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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]

In its initial form, the expensive son hypothesis postulates that sons from male‐biased sexually dimorphic species require more food during growth than daughters, which ultimately incur fitness costs for mothers predominantly producing and rearing sons. We first dissect the evolutionary framework in which the expensive son hypothesis is rooted, and we provide a critical reappraisal of its differences from other evolutionary theories proposed in the field of sex allocation. Then, we synthesize the current (and absence of) support for the costs of producing and rearing sons on maternal fitness components (future reproduction and survival). Regarding the consequences in terms of future reproduction, we highlight that species with pronounced sexual size dimorphism display a higher cost of sons than of daughters on subsequent reproductive performance, at least in mammals. However, in most studies, the relative fitness costs of producing and rearing sons and daughters can be due to sex‐biased maternal allocation strategies rather than differences in energetic demands of offspring, which constitutes an alternative mechanism to the expensive son hypothesis stricto sensu. We observe that empirical studies investigating the differential costs of sons and daughters on maternal survival in non‐human animals remain rare, especially for long‐term survival. Indeed, most studies have investigated the influence of offspring sex (or litter sex ratio) at year T on survival at year T + 1, and they rarely provide a support to the expensive son hypothesis. On the contrary, in humans, most studies have focused on the relationship between proportion of sons and maternal lifespan, but these results are inconsistent. Our study highlights new avenues for future research that should provide a comprehensive view of the expensive son hypothesis, by notably disentangling the effects of offspring behaviour from the effect of sex‐specific maternal allocation. Moreover, we emphasize that future studies should also embrace the mechanistic side of the expensive son hypothesis, largely neglected so far, by deciphering the physiological pathways linking son's production to maternal health and fitness. [ABSTRACT FROM AUTHOR]

Ectothermic vertebrates such as reptiles were assumed to be indeterminate growers, which means that there is no terminal point in time or size for growth in their lifetime. In recent years, evidence for the determinate nature of growth in lizards has accumulated, necessitating a re‐examination of models of their ontogeny and evolution of sexual size dimorphism (SSD). In the female‐larger gecko Paroedura vazimba, we monitored post‐embryonic growth over a period of 15 months. After hatching, females grew faster than males but also reached their final body size, that is, closed growth of their vertebrae, earlier than males. The closure of bone growth in females correlates with the onset of reproductive maturation. We compared this pattern with the previously minutely studied, male‐larger species Paroedura picta, where we documented determinate growth as well. We propose a model to explain the evolutionary switches in the direction of SSD in lizards based on bipotential effects of ovarian hormones on growth. In this model, male growth is assumed to require no male‐specific growth modifier, such as sex‐limited hormonal regulators, while growth is feminized by ovarian hormones in females. Low levels of ovarian hormones can promote bone growth, but high levels associated with maturation of the reproductive organs promote senescence of bone growth plates and thus cessation of bone growth. We suggest that models on growth, life‐history and evolution of body size in many lizards should acknowledge their determinate nature of growth. Research highlights: Ontogeny of sexual size dimorphism (SSD) is complex in a gecko Paroedura vazimba with determinate growth: females grow faster, but close vertebral growth plates earlier than males. Development of SSD in male‐larger and female‐larger geckos is compared. [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]

The mandible size variability including sexual size dimorphism (SSD) of the cave lion (Panthera spelaea) in the Pleistocene of Northern Eurasia time has been studied basing on the univariate and multivariate statistical analyses of 76 specimens from 43 localities. It has been confirmed that SSD in adult P. spelaea, as well as in extant P. leo, is the dominant form of group variability of mandible and, to somewhat lesser extent, of variability of cheek teeth. The lowest degree of SSD has been found in a relatively small Beringian subspecies, P. spelaea vereshchagini. The geographical variability of the cave lion from Western to Eastern Eurasia was not a cline at least in the Late Pleistocene. Our results confirm a decrease in overall mandible size from the Middle Pleistocene to the Late Pleistocene over a large part of the species' range. We speculate that evolutionary changes in mandible size, lower canines or cheek teeth may have proceeded at different rates, allometry and probable heterochrony. Our results have added a new evidence to support the subspecies status of the Beringian lion (P. spelaea vereshchagini), but they are insufficient for other decisions on cave lion taxonomy at the subspecies level. [ABSTRACT FROM AUTHOR]

