front wings. We predicted that male hind wing shape evolves faster than front wing shape, due to sexual selection. Females do not engage in sexual displays, so we predicted that females do not show differences in divergence between front- and hind wing shape. We analysed the non-allometric component of wing shape of five European Calopteryx taxa using geometric morphometrics. We found a higher evolutionary divergence of hind wing shape in both sexes. Indeed, we found no significant differences in rate of evolution between the sexes, despite clear sex-specific differences in wing shape. We suggest that evolution of hind wing shape in males is accelerated by sexual selection on pre-copulatory displays and that this acceleration is reflected in females due to genetic correlations that somehow link the rates of wing shape evolution in the two sexes, but not the wing shapes themselves.     

Sexual size dimorphism and assortative mating in Carolina Wrens

ABSTRACT.   Sexual size dimorphism (SSD) may be due to sexual and natural selection, but identifying specific mechanisms that generate such dimorphism in a species is difficult. I examined SSD in Carolina Wrens ( Thryothorus ludovicianus ) by examining (1) the degree of SSD in the population and between pairs using five morphometrics, (2) assortative mating patterns based on size and age, and (3) relationships between size and longevity. Analysis revealed that males were significantly larger than females in all body measurements. For example, mass, bill, and wing measurements yielded a canonical variable that permitted separation of the sexes and linear classification functions correctly determined the sex of 95% (238/250) of all wrens measured. No evidence was found to suggest that SSD was related to resource partitioning. However, assortative mating trends based on morphometrics (e.g., wing length), positive associations between longevity and morphometrics (e.g., wing length in females and body size in males), and intense male-male contests for territorial resources year-round provide evidence that sexual selection may contribute to SSD in Carolina Wrens.     

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.     

Does allometry of a sexually selected ornamental trait vary with sexual selection intensity? A multi‐species test in damselflies

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Ecological and phylogenetic perspectives on wing stiffness in nine Theclini species (Lepidoptera: Lycaenidae)

We studied the relationship between wing stiffness and butterfly ecology and phylogeny. Nine species belonging to the tribe Theclini of the family Lycaenidae were selected and examined for the wing stiffness of dried specimens by a three‐point bending test. It was found in Japonica lutea that the wing stiffness was not affected by the humidity to which it had been exposed, but was strongly affected by wing size and sex. Comparisons of sexual differences in four species indicated that females of patrolling species had stiffer wings than conspecific males, but that males of territorial species had stiffer wings than conspecific females. Finally, the wing stiffness was compared among males of nine species that use different mate‐locating tactics, and the results revealed a tendency that males of territorial species have stiffer wings than males of patrolling species. These results, though including a few exceptional cases, are discussed from the perspective of ecological requirements and phylogenetic constraints on the species.     

Does character displacement demonstrate density-dependent expression in females? A test on the wing shape of two species of European damselflies

Character displacement (CD) is the evolutionary process which leads to the divergence in trait expression of closely related species in regions where species co-occur, compared to allopatric populations. In Europe CD has been investigated in males of Calopteryx splendens and C. virgo and has been related to species recognition. If species recognition is relevant for males, also females should benefit from CD. The most obvious differences between females of these two species are wing profile and colour. We sampled females from allopatric and from sympatric populations with different relative abundances of these species. Wing shape and pigmentation were evaluated for each damselfly. CD was found in wing profile but not in wing transparency. The relative abundance of species significantly affected CD, but with a different pattern in each species. The prediction that wing shape become more different from the allopatric state when the species was relatively rare, but more similar to the allopatric state when the species was common was evident only for C. splendens. Wing shape changes might increase differences in flying patterns making males more effective to discriminate between heterospecific females. So, CD we observed may be the result of a selection directed to reduce interspecific reproductive interference.     

Six cryptic species on a single species of host plant: morphometric evidence for possible reproductive character displacement

Abstract 1. Diversification of some highly host‐specific herbivorous insects may occur in allopatry, without shifts in host use. Such allopatric divergence may be accelerated by sexual selection operating on courtship displays. Wing size and shape may affect visual and vibrational courtship displays in tephritid fruit flies. Geometric morphometric methods were used to examine wings of six sympatric cryptic species in the neotropical genus Blepharoneura. All six species feed on flowers of the same species of host (Gurania spinulosa), a neotropical vine in the Cucurbitaceae. Three of the fly species court and mate in close proximity on the host. Thus, courtship behaviours could serve as important reproductive isolating mechanisms. Two sets of hypotheses were tested: (i) species differ in wing shape and wing size; and (ii) species are sexually dimorphic in wing size and wing shape. Wing size differed among a few species, but wing shape differed significantly among all six species. Sexual dimorphism in wing size was found in only one species, but sexual dimorphism in wing shape was found in two of the three species known to court on the same host plant. In the two sexually dimorphic species, wing shape differed among males, but not among females. This suggests that selection for reproductive character displacement might accelerate divergence in wing shape.     

