Evolution of sexual dimorphism in the Lepidoptera

Phototaxis Characteristics of Lymantria xylina (Lepidoptera: Erebidae)

Lymantria xylina Swinhoe (Lepidoptera: Erebidae) is considered a potentially internationally invasive forest pest with limited knowledge about its phototactic behavior. This study investigated the phototaxis of L. xylina males and females using various insecticidal lamps in the field. The results showed that all lamps attracted both males and females, but females were captured in a very low numbers, with a female-to-male ratio of 1:322. The insecticidal lamp with a peak wavelength of 363 nm was most effective for male trapping. Males exhibited a distinct light-trapping rhythm, peaking around midnight (23:00-0:00), with 29.5% capture, while females were most active at dusk (19:00-20:00), with 44.4% capture. Light-trapped females were smaller and lighter than indoor-emerged females and had lower egg-carrying capacity. Females, when laying eggs, did not exhibit phototactic behavior. Only 14.6% of non-ovipositing females showed phototactic behavior, and only 0.6% flew directly toward the lamp. These findings suggest that while non-ovipositing females can exhibit phototaxis, only a small proportion will, potentially reducing the risk of long-distance dispersal of L. xylina via ocean-going freighters. The results showed that the non-ovipositing females could fly under phototaxis, but their phototaxis was limited. This study provides a basis for the risk assessment of the long-distance dispersal of L. xylina via ocean-going freighters through female moth phototactic flight.

Claw coloration in the fiddler crab Leptuca uruguayensis has no correlation with male quality

Sexual selection is thought to play a major role in the evolution of color due to the correlation between a signaler's physiological state and the displayed color. As such, researchers often investigate how color correlates to the quality of the signaler. However, research on the relationship between color and individual quality is often taxonomically limited and researchers typically investigate how color phenotypes relate to one index of quality, such as a linear measure of body size. Here, we investigated the relationship among body size, claw size, claw muscle mass, lipid content, and the color of the claw in male fiddler crabs (Leptuca uruguayensis) which wield an exaggerated claw that varies in color from brown to red. We hypothesized that if the color was correlated to one or more indices of male quality, the color displayed on the claws of male L. uruguayensis could be under sexual selection. We found L. uruguayensis claw color varies substantially among the individuals we photographed. However, we did not find a correlation between claw color and indices of quality; neither brightness nor hue correlated to the indices of quality we measured. Our findings suggest that claw color in L. uruguayensis is unlikely to have evolved to signal quality, but may instead function as a species identity or as a non-indicator sexual signal.

External Morphology, Defensive Adaptations, Aposematic Coloration, and Sexual Dimorphism of the Fifth Instar Larva of Cricula Silkmoth, Cricula trifenestrata Helfer (Lepidoptera: Saturniidae) from Thailand

This study explores the external morphology of larva of Cricula trifenestrata Helfer at the fifth instar stage, focusing on sexual dimorphism, scoli, and fluorescence hair warts. The larva displays a black body adorned with varying shades of orange to crimson-red transverse stripes and small yellow dorsal spots. Longitudinal stripes with fluorescent warts are observed in the subspiracular region, accompanied by an overall coverage of long white hairs. These distinctive features, including scoli and fluorescence hair warts, serve as effective defense mechanisms against predators and parasitoids. The results enhance our understanding of C. trifenestrata Helfer larval biology, providing valuable insights for entomology and evolutionary biology. The identification of species-specific adaptations, particularly the presence of scoli and fluorescence hair warts, underscores their significance in shaping survival strategies and ecological interactions.

Dorsoventral comparison of intraspecific variation in the butterfly wing pattern using a convolutional neural network

Butterfly wing patterns exhibit notable differences between the dorsal and ventral surfaces, and morphological analyses of them have provided insights into the ecological and behavioural characteristics of wing patterns. Conventional methods for dorsoventral comparisons are constrained by the need for homologous patches or shared features between two surfaces, limiting their applicability across species. We used a convolutional neural network (CNN)-based analysis, which can compare images of the two surfaces without focusing on homologous patches or features, to detect dorsoventral bias in two types of intraspecific variation: sexual dimorphism and mimetic polymorphism. Using specimen images of 29 species, we first showed that the level of sexual dimorphism calculated by CNN-based analysis corresponded well with traditional assessments of sexual dissimilarity, demonstrating the validity of the method. Dorsal biases were widely detected in sexual dimorphism, suggesting that the conventional hypothesis of dorsally biased sexual selection can be supported in a broader range of species. In contrast, mimetic polymorphism showed no such bias, indicating the importance of both surfaces in mimicry. Our study demonstrates the potential versatility of CNN in comparing wing patterns between the two surfaces, while elucidating the relationship between dorsoventrally different selections and dorsoventral biases in intraspecific variations.

Sex dimorphism in pupae and adults of the specialist Ipomoea batatas defoliator Bedellia somnulentella (Lepidoptera: Bedelliidae)

Bedellia somnulentella Zeller, 1847 (Lepidoptera: Bedelliidae), a global pest of the sweet potato Ipomoea batatas, was recorded in Brazil, but morphological information on the sexual dimorphism of this insect is scarce. The objective was to evaluate morphological characters of sexual dimorphism of B. somnulentella pupae and adults. External structures with sexual dimorphism were not detected in the last abdominal segments of B. somnulentella pupae. The females of this insect are heavier, which could be a distinctive sex characteristic. A pair of frenulum on the hind wings of females and only one on those of males, in addition to elongated cerci and bipartite genitalia in the latter and smaller cerci involving the last abdominal segment and an ovipositor in females, differentiate sexes of B. somnulentella.

The Sexual Dimorphism in Rectum and Protein Digestion Pathway Influence Sex Pheromone Synthesis in Male Bactrocera Dorsalis

Sexual dimorphism is a crucial aspect of mating and reproduction in many animals, yet the molecular mechanisms remain unclear. In Bactrocera dorsalis, sex pheromones trimethylpyrazine (TMP) and tetramethylpyrazine (TTMP) are specifically synthesized by Bacillus strains in the male rectum. In the female rectum, Bacillus strains are found, but TMP and TTMP are not, indicating sexually dimorphic differences in sex pheromone synthesis. Our anatomical observations and precursor measurements revealed significant differences in rectal structure and ammonium levels between sexes.  In vitro and in vivo experiments reveal that ammonium is vital for sex pheromone synthesis in rectal Bacillus strains. Comparative transcriptome analysis identified ammonium-producing genes (carboxypeptidase B and peptide transporter) in the protein digestion pathway that show much higher expression in the male rectum than in the female rectum. Knocking down the expression of either carboxypeptidase B (or inhibiting enzyme activity) or peptide transporter decreases rectal ammonium levels significantly, resulting in the failure of sex pheromone synthesis in the male rectum. This study provides insights into the presence of sexual dimorphism in internal organs and their functionalities in male-specific sex pheromone synthesis and has significant implications for understanding the molecular mechanisms underlying sex pheromone synthesis by symbionts in insects.

