The colouration toolkit of the Pipevine Swallowtail butterfly,Battus philenor: thin films,papiliochromes, and melanin

The ventral hindwings of Pipevine Swallowtail butterflies, Battus philenor, display a colourful pattern, created by variously coloured wing scales. Reflectance and transmittance measurements of single scales indicate that the cream and orange scales contain papiliochrome pigments, while brown, black and blue scales contain melanin. Microspectrophotometry and scatterometry of both sides of the wing scales show that the lower lamina acts as a thin film, with reflection properties dependent on the scale’s pigmentation. Notably in the orange scales, the reflectance spectrum of the lower lamina is tuned to the pigment’s absorbance spectrum. The dorsal hindwings of the male (but not the female) B. philenor are blue-green iridescent. At oblique illumination, the light reflected by the male’s dorsal hindwings can be highly polarised, which may have a function in intersexual signalling.     

Leaf buds, a factor in host selection by Battus philenor butterflies

ABSTRACT.

• 1 Field and laboratory experiments identified a character intrinsic to Aristolochia reticulata Nutt. host plants, the terminal leaf bud, that is involved in host-selection behaviour by female pipevine swallowtail butterflies (Battus philenor L.) searching for oviposition sites.
• 2 In the field, the frequency with which females landed on non-host buds declined seasonally as the proportion of host foliage that consisted of buds decreased. Female butterflies did not land on non-host species in proportion to their abundance; rather, females landed on those non-host species whose buds resembled those of A.reticulata.
• 3 A.reticulata plants whose terminal leaf bud was concealed by plastic tape were less susceptible to oviposition in the field than were control plants.
• 4 Female butterflies released in a large, outdoor enclosure were conditioned to search for leaf buds only when exposed to a host species bearing a prominent terminal leaf bud.
• 5 The significance of conditioning of leaf-bud searching behaviour is discussed with respect to discrimination between hosts and non-hosts, between host species, and among plants within a host species.

     

Hilltopping in the Pipevine Swallowtail Butterfly (Battus philenor)

In central Arizona, receptive females of the pipevine swallowtail, Battus philenor, are widely scattered in time and space, and in this region the butterfly's mating system is one in which males patrol mountain peaks. Hilltopping males engage intruding males in ascending flights that appear to be ritualized aerial combat with individuals defending patrolling sites for relatively short periods on any given day. The day-to-day appearance of marked males is irregular, unlike the site fidelity shown by males of many other hilltopping insects. The distinctive pattern of male territoriality in B. philenor may be partly a response to very low male and female density in the observed population. Males at the hilltop chase, court, and attempt to copulate with virgin females released near them. Males assess the receptivity of females rapidly, and receptive females permit a lengthy copulation to occur after a courtship that lasts less than 30 s. During an initial copulation males pass a spermatophore that weighs about 6% of their body mass, with partners on following days receiving a smaller but still substantial donation.     

Indicators of recent mating success in the pipevine swallowtail butterfly (Battus philenor) and their relationship to male phenotype

A key determinant of the intensity of sexual selection acting on a trait is how variation in that trait is related to variance in reproductive success of individuals. This connection compels efforts to assess lifetime mating number and how it varies among individuals in a population. In the Lepidoptera, female mating success can be assessed relatively easily by counting by the number of spermatophores in the female’s copulatory sac but male mating success in the field can often only be documented by observing copulations. Here we report a method for identifying whether or not males have recently mated that relies on the effect of mating on the appearance of the male’s reproductive tract in the pipevine swallowtail, Battus philenor. In this species laboratory experiments reveal that during mating, components of a male’s reproductive tract become shorter, decrease in mass, and change in appearance, irrespective of male age. These changes persist for at least two days after mating. After documenting these indicators of recent mating, we examined the reproductive tract of 68 field-caught males and found that twelve (17.6%) showed strong evidence of having mated recently. We found that older males were more likely to have recently mated. In addition, the color of the dorsal hindwing, a feature that females use in mate choice, was significantly greener in males, that according to our criteria, had recently-mated than in males that had not.     

