Prey from the eyes of predators: Color discriminability of aposematic and mimetic butterflies from an avian visual perspective

Predation exerts strong selection on mimetic butterfly wing color patterns, which also serve other functions such as sexual selection. Therefore, specific selection pressures may affect the sexes and signal components differentially. We tested three predictions about the evolution of mimetic resemblance by comparing wing coloration of aposematic butterflies and their Batesian mimics: (a) females gain greater mimetic advantage than males and therefore are better mimics, (b) due to intersexual genetic correlations, sexually monomorphic mimics are better mimics than female‐limited mimics, and (c) mimetic resemblance is better on the dorsal wing surface that is visible to predators in flight. Using a physiological model of avian color vision, we quantified mimetic resemblance from predators’ perspective, which showed that female butterflies were better mimics than males. Mimetic resemblance in female‐limited mimics was comparable to that in sexually monomorphic mimics, suggesting that intersexual genetic correlations did not constrain adaptive response to selection for female‐limited mimicry. Mimetic resemblance on the ventral wing surface was better than that on the dorsal wing surface, implying stronger natural and sexual selection on ventral and dorsal surfaces, respectively. These results suggest that mimetic resemblance in butterfly mimicry rings has evolved under various selective pressures acting in a sex‐ and wing surface‐specific manner.     

Experimental field tests of Batesian mimicry in the swallowtail butterfly Papilio polytes

The swallowtail butterfly Papilio polytes is known for its striking resemblance in wing pattern to the toxic butterfly Pachliopta aristolochiae and is a focal system for the study of mimicry evolution. Papilio polytes females are polymorphic in wing pattern, with mimetic and nonmimetic forms, while males are monomorphic and nonmimetic. Past work invokes selection for mimicry as the driving force behind wing pattern evolution in P. polytes. However, the mimetic relationship between P. polytes and P. aristolochiae is not well understood. In order to test the mimicry hypothesis, we constructed paper replicas of mimetic and nonmimetic P. polytes and P. aristolochiae, placed them in their natural habitat, and measured bird predation on replicas. In initial trials with stationary replicas and plasticine bodies, overall predation was low and we found no differences in predation between replica types. In later trials with replicas mounted on springs and with live mealworms standing in for the butterfly's body, we found less predation on mimetic P. polytes replicas compared to nonmimetic P. polytes replicas, consistent with the predator avoidance benefits of mimicry. While our results are mixed, they generally lend support to the mimicry hypothesis as well as the idea that behavioral differences between the sexes contributed to the evolution of sexually dimorphic mimicry.     

No Evidence that Male Choice Contributes to the Maintenance of a Shared, Sex-Limited Trait in Mimetic and Non-mimetic Female Tiger Swallowtail Butterflies, Papilio glaucus

In animal species that have morphological polymorphisms maintained by unique or divergent selection pressures, understanding the preservation of shared traits is important for identifying the factors that are influencing overall evolutionary processes. In the Eastern tiger swallowtail butterfly, Papilio glaucus, females are dimorphic. One morph (‘dark-morph’) is mostly black and mimics the toxic pipevine swallowtail, Battus philenor. These females have large amounts of blue coloration on the dorsal hind wings that enhances their mimetic resemblance. Conversely, the alternate female type (‘yellow-morph’) is similar to males in coloration with the exception of extensive dorsal blue coloration, comparable to dark-morph females. Such coloration is almost completely absent in males. We examined dorsal blue coloration in P. glaucus to determine if mimetic resemblance in dark morphs is predominantly responsible for the maintenance of dorsal blue color in both female types, or whether mate recognition and/or sexual selection by males has a stronger influence on this trait. We measured the relative amount and variance of dorsal and ventral blue coloration in females of both color morphs, as well as males. We also compared these measurements to similar ones taken in the sister species, P. canadensis (which does not exhibit female dimorphism). Lastly, we investigated mate recognition and preferences of wild males. Our results suggest that mimetic resemblance may be more important than sexual selection for sustaining dorsal blue coloration in dark-morph females and that yellow-morphs could have elevated levels of blue due to currently unknown genetic associations. Although trait correlation between sexes is common, intrasexual trait correlation in a sex-limited, polymorphic species has not been frequently observed.     

