Females show greater changes in wing colour with latitude than males in the green‐veined white butterfly,Pieris napi (Lepidoptera: Pieridae)

In butterflies, wing colour may simultaneously be under sexual selection in the context of mating selection and natural selection in the context of thermoregulation. In the present study, we collected mated females of the green‐veined white butterfly (Pieris napi) from locations spanning 960 km of latitude across Fennoscandia, and investigated sex‐specific latitudinal wing colour variation in their offspring raised under identical conditions. We measured wing colour characteristics, including reflectance at wavelengths 300–700 nm and the degree of wing melanization. At all latitudes, females reflected more light in the short wavelengths (< 400 nm) and less in the long wavelengths (> 450 nm), and they were more melanized than males. However, female wing colour varied more with latitude than that of males. Among females, long wavelength reflectance decreased, whereas short wavelength reflectance and melanization increased, towards the north. By contrast, among males, latitudinal variation was found only in the ventral hindwing melanization. These results are consistent with the idea that the balance between natural and sexual selection acting on wing colour changes with latitude differently in males than females. The dark wing colour of females in the north may be a thermoregulatory adaptation, although males may be constrained from evolving the dark dorsal wing colour favoured by natural selection because of constant sexual selection across latitudes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Variation in UV light reflected from the wings of Favonius and Quercusia butterflies

The wing colors of eight lycaenid species of the genera Favonius and Quercusia were examined with a spectrophotometer. Four (F. orientalis, F. taxila, F. jezoensis and F. ultramarinus) of five green to blue‐green Favonius species had a double‐peaked pattern, reflecting UV light (345–355 nm) and green light (515–525 nm), whereas F. cognatus reflected only visible green light (539 nm). Thus, the species considered most closely related, F. ultramarinus and F. cognatus, had quite different wing colors in terms of insect vision. Two bluish species had utterly different reflection patterns: F. saphrinus had a single peak in the UV range and Q. fujisana had two peaks, one each in the UV and visible light ranges. The black F. yuasai did not have any peak in the examined range of wavelengths (300–700 nm).     

Diversity in structural ultraviolet coloration among female sulphur butterflies (Coliadinae, Pieridae)

In some species of sulphur butterflies (Pieridae: Coliadinae) females as well as males display bright structural reflectance on their dorsal wing surfaces, although comparatively little attention has been paid to this coloration in females. We examined the spectral properties of female dorsal coloration and scale structure in three species of sulphurs for which published images show bright UV reflectance in females: the Neotropical Anteos clorinde and two species of Indo-Australian Eurema, E. hecabe and E. candida. In A. clorinde and E. hecabe, female UV reflectance is iridescent and produced by thin film interference in a system of ridges and lamellae, as it is in conspecific males. Female A. clorinde exhibit the same spatial distribution and chromaticity of UV reflectance as seen in males, but the UV reflectance in female E. hecabe is much smaller in area compared to that of conspecific males and is both less bright and less chromatic than observed in males. In contrast, UV reflectance in E. candida females is diffuse, and arises from a lack of pterin pigments in the wings, which permits a broad-band scattered reflection to be seen. This is the mechanism that is known to produce bright UV reflectance in females of the confamilial whites. Our results highlight the diversity of UV reflectances and underlying mechanisms in sulphurs and suggest multiple evolutionary pathways leading to this diversity in female sulphur butterflies.     

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.     

Sex and age-specific differences in ultraviolet reflectance of scent marks of bank voles (Clethrionomys glareolus)

Scent markings of voles are visible via their ultraviolet reflection. Kestrels, and possibly other diurnal raptors, may use this property when hunting. We performed a laboratory study on bank voles to determine whether UV-reflectance of scent marks differs in relation to sex, age and social status. When reflectance spectra of scent marks were measured with a spectroradiometer, we found UV reflectance to be strongest in mature males. There were no differences between mature females and immature juveniles, nor between sexes in juveniles or mature and immature individuals in females. Moreover, we did not find any difference in UV reflectance between dominant and subordinate mature males. The results of this study support earlier findings that UV sensitive predators may use UV reflectance of scent marks as a prey cue. Consequently, studies on differing vulnerability of voles to avian predators should take into account not only their space use and behaviour but also the UV reflectance of their scent marks. Accepted: 21 August 1999     

