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Female‐biased sexual size dimorphism stands as a widespread evolutionary pattern. Fecundity selection, favouring larger females with greater reproductive output, is a leading explanation. However, larger body sizes demand greater energy intake, potentially hindering the evolution of extreme female sizes. Thus, the evolution of more lucrative foraging tactics may allow for an increase in size. Hence, coupled with selection against larger males, fecundity selection should result in larger SSD in species with more lucrative foraging strategies. Crab spiders are sit‐and‐wait predators that hunt in several plant substrata. Species that forage on flowers or employ prey‐luring strategies likely have access to higher food intake than other species. We extracted body size measurements of 614 crab spider species from 43 genera and classified them based on their foraging strategy. Our findings show that foraging strategies that provide higher energy input (EFS) result in larger SSD. Statistical estimates indicate that females have a cephalothorax width 91% larger than males in EFS species, compared to 26% larger females than males in non‐EFS species. These differences possibly arise due to larger females and smaller males. The effects on male size reduction might result from scramble competition, whereas the increase in female size is likely due to fecundity selection. These results suggest that the shift towards more lucrative foraging strategies may have been a key event in body size and SSD evolution in crab spiders. [ABSTRACT FROM AUTHOR]

Sex differences in early‐life survival can drive skewed adult sex ratios (ASR), which play an important role in mating tactics and parental sex roles. Among birds, cuckoos exhibit the largest diversity in mating systems and thus represent an interesting system to study sex‐specific demography.Here we investigate the early‐life survival pathways shaping ASR using long‐term field data and sex‐ and stage‐specific demographic modelling of black coucals and white‐browed coucals—two sympatric Centropus cuckoo species differing in mating system and the extent of sexual size dimorphism.We hypothesized that sexual size dimorphism would lead to differential juvenile mortality due to the greater energy demands and predation risk of the larger sex during maturation. We expected higher early‐life mortality among large‐bodied females in the sexually dimorphic and classically polyandrous black coucal, whereas no bias should exist in the less dimorphic and monogamous white‐browed coucal.Both species had balanced hatching sex ratios, but in black coucals, female survival (μ = 0.64 ± 0.061 SD) was lower during the 'groundling' phase (i.e. a flightless 3‐week period following nest departure) than male survival (0.70 ± 0.066). Yet, this sex difference in survival was not strong enough to account for the species' male‐biased ASR where 70% of the adult population is male. In white‐browed coucals, survival during maturation exhibited high inter‐individual variation but lacked clear sex differences, reflecting the emergence of a balanced ASR.In summary, we found no evidence that the strongly male‐biased ASR of black coucals is driven by sex‐specific survival during maturation. In black coucals, the male‐biased ASR must therefore stem from processes occurring later in life: possibly, larger females are more likely to die during migration and/or the recruitment of young females is delayed due to competitive exclusion by more experienced females.Our results differ from studies on shorebirds, in which sex‐specific mortality of precocial young is related to ASR and mating dynamics. Hence, early‐life sex biases in survival of precocial shorebirds cannot be generalized to other taxonomic groups.Factors other than early‐life sex biases in survival are likely to be important in shaping adult sex ratios and the associated mating dynamics and social behaviours in altricial coucals. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Reproductive patterns observed in organisms are direct outcomes of the interaction among parameters such as phylogeny, body size, and environmental characteristics. However, the action of these parameters is rarely observed in an integrated perspective in the literature. Here, we collected 109 specimens of two congeneric species of treefrogs living in the same microhabitat (bromeligenous species of genus Ololygon) to compare the reproductive patterns of the two species, evaluating the effect of different parameters on the reproductive ecology of the organisms. Our results show that morphometric measurements between females of the two species were not significantly different, indicating similar body sizes. The species exhibited different degrees of sexual dimorphism, and interspecifically, females showed significant differences in breeding traits, with the species O. perpusilla demonstrating higher reproductive effort, characterized by increased ovarian mass and increased average egg size compared to O. littorea. We observed that differences in reproductive effort were strongly associated with egg size, which drove higher reproductive investment in O. perpusilla females. We conclude that although the species share many traits commonly related to the degree of reproductive investment, other drivers, not yet completely understood, may influence the reproductive aspects of organisms, generating unexpected patterns. [ABSTRACT FROM AUTHOR]

An advantage of sex chromosomes may be the potential to reduce sexual conflict because they provide a basis for selection to operate separately on females and males. However, evaluating the relationship between sex chromosomes and sexual conflict is challenging owing to the difficulty in measuring sexual conflict and substantial divergence between species with and without sex chromosomes. We therefore examined sex‐biased gene expression as a proxy for sexual conflict in three sets of Drosophila species with and without young sex chromosomes, the so‐called neo‐sex chromosomes. In all sets, we detected more sex‐biased genes in the species with neo‐sex chromosomes than in the species without neo‐sex chromosomes in larvae, pupae, and adult somatic tissues but not in gonads. In particular, many unbiased genes became either female‐ or male‐biased after linkage to the neo‐sex chromosomes in larvae, despite the low sexual dimorphism. For example, genes involved in metabolism, a key determinant for the rate of development in many animals, were enriched in the genes that acquired sex‐biased expression on the neo‐sex chromosomes at the larval stage. These genes may be targets of sexually antagonistic selection (i.e., large size and rapid development are selected for in females but selected against in males). These results indicate that acquiring neo‐sex chromosomes may have contributed to a reduction in sexual conflict, particularly at the larval stage, in Drosophila.. [ABSTRACT FROM AUTHOR]

Among extant species, the ability to sample the extremes of body size—one of the most useful predictors of an individual's ecology—is highly unlikely. This improbability is further exaggerated when sampling the already incomplete fossil record. We quantify the likelihood of sampling the uppermost limits of body size in the fossil record using Tyrannosaurus rex Osborn, 1905 as a model, selected for its comparatively well‐understood life history parameters. We computationally generate a population of 140 million T. rex (based on prior estimates), modelling variation about the growth curve both with and without sexual dimorphism (the former modelled after Alligator mississippiensis), and building in sampling limitations related to species survivorship and taphonomic bias, derived from fossil data. The 99th percentile of body mass in T. rex has likely already been sampled, but it will probably be millennia before much larger giants (99.99th percentile) are sampled at present collecting rates. Biomechanical and ecological limitations notwithstanding, we estimate that the absolute largest T. rex may have been 70% more massive than the currently largest known specimen (~15,000 vs. ~8800 kg). Body size comparisons of fossil species should be based on ontogenetically controlled statistical parameters, rather than simply comparing the largest known individuals whose recovery is highly subject to sampling intensity. [ABSTRACT FROM AUTHOR]

Abstract Female‐biased sexual size dimorphism stands as a widespread evolutionary pattern. Fecundity selection, favouring larger females with greater reproductive output, is a leading explanation. However, larger body sizes demand greater energy intake, potentially hindering the evolution of extreme female sizes. Thus, the evolution of more lucrative foraging tactics may allow for an increase in size. Hence, coupled with selection against larger males, fecundity selection should result in larger SSD in species with more lucrative foraging strategies. Crab spiders are sit‐and‐wait predators that hunt in several plant substrata. Species that forage on flowers or employ prey‐luring strategies likely have access to higher food intake than other species. We extracted body size measurements of 614 crab spider species from 43 genera and classified them based on their foraging strategy. Our findings show that foraging strategies that provide higher energy input (EFS) result in larger SSD. Statistical estimates indicate that females have a cephalothorax width 91% larger than males in EFS species, compared to 26% larger females than males in non‐EFS species. These differences possibly arise due to larger females and smaller males. The effects on male size reduction might result from scramble competition, whereas the increase in female size is likely due to fecundity selection. These results suggest that the shift towards more lucrative foraging strategies may have been a key event in body size and SSD evolution in crab spiders.