Evolutionary genetics of dorsal wing colour in Colias butterflies

The evolution of butterfly wing colouration is strongly affected by its multiple functions and by the correlated evolution of wing colour elements. Both factors may prevent local adaptation to ecological conditions. We investigated one aspect of wing colouration, the degree of dorsal wing melanization, in the butterfly Colias philodice eriphyle across an elevational gradient and its correlation with another aspect of wing colouration, ventral wing melanization. Dorsal wing melanization increased with elevation and these differences persisted in a common environment. Full-sibling analysis revealed high heritability for males but only intermediate heritability for females. The correlation between ventral and dorsal melanization showed significant elevational and sex-specific differences. In males the two traits were highly correlated, whereas in females the strength of the correlation decreased with increasing elevation. We conclude that uncoupling of ventral and dorsal melanization has evolved in females but not in males and discuss possible mechanisms underlying uncoupling.     

Ventral pigmentation variation in the meadow spittlebug Philaenus spumarius (L.) (Hemiptera,Cicadomorpha: Cercopidae)

The meadow spittlebug Philaenus spumarius (L.) (Hemiptera, Cicadomorpha: Cercopidae) exhibits heritable colour/pattern variation on the dorsal and ventral sides of the adults. Eleven principal dorsal morphs are grouped as melanics and non-melanics according to the pigmentation of the dorsal surface. An investigation of ventral pigmentation variation in Philaenus spumarius was carried out with laboratory breeding stock obtained from Llysdinam, Wales. Analyses of the 1552 individuals, 753 females and 799 males, indicated that the pigmentation on the ventral surface of the adult individuals which vary significantly is associated with dorsal morph. Ventral parts of the dorsal melanics are usually darker than in non-melanics in both females (Kruskal-Wallis one-way ANOVA: H = 372.70, d.f. = 7, P < 0.001) and males (H = 407.36, d.f. = 7, P < 0.001). The combined “C” group morphs (flavicollis + gibbus + leuco- cephalus) are always darker than all other morphs in both sexes.     

Why male butterflies are non-mimetic: natural selection,sexual selection,group selection,modification and sieving*

Thomas Belt suggested that the frequent limitation of mimicry in butterflies to the female resulted from sexual selection. Because female butterflies store sperm they can be fully fertile after only one mating; the reproductive success of a male is proportional to the number of times he mates. Sexual selection is therefore much stronger in males than females, with selection coefficients being greater by a small multiple of the number of times a female is courted during her life (long-lived species) or of the reciprocal of the female mortality rate between courtships (short-lived species). As butterflies of both sexes respond to colour when courting, sexual selection resists colour changes especially strongly in males. As a result, genes conferring new mimetic colour patterns can often become established in a butterfly population much more readily if their expression is initially limited to females; when the population size of a Batesian mimic, its model, and its predator fluctuates, such sex-limited genes have an enhanced probability of ultimate fixation in the population, and a reduced chance of loss; this effect is accentuated by the selection of modifiers which improve the mimicry. When the establishment of unimodal mimicry (expressed in both sexes) is favoured in a Batesian mimic, the gene tends to rise to an equilibrium frequency at which modifiers suppressing the expression of the mimicry only in males and'modifiers enhancing the mimicry only in females are favoured. The outcome is female-limited mimicry, or unimodal mimicry with better mimicry in the females, the males either retaining some of their sexual colour or the selective behaviour of the females becoming altered. In a Muellerian mimic there is no such equilibrium and selection ultimately favours expression of mimicry in both sexes and an appropriate alteration in the courtship responses. Hence Muellerian mimicry is seldom female-limited. Exceptional cases appear to result from the sexes flying in separate habitats. The genetical evidence in Papilio and Heliconius favours initial limitation of expression over subsequent modification as the usual basis for female-limited mimicry. Other explanations of female-limited mimicry can be found wanting in various ways; a higher predation rate on females could produce sex-limitation, but is probably not a strong factor. But the greater variability of the female in Lepidoptera may indicate lesser developmental stability, which could result in greater penetrance of mutants in the female, and hence account for the initial female-limitation. At very high densities of a mimetic species which has no non-mimetic form, mimicry tends to deteriorate more rapidly in a unimodal than in an otherwise identical sex-limited species. Although by itself this would equally favour male-limitation, and hence cannot explain the predominance of female-limitation, this effect may over evolutionary time be causing a slight increase in the proportion of sex-limited species among mimics. The stability of some mimetic polymorphisms is investigated by linear approximation: in some instances a stable equilibrium can be changed into an oscillating equilibrium by changes in the population size.     