Walleye (Sander vitreus) are a sexually dimorphic freshwater piscivore that have long been studied using bioenergetics modeling, yet robust estimates of metabolic rates for use in those models have been lacking. Therefore, we quantified the effects of body mass, water temperature, and sex, on standard metabolic rate (SMR). We estimated SMR across temperatures ranging 0.5–24 °C using intermittent-flow respirometry for male (n = 54) and female (n = 53) walleye raised in hatchery conditions. We found a significant interaction between sex and temperature, whereby males had lower SMR below 16 °C, but increased such that SMR was ∼16% higher than females at 22 °C. The mass-scaling coefficient, b, was similar for both sexes at a value around 1. These estimates are the first to be generated using respirometry for adult walleye and differ slightly from those being used by previous bioenergetics models, which may have underestimated the energetic costs of SMR, and did not include sex-specific estimates for metabolism. [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.

Voltinism and life‐history traits of the invasive fall armyworm (FAW) Spodoptera frugiperda were investigated under semi‐natural conditions for a period of 2 years. The FAW invaded the corn field in the suburbs of Nanchang (28°46′ N, 115°50′ E) in early summer and produced six complete generations. FAW had the characteristics of short developmental time, high survival rates and strong fecundity. The development time of female pupae was significantly faster than that of male pupae, resulting in the emergence of female pupae earlier than male pupae. Except for the sixth generation in 2021, there was no significant difference between female and male sex ratio, which was close to 1:1. FAW showed male‐bias sexual size dimorphism with male pupae being significantly larger than female pupae. Unlike pupal weight, in most generations, male adult weighed significantly less than females, because the weight loss of male pupae during metamorphosis was significantly greater than that of female pupae. The temporal variation of pupal weight did not conform to the temperature–size rule. Compared with 22.8°C, the 29.2°C high temperature not only significantly reduced the development time of larvae but also significantly increased pupal weight. The adult fecundity feeding on fresh corn leaves was higher than that feeding on live corn plants in most generations. In most generations, pupal weight was positively correlated with larval development time and adult weight was positively correlated with fecundity. In conclusion, climate differences between generations and years have significant effects on developmental time, body weight, sexual size dimorphism and fecundity of the FAW. These results add to the understanding of the evolution of life‐history traits in the FAW and may have important implications for predicting population dynamics of the FAW and optimising control strategies. [ABSTRACT FROM AUTHOR]

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]

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species. [ABSTRACT FROM AUTHOR]

Intraspecific resource partitioning may play a critical role in how predators optimize prey selection. The Black-footed Ferret (Mustela nigripes ; henceforth, ferret) is a highly specialized predator of prairie dogs (Cynomys spp.; henceforth, PDs). Adult ferrets are sexually dimorphic and PDs are of similar size making them a difficult prey item. PD young are born 6 to 8 weeks prior to births of ferrets, producing a crop of smaller prey items during a period when energetic needs of female ferrets are highest. We asked whether relatively small female ferrets select small PDs as prey. We examined survival rates from early to late summer for large and small black-tailed PDs (Cynomys ludovicianus) in Montana and South Dakota as a function of their distance to adult male and female ferrets using capture–mark–recapture of PDs and simultaneous summer monitoring of ferret locations. Survival of small PDs (<600 g) was low when a female ferret was nearby, but distance to nearest female ferret did not affect survival of large PDs. Distance to the nearest male ferret did not influence survival regardless of PD size. Reduced competition from males for a critical food resource needed by females rearing young would benefit fitness of both sexes. If female ferrets depend on young PDs during their reproductive period, existing habitat models may substantially overestimate ferret carrying capacity. [ABSTRACT FROM AUTHOR]

Ectotherms exhibit varying geographic size patterns shaped by environmental and evolutionary factors. This variability is noticeable within taxonomic groups. For instance, certain testudinids follow Bergmann's rule (body size increases with latitude) and Rensch's rule (sexual size dimorphism correlates with body size), while others do not. Here we hypothesize that body size patterns can even vary within a monophyletic lineage. To address this, we evaluated the body size patterns of the spur-thighed tortoise Testudo graeca that globally follows Bergmann's and Rensch's rules. We specifically investigated the influence of climate variables, latitude and elevation within the subspecies T. g. whitei throughout its natural distribution in North Africa, and in a recently expanded range in SE Spain (20 kya old). We found that males were smaller than females in both regions. The tortoises from SE Spain were smaller than those from North Africa, which showcased the smallest sizes ever reported for the species. Latitude was the main variable to explain tortoise body size. In particular, body size decreased with latitude in both regions, which contrasts with Bergmann's rule expectations based on species-level findings. Finally, to further contradict species-level expectations, we did not find any statistical correlation between sexual size dimorphism and body size across the two studied regions. Such contradictory outcomes reveal complex geographic size patterns within T. graeca and raise conservation questions about demographic viability at smaller-sized sites. [ABSTRACT FROM AUTHOR]