Pre-Copulatory Sexual Selection Predicts Sexual Size Dimorphism: A Meta-Analysis of Comparative Studies

Size differences between males and females are common across the tree of life (termed sexual size dimorphism; SSD), and have fundamental implications for ecology, life history and behaviour of both sexes. Conventionally, SSD is thought to evolve in response to sex-specific sexual selection but more recent work suggests that ecological processes can also promote sex-differences in size. Here, we provide a global test for the role of sexual selection in the evolution of sexual size dimorphism using data from 77 comparative studies spanning the major classes of the animal kingdom. We show that intense sexual selection typically correlates with male-biased SSD across species. Importantly, pre-copulatory but not post-copulatory sexual selection predicts SSD, suggesting a pervasive role of premating male-male competition and female choice to drive sex differences in body size. Collectively, our findings suggest that pre-copulatory sexual selection plays a major role in the evolution of male-biased SSD.

Heterosis effect for larval performance of fall armyworm interstrain hybrids

Spodoptera frugiperda, also known as fall armyworm (FAW), is an invasive crop pest that can feed on a variety of host plants, posing a serious threat to food security. There are two sympatric strains of FAW that are morphologically identical but described with different food preferences: the "rice strain" (SfR) and the "corn strain" (SfC). A few genetic loci exist to identify these two strains. Mitochondrial and Z-chromosome-linked haplotypes are the most used, but the biggest part of the genome displays little polymorphism between strains that could explain their adaptation to different plants. We have previously observed consistent transcription differences between the strains in both laboratory and natural populations. Therefore, we wonder if there are effects from host-strain-associated loci, maternally or paternally inherited, on FAW performance that could explain the divergence between the two FAW strains. To test this hypothesis, we first produced two F1 hybrid generations (SfR ♀ × SfC ♂, SfC ♀ × SfR ♂). These reciprocal hybrids should be heterozygous for all chromosomes except for the maternally inherited mitochondrial and sexual W chromosomes. To evaluate whether plant preference is determined by these genetic loci, we cultivated the two hybrids and the two parental strains in triplicate on an artificial diet and recorded several phenotypic traits such as weight over time, survival rate, emerging rate, developmental time, and sex ratio. Then, the same performance experiment was carried out on corn plants. Surprisingly, on the artificial diet, the two hybrid genotypes were both more performant than the two parental strains in terms of survival rate, pupal emerging rate, and developmental time, whereas they were intermediate to the inbred parental strains in pupal weight. On the corn plant diet, both hybrid genotypes outperformed the two parental strains in larval weight. Although these asymmetrical results revealed that mitochondrial or sex-linked haplotypes alone cannot explain the performance differences, they suggested a heterosis effect in FAW. A reduction of the female number for the CR genotype and the decreased F1 offspring reproduction in both hybrids suggested the possibility of Haldane's rule, which might be explained by the dominance model.

Stronger interspecific sexual differences may be favored when females search for mates in the presence of congeners

Why are some species sexually dimorphic while other closely related species are not? While all females in genus Strauzia share a multiply-banded wing pattern typical of many other true fruit flies, males of four species have noticeably elongated wings with banding patterns "coalesced" into a continuous dark streak across much of the wing. We take an integrative phylogenetic approach to explore the evolution of this dimorphism and develop general hypotheses underlying the evolution of wing dimorphism in flies. We find that the origin of coalesced and other darkened male wing patterns correlate with the inferred origin of host plant sharing in Strauzia. While wing shape among non-host-sharing species tended to be conserved across the phylogeny, shapes of male wings for Strauzia species sharing the same host plant were more different from one another than expected under Brownian models of evolution and overall rates of wing shape change differed between non-host-sharing species and host-sharing species. A survey of North American Tephritidae finds just three other genera with specialist species that share host plants. Host-sharing species in these genera also have wing patterns unusual for each genus. Only genus Eutreta is like Strauzia in having the unusual wing patterns only in males, and of genera that have multiple species sharing hosts, only in Eutreta and Strauzia do males hold territories while females search for mates. We hypothesize that in species that share host plants, those where females actively search for males in the presence of congeners may be more likely to evolve sexually dimorphic wing patterns.

A ghost moth olfactory prototype of the lepidopteran sex communication

Sex role differentiation is a widespread phenomenon. Sex pheromones are often associated with sex roles and convey sex-specific information. In Lepidoptera, females release sex pheromones to attract males, which evolve sophisticated olfactory structures to relay pheromone signals. However, in some primitive moths, sex role differentiation becomes diverged. Here, we introduce the chromosome-level genome assembly from ancestral Himalaya ghost moths, revealing a unique olfactory evolution pattern and sex role parity among Lepidoptera. These olfactory structures of the ghost moths are characterized by a dense population of trichoid sensilla, both larger male and female antennal entry parts of brains, compared to the evolutionary later Lepidoptera. Furthermore, a unique tandem of 34 odorant receptor 19 homologs in Thitarodes xiaojinensis (TxiaOr19) has been identified, which presents overlapped motifs with pheromone receptors (PRs). Interestingly, the expanded TxiaOr19 was predicted to have unconventional tuning patterns compared to canonical PRs, with nonsexual dimorphic olfactory neuropils discovered, which contributes to the observed equal sex roles in Thitarodes adults. Additionally, transposable element activity bursts have provided traceable loci landscapes where parallel diversifications occurred between TxiaOr19 and PRs, indicating that the Or19 homolog expansions were diversified to PRs during evolution and thus established the classic sex roles in higher moths. This study elucidates an olfactory prototype of intermediate sex communication from Himalaya ghost moths.

Chemical communication and its role in sexual selection across Animalia

Sexual selection has been studied as a major evolutionary driver of animal diversity for roughly 50 years. Much evidence indicates that competition for mates favors elaborate signaling traits. However, this evidence comes primarily from a few taxa, leaving sexual selection as a salient evolutionary force across Animalia largely untested. Here, we reviewed the evidence for sexual selection on communication across all animal phyla, classes, and orders with emphasis on chemoreception, the only sense shared across lifeforms. An exhaustive literature review documented evidence for sexual selection on chemosensory traits in 10 of 34 animal phyla and indications of sexual selection on chemosensory traits in an additional 13 phyla. Potential targets of sexual selection include structures and processes involved in production, delivery, and detection of chemical signals. Our review suggests sexual selection plays a widespread role in the evolution of communication and highlights the need for research that better reflects animal diversity.