Phyllopezus periosus is the largest phyllodactilid in Brazil, with a relictual distribution in the Caatinga Domain. Herein, we investigated the autecology of P. periosus, describing activity patterns, microhabitat use (spatial niche dimension), foraging mode, body temperature, reproduction, diet (trophic niche dimension), and temperature. Also, we tested the influence of seasonality and ontogeny on these biological aspects. Geckos (n = 116, 54 females, 33 males, and 29 juveniles) were sampled from October 2013 to September 2014. Phyllopezus periosus has an unimodal activity pattern, with peak activity in the early hours of the night. Males are more robust than females, and forelimbs in females are longer than in males. The body temperatures of this thermoconformer gecko are higher in the dry season. The reproductive season begins in the early dry season, with a fixed clutch of two eggs. Although we did not find evidence of more than one clutch per year, the studied population of P. periosus reproduces for an extended period throughout the dry season, as highlighted by the presence of juveniles all year. Phyllopezus periosus is saxicolous and presents a generalist diet composed mainly of arthropods, also including vertebrates such as frogs and lizards. [ABSTRACT FROM AUTHOR]

In most colony-breeding species, biparental care during both egg incubation and chick-rearing is inevitable for successful reproduction, requiring parents to coordinate their nest attendance and foraging time. The extent to which the rhythm of nest attendance is adjusted to temporal and spatial variation in food availability is poorly understood. Here, we investigate whether the rhythm of nest attendance interacts with the spatial and temporal availability of foraging habitats in Eurasian spoonbills Platalea leucorodia breeding on Schiermonnikoog, a Dutch Wadden Sea barrier island. Spoonbills are tactile foragers that forage during both day and night in habitats of varying salinity. GPS-tracking combined with acceleration-based behavioral classification of 9 female and 13 male adult spoonbills between 2013 and 2019 revealed that, despite nearby foraging opportunities following a tidal rhythm, nest attendance followed a sex-specific diel rhythm. During incubation and chick-rearing, females attended the nest at night and foraged during the day, while males showed the reverse rhythm. Females made more and shorter foraging trips to, almost exclusively, nearby marine habitats, whereas the larger males often made long trips to forage in more distant freshwater habitats. Before and after breeding, females as well as males foraged primarily at night, suggesting that this is the preferred period of foraging for both sexes. Nevertheless, foraging habitat use remained sex-specific, being most likely explained by size-dependent foraging techniques. To conclude, the sex-specific rhythm of nest attendance is not shaped by the spatial and temporal availability of foraging habitats. [ABSTRACT FROM AUTHOR]

Poison frogs of the superfamily Dendrobatoidea have fascinated researchers since the 19th century, which is reflected in multiple studies on their natural history, taxonomy, toxicity, colour pattern diversity, and elaborate territorial, reproductive and parental care behaviours. Broadly speaking, however, the term "poison frogs" may apply as well to other taxa which also possess skin toxins. Hereon, we refer to poison frogs as this extended group involving, besides Dendrobatoidea (Dendrobatidae + Aromobatidae), a few genera in families such as Bufonidae and Mantellidae (among others). Most studies on poison frogs have focused on species considered charismatic due to their bright and flashy colours, limiting possible generalisations of patterns and mechanisms explaining the high morphological, ecological, and behavioural differentiation, but also convergence, among these groups. Furthering our understanding of the evolutionary ecology of poison frogs requires increasing not only the scope and depth of our own questions, but also the number and diversity of study systems. Inspired by the special issue on dendrobatid and aromobatid poison frogs published ten years ago in this same journal, we have put together the present special issue aiming to broaden both the topics and the coverage of poison frog clades. This first part consists of 15 manuscripts covering topics ranging from larval behavioural ecology and parental care to space use and its environmental determinants, along with conservation implications. [ABSTRACT FROM AUTHOR]

Abstract An advantage of sex chromosomes may be the potential to reduce sexual conflict because they provide a basis for selection to operate separately on females and males. However, evaluating the relationship between sex chromosomes and sexual conflict is challenging owing to the difficulty in measuring sexual conflict and substantial divergence between species with and without sex chromosomes. We therefore examined sex‐biased gene expression as a proxy for sexual conflict in three sets of Drosophila species with and without young sex chromosomes, the so‐called neo‐sex chromosomes. In all sets, we detected more sex‐biased genes in the species with neo‐sex chromosomes than in the species without neo‐sex chromosomes in larvae, pupae, and adult somatic tissues but not in gonads. In particular, many unbiased genes became either female‐ or male‐biased after linkage to the neo‐sex chromosomes in larvae, despite the low sexual dimorphism. For example, genes involved in metabolism, a key determinant for the rate of development in many animals, were enriched in the genes that acquired sex‐biased expression on the neo‐sex chromosomes at the larval stage. These genes may be targets of sexually antagonistic selection (i.e., large size and rapid development are selected for in females but selected against in males). These results indicate that acquiring neo‐sex chromosomes may have contributed to a reduction in sexual conflict, particularly at the larval stage, in Drosophila..

Abstract Among extant species, the ability to sample the extremes of body size—one of the most useful predictors of an individual's ecology—is highly unlikely. This improbability is further exaggerated when sampling the already incomplete fossil record. We quantify the likelihood of sampling the uppermost limits of body size in the fossil record using Tyrannosaurus rex Osborn, 1905 as a model, selected for its comparatively well‐understood life history parameters. We computationally generate a population of 140 million T. rex (based on prior estimates), modelling variation about the growth curve both with and without sexual dimorphism (the former modelled after Alligator mississippiensis), and building in sampling limitations related to species survivorship and taphonomic bias, derived from fossil data. The 99th percentile of body mass in T. rex has likely already been sampled, but it will probably be millennia before much larger giants (99.99th percentile) are sampled at present collecting rates. Biomechanical and ecological limitations notwithstanding, we estimate that the absolute largest T. rex may have been 70% more massive than the currently largest known specimen (~15,000 vs. ~8800 kg). Body size comparisons of fossil species should be based on ontogenetically controlled statistical parameters, rather than simply comparing the largest known individuals whose recovery is highly subject to sampling intensity.