The 'bigger is better' hypothesis (BIBH) predicts that fitness increases with body size. Eastern spiny softshell turtles (Apalone spinifera) exhibit sexual size dimorphism (SSD) at maturity, and the much larger female body size is attributed to selection favouring greater reproductive output. Hatchlings exhibit sexually dimorphic markings, but hatchling SSD has not been investigated. The BIBH predicts that hatchlings will not exhibit SSD because reproductive benefits to larger, mature females drive size dimorphism at maturity, but selection on hatchlings relates only to survival. We tested this prediction with A. spinifera hatchlings (N  = 2630) incubated in controlled conditions to avoid confounding environmental effects on phenotype. Hatchling mass was similar between sexes, suggesting similar nutritional allocation to male and female offspring. Hatchling size (carapace length) was also similar between sexes. Hatchling mass and body size varied among clutches and were positively related to maternal size, suggesting morphological constraints on egg size. Surprisingly, clutch size was related only weakly to maternal size. Taken together, our results suggest that hatchling size in A. spinifera is consistent with the BIBH and that offspring quality increases with maternal age, but that maternal effects drive a large proportion of the variation in clutch size and offspring quality. [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]

Objectives: The investigation of morphological variation in animals is widely used in taxonomy, ecology, and evolution. Using large datasets for meta‐analyses has dramatically increased, raising concerns about dataset compatibilities and biases introduced by contributions of multiple researchers. Materials and Methods: We compiled morphological data on 13 variables for 3073 individual mouse lemurs (Cheirogaleidae, Microcebus spp.) from 25 taxa and 153 different sampling locations, measured by 48 different researchers. We introduced and applied a filtering pipeline and quantified improvements in data quality (Shapiro‐Francia statistic, skewness, and excess kurtosis). The filtered dataset was then used to test for genus‐wide sexual size dimorphism and the applicability of Rensch's, Allen's, and Bergmann's rules. Results: Our pipeline reduced inter‐observer bias (i.e., increased normality of data distributions). Inter‐observer reliability of measurements was notably variable, highlighting the need to reduce data collection biases. Although subtle, we found a consistent pattern of sexual size dimorphism across Microcebus, with females being the larger (but not heavier) sex. Sexual size dimorphism was isometric, providing no support for Rensch's rule. Variations in tail length but not in ear size were consistent with the predictions of Allen's rule. Body mass and length followed a pattern contrary to predictions of Bergmann's rule. Discussion: We highlighted the usefulness of large multi‐researcher datasets for testing ecological hypotheses after correcting for inter‐observer biases. Using genus‐wide tests, we outlined generalizable patterns of morphological variability across all mouse lemurs. This new methodological toolkit aims to facilitate future large‐scale morphological comparisons for a wide range of taxa and applications. [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]

In many migratory songbirds, males arrive earlier at stopover sites and at the breeding grounds ('protandry') and older birds precede younger ones, but less is known about age differences in protandry. In seasonal environments, differential timing by sex and age is thought to reflect selection imposed by seasonality (i.e., viability selection) and intrasexual competition for space and mates. Viability and sexual selection can also favor male-biased sexual size dimorphism (SSD), leading to a positive relationship between protandry and SSD among species. We evaluated whether the relationship between protandry during spring migration and SSD in wing length (SSDW) differed between age classes in 20 sexually dimorphic songbirds. Consistent with the hypothesis that older, higher-quality males can better afford to arrive early, we found a stronger relationship between protandry and SSDW among older birds than among first-time breeders. We also tested the relationship between protandry and sexual size dimorphism of the wingtip (SSDWT) and found that greater age differences in protandry were related to greater age differences in SSDWT. We conclude that larger body sizes, energetically efficient wing shapes, and experience together select for the earlier arrival timing of older males relative to first-time breeding males and females. [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]