Chemical defence of Battus philenor larvae against attack by the parasitoid Trogus pennator

Abstract 1. Parasitoids in the genus Trogus (Hymenoptera: Ichneumonidae) attack the larvae of swallowtail butterflies (Lepidoptera: Papilionidae). Only two of the three major tribes of the subfamily Papilioninae are attacked although species of all three tribes commonly occur together. The tribe Troidini is relatively free of parasitoids of any kind, and it has been proposed that the aristolochic acids sequestered by troidines protect them from parasitism.
2. The responses of T. pennator (Fabricius) to the sympatric troidine Battus philenor (Linnaeus) were examined. Three hypotheses that could explain why this wasp does not parasitise B. philenor were considered. (1) Battus philenor does not produce compounds used by the wasp to locate hosts. (2) The larval integument contains compounds that deter attack. (3) The parasitoid offspring cannot survive in B. philenor .
3. The first hypothesis was not supported as the frass of B. philenor larvae was found to act as a searching arrestant comparable to the frass of a host species.
4. The second hypothesis was supported. The B. philenor larvae were rejected when the wasps examined them using their antennae, and ethanolic washes of B. philenor cuticle deterred attack by T. pennator when applied to otherwise acceptable host larvae. Bioassays of fractions of the ethanolic wash and of pure aristolochic acids established that aristolochic acids were at least partly responsible for the deterrent effect.
5. The third hypothesis was also supported. Larvae of B. philenor attacked by the parasitoids developed into butterflies.
6. These results indicate that both behavioural and physiological barriers, the former attributable at least in part to sequestered compounds and the latter of unknown mechanism, prevent T. pennator from parasitising B. philenor .     

Nectar sugar and amino acid preferences of Battus philenor (Lepidoptera, Papilionidae)

Abstract.

• 1 Butterflies of Battus philenor were tested for their preferences for nectar sugars and amino acids in an outdoor cage experiment.
• 2 The butterflies clearly preferred both sucrose and fructose over glucose. They also preferred sucrose over fructose.
• 3 No other preferences were found to be statistically significant, although male butterflies tended to prefer a plain sugar solution over a sugar solution containing a mixture of amino acids: females consumed both of these solutions in almost equal proportions.
• 4 The results are discussed with respect to nectar composition of butterfly pollinated flowers, flower preferences, physiological and reproductive aspects of butterflies.

     

Local Enhancement in Mud-Puddling Swallowtail Butterflies (Battus philenor and Papilio glaucus)

Male butterflies aggregate at moist soil to acquire nutrients, a phenomenon termed “mud-puddling.” We studied the attraction of free-flying Papilio glaucus and Battus philenor swallowtails to dead decoys of those two species at artificial puddles moistened with NaCl solution. Both species landed preferentially at puddles with a decoy present rather than at unbaited puddles, demonstrating very strong local enhancement, a form of social facilitation. Papilio glaucus were attracted only to intraspecific decoys, whereas Battus philenor exhibited both intraspecific and interspecific attraction. Circular discs cut from the hindwings of male Battus were highly attractive to male Battus but completely unattractive to Papilio glaucus. The visual cues attractive to males in their search for salts differ between these two swallowtail species for unexplained reasons.     

Pupal colour dimorphism in California Battus philenor: pupation sites, environmental control, and diapause linkage

ABSTRACT.

• 1 Natural pupation sites and corresponding pupal colour (green or brown) were determined for samples of Battus philenor (L.) from two Californian populations.
• 2 Larvae pupate off the ground on trees, shrubs and man-made objects.
• 3 The vertical distribution of pupation sites and relative frequencies of pupae formed on narrow twigs and broad substrates show interpopulation variability, and seem to be determined by habitat-specific and possibly behavioural differences among populations.
• 4 The percentage of‘mismatched’pupae in green leafy environments (brown) is greater than that on wide substrates (green). Heterogeneity in samples of the latter suggest strong but sporadic predation pressure on non-cryptic pupae in exposed areas.
• 5 Green and brown substrates generally promoted formation of cryptic green and brown pupae although rearing conditions modified pupal colour response to substrate colour and larval pupation site choice.
• 6 Warm temperatures and long days increased the production of brown pupae. Short photoperiods increased the tendency of larvae to pupate on narrow twig-like substrates and to form green pupae.
• 7 Green pupae show less tendency to diapause than brown pupae. The difference between percentage diapause in the two colour forms increases under conditions favouring progressively more continuous development.