Simple Summary: The sex chromosome, especially specific in one sex, is considered to determine the sexual size dimorphism (SSD), a dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish unique in China, the important role of female-specific chromosome W in its female-biased SSD was previously implied. Furthermore, a W chromosome-specific gene zbed1 was identified to potentially regulate female-biased SSD in C. semilaevis. However, the chromosome's location, family members, and detailed network information are still unknown. At present, the genome-wide identification of ZBED family members and dPCR experiment both confirm that three copies of the zbed1 gene are located in chromosome W, with no zbed1 gene in chromosome Z. Phylogenetic analysis for ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis, clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. For the chromosome-W-specific zbed1, qPCR verified its predominant expression in the female brain and pituitary tissues. The dual luciferase activity test showed that transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor dmrt1. In addition, after zbed1 interfered in the brain cells, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes (tbp, cdk2, cdk4, cdk6, ccng1 and ccndx) were down-regulated. It is suggested that the cell proliferation function of zbed1 may be realized by regulating esr2, piwil1, cell cycle and the Wnt pathway. The sex chromosome, especially specific in one sex, generally determines sexual size dimorphism (SSD), a phenomenon with dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish in China, although the importance of chromosome W and its specific gene zbed1 in female-biased SSD have been suggested, its family members and regulation information are still unknown. At present, three zbed1 copies gene were identified on chromosome W, with no gametologs. Phylogenetic analysis for the ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis, clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. The predominant expression of zbed1 in the female brain and pituitary tissues was further verified by qPCR. Transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor-dmrt1. When zbed1 was interfered with, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes, including cdk4 and ccng1, were down-regulated. Thus, zbed1 is involved in cell proliferation by regulating esr2, piwil1, cell cycle and the Wnt pathway. Further research on their interactions would be helpful to understand fish SSD. [ABSTRACT FROM AUTHOR]

Adults of the migratory locust Locusta migratoria (Linnaeus, 1758) were collected in the Japanese Archipelago, which extends from the Ryukyu subtropical region to the Hokkaido cool-temperate region, covering more than 2,500 km. A saw-toothed pattern was observed in body size along the latitudinal or annual mean temperature gradient, which is similar to Masaki's clines initially described for crickets. The latitudinal cline of locusts was also observed in the laboratory, suggesting that this cline was primarily due to genetic variation. In the northern univoltine zone, locust body size increased toward the south. The latitudinal size trend was reversed in the transitional zones where the voltinism shifted from univoltine to bivoltine and from bivoltine to trivoltine life cycles. These patterns may be explained by changes in the length of the growing season for development and reproduction. Body size varied with growth efficiency but not with the variable lengths of nymphal development. Larger females had more ovarioles and produced fatter egg pods containing more eggs per pod. The morphometric ratio, F/C (hind femur length/head width), tended to decrease with latitude, but this characteristic could be primarily due to phylogenetic differences between the northern and southern clades. It was confirmed that F/C ratio decreased when the locusts were reared in a group. The sexual size dimorphism, or SSD, tended to increase as the mean body sizes of populations increased, converse to Rensch's rule. The relative body size of females and males correlated with latitude and was greatly reduced when the insects were reared in a group. The smaller rate of increase at higher latitudes may be related to male-female associations and predation pressure. [ABSTRACT FROM AUTHOR]

Ambotuy: Favoring males' specific sexual signals, female preferences play a major role in frogs' evolutionary process by selecting traits linked to those signals. However, the factors constraining and determining those preferences are scarcely explored in an evolutionary background. Here, through a phylogenetic comparative approach we check whether anuran species phylogenetic proximity and calling site predicts female preferences for dominant frequency and whether those preferences influence species sexual size dimorphism. Our hypotheses are as follows: 1) closer species have similar females' preferences related to the dominant frequency of the partners' calls; 2) the calling site influences sound propagation and consequently the preference of females for the dominant frequency of the males' calls; and 3) the preference for calls with low dominant frequency influences the size of the males and consequent reduction of the biSased dimorphism for females. We did not find support for our hypotheses, neither for the influence of phylogenetic proximity nor for calling site determining these preferences. Moreover, female preferences did not impact on species sexual size dimorphism. Besides shedding light into our hypotheses, this study represents a considerable advance on evolutionary studies of female preferences in anura, which still lacks broad species comparative approaches. Furthermore, we suggest future studies to expand knowledge regarding frogs' female preferences. Significance statement: This study advances our comprehension of female preferences in frogs by investigating the factors that shape these preferences and their implications for species sexual size dimorphism. Utilizing phylogenetic comparative methods, an approach rarely used in the context of anuran female preferences, this study represents a significant step in applying broad comparative approaches in this field. Highlighting the complex nature of mate choice and its relationship to morphology, soundscape, and phylogeny, we present important insights into evolutionary hypotheses related to female preferences. Lastly, we provide advice on how future studies could further explore this topic in a broader comparative framework while also discussing the limitations of available data on anuran mating preferences. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism (SSD) is a common phenomenon across the animal kingdom. Mammals are unusual in primarily displaying male-biased SSD, where males of a species are typically larger than females. The driving factors behind the evolution of this SSD have been much debated, with popular hypotheses invoking the influence of mating system and social organization via sexual selection, dietary niche divergence and broad-scale correlations with body size (Rensch's rule). Here, we investigate the macroevolutionary origins and maintenance of SSD among mammals, using phylogenetic general mixed linear models and a comprehensive global dataset to evaluate correlations of diet, body mass, seasonality, social organization and mating system with SSD type. We find that SSD as a whole is lost at a greater rate than it is gained, with female-biased SSD being particularly unstable. Non-monogamous mating systems, vertebrate prey consumption and temperature seasonality correlate with male-biased SSD, while polyandry correlates with female-biased SSD, and both types of SSD are positively correlated with body mass. This is in partial contrast to the predictions of Rensch's rule, which predicts that female-biased SSD would correlate negatively with body size. Taken together, our results highlight the importance of considering multiple ecological and social drivers when evaluating the macroevolutionary trajectory of sex differences in body size. [ABSTRACT FROM AUTHOR]

Parasitism is nearly ubiquitous in animals and is frequently associated with fitness costs in host organisms, including reduced growth, foraging, and reproduction. In many species, males tend to be more heavily parasitized than females and thus may bear greater costs of parasitism. Sceloporus undulatus is a female‐larger, sexually size dimorphic lizard species that is heavily parasitized by chigger mites (Eutrombicula alfreddugesi). In particular, the intensity of mite parasitism is higher in male than in female juveniles during the period of time when sex differences in growth rate lead to the development of sexual size dimorphism (SSD). Sex‐biased differences in fitness costs of parasitism have been documented in other species. We investigated whether there are growth costs of mite ectoparasitism, at a time coinciding with sex differences in growth rate and the onset of SSD. If there are sex‐biased growth costs of parasitism, then this could suggest a contribution to the development of SSD in S. undulatus. We measured growth and mite loads in two cohorts of unmanipulated, field‐active yearlings by conducting descriptive mark‐recapture studies during the activity seasons of 2016 and 2019. Yearling males had consistently higher mid‐summer mite loads and consistently lower growth rates than females. However, we found that growth rate and body condition were independent of mite load in both sexes. Furthermore, growth rates and mite loads were higher in 2019 than in 2016. Our findings suggest that juveniles of S. undulatus are highly tolerant of chigger mites and that any costs imposed by mites may be at the expense of functions other than growth. We conclude that sex‐biased mite ectoparasitism does not contribute to sex differences in growth rate and, therefore, does not contribute to the development of SSD. [ABSTRACT FROM AUTHOR]

