The erroneous courtship hypothesis: do insects really engage in aerial wars of attrition?

Males of various flying insects perform conspicuous aerial interactions around their mating stations. The broadly accepted interpretation of their aerial interaction is a war of attrition, where two contestants perform costly displays, and the one that reaches its cost threshold earlier gives up. The implicit but important requirement in this model is that some forces that match the intensity of display of the two contestants are necessary, and failure to enforce matching allows foul contestants that delay or stop their display to avoid paying contest costs. In addition, wars of attrition require flying insects to distinguish the sex of flying conspecifics because their aerial interactions begin when intruders fly into the territory. We investigated past research on the behaviour of odonates and butterflies aiming to clarify whether the two prerequisites of wars of attrition are fulfilled: (1) contestants can inflict substantial costs on nondisplaying opponents and (2) contestants can discriminate the sex of flying conspecifics. In odonates, we found an abundance of evidence suggesting that contests involve physical attack and that the ability of sexual discrimination is sufficient. Therefore, wars of attrition may occur in territorial odonates. In butterflies, however, we could not find any evidence that the two prerequisites are filled. The aerial interactions of butterflies are better interpreted as courtship between sexually active males (the erroneous courtship hypothesis). Based on these results, we discuss future directions of research on the aerial contests of flying insects.     

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.     

A game model for the daily activity schedule of the male butterfly

A game model is developed of the daily schedule of matesearching activity by male butterflies, assuming that each male maximizes his expected mating success given a limited total time for mate search. The model predicts that (1) in the early morning, no male is active even though many females are emerging; (2) at a critical time, many males suddenly become active; and (3) the male's maximum activity occurs after the peak female emergence and before the peak capture efficiency. The inverse problem is also analyzed, in which the temporal pattern of capture efficiency is estimated from the knowledge of male activity and female emergence, assuming the evolutionarily stable strategy (ESS) condition. The model is then applied to data from a cabbage white butterfly (Pieris rapae crucivora) population and predicts that (1) females remain unmated for several hours on average after emergence, and (2) the male 's capture efficiency is rather low and increases significantly with time during the morning.     

Studies on ecology and behavior of Japanese black swallowtail butterflies. 6. Nectar feeding ofPapilio helenus nicconicolens Butler andP. protenor demetrius Cramer as main pollinators of glory bower,Clerodendron trichotomum,Thunb

The butterfliesPapilio helenus andP. protenor were shown to feed mainly on the nectar of the glory bower,Clerodendron trichotomum, which was the most abundant nectar plant in summer in the study area. Both the species were found to have a proboscis longer than 24 mm corresponding to the length of the corolla tube ofC. trichotomum. Visits to the flowers by these butterflies were observed more frequently than visits by sphingid moths which had previously been believed to be the major pollinators ofC. trichotomum. The male butterflies visited trees ofC. trichotomum frequently, while visits by the females were less frequent. However, once females had visited the tree ofC. trichotomum, they remained there longer than the males. Since the flower ofC. trichotomum has long protruding sexual organs, its pollen grains were found to adhere efficiently to the bodies of butterflies, mainly the thorax, during nectar feeding. Most of the butterflies became loaded withC. trichotomum pollen, and the mean number of pollen grains per butterfly was 1,776 forP. helenus and 2,817 forP. protenor. The flowers opened at any time of day but more frequently in the morning. The nectar was secreted throughout the day. In the maturation of the protandrous flower ofC. trichotomum, the duration of the pistillate phase was about twice as long as the staminate phase. The long flowering period and the short duration of the staminate phase resulted in asynchrony of the flowering stages even within a single cyme on a tree. Such asynchrony and the abundance of attractive flowers on a tree facilitates efficient pollination by the butterflies.     

Inhibitory effect of genital photoreceptors on the activity of abdominal motoneurones in Papilio xuthus (Lepidoptera,Papilionidae)

The inhibitory effect of butterfly genital photoreceptors on the activities of abdominal motoneurones is described. In two (N1, N3) of the six lateral nerves (N1–6) belonging to the last abdominal ganglion, spontaneous motoneurone activity was inhibited by illumination of the genital photoreceptors. N1 and N3 innervate the ventral longitudinal muscles. N2 and N4, which supply branches to the spiracular muscles, were not inhibited. The results allow some of the properties of the circuits in the abdominal nervous system supplied by the genital photoreceptors to be inferred. Some possible functions of the photoreceptors are discussed.     