In many animals, body size is correlated with reproductive success. Selection sometimes generates striking differences in body size between males and females (i.e. sexual size dimorphism, SSD). SSD is common in spiders (Araneae), and is typically explained by selection for larger, more fecund females and rapidly maturing, and consequently smaller, males. Within a species males and females also often vary in body size. In the false widow spider, Steatoda grossa , females are larger than males and males trade body size for rapid development and early maturation. Moreover, males vary considerably in body size, suggesting that under certain conditions there may be advantages to large size. Here, we tested the role of male body size on mating success under noncompetitive and competitive mating conditions (i.e. male–male competition) in S. grossa. We found that body size did not influence mating success or copulation duration under noncompetitive conditions, but that larger males were more successful at obtaining access to females under competitive mating conditions. Additionally, we found that total copulation duration was significantly lower when a rival male was present. Our results show a large male advantage under male–male competition, which we suggest may contribute to the high variation in male body size observed in S. grossa. We further suggest that the reduced copulation duration observed under competitive mating conditions may have potential ramifications for male and female reproductive success and we discuss how patterns of selection acting on male body size might limit the extent of SSD in this species. • Male body size is important for mating success in many species. • Steatoda grossa males obtain mating success regardless of body size. • Under competitive conditions, larger males had greater mating success. • Female copulation duration was reduced in the presence of a male competitor. • The results offer insight into male body size evolution and sexual size dimorphism. [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.

In mammals, the dominant theory proposes that sexual size dimorphism evolved by sexual selection in a polygynous reproductive scenario. Natural selection is an alternative hypothesis where dimorphism represents an adaptation to ecological pressures. I tested evolutionary models based on sexual and natural selection processes using phylogenetic confirmatory path analyses. I employed data for 225 primate species in terms of their diel activity, body mass, sexual size dimorphism, level of sociality, and level of polygyny. The model that received the most support from path analyses was a mixed model in which dimorphism evolved after an increase in body size that resulted from a response to an ecological pressure, i.e., a change from nocturnal to diurnal habits, with a lesser role of polygyny. Phylogenetic path analysis suggests that natural selection has played an important role in the evolution of sexual size dimorphism in primates. [ABSTRACT FROM AUTHOR]

I examined sex allocation of offspring in northern flickers, Colaptes auratus , a woodpecker with biparental care and sexual size dimorphism. The analysis of data involving 8321 nestlings that were sexed over a span of 16 years revealed no significant bias towards the smaller sex (females) at the population level (all fledglings pooled), counter to the Fisherian hypothesis of equal investment at the end of parental care. At the level of the brood, high-quality parents (older and in better body condition) did not produce more of the expensive sex (males) counter to the Trivers–Willard hypothesis. Brood sex ratios were somewhat repeatable among females but did not vary significantly with year, clutch size or hatching date probably because the main food of flickers, ground-dwelling ants, is relatively invariable. Mother flickers allocated more of the cheaper sex to last-hatched offspring in asynchronous broods, consistent with the 'intrabrood sharing-out hypothesis' but not the 'competitive advantage hypothesis'. The female-bias in last-laid eggs was present in complete broods, which had no nestling mortality, suggesting that primary sex ratio manipulation was involved. However, a small shift in the direction of female-bias occurred as a result of a greater mortality of the more costly (male) nestlings. Female flickers may therefore attempt to minimize maladaptive brood reduction by allocating more of the cheaper sex to positions later in the laying sequence. • Population level offspring sex ratio of northern flickers did not differ from parity. • High-quality parents did not produce more males (the expensive sex). • Flickers allocated more females to last-hatched offspring within asynchronous broods. • Female bias in last-laid eggs was present in broods without nestling mortality. • Sex allocation was consistent with the 'intrabrood sharing-out hypothesis'. [ABSTRACT FROM AUTHOR]

Mate choice is a key driver of evolutionary phenomena such as sexual dimorphism. Social mate choice is studied less often than reproductive mate choice, but for species that exhibit biparental care, choice of a social mate may have important implications for offspring survival and success. Many species make pairing decisions based on size that can lead to population-scale pairing patterns such as assortative and disassortative mating by size. Other size-based pairing patterns, such as females pairing with males larger than themselves, have been commonly studied in humans, but less often studied in nonhuman animal systems. Here we show that sexually size-dimorphic mountain chickadees, Poecile gambeli , appear to exhibit multiple self-referential pairing patterns when choosing a social mate. Females paired with males that were larger than themselves more often than expected by chance, and they paired with males that were slightly larger than themselves more often than they paired with males that were much larger than themselves. Preference for slightly larger males versus much larger males did not appear to be driven by reproductive benefits as there were no statistically significant differences in reproductive performance between pairs in which males were slightly larger and pairs in which males were much larger than females. Our results indicate that self-referential pairing beyond positive and negative assortment may be common in nonhuman animal systems. • The factors influencing social mate choice remain unclear. • Some species, including humans, make self-referential pairing decisions. • Mountain chickadees are sexually size dimorphic and socially monogamous. • Females paired with males that were larger but not too much larger than themselves. • Reproductive performance was not related to whether a pair followed this pattern. [ABSTRACT FROM AUTHOR]