Possible Batesian mimicry to sexually different models in the tussock moth Numenes albofascia with a great sexual color dimorphism

Mimicry with warning colors includes Batesian and Müllerian mimicries. If we divide mimicry by sex, there are theoretically four types of mimicry: unimodal, female-limited, male-limited and dual mimicry. The latter three cases cause sexual dimorphism in body color and marking pattern but are rarely reported. In this study, we show that the tussock moth Numenes albofascia is possibly a dual mimic. The wing color and marking pattern of male and female N. albofascia are completely different, with the male's pattern resembling that of the smoky moth Pidorus atratus, while the female pattern resembles that of the tiger moth Arctia caja. Body size also differs greatly between the sexes of N. albofascia, matching the mimicry model species of each sex. These moths are distributed sympatrically in Japan, and their adult seasons overlap with each other. According to lizard feeding experiments, N. albofascia is palatable, while both male and female model species are unpalatable. Actograms in the laboratory and the light trapping in the field suggest that females of N. albofascia fly actively from sunset to midnight, while males fly during the twilight period around dawn. Therefore, male and female N. albofascia might be Batesian mimics of diurnally active P. atratus and nocturnally active A. caja, respectively, and the great sexual dimorphism of this moth could be caused by dual mimicry.     

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.     

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, ?? , ??–??.     

INTRASEXUAL SELECTION CONSTRAINS THE EVOLUTION OF THE DORSAL COLOR PATTERN OF MALE BLACK SWALLOWTAIL BUTTERFLIES,PAPILIO POLYXENES

Males of the eastern black swallowtail (Papilio polyxenes asterius Stoll) with typical coloration were more successful in intrasexual competition for mating territories than were males altered to have female-like mimetic coloration. Sibling males were matched for wingspan and emergence date and released as pairs, one with its pattern altered and one a control that was marked but with unaltered appearance. Significantly fewer altered males were resighted one or more days after release compared with control males (33% vs. 76%, 1990; 46% vs. 83%, 1993). Altered males were less able to establish and maintain themselves in preferred territories. The inability of released, altered males to establish a territory appears related to significantly longer male-male encounters. Encounters involving at least one participant with altered appearance averaged 66 s compared with 24 s if neither male was altered. However, altering the coloration of P. polyxenes males that already had established themselves in a territory had little effect. After courtships of similar duration (≈ 40 s), released virgin females were equally likely to mate with either altered or control males. This suggests that male-male intrasexual selection is of greater importance than female mate choice in maintaining a non-mimetic dorsal coloration in male P. polyxenes.     