Abstract Parasitism is nearly ubiquitous in animals and is frequently associated with fitness costs in host organisms, including reduced growth, foraging, and reproduction. In many species, males tend to be more heavily parasitized than females and thus may bear greater costs of parasitism. Sceloporus undulatus is a female‐larger, sexually size dimorphic lizard species that is heavily parasitized by chigger mites (Eutrombicula alfreddugesi). In particular, the intensity of mite parasitism is higher in male than in female juveniles during the period of time when sex differences in growth rate lead to the development of sexual size dimorphism (SSD). Sex‐biased differences in fitness costs of parasitism have been documented in other species. We investigated whether there are growth costs of mite ectoparasitism, at a time coinciding with sex differences in growth rate and the onset of SSD. If there are sex‐biased growth costs of parasitism, then this could suggest a contribution to the development of SSD in S. undulatus. We measured growth and mite loads in two cohorts of unmanipulated, field‐active yearlings by conducting descriptive mark‐recapture studies during the activity seasons of 2016 and 2019. Yearling males had consistently higher mid‐summer mite loads and consistently lower growth rates than females. However, we found that growth rate and body condition were independent of mite load in both sexes. Furthermore, growth rates and mite loads were higher in 2019 than in 2016. Our findings suggest that juveniles of S. undulatus are highly tolerant of chigger mites and that any costs imposed by mites may be at the expense of functions other than growth. We conclude that sex‐biased mite ectoparasitism does not contribute to sex differences in growth rate and, therefore, does not contribute to the development of SSD.

Fitness consequences of early‐life environmental conditions are often sex‐specific, but corresponding evidence for invertebrates remains inconclusive. Here, we use meta‐analysis to evaluate sex‐specific sensitivity to larval nutritional conditions in insects. Using literature‐derived data for 85 species with broad phylogenetic and ecological coverage, we show that females are generally more sensitive to food stress than males. Stressful nutritional conditions during larval development typically lead to female‐biased mortality and thus increasingly male‐biased sex ratios of emerging adults. We further demonstrate that the general trend of higher sensitivity to food stress in females can primarily be attributed to their typically larger body size in insects and hence higher energy needs during development. By contrast, there is no consistent evidence of sex‐biased sensitivity in sexually size‐monomorphic species. Drawing conclusions regarding sex‐biased sensitivity in species with male‐biased size dimorphism remains to wait for the accumulation of relevant data. Our results suggest that environmental conditions leading to elevated juvenile mortality may potentially affect the performance of insect populations further by reducing the proportion of females among individuals reaching reproductive age. Accounting for sex‐biased mortality is therefore essential to understanding the dynamics and demography of insect populations, not least importantly in the context of ongoing insect declines. [ABSTRACT FROM AUTHOR]

Abstract The mass of a bird’s egg is a critical attribute of the species’ life history and represents a fundamental component of reproductive effort. Indeed, the tradeoff between the number of eggs in a clutch and clutch mass lies at the heart of understanding how environmental attributes such as nest predation or adult mortality influence reproductive investment. However, egg masses have not been reported for the majority of avian species. We capitalized on the strong allometric relationship between avian body mass and egg mass to produce egg mass estimates for over 5,500 species previously lacking such information. These estimates are accompanied by measures of the robustness of the regressions used to produce them (e.g., sample size, root mean square error [RMSE] of estimation, coefficient of determination, and degree of extrapolation), thus allowing independent evaluation of the suitability of any estimate to address a particular research question relating to avian life history. Most estimates (~5,000) were based on family-level egg mass–body mass regressions, with the remainder derived from other relationships such as ordinal regressions. We compared estimating regressions based on adult vs. female body masses and, after finding little difference between the 2, based our final estimates on adult masses as those were more numerous in the literature. What small differences between adult- and female-based regressions that did occur were not related to sexual size dimorphism across families. These new estimates, coupled with ~5,000 egg masses reported in the literature, provide a foundation of over 10,000 species for wider investigations assessing variation in reproductive effort in birds over a broad array of ecological and evolutionary contexts.

Abstract The mass of a bird’s egg is a critical attribute of the species’ life history and represents a fundamental component of reproductive effort. Indeed, the tradeoff between the number of eggs in a clutch and clutch mass lies at the heart of understanding how environmental attributes such as nest predation or adult mortality influence reproductive investment. However, egg masses have not been reported for the majority of avian species. We capitalized on the strong allometric relationship between avian body mass and egg mass to produce egg mass estimates for over 5,500 species previously lacking such information. These estimates are accompanied by measures of the robustness of the regressions used to produce them (e.g., sample size, root mean square error [RMSE] of estimation, coefficient of determination, and degree of extrapolation), thus allowing independent evaluation of the suitability of any estimate to address a particular research question relating to avian life history. Most estimates (~5,000) were based on family-level egg mass–body mass regressions, with the remainder derived from other relationships such as ordinal regressions. We compared estimating regressions based on adult vs. female body masses and, after finding little difference between the 2, based our final estimates on adult masses as those were more numerous in the literature. What small differences between adult- and female-based regressions that did occur were not related to sexual size dimorphism across families. These new estimates, coupled with ~5,000 egg masses reported in the literature, provide a foundation of over 10,000 species for wider investigations assessing variation in reproductive effort in birds over a broad array of ecological and evolutionary contexts.

Abstract 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.

Simple Summary: Previous studies had reported sex-biased parasitism (SBP) in small rodents. In this study, we investigate the prevalence of six intestinal parasites in Brandt's voles (Lasiopodomys brandtii) that were captured in May, June, July, and August 2022 around the Xilingol Grassland in Inner Mongolia, China. Syphacia obvelata, Aspiculuris tetraptera, and the Trichostrongylidae family were the dominant intestinal parasites for the Brandt's voles captured in the study areas. Season and human activities such as grazing had no significant effect on the infection rates of parasites, but the parasite reproduction level was higher when the ambient temperature was around 18 °C. We found that the sexual size dimorphism (SSD) was ubiquitous in Brandt's voles, and males had bigger body sizes than females. Simple linear regression analysis showed a significant positive correlation between bodyweight and parasite infection rates, so the sex-biased parasitism in Brandt's voles could be explained by the body size hypothesis, as a larger body could provide more ecological niches for parasitic infection. The abundance and prevalence of parasitic infection often vary in different host sexes, and this phenomenon has been named sex-biased parasitism. Brandt's voles are the dominant rodent species in typical steppe habitat and are widely distributed in Inner Mongolia, China, but the prevalence of parasites in Brandt's voles are poorly reported. In this study, we investigated the prevalence of six intestinal parasites in Brandt's voles in May, June, July, and August 2022 around the Xilingol Grassland in Inner Mongolia, China. The results showed that Syphacia obvelata, Aspiculuris tetraptera, and Trichostrongylidae family were the dominant intestinal parasites in Brandt's voles that we captured in this study, and the infection rates of the three parasites were significantly higher in males than females, which showed obvious male-biased parasitism. Season and human activities such as grazing had no significant effect on the infection rates for different parasites, while the parasite reproduction level was higher when the ambient temperature was around 18 °C. Sexual size dimorphism was ubiquitous in Brandt's voles, and it was mainly manifested by the differences in body weight and length between males and females. Simple linear regression analysis showed a significant positive correlation between bodyweight and parasite infection rates, so the sex-biased parasitism in Brandt's voles could be explained by the body size hypothesis, as a larger body could provide more ecological niches for parasitic infection. [ABSTRACT FROM AUTHOR]

The sex chromosome, especially specific in one sex, generally determines sexual size dimorphism (SSD), a phenomenon with dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish in China, although the importance of chromosome W and its specific gene zbed1 in female-biased SSD have been suggested, its family members and regulation information are still unknown. At present, three zbed1 copies gene were identified on chromosome W, with no gametologs. Phylogenetic analysis for the ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis, clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. The predominant expression of zbed1 in the female brain and pituitary tissues was further verified by qPCR. Transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor-dmrt1. When zbed1 was interfered with, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes, including cdk4 and ccng1, were down-regulated. Thus, zbed1 is involved in cell proliferation by regulating esr2, piwil1, cell cycle and the Wnt pathway. Further research on their interactions would be helpful to understand fish SSD.