Ultraviolet and violet light: attractive orientation cues for the Indian meal moth, Plodia interpunctella

The Indian meal moth (IMM), Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), engages in long-distance or foraging flights in the twilight hours of the scotophase when blue light dominates the irradiance spectrum of the sky. We tested the hypothesis that IMM uses wavelengths of visible blue/violet light as orientation cues that trigger phototactic responses. In four-choice laboratory experiments, blue light (400–475 nm) was significantly more effective than green (475–600 nm), orange (575–700 nm), or red (590–800 nm) light in attracting males and mated females. In subsequent experiments that tested light emitting diodes (LEDs) emitting peak wavelengths in the blue/violet-light range, the 405-nm 'violet' LED was significantly more effective than the 435-, 450-, or 470-nm 'blue' LED in attracting males as well as virgin and mated females. In electroretinogram recordings, the 405-nm wavelength elicited significantly stronger receptor potentials from female and male eyes than the 350-nm (UV) wavelength, and in a behavioral experiment it significantly enhanced the known attractiveness of UV light. Equal attraction of IMMs to 405-nm LEDs at 600–700 µW/cm² with or without UV light, and significantly stronger attraction to a 405-nm LED than to a 350-nm LED at maximum light intensities, suggest that the deployment of violet instead of UV light could become one of several management tactics for control of IMMs.     

UV reflectance is associated with environmental conditions in Palaearctic Pieris napi (Lepidoptera: Pieridae)

The subject of our investigation was the visual features of wing color with special focus on the UV reflectance in the green‐veined white butterfly (Pieris napi). Previous studies had concluded that UV reflectance on dorsal wing surfaces is found only in the female P. napi. Based on UV sensitive photography, we analyzed a correlation between 12 geographic and environmental factors and UV reflectance patterns on 3 patches on the forewings of 407 P. napi specimens from the Palaearctic region. Results had shown that females significantly differ from males: they exhibit a 25% higher UV reflectance. To investigate whether and how UV reflectance levels on the forewings and hindwings of both sexes are influenced by the environment, we performed a principal component analysis (PCA) with several environmental variables. For several variables (in particular, latitude and longitude, mean annual temperature and precipitation, and temperature annual range and altitude), the generalized linear model (GLM) model revealed a significant correlation in both sexes. This suggests a link between UV reflectance levels and the environment and distribution of P. napi. We found that stronger UV reflectance is associated with generally more hostile environments and concluded that large‐scale environmental factors influence the UV reflectance on the forewings of both male and female green‐veined white butterflies.     

A quantitative analysis of geographic color variation in two Geotrupes dung beetles

We conducted a quantitative analysis of geographic color variation in two species of dung beetles: Geotrupes auratus and G. laevistriatus. The reflectance of the dorsal surfaces was measured from 300 to 700 nm using a spectrophotometer. The reflectance curves for both beetles were bimodal; there were two distinct peaks, namely, the a peak, between 400 and 700 nm, and the beta peak at around 300 nm. A stepwise discriminant analysis indicated that geographic color variation in Geotrupes beetles was primarily characterized by a shift of the a peak. Using beetles from three locations, we compared the wavelength (nm) of the a peak (lambdamax(alpha)) and its reflectance intensity (R(a)) to investigate sex and population differences. Intraspecific geographic variation in coloration was effectively detected by discriminant analysis of spectral reflectance curves. Our results showed that G. auratus and G. laevistriatus had similar coloration within each sampling location. Our study also revealed hidden sex differences in R(a); R(a) of males were significantly higher than those of females in both species. Since the dorsal surface of the beetles shows remarkable color variation, and coloration can be assessed objectively using reflectance spectra, Geotrupes beetles may be good model organisms to investigate geographic color variation.     

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.     