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]

Body size can vary across geographical gradients, and these clines have been mainly attributed to temperature (i.e., the heat conservation hypothesis). However, in tropical areas, this pattern is not necessarily fulfilled. Furthermore, it is not known whether a body size cline is sex-biased in dimorphic species. Therefore, we aimed to evaluate the intra-specific variation in body size in a tropical seabird, the Red-billed Tropicbird (Phaethon aethereus), at six breeding colonies in the Pacific Ocean (17–31° N) and to relate body traits to environmental variables in each colony. Further, we examined sexual size dimorphism (SSD) in the species and its possible influence on the pattern of inter-colony variation in body size. We measured body traits in 187 adults. SSD was evaluated using culmen, ulna, and tarsus lengths and body mass. Chlorophyll-a, air temperature, and sea surface temperature (SST) values within an 80-km radius of each breeding site and the latitude of each island were used to create an environmental index. The relationships between body traits and the environmental index were assessed using regression models. Red-billed tropicbirds exhibited a positive, south-to-north body-size cline (between 1 and 9%) related to environmental conditions, and SSD was evident at only two northern colonies (males > females). The body size cline in the species could be influenced by a set of abiotic and biotic factors, which has likely led to phenotypic plasticity. The sexual dimorphism detected in colonies with larger body sizes along with high chlorophyll-a values and low SST values suggest that environmental-mediated variation in body size is a crucial mediator of SSD. [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.

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. [ABSTRACT FROM AUTHOR]

Amblypygids display high levels of sexual dimorphism, especially larger pedipalps in males compared to females. This study examines the difference in allometric rates as a potential cause of dimorphism in pedipalps and walking legs in three Heterophrynus species: Heterophrynus batesii (Butler, 1873); Heterophrynus longicornis (Butler, 1873), and Heterophrynus elaphus (Pocock, 1903). Dimorphism is observed in all studied appendages, but higher allometric rates are shown in males more than females for only the pedipalps (for all three species) and the first walking legs (for only H. elaphus), with higher dimorphism in the pedipalp for H. batesii and lower in H. elaphus. Dimorphism in pedipalps appears to be linked to species' mating system: larger dimorphism are observed in polygamous systems, whereas moderate and small dimorphisms are observed in monogamous and solitary species, respectively. Contrary to pedipalps, the evolution of walking legs seems to occur via natural selection rather than sexual selection. [ABSTRACT FROM AUTHOR]

The African clawed frog Xenopus laevis is a largely aquatic frog occurring from central to southern Africa. This species has been used as experimental animal, and has been introduced in many countries including Japan. However, despite its importance as an experimental animal and invasive alien species across the world, but there are few studies on basic biology of X. laevis including individual variation. In this study, we investigated individual variation in external morphology and allometric patterns. Traits not directly related to the skeleton showed high variability, but ecologically important traits like eye size at the youngest stage, showed low variability. No significant external left-right differences were identified. Allometric analysis showed that males have larger heads and eyes than females, suggesting male-male combat during breeding. Male forelimb suggests also showed a faster growth rate, suggesting that longer forelimbs are advantageous for males in breeding. [ABSTRACT FROM AUTHOR]