Wing Shape Variation between Terrestrial and Coastal Populations of the Invasive Box Tree Moth, Cydalima perspectalis, in Croatia

The box tree moth (Cydalima perspectalis Walker, 1859; Lepidoptera: Crambidae) is an invasive species naturally distributed in Asia. The caterpillars in all developmental stages cause damage through defoliation of plants, and ultimately the death of the plant itself may occur. It is possible to recognize this species by its silk barriers and threads, and in the case of an intense attack, the entire plant will be covered with them. In Europe, this species' presence was first recorded in 2007 in Germany and the Netherlands, and it is now widely distributed. In Croatia, its existence was first recorded in 2012, in Istria, while substantial damages were recorded in 2013. This work aimed to determine the morphological variability of C. perspectalis from Croatia and assess its invasive character, the possibility of flight, and the risk of further spread. The methods of geometric morphometrics were used as the analysis of wing shape. A total of 269 moths from different locations in Croatia were collected, the upper wings of males and females were analyzed using 14 landmarks. Significant differences in wing shapes between terrestrial and coastal populations were found, as well as subtle wing shape sexual dimorphism. The implications of this variability in species invasiveness and capacity of spread are discussed in this paper. We also extrapolate the usefulness of our results and suggest strategies for predicting and managing invasive species.

Reproductive behaviors promote ecological and phenotypic sexual differentiation in the critically endangered Lehmann’s poison frog

Territoriality and parental care are complex reproductive behaviors found in many taxa from insects to mammals. Parental care can be carried out by the female, the male, or both, depending on the species. Territoriality, in contrast, is predominantly displayed by males. Different selective pressures imposed on individuals from the sex performing territorial or parental care behaviors may also lead to sexual differentiation in other life-history traits. Due to their territorial behavior and their diversity of parental care behaviors, Neotropical poison frogs are an excellent study system to investigate whether behavioral traits can influence sexual differentiation in intrinsic or extrinsic traits of individuals. Here, we evaluate whether territorial and parental care behaviors mediate sexual differentiation in ecological (habitat use) and phenotypic (coloration, morphology) traits in the critically endangered Lehmann’s poison frog (Oophaga lehmanni), a species in which males defend territories while females provide parental care. We found sex differences in habitat use and morphological traits, but not in coloration. Males use trunks and green leaves as perches more frequently and are found on higher substrates, than females. We found no sex differences in body size, but females have longer arms than males, which is probably associated with their parental duties (climbing trees to feed the tadpoles). Altogether, our results provide evidence that selection pressures act differently on male and female traits, and that territoriality and parental care may promote the evolution of sexual differentiation in dendrobatids. Long-term wildlife observations are essential to identify important life-history traits and to evaluate hypotheses about the behavioral ecology and conservation of this and other vertebrate species.

Phenotypic Plasticity of the Mimetic Swallowtail Butterfly Papilio polytes: Color Pattern Modifications and Their Implications in Mimicry Evolution

Simple Summary

Diverse butterfly wing color patterns are evolutionary products in response to environmental changes in the past. Environmental stress, such as temperature shock, is known to induce color pattern modifications in various butterfly species, and this phenotypic plasticity plays an important role in color pattern evolution. However, the potential contributions of phenotypic plasticity to mimicry evolution have not been evaluated. Here, we focused on the swallowtail butterfly Papilio polytes, which has nonmimetic and mimetic forms in females, to examine its plastic phenotypes. Cold shock and heat shock treatments in the nonmimetic form induced color pattern modifications that were partly similar to those of the mimetic form, and nonmimetic females were more sensitive than males and mimetic females. These results suggest that phenotypic plasticity in nonmimetic females might have provided a basis of natural selection for mimetic color patterns during evolution.

Abstract

Butterfly wing color patterns are sensitive to environmental stress, such as temperature shock, and this phenotypic plasticity plays an important role in color pattern evolution. However, the potential contributions of phenotypic plasticity to mimicry evolution have not been evaluated. Here, we focused on the swallowtail butterfly Papilio polytes, which has nonmimetic and mimetic forms in females, to examine its plastic phenotypes. In the nonmimetic form, medial white spots and submarginal reddish spots in the ventral hindwings were enlarged by cold shock but were mostly reduced in size by heat shock. These temperature-shock-induced color pattern modifications were partly similar to mimetic color patterns, and nonmimetic females were more sensitive than males and mimetic females. Unexpectedly, injection of tungstate, a known modification inducer in nymphalid and lycaenid butterflies, did not induce any modification, but fluorescent brightener 28, another inducer discovered recently, induced unique modifications. These results suggest that phenotypic plasticity in nonmimetic females might have provided a basis of natural selection for mimetic color patterns during evolution.

Deep conservation and co-option of programmed cell death facilitates evolution of alternative phenotypes at multiple biological levels

Alternative phenotypes, such as polyphenisms and sexual dimorphisms, are widespread in nature and appear at all levels of biological organization, from genes and cells to morphology and behavior. Yet, our understanding of the mechanisms through which alternative phenotypes develop and how they evolve remains understudied. In this review, we explore the association between alternative phenotypes and programmed cell death, a mechanism responsible for the elimination of superfluous cells during development. We discuss the ancient origins and deep conservation of programmed cell death (its function, forms and underlying core regulatory gene networks), and propose that it was co-opted repeatedly to generate alternative phenotypes at the level of cells, tissues, organs, external morphology, and even individuals. We review several examples from across the tree of life to explore the conditions under which programmed cell death is likely to facilitate the evolution of alternative phenotypes.

Warm-night temperature alters paternal allocation strategy in a North temperate-zone butterfly

Warming temperatures are greatly impacting wild organisms across the globe. Some of the negative impacts of climate change can be mitigated behaviorally, for example, by changes in habitat and oviposition site choice. Temperatures are reportedly warming faster at night than during the day, yet studies assessing the impacts of increasing night temperature are rare. We used the Finnish Glanville fritillary butterfly (Melitaea cinxia) as study species and exposed adult butterflies of both sexes to warmer night conditions. Under a seminatural outdoor enclosure, we assessed whether females base their oviposition choices primarily on habitat site characteristics (open, suggestive of dry meadows, versus covered by a coarse canopy, suggestive of pastures) or on plant condition (dry vs. lush), and if their choice is altered by the thermal conditions experienced at night. As exposure to warmer environmental conditions is expected to increase resting metabolic rate and potentially reduce life expectancy, we further assessed the fitness implications of warm-night temperatures. We found that females prefer open sites for oviposition and that females do not switch their oviposition strategy based on the thermal conditions they experienced at night prior to the reproductive event. Exposure to warm nights did not influence female lifespan, but the egg hatching success of their offspring was reduced. In addition, we found that males exposed to warm nights sired larger clutches with higher hatching rate. As warm-night exposure reduced male lifespan, this may imply a switch in male resource allocation strategy toward increased offspring quality. The present work adds on to the complex implications of climate warming and highlights the importance of the often-neglected role of males in shaping offspring performance.