Extreme ultraviolet sexual dimorphism in jumping spiders (Araneae: Salticidae)

Jumping spiders (Salticidae) have acute vision with some cells in the retina that are sensitive to ultraviolet (UV) spectra (< 400 nm). However, no study has documented the use of UV signals in salticids. To appreciate the function of UV vision, it is necessary to characterize the UV colours of salticids. In the present study, the UV and human-visible wavelengths of a tropical ornate salticid spider, Cosmophasis umbratica , were analysed using reflectance spectrometry to obtain evidence of sex-specific UV colours. An absolute sexual dimorphism in the UV colours of this salticid species was found. All of the body parts of adult males that are displayed to conspecifics during intra-specific interactions reflected UV (300–400 nm) light, whereas the adult females and juveniles did not reflect UV light from any body part. A great deal of variation was also found in the UV wavebands among males. This is the first full UV characterization of a salticid spider and the first study to demonstrate an extreme sexual UV dimorphism in jumping spiders. The findings obtained provide evidence that UV reflectance may comprise important sexual signals in jumping spiders.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 397–406.     

Spectral sensitivity and wing colors of Narathura and Panchala species

Spectral sensitivity and wing colors were compared among three species of lycaenid butterflies, Panchala ganesa, Narathura bazalus and Narathura japonica. Spectral sensitivity was examined by the ERG method using an integrating sphere which could stimulate the whole surface of the compound eye. Wing colors were measured using a spectrophotometer. All three species examined were sensitive to a broad wavelength range, from UV to red light, with the primary peak in the shorter wavelength region. Slight peak shifts were observed among the studied species; species with wings reflecting shorter wavelength light tended to be sensitive to shorter wavelength lights.     

Which way is up? Asymmetric spectral input along the dorsal–ventral axis influences postural responses in an amphibious annelid

Medicinal leeches are predatory annelids that exhibit countershading and reside in aquatic environments where light levels might be variable. They also leave the water and must contend with terrestrial environments. Yet, leeches generally maintain a dorsal upward position despite lacking statocysts. Leeches respond visually to both green and near-ultraviolet (UV) light. I used LEDs to test the hypothesis that ventral, but not dorsal UV would evoke compensatory movements to orient the body. Untethered leeches were tested using LEDs emitting at red (632 nm), green (513 nm), blue (455 nm) and UV (372 nm). UV light evoked responses in 100 % of trials and the leeches often rotated the ventral surface away from it. Visible light evoked no or modest responses (12–15 % of trials) and no body rotation. Electrophysiological recordings showed that ventral sensilla responded best to UV, dorsal sensilla to green. Additionally, a higher order interneuron that is engaged in a variety of parallel networks responded vigorously to UV presented ventrally, and both the visible and UV responses exhibited pronounced light adaptation. These results strongly support the suggestion that a dorsal light reflex in the leech uses spectral comparisons across the dorsal–ventral axis rather than, or in addition to, luminance.     

Polarized and specular reflectance variation with leaf surface features

The linearly polarized reflectance from a leaf depends on the characteristics of the leaf surface. In the present study the leaf reflectance of a number of plant species with varying surface characteristics was measured at the Brewster angle with a polarization photometer having 5 visible and near-infrared wavelength bands. We found that all leaf surfaces polarized incident light. Differences among species could be explained by variation in surface features. The results support our hypothesis that the polarized light is reflected by the leaf surface, not by its interior. Two mechanisms appeared responsible for the linearly polarized reflectance: (1) specular reflectance and (2) surface particle scattering. In most cases, large values of linearly polarized reflectance could be attributed to specular reflectance from the leaf surface. Attribution required knowledge of the optical dimensions of features on the leaf surface.     

