Female-biased Sexual Size Dimorphism Research Articles

A second species of Stenasellus Dollfus, 1897 (Isopoda, Stenasellidae) from sulfidic groundwater of Iran described using morphological and molecular methods

We report on a new species of Stenasellus Dollfus, 1897 (Isopoda, Stenasellidae) from groundwater of Iran. Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov. inhabits the Chah Kabootari Cave that is adjacent to the Tashan Cave, the type locality of the first recorded species of Stenasellidae from Iran, Stenasellus tashanicus Khalaji-Pirbalouty, Fatemi, Malek-Hosseini & Kuntner, 2018. Both caves are fed by sulfidic groundwater and belong to the Tashan-Chah Kabootari species-rich aquifer on the Zagros Mountains. Both species are characterized by a large body size (≥ 20 mm), a female-biased sexual size dimorphism, and a distinct black-pigmented Bellonci’s organ. Stenasellus stygopersicus differs from S. tashanicus by a short and wide protopodite of pleopod I, setae set essentially along the apical margin of pleopod I exopodite, the subequal length and width of the male pleopod II protopodite, and deeply bilobed endopodites of pleopods III–V. Molecular evidence suggests that while Stenasellus stygopersicus is sister to S. tashanicus, the species are genetically distinguishable, with divergence time estimates ranging from 23 to 39.8 Ma.

Age Structure, Body Size, and Sexual Dimorphism in a High-Altitude Population of Pelophylax ridibundus (Pallas, 1771)

This study aimed to describe the morphological characteristics and age structure of a P. ridibundus population sampled from a high altitude. For this purpose, a total of 54 adult frogs (33 males and 21 females) were collected from Şavşat district, Artvin province, Türkiye. The samples were aged based on skeletochronology method. Furthermore, von Bertalanffy growth curve models were constructed using SVL and weight data. To assess sexual size and shape dimorphism, the measurements of 23 different morphological characters were analyzed using univariate and multivariate statistical techniques. The mean SVL and weight were found to be 78.05 mm and 60.87 g for males and 93.95 mm and 109.61 g for females. The mean age was 3.67 years and 4.05 years for males and females, respectively. The maximum age was found to be 6 years for both sexes. Growth curve models revealed a significant relationship between age, SVL, and weight. A clear female-biased sexual size dimorphism was found in all morphological characters. However, SVL-adjusted values indicated that males had larger head and limb structures resulting from evolutional and sexual pressures associated with reproduction and male–male competition. The shape dimorphism was found only in forelimbs, and it was male-biased and was related to clasping in amplexus.

Among-population variation in sexual size dimorphism of Nepa cinerea (Heteroptera: Nepomorpha)

AbstractNepa cinerea is a common aquatic predator. It is widely distributed in various aquatic biotopes of the Palaearctic. Body size is an important trait that impacts the fitness and survival of animals and thus their evolution. Like most insects, N. cinerea males are smaller than females, but sexual size dimorphism (SSD) has not been investigated. We investigated the extent of SSD, the validity of Rensch's rule, and morphological differences between nine populations based on 51 morphological parameters. Females were found significantly and marginally significantly larger than males in all but one population. However, no difference in body length was found between the populations. Population had a significant effect on 12 traits for females and only on 5 for males, showing that females are more variable than males. Specifically, differences were found in the length of the second and third leg pairs. We did not find any support for the Rensch's rule. Nevertheless, female body size and SDI (sexual dimorphism index) were positively correlated. We suggest that fecundity selection accounts for female-biased SSD in N. cinerea.

Foraging strategy as a route for sexual size dimorphism evolution.

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.

Identification of candidate genes and pathways involved in the establishment of sexual size dimorphism in the olive flounder (Paralichthys olivaceus) using RNA-seq