Behaviour before beauty: Signal weighting during mate selection in the butterfly Papilio polytes

Mating displays often contain multiple signals. Different combinations of these signals may be equally successful at attracting a mate, as environment and signal combination may influence relative signal weighting by choosy individuals. This variation in signal weighting among choosy individuals may facilitate the maintenance of polymorphic displays and signalling behaviour. One group of animals known for their polymorphic patterning are Batesian mimetic butterflies, where the interaction of sexual selection and predation pressures is hypothesized to influence the maintenance of polymorphic wing patterning and behaviour. Males in the female‐limited polymorphic Batesian mimetic butterfly Papilio polytes use female wing pattern and female activity levels when determining whom to court. They court stationary females with mimetic wing patterns more often than stationary females with non‐mimetic, male‐like wing patterns and active females more often than inactive females. It is unclear whether females modify their behaviour to increase (or decrease) their likelihood of receiving male courtship, or whether non‐mimetic females spend more time in cryptic environments than mimetic females, to compensate for their lack of mimicry‐driven predation protection (at the cost of decreased visibility to males). In addition, relative signal weighting of female wing pattern and activity to male mate selection is unknown. To address these questions, we conducted a series of observational studies of a polymorphic P. polytes population in a large butterfly enclosure. We found that males exclusively courted active females, irrespective of female wing pattern. However, males did court active non‐mimetic females significantly more often than expected given their relative abundance in the population. Females exhibited similar activity levels, and selected similar resting environments, irrespective of wing pattern. Our results suggest that male preference for non‐mimetic females may play an active role in the maintenance of the non‐mimetic female form in natural populations, where males are likely to be in the presence of active, as well as inactive, mimetic and non‐mimetic females.     

Why are there so many mimicry rings? Correlations between habitat,behaviour and mimicry in Heliconius butterflies

In the new world tropics there is an extravagant array of sympatric butterfly mimicry rings. This is puzzling under strictly coevolutionary (Müllerian) mimicry: all unpalatable species should converge as ‘co-mimics' to the same pattern. If mimicry has usually evolved in unpalatable species by one-sided (Batesian) evolution, however, it is easy to see that mimicry rings centred on different models could remain distinct. If mimicry rings were also segregated by habitat, a diversity of mimicry rings could be stabilized. In this paper we report correlations between behaviour and mimicry of nine unpalatable Heliconius species. It is already known that co-mimics fly in similar habitats, and non-mimics fly in different habitats, although there is much overlap. Contrary to a previous report, we find little difference in flight heights of heliconiine mimicry rings; all species fly from ground level to the canopy. However, co-mimics roost at night in similar habitats and at similar heights above the ground, but in different habitats and at different heights from species in other mimicry rings. Heliconius (especially the erato taxonomic group) are renowned for roosting gregariously; and co-mimics roost gregariously with each other more often than with non-mimics. Gregarious roosting is therefore common between species, as well as within species. There are thus strong links between mimicry and behavioural ecology in Heliconius. The paradoxical correlation between nocturnal roosting and visual mimicry is presumably explained by bird predation at dusk when roosts are forming, or at dawn before they have disbanded. Direct evidence of predation is lacking, but there are high rates of disturbance by birds at these times. These results, together with knowledge of the phylogeny of Heliconius, suggest that species from the melpomene-group of Heliconius have radiated to occupy mimetic niches protected by model species in the Ithomiinae and the erato-group of Heliconius. A variety of sympatric mimicry rings is apparently maintained because key models fail to converge, while more rapidly-evolving unpalatable mimics evolve towards the colour patterns of the models. The maintenance of mimetic diversity would be aided by the habitat and behavioural differences between mimicry rings revealed here, provided that different predators are found in different habitats. This explanation for the maintenance of multiple mimicry rings is more plausible for Heliconius mimicry than alternatives based on visual mating constraints, thermal ecology, or camouflage.     

