Sex differences in phenotypic plasticity affect variation in sexual size dimorphism in insects: from physiology to evolution

A Comparative Morphological Study of the Ultrastructure of Antennal Sensilla in Sclerodermus guani (Hymenoptera: Bethylidae)

The morphology, number, and distribution of antennal sensilla differ between males and females, reflecting adaptations to sex-specific ecological roles and life histories. In this study, scanning electron microscopy was employed to examine the antennal structure and sensilla types of adult males and females of Sclerodermus guani Xiao et Wu 1983 (Hymenoptera: Bethylidae), with a focus on identifying morphological differences between the sexes. The results revealed that the antennae of both sexes are geniculate; however, female antennae are shorter and broader than those of males. Each antenna comprises 13 segments, including a scape (1 segment), a pedicel (1 segment), and a flagellum (11 segments). Eight distinct types of sensilla were identified on the antennae of both males and females, with notable sex-specific differences in sensilla types and subtypes. Trichoid sensilla subtype III was found exclusively in males, whereas long basiconic sensilla and basiconic sensilla subtype II were unique to females. More than 70% of the antennal sensilla in both sexes were olfactory in nature, highlighting their predominant role in chemical detection. The observed sexual dimorphism in the morphology and distribution of olfactory sensilla suggests functional specialization, potentially linked to host localization in females and mate location in males.

Synergistic effects of elevated temperature with pesticides on reproduction, development and survival of dung beetles

In times of global change, high temperatures can increase the negative effects of pesticides and other stressors. The goal of this study was to evaluate, under controlled laboratory conditions, the effect of a moderate increase in temperature in combination with ivermectin (an antiparasitic medication used in cattle that is excreted in dung), an herbicide, and parasitic pressure, on the reproductive success, development time and adult survival of dung beetles Euoniticellus intermedius. Whereas high temperature increased the number and proportion of emerged offspring, it had synergistic negative effects in combination with the ivermectin, herbicide and parasite treatments. Moreover, high temperature in combination with ivermectin and with parasitism caused a synergistic increase of adult offspring mortality and, in combination with the herbicide, it synergistically accelerated development. These results indicate that high temperatures can enhance the negative effects of other stressors and act synergistically with them, harming dung beetles, a group with high ecological and economic value in natural and productive ecosystems. Although adult sex ratio was not affected by experimental treatments, contrasting responses were found between males and females, supporting the idea that both sexes use different physiological mechanisms to cope with the same environmental challenges. The effects that combined stressors have on insects deepen our understanding of why we are losing beneficial species and their functions in times of drastic environmental changes.

Elevated ambient temperature reduces fat storage through the FoxO-mediated insulin signaling pathway

Temperature profoundly impacts all living organisms, influencing development, growth, longevity, and metabolism. Specifically, when adult flies are exposed to high temperatures, there is a notable reduction in their body fat content. We investigate the roles of the insulin signaling pathway in temperature-mediated fat storage. This pathway is not only highly conserved from insects to mammals but also crucial in regulating lipid metabolism, cell proliferation, and tissue growth. The Forkhead box O (FoxO) protein functions as a key downstream signaling molecule in this pathway, mediating the inhibitory effects of insulin signaling. At elevated temperatures, direct targets of FoxO, such as insulin receptor (InR), Thor (Drosophila eukaryotic initiation factor 4E binding protein), and FoxO itself, are significantly upregulated, which indicates an inhibition of insulin signaling. Interestingly, this inhibition seems to occur independently of Drosophila insulin-like peptide (Ilp) stimuli, as not all Ilp transcripts were reduced at elevated temperatures. Furthermore, when S2R + Drosophila cells are incubated at high temperatures, there is a marked decrease in Akt phosphorylation, directly supporting the notion that elevated temperatures can inhibit insulin signaling in a cell-autonomous manner, independent of Ilp levels. Subsequent experiments demonstrated that either constitutively active InR or knockdown of FoxO prevents the reduction of body fat at high temperatures. Together, these findings highlight the critical role of the insulin signaling-FoxO branch in regulating lipid homeostasis under heat stress conditions.

Development and sex affect respiratory responses to temperature and dissolved oxygen in the air-breathing fishes Betta splendens and Trichopodus trichopterus

Ventilation frequencies of the gills (fG) and the air-breathing organ (fABO) were measured in juveniles and adults of the air-breathing betta (Betta splendens) and the blue gourami (Trichopodus trichopterus) in response to temperature and hypoxia. Ventilatory rates were evaluated after 1 h of exposure to 27 °C (control), 23 and 31 °C (PO2 = 21.0 kPa), after acute temperature changes (ATC) from 23 to 27, and 27 to 31 °C, and under progressive hypoxia (PH; PO2 =  ~ 21 to 2.5 kPa). Complex, multi-phased ventilatory alterations were evident across species and experimental groups revealing different stress responses and shock reactions (e.g., changes in temperature sensitivity (Q10) of fG between 1-h exposure and ACT in both species). Female and male gourami showed differences in Q10 over the temperature range 23-31 °C. No such Q10 differences occurred in betta. Juveniles of both species showed higher Q10 for fABO (~ 3.7) than fG (~ 2.2). Adult fish exhibited variable Q10s for fG (~ 1.5 to ~ 4.3) and fABO (~ 0.8 to ~ 15.5) as a function of temperature, suggesting a switch from aquatic towards aerial ventilation in response to thermal stress. During PH, juveniles from both species showed higher fG than adults at all oxygen levels. Females from both species showed higher fG compared with males. Collectively, our results suggest that environmental cues modulate ventilatory responses in both species throughout ontogeny, but the actual responses reflect species-specific differences in natural habitat and ecology. Finally, we strongly suggest assessing physiological differences between male and female fish to avoid masking relevant findings and to facilitate results interpretation.

A forensic perspective on geographical and temperature-driven differences in the development of Lucilia sericata (Meigen, 1826)

The age of the oldest immature insects present on a cadaver is typically used by forensic entomologists to estimate the minimum postmortem interval (PMImin). The green bottle fly, Lucilia sericata (Meigen, 1826), known for its widespread distribution and necrophagy, is of considerable significance in forensic science. This study aimed to investigate potential regional developmental disparities between populations of L. sericata in China and to identify the origins of such variances. Developmental data of L. sericata populations from Shandong, Jiangsu, and Ningxia in China were analyzed under seven constant temperatures ranging from 16-34 °C, including developmental duration, pupal length, and thermobiological parameters. Findings showed that L. sericata from each of the three regions could complete their development within the temperature range of 16-34 °C. There was notable congruence in the total developmental period of L. sericata from different regions within the 22-28 °C range. However, at temperatures below 20 °C and exceeding 30 °C, discernible differences in developmental duration were observed between populations, and at 34 °C, the total developmental period showed statistical differences. Comparisons of pupal length indicate obvious regional differences, with an interplay between temperature and region suggesting a dual influence on L. sericata development. The thermobiological parameters revealed differences in the adaptability of L. sericata to temperature across different regions. In summary, the experimental results provide pivotal insights for applying regional L. sericata data in the estimation of PMImin, and it is recommended that regional specificity and experimental operational discrepancies be taken into account in future estimations.