Host plant adaptation during contemporary range expansion in the monarch butterfly

Herbivores that have recently expanded their host plant ranges provide opportunities to test hypotheses about the evolution of host plant specialization. Here, we take advantage of the contemporary global range expansion of the monarch butterfly (Danaus plexippus) and conduct a reciprocal rearing experiment involving monarch populations with divergent host plant assemblages. Specifically, we ask the following questions: (1) Do geographically disparate populations of monarch butterflies show evidence for local adaptation to their host plants? If so, what processes contribute to this pattern? (2) How is dietary breadth related to performance across multiple host species in monarch populations? (3) Does the coefficient of variation in performance vary across sympatric versus allopatric hosts? We find evidence for local adaptation in larval growth rate and survival based on sympatric/allopatric contrasts. Migratory North American monarchs, which have comparatively broad host breadth, have higher mean performance than derived nonmigratory populations across all host plant species. Monarchs reared on their sympatric host plants show lower coefficient of variation in performance than monarchs reared on allopatric hosts. We focus our discussion on possible mechanisms contributing to local adaptation to novel host plants and potential explanations for the reduction in performance that we observed in derived monarch populations.     

FOOD PLANT DERIVED DISEASE TOLERANCE AND RESISTANCE IN A NATURAL BUTTERFLY‐PLANT‐PARASITE INTERACTIONS

Organisms can protect themselves against parasite‐induced fitness costs through resistance or tolerance. Resistance includes mechanisms that prevent infection or limit parasite growth while tolerance alleviates the fitness costs from parasitism without limiting infection. Although tolerance and resistance affect host–parasite coevolution in fundamentally different ways, tolerance has often been ignored in animal–parasite systems. Where it has been studied, tolerance has been assumed to be a genetic mechanism, unaffected by the host environment. Here we studied the effects of host ecology on tolerance and resistance to infection by rearing monarch butterflies on 12 different species of milkweed food plants and infecting them with a naturally occurring protozoan parasite. Our results show that monarch butterflies experience different levels of tolerance to parasitism depending on the species of milkweed that they feed on, with some species providing over twofold greater tolerance than other milkweed species. Resistance was also affected by milkweed species, but there was no relationship between milkweed‐conferred resistance and tolerance. Chemical analysis suggests that infected monarchs obtain highest fitness when reared on milkweeds with an intermediate concentration, diversity, and polarity of toxic secondary plant chemicals known as cardenolides. Our results demonstrate that environmental factors—such as interacting species in ecological food webs—are important drivers of disease tolerance.     

重庆市蝴蝶多样性环境健康指示作用和环境监测评价体系构建

在重庆市生态功能区蝴蝶多样性参数研究的基础上,进行区系相似性分析;选取22个蝴蝶多样性参数和5项主要环境因子指标,进行回归和主成分分析,进而探讨监测指标、监测种类和类群的选取与评价体系的建立。分析结果表明:当进行区域级的监测时,在22个指标中,种、科、属的多样性指数和均匀度指数可以忽略;5项环境指标中,人口压力(X22)因子重于面积比例(X18)、人口密度(X19)、林地比例(X20)、土地载有量(X21)等4项因子。选出物种数(X1),蝴蝶属(X2)、科级(X3)单元的多少,种类优势度(X9),各数量等级的物种数贡献率(X10—X13),人口压力(X22)及4个主成分的综合得分等10个因子,作为重庆市生态功能区环境健康状况的10个评价指标;和24个蝴蝶监测种类,12个蝴蝶监测类群一起,探讨评价方法,共同构筑了重庆市生态功能区环境监测评价体系。在此基础上,对各功能区环境健康状况的评价表明,功能区1的环境健康评价为非常健康,5、9、10区为健康功能区;2、3、6、7、14区为亚健康功能区;不健康功能区是4、8、11、12、13区。功能区13、14是城市化区域,它们的分值在14个区中,居第十二位和第七位,不是最低的,这表明城镇化与环境质量并不完全是因果关系,即通过绿化和环境保护,城镇环境是可能得到很好改善的。期望此监测评价体系在实践中进一步完善。     

Pupal Melanization in Heliconius erato phyllis (Lepidoptera; Nymphalidae): Genetic and Environmental Effects

This paper deals with estimates of heritability and the effect of two different kinds of environment on the melanization of pupae in the butterfly Heliconius erato phyllis. The results for heritability showed greater differences when the offspring were regressed on male or female values for pupal colour. Pupal colour followed a system of discrete scores, from 2 for the light pupae to 5 for the darkest one. Estimate of the heritability (h²) was 0.44 when the average score of the siblings were regressed on the mid-parental value. When regressed on the male parent, h² was larger (0.54), being very low when regressed on the female parent (0.09). Estimate by the analysis of variance was also 0.44 when both male and female sibs were included in the analysis (for male sibs, h²=0.43 and for female sibs, 0.47). To test for the effect of the environment, each brood was divided in three, one being the control, the second subjected to a black environment when reaching the fifth instar and the third to a white environment. Those in the black environment originated dark pupae that scored 5 or 4; for those in the white environment, there was no difference with the controls. Caterpillars when entering the prepupal stage were also subjected to the black treatment (early and late prepupal stage, respectively, for treatments called black A and black B). A significant effect was observed only when early prepupal stage was subjected to the black environment.