Novel chromatic and structural biomarkers of diet in carotenoid-bearing plumage

Previous attempts to establish a link between carotenoid-based plumage reflectance and diet have focused on spectral features within the human visible range (400-700 nm), particularly on the longer wavelengths (550-700 nm) that make these plumages appear yellow, orange or red. However, carotenoid reflectance spectra are intrinsically bimodal, with a less prominent but highly variable secondary reflectance peak at near-ultraviolet (UV; 320-400 nm) wavelengths visible to most birds but not to normal humans. Analysis of physical reflectance spectra of carotenoid-bearing plumages among trophically diverse tanagers (Thraupini, Emberizinae, Passeriformes) indicated that both the absolute and relative (to long visible wavelengths) amounts of short waveband (including UV) reflectance were lower in more frugivorous species. Striking modifications to the branched structure of feathers increased with frugivory. These associations were independent of phylogenetic relatedness, or other physical (specimen age, number of carotenoid-bearing patches) or ecological (body size, elevation) variables. By comparison, reflectance at longer visible wavelengths ('redness') was not consistently associated with diet. The reflectance patterns that distinguished frugivores should be more apparent to UV-sensitive birds than to UV-blind humans, but humans can perceive the higher plumage gloss produced by modified gross feather structure. Basic aspects of carotenoid chemistry suggest that increases in pigment concentration and feather dimensions reduce short waveband reflectance by the plumages of frugivores.     

The evolution of adult light emission color in North American fireflies

Firefly species (Lampyridae) vary in the color of their adult bioluminescence. It has been hypothesized that color is selected to enhance detection by conspecifics. One mechanism to improve visibility of the signal is to increase contrast against ambient light. High contrast implies that fireflies active early in the evening will emit yellower luminescence to contrast against ambient light reflected from green vegetation, especially in habitats with high vegetation cover. Another mechanism to improve visibility is to use reflection off the background to enhance the light signal. Reflectance predicts that sedentary females will produce greener light to maximize reflection off the green vegetation on which they signal. To test these predictions, we recorded over 7500 light emission spectra and determined peak emission wavelength for 675 males, representing 24 species, at 57 field sites across the Eastern United States. We found support for both hypotheses: males active early in more vegetated habitats produced yellower flashes in comparison to later‐active males with greener flashes. Further, in two of the eight species with female data, female light emissions were significantly greener as compared to males.     

Female mating biases for bright ultraviolet iridescence in the butterfly Eurema hecabe (Pieridae)

Exaggerated male-limited coloration is widespread among butterflies,yet convincing demonstrations of intraspecific mating preferencesfor signal brightness and/or chromaticity are relatively rarein this group. Here, I couple behavioral experiments involvingmanipulations of ambient light environments and male reflectancepatterns with observation of wild mating patterns to investigatevisual mating biases in the large grass yellow (Eurema hecabe).Males in this species possess exaggerated, limited-view ultraviolet(UV) iridescence across most of their dorsal wing surface thathas putative sexual signaling function. In the first experiment,conducted in small (0.7–m³) cages, individuals were significantlyless likely to copulate when the UV portion of natural ambientillumination (i.e., 300–400 nm) was strongly reduced.In 2 subsequent experiments, conducted under full-spectrum sunlightin small and large (5 x 6 x 4 m) cages, males with their UVsignal artificially dulled by 25% consistently copulated withfewer, and smaller, females than sham-control individuals. Importantly,the manipulated levels of UV brightness in these experimentsfall well within the naturally occurring bounds of variationin male UV reflectance. These findings therefore unanimouslysupport the presence of a UV signal–based female bias.In apparent contrast, comparison of 161 in-copula and 188 free-flyingmales from a high-density field assemblage revealed that copulatingmales were significantly older and henceforth actually possessed(subtly) less UV bright wings. Copulating male UV brightnesswas, however, positively related to the size of their mate,which echoes the experimental findings and may represent a signatureof mutual mate choice. I discuss these results in light of thefull complexities of the butterfly mating system and the potentialsignaling value of iridescent coloration in butterflies andanimals generally.     

Ultraviolet reflectance mediates pollinator visitation in Mimulus guttatus

Floral colors are widely believed to be an adaptation to attract pollinators. Recently, our understanding of floral reflectance has broadened to include colors that are beyond the spectrum that human eyes can perceive (such as ultraviolet (UV) reflectance), yet we still know relatively little about which plant species reflect UV light or its effectiveness in attracting pollinators. We investigated the effect of UV reflectance in Mimulus guttatus in a number of different populations in British Columbia, Canada. We found that M. guttatus had distinct regions of the corolla where UV light was reflected and absorbed. When we manipulated the degree of contrast between the reflection and absorption area, we found that pollinator visitation was severely disrupted, in terms of frequency and foraging patterns observed. Despite the bright yellow (bee‐green) coloration and visible nectar guides in M. guttatus, we conclude that UV reflectance is critical in pollinator attraction.     