Sexual size dimorphism affecting mate choice and reproduction in the pine sawyer beetle, Monochamus alternatus

Monochamus alternatus is a notorious pest of the pine forests across East Asian countries. Both large and small individuals of either sex coexist in the wild. However, whether and how body size affects sexual selection outcomes and longevity remains unknown. In this study, we allowed a male or a female of small or large size to choose between two mates of varying sizes, which were from a wild-caught population. Our results revealed that mating latency and frequency of mating attempts varied across different social environments. Both large males and large females preferred larger mates, whereas this preference was not observed for the small males and small females. Male-male competition had no significant effect on ejaculation duration and frequency or sperm number in ejaculates. When a single male had an opportunity to choose between two females of different sizes, the reproductive investment of small males towards the small females was almost doubled compared to that of the large males, i.e., longer ejaculation duration, higher ejaculation frequency, and greater numbers of sperm transferred. However, the greater mating efforts of small males did not translate to greater fecundity/fertility of small females. We also showed that regardless of their body size, females always had greater fertility when they mated with large males but evidence for a trade-off between fecundity and longevity was not found. Alternatively, female fecundity was positively associated with longevity, and fertility was negatively associated with longevity and fecundity. We discussed these results placing it in a broader context of mate choice evolutionary dynamics.

Nutrition affects larval survival and the development of morphological traits in male and female flour beetles, but genital size and shape remains canalised

The caloric content and macronutrient ratio of diet consumed is a major source of phenotypic variation in most animal populations. While these nutritional effects have been well-documented for a variety of life-history and morphological traits, the effects of nutrition on male genitals are poorly understood but genitals are thought to be more canalised than general morphology and hence less susceptible to variation in nutrition. Even less is known about the effects of nutrition on female genital form, which to our knowledge, have never been investigated. Here we tested for effects of juvenile dietary macronutrients (protein and carbohydrate) on larval survival, adult morphology, including genital size and shape in male and female flour beetles (Tribolium castaneum). We found there was nutritionally induced plasticity in larval survival and morphology, although the latter effect was variable, with body size being most responsive to dietary macronutrients and genital size and shape being least responsive. Functionally equivalent morphological traits in the sexes responded similarly to nutrition. Previously, we showed that the genitalia of male and female T. castaneum are subject to strong stabilising sexual selection, and our current findings suggest that developmental mechanisms reduce the nutritional sensitivity of male and female genitals, possibly to ensure matching during mating.

Male Reproductive Traits Display Increased Phenotypic Variation in Response to Resource Quality and Parental Provisioning in a Tropical Rainforest Dung Beetle, Onthophagus c.f. babirussa

Reproductive traits that mediate differential fitness associated with mate acquisition and fertilisation success are often strongly linked to the overall condition. We investigated the effects of resource quality and parental provisioning in the phenotypic expression of sexual and non-sexual traits in a rainforest dung beetle, Onthophagus c.f. babirussa (Eschscholtz, 1822) from Singapore. F1 individuals were reared from wild-caught beetles and paired up to produce offspring (F2), and F2 larvae from the same F1 parents were reared on two dung substrates (herbivore and omnivore) in a full-sib design. Sexual traits displayed greater phenotypic variation in response to dung resource quality, with the precopulatory trait (horn length) responding more than the postcopulatory trait (testes weight). Notably, genotype-by-environment interactions between parental lines (genotype) and dung type (environment) affected male body size and horn length only, suggesting sex-specific variance in plasticity associated with sexually selected precopulatory traits. Dung type had significant effects on all measured traits. Offspring that were provisioned higher quality resource (omnivore dung) had larger absolute and relative trait values. Parental lines only significantly affected female body size but none of the male traits, suggesting an important role of environment and resource partitioning in determining precopulatory success of male offspring. Parental provisioning of larval resource varied with resource quality and brood sequence. Parents provisioned more dung when herbivore dung was presented than when they were given omnivore dung and provisioned more dung for their earlier broods when using herbivore dung but not omnivore dung. This suggests a trade-off between early offspring fitness and resource quality. We tested directly for genotype-by-environment (G × E) interactions in the expression of several morphological traits relevant to dung beetle fitness and documented that offspring with similar phenotypes may result from completely different parental resource allocation strategies. We discuss the importance of studying parental investment on trait variation and its implications on dung beetle ecology.

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.

Effect of temperature on sexual size dimorphism during the developmental period in the broad-horned flour beetle

Adult size in numerous insects is strongly dependent on temperature. In several cases, a temperature-size rule is observed in which developmental temperature and adult size tradeoff. Although several previous studies have demonstrated the temperature-size rule, only a few have explored the relationship between developmental temperature and weapon traits or sexual size dimorphism. This study was conducted to investigate the size of the broad-horned flour beetle Gnatocerus cornutus when it was developed under different temperatures. G. cornutus males possess weapon traits for male-male combat and exhibit sexual size dimorphism in other morphological traits. Results showed that male weapon size and body size complied with the temperature-size rule. Furthermore, the extent of sex dimorphism in genae width, a weapon-supportive trait, were larger at lower temperatures. Our findings suggest that the temperature-size rule also influences the size of sexual traits.

Differential expression of sNPF in male and female eyestalk leading to sex dimorphism of AMP expression in Procambarus clarkii intestine

Antimicrobial peptide (AMP) is an important component of crustaceans' innate immune system. In this study, a short neuropeptide F (sNPF) gene (Pc-sNPF) and a Forkhead box O (FOXO) gene (PcFOXO) from Procambarus clarkii were identified. Analysis findings showed that the expression level of AMP genes differed between male and female P. clarkii. Furthermore, Pc-sNPF and PcFOXO were related to the sex dimorphism of AMP. Knockdown of Pc-sNPF in the eyestalk significantly upregulated the expression of PcFOXO and two anti-lipopolysaccharide factors (PcALF4 and PcALFL) in the intestine of P. clarkii. The expression of PcFOXO in the intestine of female P. clarkii was higher than in that of males. Results from RNA interference revealed that PcFOXO positively regulated the expression of PcALF4 and PcALFL in the intestine of male and female P. clarkii. In summary, our study showed that differences in Pc-sNPF expression in eyestalk of male and female P. clarkii leading to sex dimorphism of AMP expression in the intestine are mediated by the sNPF-FOXO-AMP signal pathway called the eyestalk-intestine axis.

Development, survival and description of the life stages of Zatrephina lineata (Coleoptera: Chrysomelidae) fed on Ipomoea pes-caprae leaves

Zatrephina lineata (Coleoptera: Chrysomelidae) is a phytophagous insect, mainly of plants of the genera Ipomoea and Mikania. The objective was to study the development, survival and to describe the life stages of Z. lineata fed on leaves of Ipomoea pes-caprae. Biological observations were made daily with the aid of a stereoscopic microscope and the instars of this insect identified by the exuvia left between one moulting and the next. The duration of development and survival of the egg, larva and pupa stages and the first, second, third, fourth and fifth instars and of the nymph stage of Z. lineata differed, but not between sexes of this insect. The duration of development of Z. lineata was longer in the larval stage and in the fifth instar, and its survival greater in the egg and pupa stages and in the first and fifth instars. Zatrephina lineata eggs, cream-colored, are ellipsoid and deposited in groups on the adaxial surface of older I. pes-caprae leaves. The larvae of this insect go through five instars, with the first three being gregarious with chemo-behavioral defenses. The exarated pupae of Z. lineata, light yellow in color and with an oval shape flattened dorsoventrally, attach to the abaxial surface of the I. pes-caprae leaves. The shape of adults of this insect is oval, straw yellow in color with lighter longitudinal stripes and females are slightly larger than males.