GENETICS OF MIMICRY IN THE TIGER SWALLOWTAIL BUTTERFLIES,PAPILIO GLAUCUS AND P. CANADENSIS (LEPIDOPTERA: PAPILIONIDAE)

The tiger swallowtail butterfly, Papilio glaucus, exhibits a female-limited polymorphism for Batesian mimicry; the Canadian tiger swallowtail, Papilio canadensis, lacks the mimetic (dark) form entirely. The species hybridize to a limited extent where their ranges overlap. Field collections and censuses indicate that mimetic females occur throughout the range of P. glaucus but at lowest frequencies in populations at the latitudinal edges of its geographic range such as the southernmost part of Florida and along the entire northern edge of its distribution from Massachusetts to Minnesota. Frequencies of mimetic females have remained relatively stable over time. Inheritance of the mimetic form is controlled primarily by two interacting sex-linked loci. The typical matrilineal pattern of inheritance in P. glaucus can be explained by polymorphism at a Y-linked locus, b. Analysis of P. glaucus × P. canadensis crosses has also revealed an X-linked locus, s, which controls the expression of the mimetic phenotype. The P. canadensis allele, s^can, suppresses the mimetic phenotype in hybrid and backcross females. Results from more than 12 yr of rearing tiger swallowtails, including interspecies hybrids, indicate that the absence of mimetic P. canadensis females is due to both a high frequency of the “suppressing” allele s^can and low frequency of the black-pigment-determining b + allele. The frequency of s^can (or other suppressing alleles of s) in P. glaucus populations outside the hybrid zone is low. Some males heterozygous at the s locus and some suppressed mimetic females occur within the hybrid zone. A simple genetic model predicts the frequency of daughters that differ in phenotype from their mothers.     

VIABILITY SELECTION ON SEASONALLY POLYPHENIC TRAITS: WING MELANIN PATTERN IN WESTERN WHITE BUTTERFLIES

Wing melanin pattern varies seasonally among generations in many populations of the butterfly Pontia occidentalis, leading to distinctly different wing phenotypes during spring and summer generations. Estimates of directional selection on wing pattern can therefore quantify the imperfection of this phenotypically plastic (polyphenic) response in generating “optimal” phenotypes for each seasonal generation. Mark-release-recapture (MRR) studies were used to estimate directional selection on six wing traits in a natural population of P. occidentalis during both spring and summer weather conditions. Estimated survival and recapture probabilities varied substantially among the four MRR studies. When differences between males and females were detected, the survival and recapture probabilities were higher for males than for females. Estimated selection coefficients suggested that the direction of selection on one wing trait important for thermoregulation, melanin on the base of the dorsal hindwings (trait hb), fluctuated seasonally; there was evidence of directional selection for increased hb in the spring studies and for decreased hb in the summer studies. Such fluctuating seasonal selection on hb implies that the seasonal polyphenic response may not be sufficient to eliminate selection on this trait; the slope of the reaction-norm mapping hb onto seasonal environmental cues is too shallow, resulting in further selection on the reaction norm. Adaptive evolution of the reaction norm may be constrained by phenotypic and genetic correlations with other wing traits that experience different patterns of selection and by variable weather conditions within seasons and among years.     

Convergent evolution of neuroendocrine control of phenotypic plasticity in pupal colour in butterflies

Phenotypic plasticity in pupal colour occurs in three families of butterflies (the Nymphalidae, Papilionidae and Pieridae), typically in species whose pupation sites vary unpredictably in colour. In all species studied to date, larvae ready for pupation respond to environmental cues associated with the colour of their pupation sites and moult into cryptic light (yellow–green) or dark (brown–black) pupae. In nymphalids and pierids, pupal colour is controlled by a neuroendocrine factor, pupal melanization-reducing factor (PMRF), the release of which inhibits the melanization of the pupal cuticle resulting in light pupae. In contrast, the neuroendocrine factor controlling pupal colour in papilionid butterflies results in the production of brown pupae. PMRF was extracted from the ventral nerve chains of the peacock butterfly Inachis io (Nymphalidae) and black swallowtail butterfly Papilio polyxenes (Papilionidae). When injected into pre-pupae, the extracts resulted in yellow pupae in I. io but brown pupae in P. polyxenes. These results suggest that the same neuroendocrine factor controls the plasticity in pupal colour, but that plasticity in pupal colour in these species has evolved independently (convergently).     