Brain aromatase mRNA expression in two populations of the peacock blenny Salaria pavo with divergent mating systems

Aromatase, the key enzyme in the conversion of androgens to estrogens, regulates the availability of these hormones in tissues and controls many physiological and behavioral processes. In fish and other vertebrates, the regulation of aromatase expression in the brain has been implicated in the modulation of male sexual and aggressive behaviors. Here, the pattern of mRNA expression of the brain aromatase isoform (encoded by the CYP19A2 gene also referred as CYP19b) was quantified at the peak of spawning season in brain macroareas from males and females of the blenny Salaria pavo originated from two populations displaying male alternative reproductive tactics but differing in their mating systems. In Trieste (Adriatic) nesting males aggressively defend nests and take the initiative in courtship and perform sexual displays more often than females while in Ria Formosa (Southern Portugal) the pattern is reversed as a result of shortage of appropriate nesting sites. Nesting males from Ria Formosa had overall higher levels of brain aromatase mRNA expression than nesting males from Trieste, suggesting a higher brain estrogen synthesis in these males. Since in some fish species exogenous estradiol administration has been shown to decrease sexual and agonistic behaviors, the higher levels of brain aromatase in Ria Formosa nesting males may explain their reduced expression of sexual and aggressive displays when compared with nesting males from Trieste. Alternatively, the higher brain aromatase levels in nesting males from Ria Formosa could be a mechanism to decrease the putative androgen-induced activation of aggressive and sexual displays by reducing the local availability of androgens through their metabolization into estrogens. Although females and parasitic female-like males also differ in their displays between populations, the interpopulational pattern of brain aromatase mRNA expression was similar, suggesting that other neuroendocrine agents mediate the expression of female and female-like behaviors. In conclusion, brain aromatase availability seems like a probable mechanism to regulate the effects of steroids on the brain circuits underlying the expression of sexual and agonistic displays in S. pavo.     

Wing Colour Properties do not Reflect Male Condition in the American Rubyspot (Hetaerina americana)

Adult males of the American rubyspot ( Hetaerina americana ) dispute riverine territories where females arrive to mate. On the wing basis, these males bear a red pigmentation spot whose area correlates with territorial disputes and mating rate: males with larger spots are more successful. This is explained by the fact that spot size correlates with fat muscular reserves which fuel flight during territorial intrusions. To further our understanding of sexual selection acting on the spot, here we have examined possible differences in three spot colour properties (red chroma, hue and brightness) in three distinct adult male ages [young, middle-aged (when males are more likely to defend a territory) and old], social status (territorial and non-territorial in middle-aged males), and under two potentially, energetically and costly situations: when faced with an immune challenge [comparing a nylon-implanted male group vs. a non-implanted male group in two ages, teneral (previous to colour formation) and middle-aged] and low diet levels (comparing a male set of middle-aged animals that received food ad libitum vs. a male set that received no food). Our results indicate no change in colour properties across any of these comparisons. Taken together, these and previous results suggest that only spot size but not the spot characteristics we measured here, is sexually selected in males of this species at least in terms of pre-copulatory male–male competition. That some of these colour properties have been related to male condition in other calopterygid damselflies cannot be generalized to the American rubyspot.     

Wing pigmentation, immune ability, fat reserves and territorial status in males of the rubyspot damselfly, Hetaerina americana

An explanation for courting traits is that they convey information about the bearers condition to conspecifics, more specifically immune ability. Here we test a series of immune-based assumptions in the territorial damselfly Hetaerina americana, whose males bear wing pigmentation patterns, which are maintained via male–male competition. H. americana males emerge and take some time to mature sexually, after which, depending on their fat reserves, may start defending territories where females arrive at for copulation. Territorial males are eventually defeated and lose their territories. This loss is a consequence of a reduction in muscular fat reserves. We tested whether: (a) territorial males had more pigmented wings, more intense melanine-based immune response (encapsulation response to a nylon filament implant) and higher fat reserves than non-territorial males; (b) pigmentation is related to immunity and fat reserves; (c) the immune response held constant in two different episodes (3 days between each) in the same male during territorial tenure; and (d) immune response and fat reserves decreased after experimentally simulated fighting event. Our results agree with current views of immune ability and courting traits: (1) territorial males had more wing pigmentation, higher immune responses and fat reserves than non-territorial males; (2) pigmentation was also correlated with immunity and fat reserves; and (3) immune response was similarly intense in the two episodes during territorial tenure. However, this response and fat reserves were considerably lower after fighting compared to that of territorial males and non-territorial males. Our work points out a link between fat reserves and immune ability which agree with previous studies in insects. Given, however, that in this species the use of wing pigmentation via male–male competition is more likely to provide information about current fat reserves than immunity, it is suggested that immune ability is only indirectly selected and may not be the information that pigmentation would convey to conspecifics.     

Territoriality and male-biased sexual size dimorphism in Argia reclusa (Odonata: Zygoptera)

In Odonata, many species present sexual size dimorphism (SSD), which can be associated with male territoriality in Zygoptera. We hypothesized that in the territorial damselfly Argia reclusa, male–male competition can favor large males, and consequently, drive selection pressures to generate male-biased SSD. The study was performed at a small stream in southeastern Brazil. Males were marked, and we measured body size and assessed the quality of territories. We tested if larger territorial males (a) defended the best territories (those with more male intrusions and visiting females), (b) won more fights, and (c) mated more. Couples were collected and measured to show the occurrence of sexual size dimorphism. Results indicated that males are larger than females, and that territorial males were larger than non-territorial males. Larger territorial males won more fights and defended the best territories. There was no difference between the mating success of large territorial and small non-territorial males. Although our findings suggest that male territoriality may play a significant role on the evolution of sexual size dimorphism in A. reclusa, we suggest that other factors should also be considered to explain the evolution of SSD in damselflies, since non-territorial males are also capable of acquiring mates.