Within-population plastic responses to combined thermal-nutritional stress differ from those in response to single stressors, and are genetically independent across traits in both males and females

Phenotypic plasticity helps animals to buffer the effects of increasing thermal and nutritional stress created by climate change. Plastic responses to single and combined stressors can vary among genetically diverged populations. However, less is known about how plasticity in response to combined stress varies among individuals within a population or whether such variation changes across life-history traits. This is important because individual variation within populations shapes population-level responses to environmental change. Here, we used isogenic lines of Drosophila melanogaster to assess the plasticity of egg-to-adult viability and sex-specific body size for combinations of 2 temperatures (25 °C or 28 °C) and 3 diets (standard diet, low caloric diet, or low protein:carbohydrate ratio diet). Our results reveal substantial within-population genetic variation in plasticity for egg-to-adult viability and wing size in response to combined thermal-nutritional stress. This genetic variation in plasticity was a result of cross-environment genetic correlations that were often < 1 for both traits, as well as changes in the expression of genetic variation across environments for egg-to-adult viability. Cross-sex genetic correlations for body size were weaker when the sexes were reared in different conditions, suggesting that the genetic basis of traits may change with the environment. Furthermore, our results suggest that plasticity in egg-to-adult viability is genetically independent from plasticity in body size. Importantly, plasticity in response to diet and temperature individually differed from plastic shifts in response to diet and temperature in combination. By quantifying plasticity and the expression of genetic variance in response to combined stress across traits, our study reveals the complexity of animal responses to environmental change, and the need for a more nuanced understanding of the potential for populations to adapt to ongoing climate change.

On the wings of dragons: Wing morphometric differences in the sexually dichromatic common whitetail skimmer dragonfly, Plathemis lydia (Odonata: Libellulidae)

Sexual dimorphism is common throughout the animal kingdom, leading to sex-specific phenotypic differences. The common whitetail skimmer dragonfly, Plathemis lydia (Drury, 1773), is sexually dichromatic, where males of this species display a conspicuous white abdomen and females display a dark brown abdomen. Differences in abdomen conspicuousness between male and female P. lydia are likely attributed to differences in selective pressure where males use their white conspicuous abdomen during male-male territorial chases. We hypothesized that male P. lydia would exhibit wing morphology adaptations to better offset the costs of predation and territoriality and that these adaptations would differ from females. We used field-collected images to quantify differences in body length, wing length, wing area, wing shape, and wing loading between male and female P. lydia. Our results show that male P. lydia have significantly shorter fore and hind wings relative to body size with a higher wing loading when compared to females. We also found that male P. lydia have narrower and pointier fore and hind wings compared to females. These results are consistent with the idea that males are adapted for faster flight, specifically higher acceleration capacity, and higher agility whereas females are adapted for higher maneuverability.

Genetic variation for sexual dimorphism in developmental traits in Drosophila melanogaster

Sexual dimorphism in traits of insects during the developmental stages could potentially be the direct or indirect result of sex-specific selection provided that genetic variation for sexual dimorphism is present. We investigated genetic variation in sexual dimorphism in a set of Drosophila melanogaster inbred lines for 2 traits: egg to adult development time and pupation site preference. We observed considerable genetic variation in sexual dimorphism among lines in both traits. The sexual dimorphic patterns remained relatively consistent across multiple trials, despite both traits being sensitive to environmental conditions. Additionally, we measured 2 sexually dimorphic adult morphological traits in 6 sampled lines and investigated correlations in the sexual dimorphism patterns with the 2 developmental traits. The abundance of genetic variation in sexual dimorphism for D. melanogaster developmental traits demonstrated in this study provides evidence for a high degree of evolvability of sex differences in preadult traits in natural populations.

Estimation of genetic parameters for the implementation of selective breeding in commercial insect production

BACKGROUND

There is a burgeoning interest in using insects as a sustainable source of food and feed, particularly by capitalising on various waste materials and by-products that are typically considered of low value. Enhancing the commercial production of insects can be achieved through two main approaches: optimising environmental conditions and implementing selective breeding strategies. In order to successfully target desirable traits through selective breeding, having a thorough understanding of the genetic parameters pertaining to those traits is essential. In this study, a full-sib half-sib mating design was used to estimate variance components and heritabilities for larval size and survival at day seven of development, development time and survival from egg to adult, and to estimate correlations between these traits, within an outbred population of house flies (Musca domestica), using high-throughput phenotyping for data collection.

RESULTS

The results revealed low to intermediate heritabilities and positive genetic correlations between all traits except development time and survival to day seven of development and from egg to adulthood. Surprisingly, larval size at day seven exhibited a comparatively low heritability (0.10) in contrast to development time (0.25), a trait that is believed to have a stronger association with overall fitness. A decline in family numbers resulting from low mating success and high overall mortality reduced the amount of available data which resulted in large standard errors for the estimated parameters. Environmental factors made a substantial contribution to the phenotypic variation, which was overall high for all traits.

CONCLUSIONS

There is potential for genetic improvement in all studied traits and estimates of genetic correlations indicate a partly shared genetic architecture among the traits. All estimates have large standard errors. Implementing high-throughput phenotyping is imperative for the estimation of genetic parameters in fast developing insects, and facilitates age synchronisation, which is vital in a breeding population. In spite of endeavours to minimise non-genetic sources of variation, all traits demonstrated substantial influences from environmental components. This emphasises the necessity of thorough attention to the experimental design before breeding is initiated in insect populations.

Filling the gaps in ecology of tropical tiger beetles (Coleoptera: Cicindelidae): first quantitative data of sexual dimorphism in semi-arboreal Therates from the Philippine biodiversity hotspot

Background

Sexual dimorphism, driven by sexual selection, leads to varied morphological distinctions in male and female insects, providing insights into selection pressures across species. However, research on the morphometric variability within specific taxa of tiger beetles (Coleoptera: Cicindelidae), particularly arboreal and semi-arboreal species, remains very limited.

Methods

We investigate sexual dimorphism in six semi-arboreal Therates tiger beetle taxa from the Philippines, focusing on morphological traits. We employed morphometric measurements and multivariate analyses to reveal patterns of sexual dimorphism between sexes within the taxa.

Results

Our results indicate significant sexual dimorphism in elytra width, with females consistently displaying broader elytra, potentially enhancing fecundity. Notable sexual size dimorphism was observed in Therates fulvipennis bidentatus and T. coracinus coracinus, suggesting heightened sexual selection pressures on male body size. Ecological factors, mating behavior, and female mate choice might contribute to the observed morphological variation. These findings emphasize the need for further studies to comprehend mating dynamics, mate choice, and ecological influences on morphological variations in semi-arboreal and arboreal tiger beetles.

Disentangling genetic, plastic and social learning drivers of sex-specific foraging behaviour in Trinidadian guppies (Poecilia reticulata)

Evolutionary biologists have long been interested in parsing out the roles of genetics, plasticity and their interaction on adaptive trait divergence. Since males and females often have different ecological and reproductive roles, separating how their traits are shaped by interactions between their genes and environment is necessary and important. Here, we disentangle the sex-specific effects of genetic divergence, developmental plasticity, social learning and contextual plasticity on foraging behaviour in Trinidadian guppies (Poecilia reticulata) adapted to high- or low-predation habitats. We reared second-generation siblings from both predation regimes with or without predator chemical cues, and with adult conspecifics from either high- or low-predation habitats. We then quantified their foraging behaviour in water with and without predator chemical cues. We found that high-predation guppies forage more efficiently than low-predation guppies, but this behavioural difference is context-dependent and shaped by different mechanisms in males and females. Higher foraging efficiency in high-predation females is largely genetically determined, and to a smaller extent socially learned from conspecifics. However, in high-predation males, higher foraging efficiency is plastically induced by predator cues during development. Our study demonstrates sex-specific differences in genetic versus plastic responses in foraging behaviour, a trait of significance in organismal fitness and ecosystem dynamics.