Body size is a trait of fundamental ecological and evolutionary importance that is often different between males and females (sexual size dimorphism; SSD). The island rule predicts that small-bodied species tend to evolve larger following a release from interspecific competition and predation in insular environments. According to Rensch’s rule, male body size relative to female body size increases with increasing mean body size. This allometric body size – SSD scaling is explained by male-driven body size evolution. These ecogeographical rules are rarely tested within species, and has not been addressed in a cave–surface context, even though caves represent insular environments (small and isolated with simple communities). By analyzing six cave and nine surface populations of the widespread, primarily surface-dwelling freshwater isopod Asellus aquaticus with male-biased SSD, we tested whether cave populations evolved larger and showed higher SSD than the surface populations. We found extensive between-population variation in body size (maximum divergence being 74%) and SSD (males being 15%–50% larger than females). However, habitat type did not explain the body size and SSD variation and we could not reject isometry in the male–female body size relationship. Hence, we found no support for the island or Rensch’s rules. We conclude that local selective forces stemming from environmental factors other than island vs. mainland or the general surface vs. cave characteristics are responsible for the reported population variation.

Background: Cobia (Rachycentron canadum) is a species of fish with high commercial potential particularly due to fast growth rates. The evidence of sexual size dimorphism favoring females indicate potential benefits in having a monosex culture. However, the involvement of genetic factors responsible for sexual development and gonadal maintenance that produces phenotypic sex in cobia is largely unknown.Methods: In the present study, we performed transcriptome sequencing of cobia to identify sex-biased significantly differentially expressed genes (DEGs) in testes and ovaries. The reliability of the gonad transcriptome data was validated by qPCR analysis of eight selected significantly differential expressed sex-related candidate genes.Results: This comparative gonad transcriptomic analysis revealed that 7,120 and 4,628 DEGs are up-regulated in testes or ovaries, respectively. Further functional annotation analyses identified 76 important candidate genes involved in sex determination cascades or sex differentiation, including 42 known testis-biased DEGs (dmrt1, amh and sox9 etc.), and 34 known ovary-biased DEGs (foxl2, sox3 and cyp19a etc.). Moreover, eleven significantly enriched pathways functionally related to sex determination and sex differentiation were identified, including Wnt signaling pathway, oocyte meiosis, the TGF-beta signaling pathway and MAPK signaling pathway.Conclusion: This work represents the first comparative gonad transcriptome study in cobia. The putative sex-associated DEGs and pathways provide an important molecular basis for further investigation of cobia’s sex determination, gonadal development as well as potential control breeding of monosex female populations for a possible aquaculture setting.

Sexual dimorphism is a very common strategy in polygamous mammals. In mustelids, sexual size dimorphism (SSD) is present in several species, while sexual shape dimorphism (SShD) is not as common. The Eurasian otter is a semiaquatic mustelid, exclusively feeding on aquatic prey, mainly fish, amphibians, and crustaceans. It is well-known that male otters tend to be larger, whereas information on SShD is contrasting. We used a 3D geometric morphometric approach to investigate SSD and SShD in three genetically distinct populations of otters located in Northern, Central and Southern Sweden. We analyzed 71 otter skulls (M=41, F=30), using photogrammetric techniques to produce 3D models of each skull, placing 30 3D landmarks on each model. We found that sexual dimorphism varies among populations. Neither SSD nor SShD occurred in the North, only SSD occurred in the Centre, and both SSD and SShD are present in the South of Sweden. Allometric trajectories of males and females from the North population differed from those of the other two populations. Our results highlighted a great variability in sexual dimorphism in Swedish Eurasian otters, that probably derives from different responses to prey availability and historical contingencies. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug is a relatively new member of the Croatian entomofauna, whose biology and ecology are still being researched. The species is known for its polyphagy and is invasive, as evidenced by damage to field, vegetable, and fruit crops around the world. The aim of this study was to determine the sexual dimorphism of Halyomorpha halys based on phenotypic characters on the dorsal and ventral sides of the body. Sixty individuals of each sex were isolated. Each individual was photographed from the dorsal and ventral sides using a digital camera, then the forewing and hindwing pairs were removed, mounted on microscope slides, and photographed. Photographs of the dorsal side of the body were used to measure the values of body length, pronotum width, body surface area, and the surfaces of the forewing and hindwing pairs. Differences on the ventral side of the body were determined by visual inspection. The results of the study showed that males and females differed statistically in all measurements and that the species exhibited female-biased sexual size dimorphism. These traits (larger and more powerful physique and especially wings) make females the more suitable sex for migratory flight and thus responsible for the rapid expansion of the population into new areas. Differences between the sexes have also been noted in coloration on the ventral side of the body. The red pigmentation of the sternum was much more pronounced in males than in females, further confirming the sexual dimorphism of the species in body coloration.

The role of bare body parts in sexual signalling in birds has received relatively little attention. I describe how the bare-throated spurfowl males saturate the colours of their throats to attract females. Of the 23 Afrotropical spurfowl species, the bare-throated subgroup includes Yellow-necked Spurfowl (Pternistis leucosceptus), Red-necked Spurfowl (P. afer), Grey-breasted Spurfowl (P. rufopictus) and Swainson's Spurfowl (P. swainsonii). The rest of the species include fully feathered throated spurfowls. Throat colour intensity of bare throats was scored using an extensive online digital photographic archive encompassing the four species across the year's seasons. Each throat (n ​= ​836) was assigned to one of four colour-intensity categories to explore the relationship between colour intensities, breeding cycles, and environmental variation. Except for Swainson's Spurfowl male saturation of throat colours correlated with monthly rainfall, which peaks one or two months before egg laying. Swainson's Spurfowl peaks during egg laying. Yellow-necked Spurfowl has the largest bare throat. Bare-throated spurfowl males perform an elevated courtship display posture above the female to feature their throat colour. No such displays occur in feather-throated spurfowl. Males with low throat colour saturation harbour more ectoparasites on their bare throats than birds with saturated throats. Male Red-necked Spurfowls have significantly larger bare throats than females. The primary function of bare throats probably assists in thermoregulation, particularly in arid regions. The bare throat may have evolved a secondary role in mating. Yellow-necked, Red-necked, and Grey-breasted Spurfowls use their saturated throat colours as ornaments to court females during the breeding season. Unobtrusive female throat colours (unsaturated) may discourage male interlopers and predation during egg laying. Saturation appears to be carotenoid-food based. The different colours among the bare-throated species may serve as prezygotic mechanisms that inhibit cross-breeding and explain why females also have coloured throats.