Evolution of sexual dimorphism and polychromatism in a lineage of tiger moths (Lepidoptera: Erebidae): advancing knowledge of a taxonomically chaotic group

Pericopina is divided into 36 genera, with the greatest diversity recorded in the Neotropics. Studies on the taxonomy and systematics of pericopines are scarce, and one of the few phylogenetic hypotheses available in the literature places some Afro-Indo-Malayan lineages among the Neotropical representatives. Through a survey of adult morphological characters, we analyzed the phylogenetic relationships in Pericopina including Nyctemera and other Afro-Indo-Malayan genera as putative members of this subtribe. Additionally, we tested the monophyly of Dysschema, a key genus to understanding the evolutionary patterns of the extreme sexual dimorphism and polychromatism in Pericopina. Our cladistic analysis, based on 162 morphological characters, suggests that Pericopina is a polyphyletic group. Xenosoma is the only genus among the Neotropical pericopines related to the Afro-Indo-Malayan species; Scearctia is closely related to Lithosiini, and Pteroodes shows morphological similarities with Phaegopterina. Additionally, Seileria is a new junior subjective synonym of Thyrgis. The monophyly of Dysschema is supported only if the monotypic genera Myserla and Are are included. These are herein designated new synonyms of Dysschema. Our findings suggest that intersexual polychromatism and intersexual polymorphism for wing characters have arisen multiple times in the evolutionary history of Pericopina. Intersexual polychromatism is also widely distributed within Dysschema, perhaps representing a derived feature with multiple origins in the genus.

Sensory Organ Investment Varies with Body Size and Sex in the Butterfly Pieris napi

In solitary insect pollinators such as butterflies, sensory systems must be adapted for multiple tasks, including nectar foraging, mate-finding, and locating host-plants. As a result, the energetic investments between sensory organs can vary at the intraspecific level and even among sexes. To date, little is known about how these investments are distributed between sensory systems and how it varies among individuals of different sex. We performed a comprehensive allometric study on males and females of the butterfly Pieris napi where we measured the sizes and other parameters of sensory traits including eyes, antennae, proboscis, and wings. Our findings show that among all the sensory traits measured, only antenna and wing size have an allometric relationship with body size and that the energetic investment in different sensory systems varies between males and females. Moreover, males had absolutely larger antennae and eyes, indicating that they invest more energy in these organs than females of the same body size. Overall, the findings of this study reveal that the size of sensory traits in P. napi are not necessarily related to body size and raises questions about other factors that drive sensory trait investment in this species and in other insect pollinators in general.

Conserved and Divergent Aspects of Plasticity and Sexual Dimorphism in Wing Size and Shape in Three Diptera

The ability of powered flight in insects facilitated their great evolutionary success allowing them to occupy various ecological niches. Beyond this primary task, wings are often involved in various premating behaviors, such as the generation of courtship songs and the initiation of mating in flight. These specific functions imply special adaptations of wing morphology, as well as sex-specific wing morphologies. Although wing morphology has been extensively studied in Drosophila melanogaster (Meigen, 1830), a comprehensive understanding of developmental plasticity and the impact of sex on wing size and shape plasticity is missing for other Diptera. Therefore, we raised flies of the three Diptera species Drosophila melanogaster, Ceratitis capitata (Wiedemann, 1824) and Musca domestica (Linnaeus, 1758) at different environmental conditions and applied geometric morphometrics to analyze wing shape. Our data showed extensive interspecific differences in wing shape, as well as a clear sexual wing shape dimorphism in all three species. We revealed an impact of different rearing temperatures on wing shape in all three species, which was mostly explained by plasticity in wing size in D. melanogaster. Rearing densities had significant effects on allometric wing shape in D. melanogaster, while no obvious effects were observed for the other two species. Additionally, we did not find evidence for sex-specific response to different rearing conditions in D. melanogaster and C. capitata, while a male-specific impact of different rearing conditions was observed on non-allometric wing shape in M. domestica. Overall, our data strongly suggests that many aspects of wing morphology underly species-specific adaptations and we discuss potential developmental and functional implications of our results.

Why do males emerge before females? Sexual size dimorphism drives sexual bimaturism in insects

Conspecific females and males often follow different development trajectories which leads to sex differences in age at maturity (sexual bimaturism, SBM). Whether SBM is typically selected for per se (direct selection hypothesis) or merely represents a side-effect of other sex-related adaptations (indirect selection hypothesis) is, however, still an open question. Substantial interspecific variation in the direction and degree of SBM, both in invertebrates and vertebrates, calls for multi-species studies to understand the relative importance of its evolutionary drivers. Here we use two complementary approaches to evaluate the evolutionary basis of SBM in insects. For this purpose, we assembled an extensive literature-derived data set of sex-specific development times and body sizes for a taxonomically and ecologically wide range of species. We use these data in a meta-analytic framework to evaluate support for the direct and indirect selection hypotheses. Our results confirm that protandry - males emerging as adults before females - is the prevailing form of SBM in insects. Nevertheless, protandry is not as ubiquitous as often presumed: females emerged before males (= protogyny) in about 36% of the 192 species for which we had data. Moreover, in a considerable proportion of species, the sex difference in the timing of adult emergence was negligible. In search for the evolutionary basis of SBM, we found stronger support for the hypothesis that explains SBM by indirect selection. First, across species, the direction and degree of SBM appeared to be positively associated with the direction and degree of sexual size dimorphism (SSD). This is consistent with the view that SBM is a correlative by-product of evolution towards sexually dimorphic body sizes. Second, within protandrous species, the degree of protandry typically increased with plastic increase in development time, with females prolonging their development more than males in unfavourable conditions. This pattern is in conflict with the direct selection hypothesis, which predicts the degree of protandry to be insensitive to the quality of the juvenile environment. These converging lines of evidence support the idea that, in insects, SBM is generally a by-product of SSD rather than a result of selection on the two sexes to mature at different times. It appears plausible that selective pressures on maturation time per se generally cannot compete with viability- and fecundity-mediated selection on insect body sizes. Nevertheless, exceptions certainly exist: there are undeniable cases of SBM where this trait has evolved in response to direct selection. In such cases, either the advantage of sex difference in maturation time must have been particularly large, or fitness effects of body size have been unusually weak.