Sexually transmitted mutualist nematodes shape host growth across dung beetle species

Many symbionts are sexually transmitted and impact their host's development, ecology, and evolution. While the significance of symbionts that cause sexually transmitted diseases (STDs) is relatively well understood, the prevalence and potential significance of the sexual transmission of mutualists remain elusive. Here, we study the effects of sexually transmitted mutualist nematodes on their dung beetle hosts. Symbiotic Diplogastrellus monhysteroides nematodes are present on the genitalia of male and female Onthophagus beetles and are horizontally transmitted during mating and vertically passed on to offspring during oviposition. A previous study indicates that the presence of nematodes benefits larval development and life history in a single host species, Onthophagus taurus. However, Diplogastrellus nematodes can be found in association with a variety of beetle species. Here, we replicate these previous experiments, assess whether the beneficial effects extend to other host species, and test whether nematode-mediated effects differ between male and female host beetles. Rearing three relatively distantly related dung beetle species with and without nematodes, we find that the presence of nematodes benefits body size, but not development time or survival across all three species. Likewise, we found no difference in the benefit of nematodes to male compared to female beetles. These findings highlight the role of sexually transmitted mutualists in the evolution and ecology of dung beetles.

Temperature and nutrition do not interact to shape the evolution of metabolic rate

Metabolic cold adaptation, or Krogh's rule, is the controversial hypothesis that predicts a monotonically negative relationship between metabolic rate and environmental temperature for ectotherms living along thermal clines measured at a common temperature. Macrophysiological patterns consistent with Krogh's rule are not always evident in nature, and experimentally evolved responses to temperature have failed to replicate such patterns. Hence, temperature may not be the sole driver of observed variation in metabolic rate. We tested the hypothesis that temperature, as a driver of energy demand, interacts with nutrition, a driver of energy supply, to shape the evolution of metabolic rate to produce a pattern resembling Krogh's rule. To do this, we evolved replicate lines of Drosophila melanogaster at 18, 25 or 28°C on control, low-calorie or low-protein diets. Contrary to our prediction, we observed no effect of nutrition, alone or interacting with temperature, on adult female and male metabolic rates. Moreover, support for Krogh's rule was only in females at lower temperatures. We, therefore, hypothesize that observed variation in metabolic rate along environmental clines arises from the metabolic consequences of environment-specific life-history optimization, rather than because of the direct effect of temperature on metabolic rate. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.

Sex-biased phenotypic plasticity affects sexual dimorphism patterns under changing environmental conditions

Sexual dimorphism is almost ubiquitous in animals. A common pattern observed across multiple taxa involves differences in development time (sexual bimaturism) and body size (sexual size dimorphism) between conspecific males and females. Furthermore, a strict association of dimorphism at these traits has been documented in several taxa, where the sex showing shorter development time also has a smaller body size than the other sex. Growth and development are strongly dependent on environmental conditions during individual life-cycle in ectotherms, inducing considerable phenotypic plasticity. However, how phenotypic plasticity affects the association between sexual dimorphism in development time and body size remains unclear. Here, we tracked development time, body size, and body mass throughout the ontogeny of the mosquito Aedes mariae. The larval development of this species is strictly linked to Mediterranean Sea rock-pools, whose highly variable environmental conditions over minimal time frames make this organism-environment system ideal for exploring plasticity-led eco-evolutionary processes. We found differential plasticity between males and females, dissolving the link between dimorphism in development time and body size under increasing temperature and decreasing salinity conditions. These findings contrast with the current hypotheses proposed to explain the origin of the association between sexual bimaturism and sexual size dimorphism, highlighting the condition dependence of sexual dimorphism patterns and the need to consider phenotypic plasticity in future studies on their evolution.

How plastic are upper thermal limits? A comparative study in tsetse (family: Glossinidae) and wider Diptera

Critical thermal maximum (CTmax) describes the upper thermal tolerance of an animal where biological functions start to fail. A period of acclimation can enhance CTmax through plasticity, potentially buffering animals from extreme temperatures caused by climate change. Basal and acclimated CTmax vary within and between species and may be explained by traits related to thermal physiology, such as body size and sex. Differences in CTmax have not been established among species of tsetse fly (Glossina spp.), vectors of animal and human African trypanosomiasis. Here, we investigated basal CTmax and its plasticity for five tsetse species following adult acclimation at constant 25 or 30 °C for five days. We then set our findings in context using a meta-analysis on 33 species of Diptera. We find that, of the five tsetse species considered, only Glossina palpalis gambiensis and Glossina brevipalpis exhibited plasticity of CTmax, with an increase of 0.12 °C and 0.10 °C per 1 °C acclimation respectively. Within some species, higher basal CTmax values were associated with larger body size and being female, while variation in plasticity (i.e., response to the acclimation temperature) could not be explained by sex or size. Our broader meta-analysis across Diptera revealed overall CTmax plasticity of 0.06 °C per 1 °C acclimation, versus a similar 0.05 °C mean increase in tsetse. In contrast, there was greater CTmax plasticity in males compared to females in Diptera. Our study highlights that CTmax and its plasticity varies even among closely related species. Broader patterns across groups are not always reflected at a finer resolution; we thus emphasise the need for detailed experimental studies across a wide range of insect species to capture their capacity to cope with rapidly warming temperatures.

Vertically inherited microbiota and environment-modifying behaviors indirectly shape the exaggeration of secondary sexual traits in the gazelle dung beetle

Many organisms actively manipulate the environment in ways that feed back on their own development, a process referred to as developmental niche construction. Yet, the role that constructed biotic and abiotic environments play in shaping phenotypic variation and its evolution is insufficiently understood. Here, we assess whether environmental modifications made by developing dung beetles impact the environment-sensitive expression of secondary sexual traits. Gazelle dung beetles both physically modify their ontogenetic environment and structure their biotic interactions through the vertical inheritance of microbial symbionts. By experimentally eliminating (i) physical environmental modifications and (ii) the vertical inheritance of microbes, we assess the degree to which (sym)biotic and physical environmental modifications shape the exaggeration of several traits varying in their degree and direction of sexual dimorphism. We expected the experimental reduction of a larva's ability to shape its environment to affect trait size and scaling, especially for traits that are sexually dimorphic and environmentally plastic. We find that compromised developmental niche construction indeed shapes sexual dimorphism in overall body size and the absolute sizes of male-limited exaggerated head horns, the strongly sexually dimorphic fore tibia length and width, as well as the weakly dimorphic elytron length and width. This suggests that environmental modifications affect sex-specific phenotypic variation in functional traits. However, most of these effects can be attributed to nutrition-dependent plasticity in size and non-isometric trait scaling rather than body-size-independent effects on the developmental regulation of trait size. Our findings suggest that the reciprocal relationship between developing organisms, their symbionts, and their environment can have considerable impacts on sexual dimorphism and functional morphology.

How often are male mosquitoes attracted to humans?