Understanding evolutionary phenomena that involve size assortative mating requires elucidating the generating mechanisms on which assortment is based. Although various mechanisms have been suggested, their relative importance may differ across taxonomic groups. Males selecting for large, fecund females combined with the dominance of large males in the competition for females has been suggested as a major mechanism in specific groups. However, raptors do not appear to conform to this, because the selection for smallness among males (assumed in a theory of reversed sexual size dimorphism) and the selection for largeness among males (assumed in the theory of size assortative mating) are in opposite directions. We studied the assortative mating during a long‐term study of the Ryukyu Scops Owls Otus elegans interpositus. Significant assortative mating was found for culmen length (from the base to the tip of the bill) and wing length (from the bend of the wing to the tip of the longest primary). Statistical control of the spatial and temporal accessibility of potential mates did not affect the assortment. Males with short wings had slightly higher fitness components than those with long wings, and females settling early tended to have small wings. Considering that early‐settling females can preferentially choose their mates, these results suggest that smaller females have an advantage when choosing smaller males with good reproductive performance. Improved flying and hunting ability of smaller individuals may be the background of choosing smaller individuals. We propose that, not passive process like similarity between individuals and their potential mates, but active mate choice for small individuals is an explanation for the assortative mating in this owl. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Simple Summary: Chinese tongue sole (Cynoglossus semilaevis) typically displays female-biased sexual size dimorphism (SSD), but its epigenetic regulatory mechanisms are poorly understood, especially the role of circRNAs. To explore the function of circRNAs in Chinese tongue sole SSD, we firstly identified differentially expressed circular RNAs (DE circRNAs) in female, male, and pseudo-male C. semilaevis. Secondly, the ceRNA network containing DE circRNAs, miRNAs, and mRNAs in the three genders was constructed. Among the ceRNA network, several circRNAs such as novel_circ_004374 and novel_circ_014597 may regulate hipk2 expression by sponging miR-130-x. It is also worth exploring whether or how novel_circ_008696 regulates setd2 by binding to novel-m0387-3p. The present study provided the cirRNA and its ceRNA network that potentially regulate C. semileavis female-biased SSD for the first time. Sexual size dimorphism (SSD), which is the sexual differences in body size, has been widely reported in various species including fishes. For Chinese tongue sole (Cynoglossus semilaevis), a flatfish exhibiting typically female-biased SSD, little is known for its epigenetic regulation mechanism, especially the role of circRNAs. Here, we identified the differently expressed abundances of circRNAs in females, males, and pseudo-males to explore the potential functions of circRNAs in Chinese tongue sole SSD. In total, 14,745 novel circRNAs were screened, among which 1461 DE circRNAs were identified from the brain, gonad, liver, and muscle in female, male, and pseudo-male individuals. The ceRNA network was subsequently constructed, including 10 circRNAs, 26 mRNAs, and 11 miRNAs. These DE mRNAs were mainly related to the mRNA surveillance pathway, metabolic pathways, and cellular senescence. Importantly, the ceRNA network has revealed that several circRNAs such as novel_circ_004374 and novel_circ_014597 may regulate homeodomain interacting protein kinase 2 (hipk2) expression by sponging miR-130-x. It is also worth exploring whether or how novel_circ_008696 regulates SET Domain Containing 2, histone lysine methyltransferase (setd2), which in turn affects the epigenetic patterns of different sexual individuals. The present study not only enriches the knowledge on the potential roles of circRNA in the physiological process, but also provides new clues for the explanation of fish SSD. In future studies, the precise function and involvement of circRNAs in female-biased SSD will require more efforts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Squamate reptiles have been considered to be indeterminate growers for a long time. However, recent studies demonstrate that bone prolongation is stopped in many lizards by the closure of bone growth plates. This shift in the paradigm of lizard growth has important consequences for questions concerning the proximate causes of sexual size dimorphism. The traditional model of highly plastic and indeterminate growth would correspond more to a long-term action of a sex-specific growth regulator. On the other hand, determinate growth would be more consistent with a regulator acting in a sex-specific manner on the activity of bone growth plates operating during the phase when a dimorphism in size develops. We followed the growth of males and females of the male-larger Madagascar ground gecko (Paroedura picta) and monitored the activity of bone growth plates, gonad size, levels of steroids, expression of their receptors (AR, ESR1), and expression of genes from the insulin-like growth factor network (IGF1, IGF2, IGF1R, and IGF2R) in livers. Specifically, we measured gene expression before the onset of dimorphic growth, at the time when males have more active bone growth plates and sexual size dimorphism was clearly visible, and after a period of pronounced growth in both sexes. We found a significant spike in the expression of IGF1 in males around the time when dimorphism develops. This overexpression in males comes long after an increase in circulating testosterone levels and sexual maturation in males, and it might be suppressed by ovarian hormones in females. The results suggest that sexual size dimorphism in male-larger lizards can be caused by a positive effect of high levels of IGF1 on bone growth. The peak in IGF1 resembles the situation during the pubertal growth spurt in humans, but in lizards, it seems to be sex-specific and disconnected from sexual maturation. [ABSTRACT FROM AUTHOR]

The abundance and prevalence of parasitic infection often vary in different host sexes, and this phenomenon has been named sex-biased parasitism. Brandt’s voles are the dominant rodent species in typical steppe habitat and are widely distributed in Inner Mongolia, China, but the prevalence of parasites in Brandt’s voles are poorly reported. In this study, we investigated the prevalence of six intestinal parasites in Brandt’s voles in May, June, July, and August 2022 around the Xilingol Grassland in Inner Mongolia, China. The results showed that Syphacia obvelata, Aspiculuris tetraptera, and Trichostrongylidae family were the dominant intestinal parasites in Brandt’s voles that we captured in this study, and the infection rates of the three parasites were significantly higher in males than females, which showed obvious male-biased parasitism. Season and human activities such as grazing had no significant effect on the infection rates for different parasites, while the parasite reproduction level was higher when the ambient temperature was around 18 °C. Sexual size dimorphism was ubiquitous in Brandt’s voles, and it was mainly manifested by the differences in body weight and length between males and females. Simple linear regression analysis showed a significant positive correlation between bodyweight and parasite infection rates, so the sex-biased parasitism in Brandt’s voles could be explained by the body size hypothesis, as a larger body could provide more ecological niches for parasitic infection.