The evolution and genetics of sexually dimorphic 'dual' mimicry in the butterfly Elymnias hypermnestra

Sexual dimorphism is a major component of morphological variation across the tree of life, but the mechanisms underlying phenotypic differences between sexes of a single species are poorly understood. We examined the population genomics and biogeography of the common palmfly Elymnias hypermnestra, a dual mimic in which female wing colour patterns are either dark brown (melanic) or bright orange, mimicking toxic Euploea and Danaus species, respectively. As males always have a melanic wing colour pattern, this makes E. hypermnestra a fascinating model organism in which populations vary in sexual dimorphism. Population structure analysis revealed that there were three genetically distinct E. hypermnestra populations, which we further validated by creating a phylogenomic species tree and inferring historical barriers to gene flow. This species tree demonstrated that multiple lineages with orange females do not form a monophyletic group, and the same is true of clades with melanic females. We identified two single nucleotide polymorphisms (SNPs) near the colour patterning gene WntA that were significantly associated with the female colour pattern polymorphism, suggesting that this gene affects sexual dimorphism. Given WntA's role in colour patterning across Nymphalidae, E. hypermnestra females demonstrate the repeatability of the evolution of sexual dimorphism.

Dispersal and migration have contrasting effects on butterfly flight morphology and reproduction

Movement may fundamentally alter morphology and reproductive states in insects. In long-distance migrants, reproductive diapause is associated with trade-offs between diverse life-history traits such as flight morphology and lifespan. However, many non-diapausing insects engage in shorter resource-driven dispersals. How diapause and other reproductive states alter flight morphology in migrating versus dispersing insects is poorly understood. To find out, we compared flight morphology in different reproductive states of multiple butterfly species. We found that dispersers consisted of ovulating females with higher egg loads compared with non-dispersing females. This trend was in stark contrast with that of migrating female butterflies in reproductive diapause, which made substantially higher investment in flight tissue compared with reproductively active, non-migrating females. Thus, long-distance migration and shorter resource-driven dispersals had contrasting effects on flight morphology and egg loads. By contrast, male flight morphology was not affected by dispersal, migration or associated reproductive states. Thus, dispersal and migration affected resource allocation in flight and reproductive tissue in a sex-specific manner across relatively mobile versus non-dispersing individuals of different species. These findings suggest that dispersals between fragmented habitats may put extra stress on egg-carrying females by increasing their flight burdens.

Unlocking the potential of historical abundance datasets to study biomass change in flying insects

Trends in insect abundance are well established in some datasets, but far less is known about how abundance measures translate into biomass trends. Moths (Lepidoptera) provide particularly good opportunities to study trends and drivers of biomass change at large spatial and temporal scales, given the existence of long-term abundance datasets. However, data on the body masses of moths are required for these analyses, but such data do not currently exist.To address this data gap, we collected empirical data in 2018 on the forewing length and dry mass of field-sampled moths, and used these to train and test a statistical model that predicts the body mass of moth species from their forewing lengths (with refined parameters for Crambidae, Erebidae, Geometridae and Noctuidae).Modeled biomass was positively correlated, with high explanatory power, with measured biomass of moth species (R 2 = 0.886 ± 0.0006, across 10,000 bootstrapped replicates) and of mixed-species samples of moths (R 2 = 0.873 ± 0.0003), showing that it is possible to predict biomass to an informative level of accuracy, and prediction error was smaller with larger sample sizes.Our model allows biomass to be estimated for historical moth abundance datasets, and so our approach will create opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions.

Characterization of the First W-Specific Protein-Coding Gene for Sex Identification in Helicoverpa armigera

Helicoverpa armigera is a globally-important crop pest with a WZ (female)/ZZ (male) sex chromosome system. The absence of discernible sexual dimorphism in its egg and larval stages makes it impossible to address any sex-related theoretical and applied questions before pupation unless a W-specific sequence marker is available for sex diagnosis. To this end, we used one pair of morphologically pre-sexed pupae to PCR-screen 17 non-transposon transcripts selected from 4855 W-linked candidate reads identified by mapping a publicly available egg transcriptome of both sexes to the male genome of this species and detected the read SRR1015458.67499 only in the female pupa. Subsequent PCR screenings of this read and the previously reported female-specific RAPD (random amplified polymorphic DNA) marker AF18 with ten more pairs of pre-sexed pupae and different annealing positions and/or temperatures as well as its co-occurrence with the female-specific transcript splicing isoforms of doublesex gene of H. armigera (Hadsx) and amplification and sequencing of their 5′ unknown flanking sequences in three additional pairs of pre-sexed pupae verified that SRR1015458.67499 is a single copy protein-coding gene unique to W chromosome (named GUW1) while AF18 is a multicopy MITE transposon located on various chromosomes. Test application of GUW1 as a marker to sex 30 neonates of H. armigera yielded a female/male ratio of 1.14: 1.00. Both GUW1 and Hadsx splicing isoforms assays revealed that the H. armigera embryo cell line QB-Ha-E-1 is a male cell line. Taken together, GUW1 is not only a reliable DNA marker for sexing all stages of H. armigera and its cell lines, but also represents the first W-specific protein-coding gene in lepidopterans.

Botanical Volatiles Selection in Mediating Electrophysiological Responses and Reproductive Behaviors for the Fall Webworm Moth Hyphantria cunea

Host-plant volatiles play vital roles for insects to locate foraging, mating, and oviposition sites in the environment. As one of the devastating invasive forestry pests, Hyphantria cunea causes a great annual loss in China, and understanding its chemical ecology is an important task. The current research was done in terms of chemical analysis, electrophysiology, and behavioral assays on H. cunea to assess its olfactory reception toward host-plant volatiles. A screen of possible common host volatiles was done, targeting on five favored hosts of H. cunea, harvesting six potential bioactive compounds from a total of 78 odorant components. Six types of antennal sensilla were investigated on their distributions on the antennae, and sexual dimorphism was described. H. cunea showed responses to all selected host-related volatiles in electroantennogram tests, and linalyl butyrate elicited the strongest responses. Furthermore, mating rates in adult pairs that are exposed to dibutyl phthalate and phytol have been significantly increased, while oviposition rates and female fecundity were not influenced. The results of the current study provide initial evidence showing that universal host-derived volatile cues are essential for H. cunea moth in terms of mating, which can also provide insights into the development of botanical attractants.

Flight Muscle and Wing Mechanical Properties are Involved in Flightlessness of the Domestic Silkmoth, Bombyx mori

Flight loss has occurred in many winged insect taxa. The flightless silkmoth Bombyx mori, is domesticated from the wild silkmoth, Bombyx mandarina, which can fly. In this paper, we studied morphological characteristics attributed to flightlessness in silkmoths. Three domestic flightless B. mori strains and one B. mandarina population were used to compare morphological components of the flight apparatus, including wing characteristics (shape, forewing area, loading, and stiffness), flight muscle (weight, ratio, and microscopic detail) and body mass. Compared with B. mandarina, B. mori strains have a larger body, greater wing loading, more flexible wings and a lower flight muscle ratio. The arrangement in microscopy of dorsal longitudinal flight muscles (DLFMs) of B. mori was irregular. Comparative analysis of the sexes suggests that degeneration of flight muscles and reduction of wing mechanical properties (stiffness) are associated with silkmoth flightlessness. The findings provide important clues for further research of the molecular mechanisms of B. mori flight loss.