Many mosquito species live close to humans where females feed on human blood. While male mosquitoes do not feed on blood, it has long been recognized that males of some species can be attracted to human hosts. To investigate the frequency of male mosquito attraction to humans, we conducted a literature review and human-baited field trials, as well as laboratory experiments involving males and females of three common Aedes species. Our literature review indicated that male attraction to humans is limited to a small number of species, including Ae. aegypti and Ae. albopictus. In our human-baited field collections, only 4 out of 13 species captured included males. In laboratory experiments, we found that male Ae. notoscriptus and Ae. vigilax showed no attraction to humans, while male Ae. aegypti exhibited persistent attraction for up to 30 min. Both male and female Ae. aegypti displayed similar preferences for different human subjects, suggesting that male Ae. aegypti respond to similar cues as females. Additionally, we found that mosquito repellents applied to human skin effectively repelled male mosquitoes. These findings shed light on mosquito behaviour and have implications for mosquito control programmes, particularly those involving the release or monitoring of the male mosquito population.

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.

Infection patterns of 'Candidatus Liberibacter europaeus' in Cacopsylla oluanpiensis, a psyllid pest of Pittosporum pentandrum

'Candidatus Liberibacter' is a genus of plant-associated bacteria that can be transmitted by insects of the superfamily Psylloidea. Since many members of this genus are putative causal agents of plant diseases, it is crucial in studying their interactions with the psyllid vectors. However, previous studies have mainly focused on few species associated with diseases of economic significance, and this may potentially hinder the development of a more comprehensive understanding of the ecology of 'Ca. Liberibacter'. The present study showed that an endemic psyllid species in Taiwan, Cacopsylla oluanpiensis, is infected with a species of 'Ca. Liberibacter'. The bacterium was present in geographically distant populations of the psyllid and was identified as 'Ca. Liberibacter europaeus' (CLeu), a species which generally does not induce plant symptoms. Analysis of CLeu infection densities in male and female C. oluanpiensis with different abdominal colors using quantitative polymerase chain reaction revealed that CLeu infection was not significantly associated with psyllid gender and body color. Instead, CLeu infection had a negative effect on the body sizes of both male and female psyllids, which is influenced by bacterial titer. Investigation on CLeu's distribution patterns in C. oluanpiensis's host plant Pittosporum pentandrum indicated that CLeu does not behave as a plant pathogen. Also, results showed that nymph-infested twigs had a greater chance of carrying high loads of CLeu, suggesting that ovipositing females and the nymphs are the main source of the bacterium in the plants. This study is not only the first to formally report the presence of CLeu in C. oluanpiensis and plants in the family Pittosporaceae, but also represents the first record of the bacterium in Taiwan. Overall, the findings in this work broaden the understanding of associations between psyllids and 'Ca. Liberibacter' in the field.

Genetic Variation in Sexual Size Dimorphism Is Associated with Variation in Sex-Specific Plasticity in Drosophila

AbstractThe difference in body size between females and males, or sexual size dimorphism (SSD), is ubiquitous, yet we have a poor understanding of the developmental genetic mechanisms that generate it and how these mechanisms may vary within and among species. Such an understanding of the genetic architecture of SSD is important if we are to evaluate alternative models of SSD evolution, but the genetic architecture is difficult to describe because SSD is a characteristic of populations, not individuals. Here, we overcome this challenge by using isogenic lineages of Drosophila to measure SSD for 196 genotypes. We demonstrate extensive genetic variation for SSD, primarily driven by higher levels of genetic variation for body size among females than among males. While we observe a general increase in SSD with sex-averaged body size (pooling for sex) among lineages, most of the variation in SSD is independent of sex-averaged body size and shows a strong genetic correlation with sex-specific plasticity, such that increased female-biased SSD is associated with increased body size plasticity in females. Our data are consistent with the condition dependence hypothesis of sexual dimorphism and suggest that SSD in Drosophila is a consequence of selection on the developmental genetic mechanisms that regulate the plasticity of body size.

Mapping the nutritional landscape in the yellow mealworm: testing the nutrient-mediated life-history trade-offs

Animals must acquire an ideal amount and balance of macronutrients to optimize their performance, health and fitness. The nutritional landscape provides an integrative framework for analysing how animal phenotypes are associated with multiple nutritional components. Here, we applied this powerful approach to examine how the intake of protein and carbohydrate affects nutrient acquisition and performance in the yellow mealworm (Tenebrio molitor) reared on one of 42 synthetic foods varying in protein and carbohydrate content. Tenebrio molitor larvae increased their food consumption rate in response to nutrient dilution, but this increase was not sufficient to fully compensate for the dilution. Diluting the food nutrient content with cellulose reduced the efficiency of post-ingestive nutrient utilization, further restricting macronutrient acquisition. Tenebrio molitor larvae utilized macronutrients most efficiently at a protein to carbohydrate (P:C) ratio of 1.77:1, but became less efficient at imbalanced P:C ratios. Survivorship was high at high protein intake and fell with decreasing protein intake. Pupal mass and growth rate exhibited a bell-shaped landscape, with the nutritional optima being located around protein-biased P:C ratios of 1.99:1 to 2.03:1 and 1.66:1 to 2.86:1, respectively. The nutritional optimum for development time was also identified at high P:C ratios (1.66:1  to 5.86:1). Unlike these performance traits, lipid content was maximized at carbohydrate-biased P:C ratios of 1:3.88 to 1:3.06. When given a food choice, T. molitor larvae self-composed a slightly carbohydrate-biased P:C ratio of 1:1.24, which lies between the P:C ratios that maximize performance and lipid content. Our findings indicate the occurrence of a nutrient-mediated trade-off between performance and energy storage in this insect.

Differential impacts of ionizing radiation on a sexually dimorphic trait in male and female Acheta domesticus

PURPOSE

In many Orthopteran species, including crickets, forewings exhibit substantial sexual dimorphism driven by sexual selection. In the cricket, Acheta domesticus, females are the 'choosy' sex and males exhibit multiple sexual signals to attract and successfully mate. Male forewings have highly specialized structures critical for acoustic signaling and mating. In contrast, female forewings currently serve no known purpose in this flightless species. Forewings also differ morphologically with male forewings containing complex acoustic producing and resonating regions and females lacking any defined structures. Due to their importance to mating as well as their structural complexity, impacts of environmental stress that target cricket forewing development may therefore have more severe consequences in males than females. Here, we investigate the sensitivity of a sexually dimorphic trait, forewing morphology, to an early life environmental stressor.

MATERIALS AND METHODS

We applied ionizing radiation (0--27.8 Gy) as a stressor as dose can be precisely applied as well as its relevance in both environmental contamination and use in the Sterile Insect Technique.

RESULTS

A canonical variate analysis indicated that wing shape was significantly altered in males at all doses; .58 Gy, 2.3 Gy, 4.6 Gy, 16.2 Gy, and 23.2 Gy. In females, shape was significantly altered at 27.8 Gy and 23.2 Gy groups and to a lesser extent at .58 Gy and 16.2 Gy. Linear regression analysis of centroid size indicated a dose dependent decline in wing size in both sexes, with males exhibiting more decline. Fluctuating asymmetry, a measure of environmental sensitivity, revealed that males were more sensitive to shape changes due to stress than females. This difference in sensitivity is likely due to the complexity of male forewings.

CONCLUSION

These results expand understanding of sex dimorphism in stress responses and sensitivity to ionizing radiation.