Olive flounder (Paralichthys olivaceus) is a valuable mariculture fish that shows female-biased sexual size dimorphism (SSD), yet the molecular mechanisms responsible for this phenomenon remain poorly understood. In this study, the growth differences between females and males were compared, and comparative transcriptome analyses of brains/pituitaries, livers, muscles, and gonads from 13-month-old females and males were performed. The critical time window for SSD was from 13- to 14-month-old, with females reaching significantly larger sizes than males. Muscle cell size and plasma growth hormone (GH), insulin-like growth factor 1 and 2 (IGF1, IGF2), 11-ketotestosterone (11-KT), and 17β-estradiol (E2) levels had no significant differences between the sexes of 13- and 14-month-old flounders. Furthermore, the RNA-seq data revealed differential expression in the genes encoding the receptors for these hormones, suggesting that regulation may occur at the receptor level, potentially leading to SSD during the critical window. RNA-seq analysis identified 88, 645, 414, and 15,833 differentially expressed genes between females and males in brains/pituitaries, livers, muscles, and gonads, respectively. KEGG (Kyoto Encyclopedia of Genes and Genomes) and GSEA-based KEGG analyses revealed that some pathways associated with growth and development, including “prolactin signaling pathway” in brains/pituitaries, “cell cycle”, “oocyte meiosis”, and “DNA replication” in livers, “focal adhesion”, “ECM-receptor interaction”, “protein digestion and absorption”, “arginine and proline metabolism”, and “cysteine and methionine metabolism” in muscles, and “Hippo signaling pathway” and “JAK-STAT signaling pathway” in gonads may be involved in the establishment of sexual growth differences. Notably, females had lower steroid hormone synthesis abilities than males in brains/pituitaries, livers, and gonads, indicating the importance of sex steroid hormones in the establishment of SSD. Moreover, genes including frizzled3 (fzd3) and prolactin (prl) in brains/pituitaries, and growth hormone receptor (ghr), estrogen receptor (esr1), insulin-like growth factor binding protein-3 (igfbp3), bone morphogenetic protein 8A-like (bmp8a), leptin receptor (lepr), and lipoprotein lipase-like (lpl) in livers emerge as potential candidates for the establishment of SSD. In conclusion, this study may help clarify the molecular mechanisms involved in SSD-related growth traits in flounder and provide basic data for genetic breeding of flounder.

Viviparity is associated with larger female size and higher sexual size dimorphism in a reproductively bimodal lizard.

Squamate reptiles are central for studying phenotypic correlates of evolutionary transitions from oviparity to viviparity because these transitions are numerous, with many of them being recent. Several models of life-history theory predict that viviparity is associated with increased female size, and thus more female-biased sexual size dimorphism (SSD). Yet, the corresponding empirical evidence is overall weak and inconsistent. The lizard Zootoca vivipara, which occupies a major part of Northern Eurasia and includes four viviparous and two non-sister oviparous lineages, represents an excellent model for testing these predictions. We analysed how sex-specific body size and SSD is associated with parity mode, using body length data for nearly 14,000 adult individuals from 97 geographically distinct populations, which cover almost the entire species' range and represent all six lineages. Our analyses controlled for lineage identity, climatic seasonality (the strongest predictor of geographic body size variation in previous studies of this species) and several aspects of data heterogeneity. Parity mode, lineage and seasonality are significantly associated with female size and SSD; the first two predictors accounted for 14%-26% of the total variation each, while seasonality explained 5%-7%. Viviparous populations exhibited a larger female size than oviparous populations, with no concomitant differences in male size. The variation of male size was overall low and poorly explained by our predictors. Albeit fully expected from theory, the strong female bias of the body size differences between oviparous and viviparous populations found in Z. vivipara is not evident from available data on three other lizard systems of closely related lineages differing in parity mode. We confront this pattern with the data on female reproductive traits in the considered systems and the frequencies of evolutionary changes of parity mode in the corresponding lizard families and speculate why the life-history correlates of live-bearing in Z. vivipara are distinct. Comparing conspecific populations, our study provides the most direct evidence for the predicted effect of parity mode on adult body size but also demonstrates that the revealed pattern may not be general. This might explain why across squamates, viviparity is only weakly associated with larger size.

The potential role of hippo pathway effector yap1/yap1b in female-biased sexual size dimorphism of Chinese tongue sole (Cynoglossus semilaevis)

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 yap1b, 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.

Correction to: Variation in female-biased sexual size dimorphism of northern pike (Esox lucius) associated with environment and life history

Correction to: Variation in female-biased sexual size dimorphism of northern pike (Esox lucius) associated with environment and life history

The effect of miniaturization on the evolution of sexual size dimorphism in geckos.

The evolution of miniaturization can result in dramatic alterations of morphology, physiology, and behavior; however, the effects of miniaturization on sexual dimorphism remain largely unknown. Here we investigate how miniaturization influences patterns of sexual size dimorphism (SSD) in geckos. Measuring 1,875 individuals from 131 species, we characterized patterns of SSD relative to body size across two families. We found that miniaturized species were more female biased than non-miniaturized species. Additionally, one family that contained many miniaturized species (Sphaerodactylidae) displayed allometric patterns in SSD with body size, where larger species were male biased and smaller species were more female biased. Smaller species in this lineage also produced proportionally larger eggs. By contrast, another family containing few miniaturized species (Phyllodactylidae) displayed a more isometric trend. Together, these observations are consistent with the hypothesis that selection for increased reproductive success in small species of Sphaerodactylidae results in female-biased SSD in these taxa, which in turn drives the positive SSD allometry observed in this lineage. Thus, selection for increased miniaturization in the clade may be offset by selection on maintaining a female size in smaller taxa that ensures reproductive success.