     

Use of contact chemical cues in prey discrimination by Cerceris fumipennis

Cerceris fumipennis Say (Hymenoptera: Crabronidae) uses a wide range of adult buprestid beetles to provision nests. Wasps seldom make ‘mistakes’ and attack beetles in other families. Bioassays showed that the wasps use contact chemical cues in the beetles’ epicuticle to discriminate buprestids from other beetles. Wasps rejected buprestids that had their cuticular hydrocarbons (CHC) removed by being washed in solvents. The washed, rejected buprestids became acceptable to 70% of wasps when they were coated with an extract of buprestids’ own CHC. Washed buprestids coated with extracts of non‐buprestid beetle CHC were not accepted. Analyses of buprestid CHC profiles showed that they are relatively simple, consisting of five classes. Other coleopteran families that may co‐occur in the arboreal hunting habitat of C. fumipennis have a broader range of CHC classes. Experiments adding buprestid hydrocarbons to a non‐buprestid beetle, unwashed Popillia japonica Newman (Coleoptera: Scarabaeidae), suggested that wasps may be deterred by the presence of CHC classes not found in Buprestidae. Adding a synthesized dimethyl‐branched hydrocarbon, a class of CHC found in Chrysomelidae but not Buprestidae, to the cuticle of unwashed buprestid beetles, caused wasps to reject the buprestid beetles. We propose that CHC act as a kairomone for C. fumipennis, triggering attack, whereas classes of CHC not found in Buprestidae disrupt this response, and thus help to determine the prey range of the wasp.     

Genetic differences and phenotypic plasticity as causes of variation in oviposition preference in Battus philenor

Summary Bradshaw (1965) proposed that phenotypic plasticity would be more common than adaptive genetic variability in species for which environmental fluctuations occur over periods roughly equal to that species' generation time. In an effort to examine this notion, sources of seasonal variation in two components of oviposition behavior in an east Texas population of pipevine swallowtail butterflies (Battus philenor) were investigated under natural and seminatural conditions. Variability in a visually-based prealighting component involving orientation to leaf shape was primarily due to phenotypic plasticity in the form of adult learning; no seasonally-based genotypic differences in leaf-shape discrimination behavior were observed. By contrast, a chemotactile post-alighting component involving elicitation of oviposition after landing on the host plant was not phenotypically plastic, i.e., not susceptible to learning. In addition, only slight and nonsignificant seasonally-based differences in post-alighting responses to different host species were observed.     

Contemporary patterns in a historical context: phylogeographic history of the pipevine swallowtail,Battus philenor (Papilionidae)

Abstract We examined mitochondrial DNA (mtDNA) variation in pipevine swallowtail butterflies ( Battus philenor ) from throughout its extant range to provide a historical, phylogeographical context for ecological studies of the disjunct population in California. We evaluate current hypotheses regarding host plant use, behavior, and mimetic relationships of B. philenor populations and generate alternative hypotheses. Compared to populations throughout the rest of the species' range, California populations are ecologically distinct in that they lack mimics, lay significantly larger clutches of eggs, and exclusively use a unique, endemic larval host plant. Analysis of molecular variance, tests of population differentiation, and nested clade analysis of mtDNA variation indicate that, despite low levels of population genetic structure across the species' range, there is evidence of recent range expansion from presumed Pleistocene refuge(s) in southeastern North America. Colonization of California appears to have been a recent event. This phylogeographic investigation also suggests that the evolution of life-history adaptations to a novel larval host has occurred rapidly in California and the lack of mimics in California may be attributable to the recency of colonization.     

Larger clutches of chemically defended butterflies reduce egg mortality: evidence from Battus philenor

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The use of chemical and visual cues in female choice in the butterfly Bicyclus anynana

Investigating the relative importance of multiple cues for mate choice within a species may highlight possible mechanisms that led to the diversification of closely related species in the past. Here, we investigate the importance of close-range pheromones produced by male Bicyclus anynana butterflies and determine the relative importance of these chemical cues versus visual cues in sexual selection by female choice. We first blocked putative androconial organs on the fore- and hindwings of males, while also manipulating the ability of females to perceive chemical signals via their antenna. We found that male chemical signals were emitted by both fore- and hindwing pairs and that they play an important role in female choice. We subsequently tested the relative importance of these chemical cues versus visual cues, previously identified for this species, and found that they play an equally important role in female choice in our laboratory setting. In addition, females will mate with males with only one signal present and blocking both androconial organs on males seems to interfere with male to male recognition. We discuss the possible functions of these signals and how this bimodal system may be used in intra- and interspecific mate evaluation.     