Temporal regulation of temperature tolerances and gene expression in an arctic insect

Terrestrial arthropods in the Arctic are exposed to highly variable temperatures that frequently reach cold and warm extremes. Yet, ecophysiological studies on arctic insects typically focus on the ability of species to tolerate low temperatures, whereas studies investigating physiological adaptations of species to periodically warm and variable temperatures are few. In this study, we investigated temporal changes in thermal tolerances and the transcriptome in the Greenlandic seed bug Nysius groenlandicus, collected in the field across different times and temperatures in Southern Greenland. We found that plastic changes in heat and cold tolerances occurred rapidly (within hours) and at a daily scale in the field, and that these changes are correlated with diurnal temperature variation. Using RNA sequencing, we provide molecular underpinnings of the rapid adjustments in thermal tolerance across ambient field temperatures and in the laboratory. We show that transcriptional responses are sensitive to daily temperature changes, and days characterized by high temperature variation induced markedly different expression patterns than thermally stable days. Further, genes associated with laboratory-induced heat responses, including expression of heat shock proteins and vitellogenins, were shared across laboratory and field experiments, but induced at time points associated with lower temperatures in the field. Cold stress responses were not manifested at the transcriptomic level.

Multilevel selection in the evolution of sexual dimorphism in phenotypic plasticity

Phenotypes are partly shaped by the environment, which can impact both short-term adaptation and long-term evolution. In dioecious species, the two sexes may exhibit different degrees of phenotypic plasticity and theoretical models indicate that such differences may confer an adaptive advantage when the population is subject to directional selection, either because of a systematically varying environment or a load of deleterious mutations. The effect stems from the fundamental asymmetry between the two sexes: female fertility is more limited than male fertility. Whether this asymmetry is sufficient for sexual dimorphism in phenotypic plasticity to evolve is, however, not obvious. Here, we show that even in conditions where it provides an adaptive advantage, dimorphic phenotypic plasticity may be evolutionarily unstable due to sexual selection. This is the case, in particular, for panmictic populations where mating partnerships are formed at random. However, we show that the effects of sexual selection can be counteracted when mating occurs within groups of related individuals. Under this condition, sexual dimorphism in phenotypic plasticity can not only evolve but offset the twofold cost of males. We demonstrate these points with a simple mathematical model through a combination of analytical and numerical results.

Effects of transgenerational photoperiod experience on the reproduction and development of Anastatus orientalis, an egg parasitoid of the spotted lanternfly

Transgenerational experience can affect a range of natural enemies' life-history traits and can be involved in the control of developmental plasticity. As a major egg parasitoid of the spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), the wasp Anastatus orientalis (Hymenoptera: Eupelmidae) is effective at suppressing its host populations. The reproductive and developmental traits of A. orientalis is known to depend on photoperiod conditions, but transgenerational photoperiodic effects have yet to be evaluated. To evaluate the transgenerational photoperiodic effects on A. orientalis, we assessed wasp adult longevity, female fecundity, sex ratio, and diapause rate over three consecutive generations under different experimental photoperiods (L16:D8, L12:D12, and L8:D16), using Antheraea pernyi (Lepidoptera: Saturniidae) eggs as hosts. The results suggest that transgenerational experience significantly impacts several biological parameters of progeny. All parasitoids entered a diapause under the long photoperiod condition (i.e., L16:D8), after which the number of female parasitoids and fecundity of the 2nd and 3rd generations increased significantly as compared to the 1st generation. With the long photoperiod conditions, the female ratio rose from 68.1% (1st generation) to 86.0% (3rd generation) and the progeny per females increased from 35.8 to 75.7. However, adult longevity of females and males were shortened significantly. With the intermediate photoperiod (L12:D12) conditions, fecundity and sex ratio of the 2nd and 3rd generations increased significantly as compared to the 1st generation. With the short photoperiod (L8:D16) conditions, there were no significant differences in fecundity among three generations, but sex ratio of the 2nd and 3rd generations increased significantly as compared to the 1st generation. These results on transgenerational photoperiodic effects can be applied to improve laboratory rearing efficiency of parasitoids and to better understand population dynamics in the field across a latitudinal gradient.

Developmental temperature alters the thermal sensitivity of courtship activity and signal-preference relationships, but not mating rates

Mating behaviors are sensitive to novel or stressful thermal conditions, particularly for ectothermic organisms. An organism's sensitivity to temperature, which may manifest in altered mating outcomes, can be shaped in part by temperatures experienced during development. Here, we tested how developmental temperature shapes the expression of adult mating-related behaviors across different ambient conditions, with a focus on courtship behavior, mating rates, and mating signals and preferences. To do so, we reared treehoppers under two temperature regimes and then tested the expression of male and female mating behaviors across a range of ambient temperatures. We found that developmental temperature affects the thermal sensitivity of courtship behavior and mating signals for males. However, developmental temperature did not affect the thermal sensitivity of courtship or mate preferences in females. This sex-specific plasticity did not alter the likelihood of mating across ambient temperatures, but it did disrupt how closely mating signals and preferences matched each other at higher ambient temperatures. As a result, developmental temperature could alter sexual selection through signal-preference de-coupling. We further discuss how adult age may drive sex-specific results, and the potential for mismatches between developmental and mating thermal environments under future climate change predictions.

Sexual size and shape dimorphism, and allometric scaling in the pupal and adult traits of Eristalis tenax

The patterns and amount of variation in size, shape, and/or life history traits between females and males are fundamentally important to gain the comprehensive understanding of the evolution of phenotypic diversity. In addition, the covariation of phenotypic traits can significantly contribute to morphological diversification and sexual dimorphism (SD). Using linear and geometric morphometrics, 237 Eristalis tenax specimens sampled from five populations were, therefore, comparatively assessed for the variation in sexual size dimorphism (SSD), sexual shape dimorphism (SShD), and life history traits, as well as for trait covariation (ontogenetic and static allometry). Pupal body, adult wing, and body mass traits were analyzed. Female-biased SSD was observed for pupal length, width, and centroid size, adult wing centroid size, mass, wing loading, and wing area. Conversely, pupal length/width ratio, developmental time, and mass were not found to be sexually dimorphic. Next, wing SShD, but not pupal body SShD was revealed, while allometry was found to be an important "determinant of SD" at the adult stage, with only a minor impact at the pupal stage. By comparing the patterns of covariance (based on allometric slope and intercept) between respective body mass and morphometric traits of pupae and adults, greater variation in allometric slopes was found in adult traits, while static allometries of the two stages significantly differed, as well. Finally, the results indicate that changes in the allometric intercept could be an important source of intraspecific variation and SD in drone fly adults.

The insulin signaling pathway a century after its discovery: Sexual dimorphism in insulin signaling

Since practically a century ago, the insulin pathway was discovered in both vertebrates and invertebrates, implying an evolutionarily ancient origin. After a century of research, it is now clear that the insulin signal transduction pathway is a critical, flexible and pleiotropic pathway, evolving into multiple anabolic functions besides glucose homeostasis. It regulates paramount aspects of organismal well-being like growth, longevity, intermediate metabolism, and reproduction. Part of this diversification has been attained by duplications and divergence of both ligands and receptors riding on a common general signal transduction system. One of the aspects that is strikingly different is its usage in reproduction, particularly in male versus female development and fertility within the same species. This review highlights sexual divergence in metabolism and reproductive tract differences, the occurrence of sexually "exaggerated" traits, and sex size differences that are due to the sexes' differential activity/response to the insulin signaling pathway.