The macroevolution of sexual size dimorphism in birds

Abstract There is considerable variation of sexual size dimorphism (SSD) in body mass among animal groups, yet the drivers of interspecific variation in SSD are still poorly understood. Possible mechanisms have been suggested, including sexual selection, selection for fecundity in females, niche divergence between sexes, and allometry, yet their relative importance is still poorly understood. Here, we tested predictions of these four hypotheses in different avian groups using a large-scale dataset on SSD of body mass for 4761 species. Specifically, we estimated the probability of transition between male- and female-biased SSD, tested for differences in evolutionary rates of body mass evolution for males and females, and assessed the potential ecological and spatial correlates of SSD. Our results were consistent with the sexual selection, fecundity, and niche divergence hypotheses, but their support varied considerably among avian orders. In addition, we found little evidence that the direction of SSD affected the evolution of male or female body mass, and no relationship was detected between SSD and environmental predictors (i.e. temperature and precipitation seasonality, productivity, species richness, and absolute latitude). These results suggest that avian evolution of SSD is likely to be multifactorial, with sexual selection, fecundity, and niche divergence playing important roles in different avian orders.

Variation in female-biased sexual size dimorphism of northern pike (Esox lucius) associated with environment and life history

Variation in female-biased sexual size dimorphism of northern pike (Esox lucius) associated with environment and life history

Revisiting niche divergence hypothesis in sexually dimorphic birds: Is diet overlap correlated with sexual size dimorphism?

The evolution of sexual size dimorphism (SSD) is a long-standing topic in evolutionary biology, but there is little agreement on the extent to which SSD is driven by the different selective forces. While sexual selection and fecundity selection have traditionally been proposed as the two leading hypotheses, SSD may also result from natural selection through mechanisms such as sexual niche divergence, which might have reduced resource competition between sexes. Here, we revisited the niche divergence hypothesis by testing the relationship between the sexual overlap in diet and SSD of 56 bird species using phylogenetic comparative analyses. We then assessed how SSD variation relates to the three main hypotheses: sexual selection, fecundity selection, and sexual niche divergence using phylogenetic generalized least squares (PGLS). Then, we compared sexual selection, fecundity selection and niche divergence selection as SSD drivers through phylogenetic confirmatory path analyses to disentangle the possible causal evolutionary relationships between SSD and the three hypotheses. Phylogenetic generalized least squares showed that SSD was negatively correlated with diet overlap, that is, the greater the difference in body size between males and females, the less diet overlap. As predicted by sexual selection theory, the difference in body size between sexes was higher in polygynous species. Confirmatory phylogenetic path analyses suggested that the most likely evolutionary path might include the mating system as a main driver in SSD and niche divergence as a result of SSD. We found no evidence of a role of fecundity selection in the evolution of female-biased SSD. Our study provides evidence that sexual selection has likely been the main cause of SSD and that dietary divergence is likely an indirect effect of SSD.

Three Copies of zbed1 Specific in Chromosome W Are Essential for Female-Biased Sexual Size Dimorphism in Cynoglossus semilaevis.

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.

Sharks Violate Rensch's Rule for Sexual Size Dimorphism.

Systematic trends in body size variation exist in a multitude of vertebrate radiations, however their underlying ecological and evolutionary causes remain poorly understood. Rensch's rule describes one such trend-in which the scaling of sexual size dimorphism (SSD) depends on which sex is larger. Where SSD is male-biased, SSD should scale hyperallometrically, as opposed to hypoallometrically where SSD is female-biased. The evidence for Rensch's rule is mixed, and comes from a small subset of total vertebrate diversity. We conducted the first empirical test of Rensch's rule in sharks, seeking to confirm or refute a long-hypothesied trend. We find that sharks violate Rensch's rule, as the magnitude of SSD increases with body size despite sharks predominantly exhibiting female-biased SSD. This adds to a growing literature of vertebrate clades that appear not to follow Rensch's rule, suggesting the absence of a single, conserved scaling trend for SSD amongst vertebrates. It is likely that selection associated with fecundity results in the "inverse Rensch's rule" observed in sharks, although additional studies will be required to fully reveal the factors underlying SSD variation in this clade.

The macroevolutionary dynamics of mammalian sexual size dimorphism.

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.

A diving beetle’s dilemma: the impact of sexual conflict on Rensch’s rule

Abstract Sexual conflict is believed to be an important evolutionary force driving phenotypic diversification, especially sexual dimorphism. Males of diving beetles sometimes resort to coercive tactics to increase their chances of successful reproduction, which can impose costs on females. Sexual conflict can also drive sexual size dimorphism (SSD), particularly in species where males are larger than females. In this context, Rensch’s rule states that SSD tends to increase with body size in species with male-biased SSD and decrease with body size in species with female-biased SSD. The role of sexual conflict in driving the evolution of the allometric relationships between males and females remains unclear. We addressed whether sexual conflict in diving beetles might drive SSD. We found that dytiscids do not follow Rensch’s rule, whereby the SSD is isometric in relationship to species body size. Species with adhesive pads (Dytiscinae) showed a more pronounced SSD than other diving beetle species. These results suggest that the presence of adhesive pads might reduce the force necessary to control female movement during copulation and drive the evolution of smaller males. The findings of this study provide new insights into the role of sexual conflict in driving the evolution of SSD in animals.