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 Furnariidae is a very diverse family of Neotropical passerines in which the role of sexes in nest attendance and the possible existence of sexual dimorphism still remain poorly known for most species. Here, in a study spanning two breeding seasons, we analyzed the sexual dimorphism in morphology and the parental roles during incubation and chick rearing in the Wren-like Rushbird Phleocryptes melanops, a typical furnariid distributed in the southern wetlands of South America. Given previous knowledge of natural history of this family, we expected a slight dimorphism in size and a similar role of the sexes in parental care. Adults were captured and measured, and blood samples taken for molecular sex determination. Males had on average, 10.3%, 10.2%, 5.3%, and 4.4% larger bill lengths, tail lengths, wing chord lengths, and tarsus lengths than females, respectively, whereas no significant sexual differences were found for bill widths and depths. In addition, we found that both parents participated similarly in all reproductive activities during incubation and nestling stages, in line with the general pattern reported in furnariids. The sexual selection hypothesis may best explain the size differences between the sexes and in the behaviour of the species at the beginning of the nesting cycle. —Pretelli, M.G., Chiaradia, N., Cardoni, A., Baladrón, A., Cavalli, M., Madrid, E. & Isacch, J.P. (2023). Sexual dimorphism and parental care in the Wren-like Rushbird Phleocryptes melanops. Ardeola, 70: 29-40. Furnariidae es una familia con una gran diversidad de paseriformes neotropicales, sin embargo, el rol de los sexos en la atención del nido y la posible existencia de dimorfismo sexual aún permanecen poco conocidos para la mayoría de las especies. Durante dos temporadas reproductivas, analizamos el dimorfismo sexual y el rol de los parentales durante la incubación y cría de pollos en el junquero Phleocryptes melanops, un furnárido típico que habita en los humedales del sur de Sudamérica. Dado el conocimiento previo sobre la historia natural de esta familia, esperamos un leve dimorfismo en tamaño y un rol similar de los sexos en el cuidado parental. Los adultos fueron capturados y medidos, y se les extrajo una muestra de sangre para el sexado molecular. Hallamos que los machos, en promedio, fueron 10,3%, 10,2%, 5,3% y 4,4% más grandes que las hembras en el largo del pico, cola, cuerda de ala y tarso, mientras que el ancho y la profundidad del pico no difirieron. Además, encontramos que ambos parentales participan similarmente en todas las actividades reproductivas durante la incubación y en la etapa de pollos, lo que concuerda con el patrón general reportado para furnáridos. La hipótesis de selección sexual es la que mejor podría explicar las diferencias halladas en el tamaño entre sexos y en el comportamiento de la especie al comienzo del ciclo reproductivo.—Pretelli, M.G., Chiaradia, N., Cardoni, A., Baladrón, A., Cavalli, M., Madrid, E. e Isacch, J.P. (2023). Dimorfismo sexual y cuidado parental en el junquero Phleocryptes melanops. Ardeola, 70: 29-40. [ABSTRACT FROM AUTHOR]

One fundamental question in biology is how animals control their proper body size. Hippo signaling pathway has emerged as an evolutionarily conserved network to regulate organ size from Drosophila to mammals. Interestingly, our previous study has also implied the roles of hippo signaling in Chinese tongue sole (Cynoglossus semilaevis), a flatfish exhibiting female-biased sexual size dimorphism (SSD). Specifically, two yes-associated protein 1 (yap1) homologs, key effectors within hippo signaling, exhibited the opposite expression pattern in the female and male gonads of C. semilaevis. Whether and how these two yap1 genes participate in female-biased SSD is unknown. In the present study, phylogenetic tree analysis firstly designated these two yap1 genes as yap1 and yap1b , with no taz gene available in C. semilaevis. Subsequent quantitative PCR analysis demonstrated that yap1 exhibited the highest expression levels within the male gonad at three-month-old, while the predominant expression of yap1b was detected in the female gonad at two-year-old. The co-localization of yap1 and yap1b was observed in the cytoplasm of oocyte and sperm. Cebpα , a negative regulator for dmrt1 , exhibited positive and negative regulation on the yap1 and yap1 b , respectively. Myog , a crucial transcription factor for myogenesis, specifically binded and activated yap1b promoter, not yap1. Furthermore, DAP-seq revealed the regulatory networks of yap1 and yap1b in C. semilaevis. Importantly, many growth and reproduction-related pathways, including the JAK-STAT signaling pathway, prolactin signaling pathway, axonal regeneration, and steroid hormone synthesis, were included in the common peaks of yap1 and yap1b. Moreover, the application of verteporfin reagents into testis and ovary cells resulted in a decrease in yap1 and yap1b levels. Consequently, the expression of growth hormone receptor (ghr), growth hormone actin α (smtla), estrogen receptor (esr2b), and 17β-hydroxysteroid dehydrogenase type 7 (hsd17b7), were also affected. In addition, the administration of verteporfin on C. semilaevis caused a significant reduction in growth rate. These findings provided insights into the role of the hippo signaling pathway in regulating SSD of C. semilaevis. • Yap1 and yap1b were identified in C. semilaevis , with no taz gene. • The co-localization of yap1 and yap1b was observed in the cytoplasm of oocyte and sperm. • Cebpα , a negative regulator for dmrt1, showed positive and negative regulation on the yap1 and yap1b , respectively. • Dap-seq revealed that yap1 and yap1b regulated JAK-STAT, prolactin, and steroid signaling pathways. • Verteporfin treatment caused a decrease of yap1 / yap1b and a reduction in C. semilaevis growth rate. [ABSTRACT FROM AUTHOR]