Male-specific Iridescent Coloration in the Pipevine Swallowtail (Battus philenor) is Used in Mate Choice by Females but not Sexual Discrimination by Males

We investigated the potential roles in behavioral interactions of sexually dichromatic iridescent blue coloration found on the dorsal hindwing of male Pipevine Swallowtails (Battus philenor). Behavioral experiments in a large enclosure addressed whether male dorsal hindwing coloration mediated sexual recognition by males, female choice of mates, or both. Models presented to males in the enclosure produced responses that show that males discriminate females from other males using chemical but not visual cues. In contrast, ablation of male dorsal iridescence significantly reduced male mating success with virgin females in the enclosure. The results support the hypothesis that male-specific iridescent coloration in this species is a signal that is important for females in assessing either male species identity or quality in intersexual interactions.     

No geographic variation in thermoregulatory colour plasticity and limited variation in heat‐avoidance behaviour in Battus philenor caterpillars

Phenotypic plasticity can help organisms cope with variation in their current environment, including temperature variation, but not all environments are equally variable. In the least variable or extreme environments, plasticity may no longer be used. In this case, the plasticity could be lost altogether, or it could persist with either the same or an altered reaction norm, depending on factors such as the plasticity's costs. In the pipevine swallowtail caterpillar (Battus philenor), I tested for changes in two forms of heat‐avoidance plasticity, colour change and refuge‐seeking behaviour, across the species’ range in the United states, including the cooler eastern parts of its range where colour change has not been observed and is unlikely to be needed. I found that both heat‐avoidance behaviour and colour change persisted in all surveyed populations. Indeed, the reaction norm for colour change remained nearly unaltered, whereas the threshold for refuge‐seeking only changed slightly across populations. These results suggest that the costs of these plastic traits are low enough for them to be maintained by whatever minimal gene flow the population receives. I show that plasticity can be maintained unaltered in populations where it is not used and discuss the potential consequences of this persistence for both the ecology and evolution of plasticity.     

Polarization-based brightness discrimination in the foraging butterfly, Papilio xuthus

The human eye is insensitive to the angular direction of the light e-vector, but several animal species have the ability to discriminate differently polarized lights. How the polarization is detected is often unclear, however. Egg-laying Papilio butterflies have been shown to see false colours when presented with differently polarized lights. Here we asked whether this also holds in foraging butterflies. After training individuals to feed on nectar in front of an unpolarized spectral light, we carried out three dual-choice tests, where the discrimination of (i) the spectral content, (ii) the light intensity, and (iii) the e-vector orientation were investigated. In the first test, the butterflies selected the trained spectrum irrespective of its intensity, and in the second test they chose the light with the higher intensity. The result of the e-vector discrimination test was very similar to that of the second test, suggesting that foraging butterflies discriminate differently polarized lights as differing in brightness rather than as differing in colour. Papilio butterflies are clearly able to use at least two modes of polarization vision depending on the behavioural context.     

Genetic and environmental factors influencing pupal colour in the Swallowtail butterflies Battus philenor (L.) and Papilio polytes L.

An account is given of the correlation of pupal coloration in Battus philenor and Papilio polytes with the colour of the substratum on which the larva pupates.     

Eye morphology and visual acuity in the pipevine swallowtail (Battus philenor) studied with a new method of measuring interommatidial angles

Because of the important role sensory systems play in the behaviour of animals, information on sensory capabilities is of great value to behavioural ecologists in the development of hypotheses to explain behaviour. In compound eyes, interommatidial angles are a key determinant of visual acuity but methods for measuring these angles are often demanding and limited to live animals with a pseudopupil. Here we present a new technique for measuring interommatidial angles that is less demanding in terms of technology than other techniques but still accurate. It allows measurements in eyes without a pseudopupil such as dark eyes or even museum specimens. We call this technique the radius of curvature estimation (RCE) method. We describe RCE and validate the method by comparing results from RCE with those from pseudopupil analysis for the butterfly Asterocampa leilia. As an application of RCE we measure the eyes of the butterfly Battus philenor, a species whose visually guided behaviour is well known but whose eye structure and visual acuity are unknown. We discuss the results of the eye morphology in B. philenor in relation to their behaviour and ecology. We contend that RCE fills a gap in the repertoire of techniques available to study peripheral determinants of spatial resolution in compound eyes, because it can be applied on species with dark eyes. RCE then opens up for sampling a larger number of specimens, which, in combination with being able to use museum specimens, makes it possible to quantitatively test ecologically and evolutionarily driven hypotheses about vision in animals in a new way.