Limited sex differences in plastic responses suggest evolutionary conservatism of thermal reaction norms: A meta-analysis in insects

Temperature has a profound effect on the growth and development of ectothermic animals. However, the extent to which ecologically driven selection pressures can adjust thermal plastic responses in growth schedules is not well understood. Comparing temperature-induced plastic responses between sexes provides a promising but underexploited approach to evaluating the evolvability of thermal reaction norms: males and females share largely the same genes and immature environments but typically experience different ecological selection pressures. We proceed from the idea that substantial sex differences in plastic responses could be interpreted as resulting from sex-specific life-history optimization, whereas similarity among the sexes should rather be seen as evidence of an essential role of physiological constraints. In this study, we performed a meta-analysis of sex-specific thermal responses in insect development times, using data on 161 species with comprehensive phylogenetic and ecological coverage. As a reference for judging the magnitude of sex specificity in thermal plasticity, we compared the magnitude of sex differences in plastic responses to temperature with those in response to diet. We show that sex-specific responses of development times to temperature variation are broadly similar. We also found no strong evidence for sex specificity in thermal responses to depend on the magnitude or direction of sex differences in development time. Sex differences in temperature-induced plastic responses were systematically less pronounced than sex differences in responses induced by variations in larval diet. Our results point to the existence of substantial constraints on the evolvability of thermal reaction norms in insects as the most likely explanation. If confirmed, the low evolvability of thermal response is an essential aspect to consider in predicting evolutionary responses to climate warming.

Ecological and evolutionary trends of body size in Pristimantis frogs, the world's most diverse vertebrate genus

Body size is a key organismal trait. However, the environmental and evolutionary factors that drive body size patterns at the interspecific level remain unclear. Here, we explored these relationships between phenotype-environment using neotropical frogs of Pristimantis, the world's most diverse vertebrate genus. We analyzed: (a) whether this group follows the Rensch's rule, a trend of sexual size dimorphism (SSD) to increase with size when males are the larger sex; (b) whether environmental constraints have influenced body size variation; and (c) how the rates of body size evolution have varied over time. Analyses were based on two information sources, the first one including body sizes of ~ 85% (495 species) of known species in the genus, and a second one incorporating molecular phylogenetic information for 257 species. Our results showed that all Pristimantis species exhibited marked SSD but did not follow Rensch's rule. We found that the models that best explained body size in males, females, and SSD contained environmental variations in temperature, precipitation, and elevation as predictors. In turn, body size has evolved toward an optimum, with a decelerating rate of evolution differentiated between the large Pristimantis clades.

The potential for the evolution of thermally sensitive courtship behaviours in the treehopper, Enchenopa binotata

The ability of animals to adapt to warming will depend on the evolutionary potential of thermally sensitive traits. The number of studies measuring the quantitative genetics of a wide variety of thermally sensitive traits has steadily increased; however, no study has yet investigated the quantitative genetics of thermal sensitivity for courtship traits. Since courtship often precedes mating, the ability of these traits to respond to warming may impact reproduction and therefore population persistence. Here, we use classic quantitative genetics breeding design to estimate heritability of various aspects of the thermal sensitivity of courtship behaviours in the treehopper Enchenopa binotata. We generated individual-level thermal courtship activity curves for males and females and measured levels of genetic variation in the thermal sensitivity of courtship activity. We found low heritability with 95% credible intervals that did not approach zero for most traits. Levels of genetic variation were highest in traits describing thermal tolerance. We also found some evidence for genetic correlations between traits within but not across sexes. Together, our results suggest that the range of temperatures over which these treehoppers actively court can evolve, although it remains unclear whether adaptation can happen quickly enough to match the speed of warming.

Effects of Fluctuating Thermal Regimes on Life History Parameters and Body Size of Ophraella communa

The beetle Ophraella communa is an effective biological control agent against the invasive common ragweed spread across various ecosystems with variable temperature ranges. The trend in climate change attributed to fluctuating temperatures and abrupt rainfalls is expected to continue. This study aimed to better understand the effects of thermal fluctuation on O. communa by exposing all their life stages to heat stress under different treatments. Repeated exposure to high temperatures, relative to constant milder temperatures, increased the duration of immature development, mean generation time, and the adult longevity, decreased the intrinsic rate of increase, finite rate of population increase, net reproductive rate, survival rate, overall longevity, body length, and mass of adults and positively affected overall fecundity by prolonging the oviposition period, biasing sex ratio towards females. After exposure to heat stress, the mating success and production of viable offspring were higher in O. communa. Our findings demonstrate that exposure to heat stress negatively affects ragweed beetles, but they were able to survive and reproduce.

Meta-analysis reveals weak but pervasive plasticity in insect thermal limits

Extreme temperature events are increasing in frequency and intensity due to climate change. Such events threaten insects, including pollinators, pests and disease vectors. Insect critical thermal limits can be enhanced through acclimation, yet evidence that plasticity aids survival at extreme temperatures is limited. Here, using meta-analyses across 1374 effect sizes, 74 studies and 102 species, we show that thermal limit plasticity is pervasive but generally weak: per 1 °C rise in acclimation temperature, critical thermal maximum increases by 0.09 °C; and per 1 °C decline, critical thermal minimum decreases by 0.15 °C. Moreover, small but significant publication bias suggests that the magnitude of plasticity is marginally overestimated. We find juvenile insects are more plastic than adults, highlighting that physiological responses of insects vary through ontogeny. Overall, we show critical thermal limit plasticity is likely of limited benefit to insects during extreme climatic events, yet we need more studies in under-represented taxa and geographic regions.

The ability of organisms to acclimate to high temperatures is increasingly put to test by climate change. This global meta-analysis shows that plasticity of thermal limits in insects is widespread but unlikely to keep pace with climate change.

Sexual size dimorphism and male reproductive traits vary across populations of a tropical rainforest dung beetle species (Onthophagus babirussa)

Sexual size dimorphism (SSD) arises when natural selection and sexual selection act differently on males and females. Male-biased SSD is rarer in insects and usually indicates strong sexual selection pressure on male body size in a species. Patterns of SSD can also vary between populations of species that are exposed to different environmental conditions, such as differing resource availability and diversity. Here, we investigate intraspecific variation in SSD as well as relative investment in precopulatory (horn length) and postcopulatory traits (sperm length and testes weight) in a tropical rainforest dung beetle Onthophagus babirussa across Singapore and Peninsular Malaysia. Overall, three out of four populations displayed significant male-biased SSD, and SSD was greater in populations with smaller overall body size. Average male body size was similar across all populations while female body size was significantly smaller in Singapore, suggesting that the pronounced SSD may also be due to stronger sexual selection on male body size in Singapore populations. All populations showed significant investment in horns as a weapon likely used in male-male competition, while postcopulatory traits showed no clear scaling relationship with body size, suggesting a higher priority on precopulatory sexual traits in the mating system of this species.

Effects of developmental and adult environments on ageing

Developmental and adult environments can interact in complex ways to influence the fitness of individuals. Most studies investigating effects of the environment on fitness focus on environments experienced and traits expressed at a single point in an organism's life. However, environments vary with time, so the effects of the environments that organisms experience at different ages may interact to affect how traits change throughout life. Here, we test whether thermal stress experienced during development leads individuals to cope better with thermal stress as adults. We manipulated temperature during both development and adulthood and measured a range of life-history traits, including senescence, in male and female seed beetles (Callosobruchus maculatus). We found that thermal stress during development reduced adult reproductive performance of females. In contrast, life span and age-dependent mortality were affected more by adult than developmental environments, with high adult temperatures decreasing longevity and increasing age-dependent mortality. Aside from an interaction between developmental and adult environments to affect age-dependent changes in male weight, we did not find any evidence of a beneficial acclimation response to developmental thermal stress. Overall, our results show that effects of developmental and adult environments can be both sex and trait specific, and that a full understanding of how environments interact to affect fitness and ageing requires the integrated study of conditions experienced during different stages of ontogeny.