Colour dimorphism in labrid fishes as an adaptation to life on coral reefs

Conspicuous coloration displayed by animals that express sexual colour dimorphism is generally explained as an adaptation to sexual selection, yet the interactions and relative effects of selective forces influencing colour dimorphism are largely unknown. Qualitatively, colour dimorphism appears more pronounced in marine fishes that live on coral reefs where traits associated with strong sexual selection are purportedly more common. Using phylogenetic comparative analysis, we show that wrasses and parrotfishes exclusive to coral reefs are the most colour dimorphic, but surprisingly, the effect of habitat is not influenced by traits associated with strong sexual selection. Rather, habitat-specific selective forces, including clear water and structural refuge, promote the evolution of pronounced colour dimorphism that manifests colours less likely to be displayed in other habitats. Our results demonstrate that environmental context ultimately determines the evolution of conspicuous coloration in colour-dimorphic labrid fishes, despite other influential selective forces.

Altitude and life-history shape the evolution of Heliconius wings

Phenotypic divergence between closely related species has long interested biologists. Taxa that inhabit a range of environments and have diverse natural histories can help understand how selection drives phenotypic divergence. In butterflies, wing color patterns have been extensively studied but diversity in wing shape and size is less well understood. Here, we assess the relative importance of phylogenetic relatedness, natural history, and habitat on shaping wing morphology in a large dataset of over 3500 individuals, representing 13 Heliconius species from across the Neotropics. We find that both larval and adult behavioral ecology correlate with patterns of wing sexual dimorphism and adult size. Species with solitary larvae have larger adult males, in contrast to gregarious Heliconius species, and indeed most Lepidoptera, where females are larger. Species in the pupal-mating clade are smaller than those in the adult-mating clade. Interestingly, we find that high-altitude species tend to have rounder wings and, in one of the two major Heliconius clades, are also bigger than their lowland relatives. Furthermore, within two widespread species, we find that high-altitude populations also have rounder wings. Thus, we reveal novel adaptive wing morphological divergence among Heliconius species beyond that imposed by natural selection on aposematic wing coloration.

Comparative Transcriptomics Provides Insights into Reticulate and Adaptive Evolution of a Butterfly Radiation

Butterfly eyes are complex organs that are composed of a diversity of proteins and they play a central role in visual signaling and ultimately, speciation, and adaptation. Here, we utilized the whole eye transcriptome to obtain a more holistic view of the evolution of the butterfly eye while accounting for speciation events that co-occur with ancient hybridization. We sequenced and assembled transcriptomes from adult female eyes of eight species representing all major clades of the Heliconius genus and an additional outgroup species, Dryas iulia. We identified 4,042 orthologous genes shared across all transcriptome data sets and constructed a transcriptome-wide phylogeny, which revealed topological discordance with the mitochondrial phylogenetic tree in the Heliconius pupal mating clade. We then estimated introgression among lineages using additional genome data and found evidence for ancient hybridization leading to the common ancestor of Heliconius hortense and Heliconius clysonymus. We estimated the Ka/Ks ratio for each orthologous cluster and performed further tests to demonstrate genes showing evidence of adaptive protein evolution. Furthermore, we characterized patterns of expression for a subset of these positively selected orthologs using qRT-PCR. Taken together, we identified candidate eye genes that show signatures of adaptive molecular evolution and provide evidence of their expression divergence between species, tissues, and sexes. Our results demonstrate: 1) greater evolutionary changes in younger Heliconius lineages, that is, more positively selected genes in the cydno-melpomene-hecale group as opposed to the sara-hortense-erato group, and 2) suggest an ancient hybridization leading to speciation among Heliconius pupal-mating species.

A Dynamic Optical Signal in a Nocturnal Moth

The wings of butterflies and moths generate some of the most spectacular visual displays observed in nature [1-3]. Particularly striking effects are seen when light interferes with nanostructure materials in the wing scales, generating bright, directional colors that often serve as dynamic visual signals [4]. Structural coloration is not known in night-flying Lepidoptera, yet here we show a highly unusual form of wing coloration in a nocturnal, sexually dimorphic moth, Eudocima materna (Noctuidae). Males feature three dark wing patches on the dorsal forewings, and the apparent size of these patches strongly varies depending on the angle of the wing to the viewer. These optical special effects are generated using specialized wing scales that are tilted on the wing and behave like mirrors. At near-normal incidence of light, these "mirror scales" act as thin-film reflectors to produce a sparkly effect, but when light is incident at ∼20°-30° from normal, the reflectance spectrum is dominated by the diffuse scattering of the underlying, black melanin-containing scales, causing a shape-shifting effect. The strong sexual dimorphism in the arrangement and architecture of the scale nanostructures suggests that these patterns might function for sexual signaling. Flickering of the male's wings would yield a flashing, supernormal visual stimulus [5] to a viewer located 20°-30° away from the vertical, while being invisible to a viewer directly above the animal. Our findings reveal a novel use of structural coloration in nature that yields a dynamic, time-dependent achromatic optical signal that may be optimized for visual signaling in dim light.

Ontogeny of sexual size dimorphism revisited: Females grow for a longer time and also faster

Sex-specific mechanisms of the determination of insect body sizes are insufficiently understood. Here we use the common heath moth, Ematurga atomaria (Lepidoptera: Geometridae) to examine how larval growth trajectories differ between males and females. We monitored the development of 1379 larvae in controlled laboratory conditions. Sexually dimorphic development times during the first four instars were associated with sexual size dimorphism (SSD) in the beginning of the fifth (last) instar, when females were on average 15% heavier than males. Similarly, the duration of the last instar was about 13% longer in females. Further, we specifically focussed on the estimates of differential (instantaneous) growth rates of the larvae based on 24h mass increments of the 2^nd, 3^rd, 4^th and 5^th day in the beginning of the last instar. We calculated ‘allometric’ differential growth rates as the per-day increase in cube-root-transformed mass of the larvae. We found that allometric growth rates were slightly but significantly larger in females than in males. As this measure of growth rate (in contrast to the relative growth rate, based on the ratio of masses recorded at consecutive measurements) did not depend on body size, it allows an unambiguous separation of the effects of sex and size. We conclude that in accordance with an emerging general pattern, larger female body size in E. atomaria is achieved primarily by means of a longer growth period. Furthermore, our study shows that the differential growth rate can also be sexually dimorphic and contribute to SSD. This contribution, however, is lower than that of the development time by an order of magnitude. In addition to development periods and growth rates, other parameters of the non-linear growth curves of insect larvae also need to be considered in the context of SSD determination. In particular, weight loss prior to pupation was shown to be considerably larger in females than in males.