Independent evolution of sexual dimorphism and female‐limited mimicry in swallowtail butterflies (Papilio dardanus and Papilio phorcas)

Several species of swallowtail butterflies (genus Papilio) are Batesian mimics that express multiple mimetic female forms, while the males are monomorphic and nonmimetic. The evolution of such sex‐limited mimicry may involve sexual dimorphism arising first and mimicry subsequently. Such a stepwise scenario through a nonmimetic, sexually dimorphic stage has been proposed for two closely related sexually dimorphic species: Papilio phorcas, a nonmimetic species with two female forms, and Papilio dardanus, a female‐limited polymorphic mimetic species. Their close relationship indicates that female‐limited polymorphism could be a shared derived character of the two species. Here, we present a phylogenomic analysis of the dardanus group using 3964 nuclear loci and whole mitochondrial genomes, showing that they are not sister species and thus that the sexually dimorphic state has arisen independently in the two species. Nonhomology of the female polymorphism in both species is supported by population genetic analysis of engrailed, the presumed mimicry switch locus in P. dardanus. McDonald–Kreitman tests performed on SNPs in engrailed showed the signature of balancing selection in a polymorphic population of P. dardanus, but not in monomorphic populations, nor in the nonmimetic P. phorcas. Hence, the wing polymorphism does not balance polymorphisms in engrailed in P. phorcas. Equally, unlike in P. dardanus, none of the SNPs in P. phorcas engrailed were associated with either female morph. We conclude that sexual dimorphism due to female polymorphism evolved independently in both species from monomorphic, nonmimetic states. While sexual selection may drive male–female dimorphism in nonmimetic species, in mimetic Papilios, natural selection for protection from predators in females is an alternative route to sexual dimorphism.     

Female Bicyclus anynana butterflies choose males on the basis of their dorsal UV-reflective eyespot pupils

Sexual and natural selection pressures are thought to shape the characteristic wing patterns of butterfly species. Here we test whether sexual selection by female choice plays a role in the maintenance of the male wing pattern in the butterfly Bicyclus anynana. We perform one of the most extensive series of wing pattern manipulations in butterflies, dissecting every component of the 'bulls-eye' eyespot patterns in both ventral and dorsal wing surfaces of males to test the trait's appeal to females. We conclude that females select males on the basis of the size and brightness of the dorsal eyespot's ultraviolet reflecting pupils. Pupil absence is strongly selected against, as are artificially enlarged pupils. Small to intermediate (normal sized) pupils seem to function equally well. This work contradicts earlier experiments that suggest that the size of dorsal eyespots plays a role in female choice and explains why male dorsal eyespots are very variable in size and often have indistinct rings of coloration, as the only feature under selection by females seems to be the central white pupil. We propose that sexual selection by female choice, rather than predator avoidance, may have been an important selective factor in the early stages of eyespot evolution in ancestral Lepidopteran lineages.     

Subtle variation in size and shape of the whole forewing and the red band among co‐mimics revealed by geometric morphometric analysis in Heliconius butterflies