Ecosystem heating experiment reveals sex-specific growth responses in fish

Size-specific body growth responses to warming are common among animal taxa, but sex-specific responses are poorly known. Here we ask if body growth responses to warming are sex-dependent, and if such sex-specific responses vary with size and age. This was tested with sex-specific data of back-calculated individual growth trajectories, in European perch ( Perca fluviatilis) from a long-term whole-ecosystem warming experiment (6.3 °C above the surrounding sea). Warming led to both size- and sex-specific differences in growth responses. Warming had a consistent positive effect on body growth of females, but negative effects on male growth at size > 10 cm and age > 2 years. These sex-specific growth responses translate to an increased degree of female-biased sexual size dimorphism (in length-at-age) with warming. Although the exact temperature-mediated effects underlying differential growth responses could not be resolved, results imply global warming may have highly different effects during ontogeny of male and female perch. Such effects should be considered in climate warming scenarios concerning fish growth, population size-structure, and dynamics of aquatic food webs that include fish exhibiting sexual size dimorphism.

Genome-wide analysis of BMP/GDF family and DAP-seq of YY1 suggest their roles in Cynoglossus semilaevis sexual size dimorphism

Sexual size dimorphism (SSD) characterized by different body size between females and males have been reported in various animals. Gonadectomy experiments have implied important regulatory roles of the gonad in SSD. Among multiple factors from the gonad, TGF-β superfamily (especially BMP/GDF family) attracted our interest due to its pleiotropy in growth and reproduction regulations. Thus, whether BMP/GDF family members serve as crucial regulators for SSD was studied in a typically female-biased SSD flatfish named Chinese tongue sole (Cynoglossus semilaevis). Firstly, a total of 26 BMP/GDF family members were identified. The PPI network analysis showed that they may interact with ACVR2a, ACVR2b, ACVR1, BMPR2, SMAD3, BMPR1a, and other proteins. Subsequently, DAP-seq was employed to reveal the binding sites for yin yang 1 (yy1), a transcription factor involved in gonad function and cell growth partly by regulating TGF-β superfamily. The results revealed that two yy1 homologues yy1a and yy1b in C. semilaevis could regulate Hippo signaling pathway, mTOR signaling pathway, and AMPK signaling pathway. Moreover, BMP/GDF family genes including bmp2, bmp4, bmp5, gdf6a, and gdf6b were important components of Hippo pathway. In future, the crosstalk among yy1a, yy1b, and TGF-β family would provide more insight into sexual size dimorphism in C. semilaevis.

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

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

Extrinsic and intrinsic musculature of the raptorial forelegs in Mantodea (Insecta) in the light of functionality and sexual dimorphism.

Prehensile raptorial forelegs are prey capturing and grasping devices, best known for praying mantises (Mantodea) within insects. They show strong morphological and behavioral adaptations towarda lifestyle as generalist arthropod predators. In the past, few species of Mantodea were investigated, concerning morphological variability of the raptorial forelegs. Especially the knowledge of foreleg anatomy in the light of functional and comparative morphology is scarce. Our comparative approach is based on the, for arthropods very common, "female-biased sexual size dimorphism"(SSD) that occurs in almost every Mantodea species. Within Mantodea, this SSD is likely leading to a shift of the exploited ecological niche between male and female individuals due to changes in, for example, the possible prey size; which might be reflected in the chosen ecomorphs. In this context, we analyzed the musculature of the raptorial forelegs of female and male specimens in five different species with varying SSD, using high-resolution microcomputed tomography and dissection. We were able to confirm the presence of 15 extrinsic and 15 intrinsic muscles-including one previously undescribed muscle present in all species. Thus, presenting a detailed description and illustrative three-dimensional anatomical visualization of the musculature in Mantodea. Interestingly, almost no observable differences were found, neither between species, nor between the sexes. Furthermore, we homologized all described muscles, due to their attachment points, to the comprehensive nomenclature established by Friedrich and Beutel (2008), discussed potential functionality of the muscles and possible homologies to the neuropteran Mantispa styriaca (Büsse et al., 2021) and the newly introduced leg nomenclature by Aibekova et al. (2022). By elucidating the anatomy, particularly in the context of functionality and SSD, our results complement previous knowledge of the raptorial forelegs, and facilitate a better understanding of the underlying biomechanical system of the predatory strike, and ultimately, a future comparison to other insect taxa.