Adaptive evolution of butterfly wing shape: from morphology to behaviour

Butterflies display extreme variation in wing shape associated with tremendous ecological diversity. Disentangling the role of neutral versus adaptive processes in wing shape diversification remains a challenge for evolutionary biologists. Ascertaining how natural selection influences wing shape evolution requires both functional studies linking morphology to flight performance, and ecological investigations linking performance in the wild with fitness. However, direct links between morphological variation and fitness have rarely been established. The functional morphology of butterfly flight has been investigated but selective forces acting on flight behaviour and associated wing shape have received less attention. Here, we attempt to estimate the ecological relevance of morpho-functional links established through biomechanical studies in order to understand the evolution of butterfly wing morphology. We survey the evidence for natural and sexual selection driving wing shape evolution in butterflies, and discuss how our functional knowledge may allow identification of the selective forces involved, at both the macro- and micro-evolutionary scales. Our review shows that although correlations between wing shape variation and ecological factors have been established at the macro-evolutionary level, the underlying selective pressures often remain unclear. We identify the need to investigate flight behaviour in relevant ecological contexts to detect variation in fitness-related traits. Identifying the selective regime then should guide experimental studies towards the relevant estimates of flight performance. Habitat, predators and sex-specific behaviours are likely to be major selective forces acting on wing shape evolution in butterflies. Some striking cases of morphological divergence driven by contrasting ecology involve both wing and body morphology, indicating that their interactions should be included in future studies investigating co-evolution between morphology and flight behaviour.

Antennal scales improve signal detection efficiency in moths

The elaborate bipectinate antennae of male moths are thought to increase their sensitivity to female sex pheromones, and so should be favoured by selection. Yet simple filamentous antennae are the most common structure among moths. The stereotypic arrangements of scales on the surface of antennae may resolve this paradox. We use computational fluid dynamics techniques to model how scales on the filamentous antennae of moths affect the passage of different particles in the airflow across the flagellum in both small and large moths. We found that the scales provide an effective solution to improve the efficacy of filamentous antennae, by increasing the concentration of nanoparticles, which resemble pheromones, around the antennae. The smaller moths have a greater increase in antennal efficiency than larger moths. The scales also divert microparticles, which resemble dust, away from the antennal surface, thereby reducing contamination. The positive correlations between antennal scale angles and sensilla number across Heliozelidae moths are consistent with the predictions of our model.

Male Bicyclus anynana Butterflies Choose Females on the Basis of Their Ventral UV-Reflective Eyespot Centers

Butterflies often use their dorsal and ventral wing color patterns for distinct signaling functions. Color patterns on hidden dorsal wing surfaces are often used in sexual signaling, while exposed ventral patterns are often used to ward off predator attacks. At rest, however, part of the ventral forewings are often hidden by the hindwings, allowing individuals to also use the patterns on this wing surface for sexual signaling. Here, we test this hypothesis in Bicyclus anynana (Butler, Lepidoptera, Nymphalidae) butterflies by first determining the degree of sexual dimorphism in ventral forewing patterns, focusing on the eyespots, from both wet and dry season forms, and then testing the role of the larger ventral forewing eyespots of dry season females in male mate choice. We also test male investment in reproduction. We show that ventral forewing UV-reflective eyespot centers, in addition to dorsal forewing eyespot centers previously examined in this species, play a role in sexual signaling as males preferentially mated with females with their ventral eyespot centers intact instead of blocked with black paint. This male preference, however, did not translate into a detectable higher reproductive investment via a single mating toward ornamented females. This study provides an example of how ventral forewing patterns, often hidden by hindwings, are used in sexual communication, in this case by females to attract males.

Comparative transcriptomic analysis of larval and adult Malpighian tubules from the cotton bollworm Helicoverpa armigera

Malpighian tubules (MTs) are usually considered the key excretory and osmoregulatory organs of insects. However, increasing evidence has suggested that MTs perform many more functions than just osmoregulation. Until now, the molecular and physiological functions of MTs in the cotton bollworm (Helicoverpa armigera), a very important agricultural pest, are largely unknown. In this study, the transcriptomes of H. armigera MTs from larvae, male adults and female adults were sequenced using RNA-Seq technology, and comparative analyses of transcriptomes between two life stages (larval and adult) and between adult sexes were conducted. We generated a total of 84 643 high-quality unigenes, and identified a large number of abundant transcripts putatively encoding proteins involved in diuresis, detoxification, immunity, carbohydrate transport and metabolism, development and reproduction. We found that the expression pattern of unigenes was relatively similar between female and male adult MTs, but different between larval and adult MTs. Our data suggest that insect MTs may take multiple physiological functions as versatile organs. The extensive alterations in gene expression in MTs occurred from larvae to adults reflect an ecological adaptation to different feeding habits. Sexual dimorphism in the cotton bollworm is somewhat indicated by the transcriptional difference of genes related to carbohydrate metabolism, detoxification, immunity and reproduction in the MTs of male and female adults.

Sexual dimorphism in the alpine butterflies Boloria pales and Boloria napaea: differences in movement and foraging behavior (Lepidoptera: Nymphalidae)

Sexual dimorphism is a widespread phenomenon in Lepidoptera. It is reflected in differences in life history, behavior and morphology. Analyses of differences in behavior are mostly difficult and time-consuming, especially in high mountain ecosystems. To enhance our knowledge on sexual dimorphisms of alpine butterflies, we performed a mark-release-recapture study on 2 species common in the Alps: Boloria pales and Boloria napaea. We analysed movement and foraging behavior to investigate differences between sexes. Both sexes were mostly sedentary and the movement distances of males and females similar. However, obvious differences in dispersal behavior between the sexes were found in the movement patterns. Three different patterns were distinguished. Most males showed intensive flight activity, but mostly flew only in a limited part of the entire habitat (i.e., their individual home range) searching for females, whereas females were less flight active and flew only to find places for oviposition or feeding. The third pattern, where individuals flew larger distances, was only observed in a small number of males, which always returned to their home range. Nearly all feeding was observed on Asteraceae. However, males preferred the genera Leontodon and Crepis, while females preferred Leontodon and Carduus. Apart from this sexual difference in foraging, individuals of both sexes were found to be more or less specialised on nectar sources. Flight activity was generally greater in males than females. Therefore, we think that sex-specific requirements in nectar ingredients exist, that is, sugar for the intensive flight activity of males and amino acids for egg production of females.