Wing colors based on arrangement of the multilayer structure of wing scales in lycaenid butterflies (Insecta: Lepidoptera)

Male wing colors and wing scale morphology were examined for three species of lycaenid butterflies: Chrysozephyrus ataxus, Favonius cognatus and F. jezoensis. Measurement of spectral reflectance on the wing surface with a spectrophotometer revealed species‐specific reflection spectra, with one or two peaks in the ultraviolet and/or green ranges. Observations of wing scales using an optical microscope revealed that light was reflected from the inter‐ridge regions, where transmission electron microscopy revealed a multilayer structure. Based on the multilayer dimensions obtained, three models were devised and compared to explain the measured reflectance spectrum. The results showed that the best fit is a model in which thicknesses of thin films of the multilayer system are not constant and air spaces between cuticle layers are more or less packed with cuticle spacers. This suggests that the specific wing colors of the species examined are produced by the species‐specific arrangement of the multilayer structure of wing scales.     

Variation in ultraviolet reflectance by carotenoid-bearing feathers of tanagers (Thraupini: Emberizinae: Passeriformes)

Avian visual sensitivity encompasses both the human visible range (400–700 nm) and also near‐ultraviolet (UV) wavelengths (320–400 nm) invisible to normal humans. I used reflectance spectrophotometry to assess variation in UV reflectance for yellow, orange and red plumage in 67 species of tanager (Passeriformes). Previous chemical studies, and my analysis of reflectance minima, suggest that carotenoids are the dominant pigments in yellow, orange and red tanager plumage. Spectra recorded over the range of wavelengths to which birds are sensitive (320–700 nm) were invariably bimodal, with both a plateau of high reflectance at longer (> 500 nm) wavelengths and a distinct secondary peak at UV (< 400 nm) wavelengths. Within this overall framework, variation in UV reflectance was expressed within well‐defined quantitative limits: (1) peak reflectance was always lower than the corresponding plateau of reflectance at longer visible wavelengths; (2) the intensity of peak reflectance declined steadily below 350 nm; (3) wavelengths of peak reflectance clustered between 350 and 370 nm. Significant correlations were detected between various measures of total reflectance in the UV and visible wavebands, but not between various measures of spectral location of UV and visible reflectance. I propose that the strong absorption band at short visible wavelengths (～ 380–550 nm) responsible for bimodal spectra of carotenoids in vitro is also responsible for bimodal reflectance by carotenoid‐based plumage colours. The construction of the UV and visible reflectance bands from different sides of this same absorbance band provides a mechanism for the observed covariation between UV and visible wavelengths. Lack of an association between the spectral locations of the UV and visible reflectance bands may result from the limited variation in spectral location of the UV band. These patterns suggest that plumage colours are subject to constraints, just as are more traditional morphological characters. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 243–257.     

Does ultraviolet reflectance accentuate a sexually selected signal in terns?

Unlike the majority birds that replace their primaries once each year, most Sterna terns practice an unusual repeated wing molt, wherein a variable number of inner primaries are replaced twice or even three times in a single year. This seemingly redundant replacement of the primaries may serve as a sexually selected indicator of quality in that terns may evaluate potential mates based on the number of primaries they were able to replace twice or three times prior to the breeding season. To evaluate the potential of repeated molt as a social signal, we compared light-reflectance curves and photon catches for new (twice-molted) and old (once-molted) primaries in three species of terns. We observed that old feathers reflected considerably less light across all wavelengths and found that in two of the three species examined the ultraviolet reflectance was disproportionably reduced in old feathers relative to the reduction in visible reflectance. Thus, the UV component of coloration in tern wing feathers may accentuate the difference between the new feathers generated by repeated wing molt and older, more worn feathers, thereby reinforcing a sexually selected signal of quality.