Simple Summary: Age determination is very important for observing life history traits, evaluating vulnerable life stages, and setting proper management and conservation strategies. Age determination in animals has always been tricky. Among other approaches, skeletochronology, an age determination method that involves counting the lines of arrested growth (LAGs) produced during inactive periods, similar to plant year rings, is well-practiced in many animal groups. However, the applicability of this method remains questioned for many species, including amphibians, because of concerns around the scarcity of information on confirmed numbers of annual LAGs (e.g., once or twice in a year), chances of the disappearance of LAGs over time, and which lines exactly to count. Herein, we tested its applicability to Kaloula borealis, a class II endangered amphibian in South Korea, by rearing juveniles in the laboratory for more than one year and comparing the results with the wild population at Lake Sihwa. This study confirmed the formation of one LAG each year and no disappearance of LAGs over time in this species. Furthermore, we were also able to determine the age structure of this wild population accurately. Hence, our study validates using skeletochronology in this species and recommends it for others that show similar growth patterns. Despite having some limitations, the use of skeletochronology—age determination by counting lines of arrested growth (LAGs)—in amphibians is increasing. The main limitation of using skeletochronology is identifying the innermost visible line (IVL) and counting the exact number of LAGs. Thus, we tested its applicability to Kaloula borealis, a class II endangered amphibian in South Korea. We reared juveniles in the lab to investigate the process of bone formation. This confirmed the development of one LAG each year. Hence, our study validates skeletochronology for the age determination of this species and recommends it for others that show similar growth patterns. Furthermore, the comparison of threshold diameters with the IVL of wild individuals confirmed no LAG1 resorption. The average age of males and females in this population was 2.75 ± 1.05 and 3.64 ± 3 years, respectively. We estimated sexual maturity at 2 years with rapid growth up to that stage in both sexes. We found a female-dominated sexual size dimorphism. This study offers accurate information on the life history traits and age structure of K. borealis that may help to evaluate population dynamics in other areas, identify vulnerable life stages and sites, assess the causes of population decline, and set conservation priorities. [ABSTRACT FROM AUTHOR]

Sexual cannibalism is common in many species of arachnids. Studies investigating Dolomedes tenebrosus Hentz, 1844, have even discovered the occurrence of obligatory male self-sacrifice during copulation. In this system, females subsequently cannibalize males, and this cannibalism leads to higher fitness for both partners. Unfortunately, our understanding of the evolution of such an extreme mating system is challenged by the absence of information for close relatives. To that end, this study explores the courtship behavior, mating system and cannibalism dynamics of the spider Dolomedes scriptus Hentz, 1845. To determine whether female and male D. scriptus mate multiply, we recorded interactions of repeatedly exposed focal females and focal males to new mating partners for three days. We also quantified attacks and cannibalism events that occurred both before and after every copulation. We found male D. scriptus court females by waving their forelegs during their approach and tapping the females prior to mounting. In our remating trials, none of the female D. scriptus accepted additional males after their first mating over the three-day period. In contrast, male D. scriptus were polygynous, often mating with multiple females. Across the trials, sexual size dimorphism was a predictor of whether mating occurred, with similarly sized pairs being more likely to mate. Additionally, previously mated females were less likely to cannibalize males--an unusual pattern for spiders. Like other species of Dolomedes Latreille, 1804, our results suggest a strong role of female aggression in D. scriptus mating system dynamics. [ABSTRACT FROM AUTHOR]

Calliphora vicina Robineau-Desvoidy is a primary colonizing species of decomposing bodies, being predominant in the cold seasons in Buenos Aires province, Argentina. The minimum post-mortem interval (PMImin) was estimated using growth and larval length parameters as the accurate entomological evidence of the elapsed time since death. Specimens were reared at 12, 14, 16, and 18 °C, and the larval and pupal growth rates were determined. Differences in the developmental times were registered (43.2 days at 12 °C, 34.3 days at 14 °C, 29.1 days at 16 °C, and 24.3 days at 18 °C), with the lifespan shortened at higher temperatures, without changing the larval length range (-1.5--18.0 mm). Temperature also influenced the survival and size of emerged adults; the highest percentage of survival registered at 14 (29.73%) and 16 °C (38.65%), and more mortality in extreme temperatures (19.00% at 12 °C and 12.61% at 18 °C). Adults reared at 12 °C were the largest of all, females were longer than males, and body size showed an inverse relationship with survival. These results allowed the PMI estimation based on data from local populations instead of consulting papers based on other regions. [ABSTRACT FROM AUTHOR]

We investigated morphological differences between sexes, and mating patterns respect to their body size and condition in a wild population of the grey-capped greenfinch Chloris sinica. The results showed that male birds with significant longer bill and wing than female; breeding pairs assortative mated positively by culmen height, wing length, body mass and body condition. We argued that the body condition of greenfinches may be important in mutual mate choice. Male air courtship and incubation feeding behaviour provide evidence that female mate choice may be responsible for sexual dimorphism of bill size and wing length. Mutual mate choice and life histories may be responsible for non-randomly mating pattern by body condition, high quality individual prefer to mate with each other. [ABSTRACT FROM AUTHOR]

Sex roles describe sex differences in courtship, mate competition, social pair‐bonds and parental care. A key challenge is to identify associations among the components and the drivers of sex roles. Here, we investigate sex roles using data from over 1800 bird species. We found extensive variation and lability in proxies of sex roles, indicating remarkably independent evolution among sex role components. Climate and life history showed weak associations with sex roles. However, adult sex ratio is associated with sexual dimorphism, mating system and parental care, suggesting that social environment is central to explaining variation in sex roles among birds. Our results suggest that sex differences in reproductive behaviour are the result of diverse and idiosyncratic responses to selection. Further understanding of sex roles requires studies at the population level to test how local responses to ecology, life histories and mating opportunities drive processes that shape sex role variation among higher taxa. [ABSTRACT FROM AUTHOR]

Due to phenotypic plasticity and sex-biased selective pressures, intraspecific variation in tortoise morphology is usually assessed by studying sexual dimorphism. However, inferences may differ based on the choice of shell size measurements for analyses. In this work, we identified linear measurements that best describe sexual dimorphism for the spur-thighed tortoise Testudo graeca whitei. We assessed 34 carapace and plastron measurements in 67 individuals (24 males, 43 females) in a population at the natural Mergueb site located on the central limit of the Algerian steppe. Twenty-two out of 34 measurements significantly showed sexual size dimorphism in ANOVA tests. When analyzing sexual shape dimorphism with ANCOVAs, nine measurements showed no shared allometry with the measurements used as covariates to correct by size. Meanwhile, 17 out of the remaining 23 measurements showed significant differences in shape. PCA analyses similarly described T. graeca's sexual dimorphism. In general, females tend to be bigger than males, especially in central scutes what is probably linked with clutch sizes commitments. On the other hand, males are larger-sized in anterior and posterior scutes, probably as a result of courtship, male fighting and copulation. Some of the analyzed measurements are revealed as being especially adequate for further studying the geographical variation of sexual dimorphism in Testudo graeca. [ABSTRACT FROM AUTHOR]