The structure and morphologic changes of antennae of Cyrtorhinus lividipennis (Hemiptera: Miridae: Orthotylinae) in different instars

Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae: Orthotylinae), including nymphs and adults, are one of the dominant predators and have a significant role in the biological control of leafhoppers and planthoppers in irrigated rice. In this study, we investigated the antennal morphology, structure and sensilla distribution of C. lividipennis in different instars using scanning electron microscopy. The antennae of both five different nymphal stages and adults were filiform in shape, which consisted of the scape, pedicel and flagellum with two flagellomeres. There were significant differences found in the types of antennal sensilla between nymphs and adults. The multiporous placodea sensilla (MPLA), basiconica sensilla II (BAS II), and sensory pits (SP) only occurred on the antennae of adult C. lividipennis of both sexes. Moreover, there was chaetica sensilla III (CHA III) only observed in males. Sixteen types of antennal sensilla were recorded altogether. They were microtrichia sensilla (MIC), three types of trichoidea sensilla (TRI I-III), three types of chaetica sensilla (CHA I-III), three types of basiconica sensilla (BAS I-III), two types of coeloconica sensilla (COE I and COE II), placodea sensilla (PLA), campaniform sensilla (CAM), MPLA, and SP. In the five different nymphal stages of C. lividipennis, the length of their antennae was significantly increased with the increase of the instar, as well as the number of the TRI II and TRI III. Moreover, sexual dimorphism usually occurred not only in the distribution (CHA III and SP) and the number of antennal sensilla (MIC, BAS II, TRI II, TRI III and MPLA), but also in the length of flagellum (F1 and F2). The possible functions of antennal sensilla are discussed. Those observations could contribute to a better understanding of the development of the olfactory system, and facilitate future studies on the antennal functions in C. lividipennis.

Multiple origins of sexual dichromatism and aposematism within large carpenter bees

The evolution of reversed sexual dichromatism and aposematic coloration has long been of interest to both theoreticians and empiricists. Yet despite the potential connections between these phenomena, they have seldom been jointly studied. Large carpenter bees (genus Xylocopa) are a promising group for such comparative investigations as they are a diverse clade in which both aposematism and reversed sexual dichromatism can occur either together or separately. We investigated the evolutionary history of dichromatism and aposematism and a potential correlation of these traits with diversification rates within Xylocopa, using a newly generated phylogeny for 179 Xylocopa species based on ultraconserved elements (UCEs). A monochromatic, inconspicuous ancestor is indicated for the genus, with subsequent convergent evolution of sexual dichromatism and aposematism in multiple lineages. Aposematism is found to covary with reversed sexual dichromatism in many species; however, reversed dichromatism also evolved in non-aposematic species. Bayesian Analysis of Macroevolutionary Models (BAMM) did not show increased diversification in any specific clade in Xylocopa, whereas support from Hidden State Speciation and Extinction (HiSSE) models remained inconclusive regarding an association of increased diversification rates with dichromatism or aposematism. We discuss the evolution of color patterns and diversification in Xylocopa by considering potential drivers of dichromatism and aposematism.

Lack of support for Rensch's rule in an intraspecific test using red flour beetle (Tribolium castaneum) populations

Rensch's rule proposes a universal allometric scaling phenomenon across species where sexual size dimorphism (SSD) has evolved: in taxa with male-biased dimorphism, degree of SSD should increase with overall body size, and in taxa with female-biased dimorphism, degree of SSD should decrease with increasing average body size. Rensch's rule appears to hold widely across taxa where SSD is male-biased, but not consistently when SSD is female-biased. Furthermore, studies addressing this question within species are rare, so it remains unclear whether this rule applies at the intraspecific level. We assess body size and SSD within Tribolium castaneum (Herbst), a species where females are larger than males, using 21 populations derived from separate locations across the world, and maintained in isolated laboratory culture for at least 20 years. Body size, and hence SSD patterns, are highly susceptible to variations in temperature, diet quality and other environmental factors. Crucially, here we nullify interference of such confounds as all populations were maintained under identical conditions (similar densities, standard diet and exposed to identical temperature, relative humidity and photoperiod). We measured thirty beetles of each sex for all populations, and found body size variation across populations, and (as expected) female-biased SSD in all populations. We test whether Rensch's rule holds for our populations, but find isometry, i.e. no allometry for SSD. Our results thus show that Rensch's rule does not hold across populations within this species. Our intraspecific test matches previous interspecific studies showing that Rensch's rule fails in species with female-biased SSD.

The anti-bat strategy of ultrasound absorption: the wings of nocturnal moths (Bombycoidea: Saturniidae) absorb more ultrasound than the wings of diurnal moths (Chalcosiinae: Zygaenoidea: Zygaenidae)

The selection pressure from echolocating bats has driven the development of a diverse range of anti-bat strategies in insects. For instance, several studies have proposed that the wings of some moths absorb a large portion of the sound energy contained in a bat's ultrasonic cry; as a result, the bat receives a dampened echo, and the moth becomes invisible to the bat. To test the hypothesis that greater exposure to bat predation drives the development of higher ultrasound absorbance, we used a small reverberation chamber to measure the ultrasound absorbance of the wings of nocturnal (Bombycoidea: Saturniidae) and diurnal moths (Chalcosiinae: Zygaenoidea: Zygaenidae). The absorption factor of the nocturnal saturniids peaks significantly higher than the absorption factor of the diurnal chalcosiines. However, the wings of the chalcosiines absorb more ultrasound than the wings of some diurnal butterflies. Following a phylogenetic analysis on the character state of diurnality/ nocturnality in the Zygaenidae, we propose that diurnality in the Chalcosiinae is plesiomorphic (retained); hence, the absorbance of their wings is probably not a vestigial trait from an ancestral, nocturnal form but an adaptation to bat activity that overlaps their own. On a within-species level, females of the saturniids Argema mittrei and Samia cynthia ricini have significantly higher absorption factors than the males. In the female S. c. ricini, the higher absorption factor corresponds to a detection distance by bats that is at best 20-30% shorter than that of the male.

Summary: Moth wings partly absorb the ultrasonic calls of bats to reduce predation. Different moths fly at night or day, and this work compares their absorption of ultrasound.

Missing concepts in natural selection theory reconstructions

The concept of fitness has generated a lot of discussion in philosophy of biology. There is, however, relative agreement about the need to distinguish at least two uses of the term: ecological fitness on the one hand, and population genetics fitness on the other. The goal of this paper is to give an explication of the concept of ecological fitness by providing a reconstruction of the theory of natural selection in which this concept was framed, that is, based on the way the theory was put to use in Darwin's main texts. I will contend that this reconstruction enables us to account for the current use of the theory of natural selection. The framework presupposed in the analysis will be that of metatheoretical structuralism. This framework will provide both a better understanding of the nature of ecological fitness and a more complete reconstruction of the theory. In particular, it will provide what I think is a better way of understanding how the concept of fitness is applied through heterogeneous cases. One of the major advantages of my way of thinking about natural selection theory is that it would not have the peculiar metatheoretical status that it has in other available views. I will argue that in order to achieve these goals it is necessary to make several concepts explicit, concepts that are frequently omitted in usual reconstructions.