Heliconius are unpalatable butterflies that exhibit remarkable intra‐ and interspecific variation in wing color pattern, specifically warning coloration. Species that have converged on the same pattern are often clustered in Müllerian mimicry rings. Overall, wing color patterns are nearly identical among co‐mimics. However, fine‐scale differences exist, indicating that factors in addition to natural selection may underlie wing phenotype. Here, we investigate differences in shape and size of the forewing and the red band in the Heliconius postman mimicry ring (H. erato phyllis and the co‐mimics H. besckei, H. melpomene burchelli, and H. melpomene nanna) using a landmark‐based approach. If phenotypic evolution is driven entirely by predation pressure, we expect nonsignificant differences among co‐mimics in terms of wing shape. Also, a reinforcement of wing pattern (i.e., greater similarity) could occur when co‐mimics are in sympatry. We also examined variation in the red forewing band because this trait is critical for both mimicry and sexual communication. Morphometric results revealed significant but small differences among species, particularly in the shape of the forewing of co‐mimics. Although we did not observe greater similarity when co‐mimics were in sympatry, nearly identical patterns provided evidence of convergence for mimicry. In contrast, mimetic pairs could be distinguished based on the shape (but not the size) of the red band, suggesting an “advergence” process. In addition, sexual dimorphism in the red band shape (but not size) was found for all lineages. Thus, we infer that natural selection due to predation by birds might not be the only mechanism responsible for variation in color patterns, and sexual selection could be an important driver of wing phenotypic evolution in this mimicry ring.     

No evidence of sexual dimorphism in the tails of the swallowtail butterflies Papilio machaon gorganus and P. m. britannicus

The European swallowtail butterfly (Papilio machaon) is so named, because of the long and narrow prominences extending from the trailing edge of their hindwings and, although not a true tail, they are referred to as such. Despite being a defining feature, an unequivocal function for the tails is yet to be determined, with predator avoidance (diverting an attack from the rest of the body), and enhancement of aerodynamic performance suggested. The swallowtail, however, is sexually size dimorphic with females larger than males, but whether the tail is also sexually dimorphic is unknown. Here, museum specimens were used to determine whether sexual selection has played a role in the evolution of the swallowtail butterfly tails in a similar way to that seen in the tail streamers of the barn swallow (Hirundo rustica), where the males have longer streamers than those of the females. Previously identified sexual dimorphism in swallowtail butterfly size was replicated, but no evidence for dimorphism in tail length was found. If evolved to mimic antennae and a head to divert a predatory attack, and if an absolute tail size was the most effective for this, then the tail would probably be invariant with butterfly hindwing size. The slope of the relationship between tail length and size, however, although close to zero, was nonetheless statistically significantly above (tail length ∝ hindwing area ^{0.107 ± 0.011}). The slope also did not equate to that expected for geometric similarity (tail length ∝ hindwing area^1/2) suggesting that tail morphology is not solely driven by aerodynamics. It seems likely then, that tail morphology is primarily determined by, and perhaps a compromise of several, factors associated with predator avoidance (e.g. false head mimicry and a startling function). Of course, experimental data are required to confirm this.     

Role of superoxide dismutase in the protection and tolerance to the prooxidant allelochemical quercetin in Papilio polyxenes,Spodoptera eridania,and Trichoplusia ni

Larvae of the black swallowtail butterfly, Papilio polyxenes, the southern armyworm, Spodoptera eridania, and the cabbage looper, Trichoplusia ni, have different feeding habits and dietary breadth, which contributes to differences in their exposure and tolerance to dietary prooxidant allelochemicals. The antioxidant enzyme activities of larvae of these insects have been previously determined, with the levels being P. polyxenes > S. eridania > T. ni. The relative activities of these antioxidant enzymes are consistent with the relative exposure of these insects to prooxidants. This suggests that the antioxidant enzymes may play a role in the defense against allelochemical toxicity in these insects. Dietary diethlydithiocarbamate (DETC), a copper chelating agent and superoxide dismutase (SOD) inhibitor, was shown to inhibit SOD in all three insects. Toxicological studies were conducted using four diets for each insect. The standard diets for each insect were supplemented with either control (solvent), quercetin (a prooxidant), DETC, or DETC plus quercetin. Nontoxic doses of each compound for each insect were used. Inhibition of SOD in P. polyxenes and S. eridania dramatically increased quercetin-induced toxicity as measured by relative growth and consumption rates in these species. DETC had no effect on quercetin toxicity in T. ni. These results elucidate the important role of SOD in the prooxidant allelochemical defense of insects.