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In mammals, the mutation of nipped-B-like protein (nipbl) leads to Cornelia de Lange Syndrome (CdLS), characterized by low birth weight, short stature, and structural abnormalities of the skeleton, heart, and gut. In Chinese tongue sole (Cynoglossus semilaevis), a typical marine fish exhibiting sexual size dimorphism, the nipbl homolog gene (nipped-B-like protein A (nipbla)) was also screened with female higher expression level by somatotropic and reproductive tissues’ transcriptomic analysis. In this study, two nipbla genes, namely, nipbla-w and nipbla-z, were identified from the W and Z chromosomes of C. semilaevis, respectively. Similar to other mammalian and fish species nipbl, the two homolog proteins of C. semilaevis contained two conserved domains, namely, cohesion_HEAT and Nipped-B_C. The phylogenetic tree analysis showed that these two nipbla gametolog proteins were first clustered together and then grouped with other fish species. At least two types of alternative splicing sites were observed in exon 12 of the nipbla-z gene, which produced nipbla-z-tv1 and nipbla-z-tv2. Also, the sex-biased expression patterns of different nipbla-w and nipbla-z transcripts in female and male tissues were revealed by quantitative PCR (qPCR). The highest expression level of nipbla-w was observed in female gonad. While nipbla-z-tv1 exhibited relatively high expression in the muscle, liver, gonad, and brain, nipbla-z-tv2 only showed its expression superiority in the muscle of male individuals. The promoter regions of nipbla genes were amplified, and their transcription activity was successfully verified by a dual-luciferase reporter system. After nipbla-w and nipbla-z knockdown in the brain cell lines by RNA interference, a series of growth-related genes were influenced, including Bone Morphogenetic Protein 4 (bmp4), Wnt Family Member 11 (wnt11), and Sprouty Related EVH1 Domain Containing 2 (spred2). The prediction of transcription factors suggested that c-Jun, sex-determining region Y (SRY), POU Class 1 Homeobox 1 (POU1F1a), myogenic differentiation antigen (MyoD), signal transducer and activator of transcription 5a (STAT5A), and nuclear factor I C (Nfic) might be the putative upstream regulatory factors for nipbla; among them, c-Jun has been verified to effectively regulate the transcriptional activity of nipbla. The identification of two nipbla genes provided important data for interpreting the sexual size dimorphism in C. semilaevis.

Chinese tongue sole (Cynoglossus semilaevis) is a flatfish species unique to Northeast Asia, exhibiting the typical female-biased sexual size dimorphism (SSD). To explore the possible regulatory roles of non-coding RNAs (ncRNAs) on this phenomenon, whole transcriptomic analysis was performed by using female, male, and pseudomale C. semilaevis to identify differentially expressed (DE) long ncRNAs (DE lncRNAs), microRNA (DE miRNAs), and differentially expressed genes (DEGs) from the brain, gonad, liver, and muscle tissues. Most of them were concentrated in the gonad and muscle, and the gene expression patterns of pseudomale individuals were similar to male individuals. The association of DE lncRNAs and target messenger RNAs (mRNAs) was predicted based on antisense, cis-, and trans-regulatory mechanisms, with enriched protein digestion and absorption, cyclic adenosine monophosphate (cAMP) signaling pathway, sulfur metabolism, cell cycle, and splicesome (p < 0.05). Furthermore, weighted gene co-expression network analysis (WGCNA) was employed to cluster the expression patterns of DE lncRNA, and two modules (greenyellow and blue) had the highest positive and negative correlations with growth traits, respectively. Importantly, the female-biased expression in the greenyellow module and the male- and pseudomale-biased expression in the blue module were observed in the gonad. The target gene analysis for DE miRNA revealed 3,034 mRNA-miRNA pairs with the opposite expression patterns. Finally, the lncRNA-miRNA-mRNA network, including 385 DE lncRNAs, 138 DE miRNAs, and 456 DEGs, was constructed. Among which, 78 DE lncRNAs, 12 DE miRNAs, and 13 DEGs involved in cell growth and death pathway were related to the SSD of C. semilaevis. This study described the lncRNA-miRNA-mRNA regulatory network in the SSD of C. semilaevis for the first time. The functional prediction analysis suggested that these DE lncRNAs and DE miRNAs might be involved in flatfish SSD by regulating several potential growth-related pathways (e.g., cell cycle, cAMP signaling, and Rap1 signaling). Further studies related to these ncRNAs will enlarge our understanding of the regulatory effects of ncRNAs on fish SSD.

ABSTRACT As commonly observed in turtles, sexual size dimorphism (SSD) is pronounced in the Neotropical freshwater turtle Mesoclemmys vanderhaegei (Bour, 1973), a species in which females are usually larger than males. We studied SSD in two populations of M. vanderhaegei from the Brazilian Cerrado savannah, based on 245 specimens captured between November 2010 and August 2013. The carapace length of the largest male was 201 mm (9.15% shorter than that of the largest female, 220 mm). The mean sizes of males and females did not differ in the two populations. However, a comparison of eight selected morphological variables revealed that the size distribution pattern differed between the populations. Using model selection, seven out of 34 morphometric variables - from the head, plastron, bridge, and tail - were selected as the most suitable ones to distinguish between males and females. The pattern of SSD found in M. vanderhaegei is similar to that found in other chelonian species and may be the result of natural selection rather than ecological factors, since individuals of both sexes use the same habitats.

The responses of ground-dwelling birds to heat and cold stress encompass a variety of behavioural, physiological and even morphological mechanisms. However, the role of glabrous skin in this respect has been marginally addressed so far. The Helmeted Guineafowl (Numida meleagris) is a landfowl distributed across Sub-Saharan Africa with eight traditionally recognised extant subspecies. Among the most prominent morphological traits underlying intraspecific variability are size and pigmentation of the bare throat skin (or sack), which might be related to the different habitats and environmental conditions across its wide range. In order to explore the Helmeted Guineafowl range-wide sack variation and pigmentation in relation to thermoregulation and sexual signalling, we collected morphometric and environmental information for N. m. coronata integrating field data with the inspection of photographic material encompassing seven subspecies and environmental information from their habitats. Field data evidenced that sack size was significantly correlated with ambient temperature, thus pointing to a likely involvement of the throat sack in thermoregulation. When the pictorial data from all subspecies were pooled, sack size correlated negatively with biomass, rainfall and humidity, while a positive correlation was found with annual solar irradiation. Sack size correlated positively with monthly temperature variation among the blue-throated subspecies from southern Africa as opposed to the black-throated subspecies ranging north to Zambia and Mozambique. Still, in this latter group the sack was often larger during winter months, possibly to maximise solar radiation absorbance. Noteworthy, sack size was related to sex dimorphism in two subspecies. Sack morphology and colour in the Helmeted Guineafowl likely modulate body temperature by evaporative cooling or heating upon needs, but in some subspecies it is also seemingly related to sexual signalling. Additional studies are needed to fully understand the multifunctionality of this important morphological feature in this species.

Certain members of the Actinopterygii class are known to exhibit sexual dimorphism (SD) that results in major phenotypic differences between male and female fishes of a species. One of the most common differences between the two sexes is in body weight, a factor with a high economic value in aquaculture. In this study, we used RNA sequencing (RNA-seq) to study the liver and brain transcriptomes of Ancherythroculter nigrocauda , a fish exhibiting SD. Females attain about fourfold body weight of males at sexual maturity. Sample clustering showed that both sexes were grouped well with their sex phenotypes. In addition, 2,395 and 457 differentially expressed genes (DEGs) were identified in the liver and brain tissues, respectively. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses predicted the association of PPAR signaling, cytochrome P450, and steroid hormone biosynthesis to the differences in sexual size. In addition, weighted gene co-expression network analyses (WGCNA) were conducted, and the green module was identified to be significantly correlated with sexual size dimorphism (SSD). Altogether, these results improve our understanding of the molecular mechanism underlying SSD in A. nigrocauda. [ABSTRACT FROM AUTHOR]