Trans- and Within-Generational Developmental Plasticity May Benefit the Prey but Not Its Predator during Heat Waves

Theoretically, parents can adjust vital offspring traits to the irregular and rapid occurrence of heat waves via developmental plasticity. However, the direction and strength of such trait modifications are often species-specific. Here, we investigated within-generational plasticity (WGP) and trans-generational plasticity (TGP) effects induced by heat waves during the offspring development of the predator Phytoseiulus persimilis and its herbivorous prey, the spider mite Tetranychus urticae, to assess plastic developmental modifications. Single offspring individuals with different parental thermal origin (reared under mild or extreme heat waves) of both species were exposed to mild or extreme heat waves until adulthood, and food consumption, age and size at maturity were recorded. The offspring traits were influenced by within-generational plasticity (WGP), trans-generational plasticity (TGP), non-plastic trans-generational effects (TGE) and/or their interactions. When exposed to extreme heat waves, both species speeded up development (exclusively WGP), consumed more (due to the fact of WGP but also to TGP in prey females and to non-plastic TGE in predator males), and predator females got smaller (non-plastic TGE and WGP), whereas prey males and females were equally sized irrespective of their origin, because TGE, WGP and TGP acted in opposite directions. The body sizes of predator males were insensitive to parental and offspring heat wave conditions. Species comparisons indicated stronger reductions in the developmental time and reduced female predator-prey body size ratios in favor of the prey under extreme heat waves. Further investigations are needed to evaluate, whether trait modifications result in lowered suppression success of the predator on its prey under heat waves or not.

Contamination effects on sexual selection in wild dung beetles

Sexual selection influences the expression of secondary sexual traits, which are costly to produce and maintain and are thus considered honest indicators of individual condition. Therefore, sexual selection could select for high-quality individuals able to respond to stressful conditions, with impacts on population-level fitness. We sampled dung beetles from 19 pastures and investigated if contamination by herbicides and veterinary drugs modifies male investment in sexually selected traits and has associated population-level effects. We measured horn size, condition dependence (i.e. size-corrected body mass) and allometry, besides abundance and sexual size dimorphism in three species: Copris incertus, Euoniticellus intermedius and Digitonthophagus gazella. In contrary to our expectations, horn size was independent of contamination and individual condition. However, strong positive allometric relationships were reduced by herbicide contamination for C. incertus and D. gazella and were increased by ivermectin for C. incertus, revealing differential investment in horn production according to body size in contaminated habitats. At the population level, large-horned C. incertus males were more abundant in contaminated pastures, potentially revealing a case of evolutionary rescue by sexual selection or a plastic response to higher population densities. Finally, chemical compounds affected the sexual size dimorphism of all three species, with potential effects on female fecundity or intrasexual selection. Together, our findings indicate that contamination interferes with sexual selection processes in the wild, opening new questions regarding the role of sexual selection in favouring species persistence in contaminated environments.

Sexual size monomorphism may evolve in lizards with a body size maximizing reproductive performance for both sexes

We used Takydromus septentrionalis, a sexually size-monomorphic lacertid lizard, as a model system to test the hypothesis that sexual size monomorphism may evolve in lizards where reproductive performance is maximized at a similar body size for both sexes. We allowed lizards housed in laboratory enclosures to lay as many clutches (for females) as they could or to mate as many times (for males) as they could in a breeding season. Size-assortative mating was weak but evident in T. septentrionalis, as revealed by the fact that male and female snout-vent lengths (SVLs) in mating pairs were significantly and positively correlated. Mating frequency (indicative of male reproductive performance) varied from 1 to 8 per breeding season, generally increasing as SVL increased in adult males smaller than 67.4 mm snout-vent length (SVL). Clutch frequency varied from 1 to 7 per breeding season, with female reproductive performance (determined by clutch frequency, annual fecundity and annual reproductive output) maximized in females with a SVL of 68.0 mm. Accordingly to our hypothesis, the reproductive performance was maximized in the intermediate-sized rather than the largest individuals in both sexes, and the body size maximizing reproductive performance was similar for both sexes. Future work could usefully investigate other lineages of lizards with sexually monomorphic species in a phylogenetic context to corroborate the hypothesis of this study.

Sex-specific regulation of development, growth and metabolism

Adult females and males of most species differ in many aspects of their morphology, physiology and behavior, in response to sex-specific selective pressures that maximize fitness. While we have an increasingly good understanding of the genetic mechanisms that initiate these differences, the sex-specific developmental trajectories that generate them are much less well understood. Here we review recent advances in the sex-specific regulation of development focusing on two models where this development is increasingly well understood: Sexual dimorphism of body size in the fruit fly Drosophila melanogaster and sexual dimorphism of horns in the horned beetle Onthophagus taurus. Because growth and development are also supported by metabolism, the regulation of sex-specific metabolism during and after development is an important aspect of the generation of female and male phenotypes. Hitherto, the study of sex-specific development has largely been independent of the study of sex-specific metabolism. Nevertheless, as we discuss in this review, recent research has begun to reveal considerable overlap in the cellular and physiological mechanisms that regulate sex-specific development and metabolism.

Morphological, functional, and phylogenetic aspects of the head capsule of the cockroach Ergaula capucina (Insecta/Blattodea)

Background

Cockroaches are usually typical omnivorous detritivores and their cephalic morphology is considered to be ancestral in various aspects. Thus, several studies addressed the morphology and function of the blattodean head, and the cockroach usually serves as a model for standard mouthparts in text books. However, so far only two of the three major lineages of Blattodea have been studied and no detailed information for the head of any Corydioidea was available. The present study closes this gap by providing a detailed morphological description of the head of Ergaula capucina, studying some important functional parameters of the mandible and discussing it in a phylogenetic framework.

Methods

The cephalic morphology of Ergaula studied in detail using a broad set of different techniques including digital microscopy, µ-computed tomography, and 3-dimensional reconstructions. Concerning the functional morphology of the mandible, we compared the volume and effective cross sections of the eight compartments of the primary mandibular adductor muscle for Ergaula, Blattella germanica, and Salganea rossi and measured the mechanical advantage, i.e., the force transmission ratio for all teeth of the mandible of Ergaula.

Results

The head capsule of Ergaula is characterized by a strong sexual dimorphism and typical orthopteran mouthparts. It resembles the head capsule of other roaches in several respects and confirms oesotendons, the reduction of the mesal occelus, and bipartite M. verticopharyngealis and M. hypopharyngosalivaris as blattodean apomorphies. But it also shows some unique adaptations. It is the first described cockroach that lacks the dorsal tentorial arms which has various consequences for the cephalic musculature. On the maxillary lacinia, Ergaula is the first described blattodean to show strong and blunt setae instead of a lacinula, which might be homologues to the dentisetae of dragonflies and mayflies. Like other corydiid roaches that inhabit xeric areas, Ergaula has an atmospheric water-vapor absorption mechanism that includes a gland and a ductus on the epipharnyx and bladders on the hypopharynx. The mandibular adductor is in cockroaches asymmetric, a pattern not found in termites, mantids, or other closely related insects.