Male Dimorphism Research Articles

Two new species of Caribbiantes, with the redescription of the type species and a review of male genital patterns in Antillean Stenostygninae (Opiliones: Laniatores: Biantidae)

Caribbiantes cubanus Šilhavý, 1973, type species of genus Caribbiantes Šilhavý, 1973, is redescribed based on abundant material from the type locality, providing new data on its morphological variability and penis morphology. Two new species of Caribbiantes are described, C. obtusus sp. nov. and C. barbai sp. nov., based on additional specimens from central and eastern Cuba, for which we give information on their geographical distribution, intraspecific variability and habitat. A new diagnosis for Caribbiantes and updated geographic distributions of the included species are provided. The sexually dimorphic glandular structures on the metatarsus III of males for all Caribbiantes species are described. Male dimorphism, most evident in the robustness of the chelicerae, is reported for the studied species. The male genitalia patterns of Antillean stenostygnines species are described. The phylogenetic affinity of Antillean stenostygnines with Stenostygnus Simon, 1879, a genus from the north of South America, is discussed based on some morphological traits.

Are weapon allometries steeper in major or minor males? A meta-analysis

Abstract Competition for mates can drive the evolution of exaggerated weaponry and male dimorphism associated with alternative reproductive tactics. In terrestrial arthropods, male dimorphism is often detected as non-linear allometries, where the scaling relationship between weapon size and body size differs in intercept and/or slope between morphs. Understanding the patterns of non-linear allometries is important as it can provide insights into threshold evolution and the strength of selection experienced by each morph. Numerous studies in male-dimorphic arthropods have reported that allometric slopes of weapons are shallower in large “major” males compared to small “minor” males. Because this pattern is common among beetles that undergo complete metamorphosis (holometabolous), researchers have hypothesized that the slope change reflects resource depletion during pupal development. However, no comprehensive survey has examined the generality of this trend. We systematically searched the literature for reports of weapon allometries in male dimorphic species and conducted a phylogenetically controlled meta-analysis to explore the factors influencing the difference in slopes between morphs. Our search identified 59 effect sizes from 19 studies, 50 species, and 5 orders of terrestrial arthropods. We found strong evidence that metamorphosis type influences the patterns of weapon allometries. Slopes were significantly steeper in minor males compared to major males in holometabolous species, but there was no difference in slopes between morphs in hemimetabolous species (i.e. those that undergo incomplete or no metamorphosis). These results support the hypothesis that holometabolous species face a resource ceiling during pupal development that limits the exaggeration of weapon size.

Contribution to knowledge of the oribatid mite genus Idiozetes (Acari, Oribatida, Idiozetidae), with description of a new sexually dimorphic species from Vietnam

A new species of Idiozetes (Oribatida, Idiozetidae)—I. schusteri sp. n.—is described, based on adults (males and females) collected from litter, tree branches and tree bark in southern Vietnam. This species is characterized by the following morphological traits: sexually dimorphic males with two large tubercles posteriorly on the notogaster; tutoria fused dorsally on prodorsum forming bidentate structure; nine pairs of notogastral setae (c, la, lm, h<sub>1</sub>–h<sub>3</sub>, p<sub>1</sub>–p<sub>3</sub>); five pairs of notogastral saccules; eight pairs of genital setae; monodactylous. The generic diagnosis is revised. An identification key, distribution and habitats to the known representatives of Idiozetes are provided.

Weapon allometry and shape variation in the Helm’s stag beetle (Geodorcus helmsi)

Abstract Many animals develop and use exaggerated weapons in contests over access to mating opportunities. Stag beetles (family Lucanidae) show striking sexual dimorphism, where the males have heavily exaggerated mandibles that the females do not possess. In some genera, size and shape can also vary drastically between small and large males resulting in discrete alternative male morphs, described as male dimorphism. The genus Geodorcus is a poorly studied and threatened group of stag beetles that are endemic to New Zealand. Geodorcus helmsi is the most widespread species in this genus and presents an opportunity to test for the presence of both sexual and male dimorphism and investigate the scaling relationships (allometry) of mandibles in this group. We used linear and geometric morphometric analyses on wild populations and museum specimens from Stewart Island, New Zealand, to assess whether G. helmsi exhibits male dimorphism. We found that within a single population, there is no evidence for alternative male morphs, but a gradual shift between smaller and larger individuals. We also found that male mandibles exhibit steep positive allometry in contrast to the negative allometry found in the mandibles of females, as is often found for sexually selected weaponry. Moreover, we found evidence that left and right mandibles of G. helmsi are subtly asymmetric. Our results provide context for the competitive behaviour observed in this species, and give insights into potential trade-offs between smaller and larger individuals of the Helm’s stag beetle.

Revision of Troporhogas Cameron (Hymenoptera, Braconidae, Rogadinae) with six new species from India and Thailand.

The genus Troporhogas Cameron, 1905 from the Indo-Malayan region is reviewed. Six new species, Troporhogasalboniger Quicke, Loncle & Butcher, sp. nov., T.benjamini Quicke, Loncle & Butcher, sp. nov., T.hugoolseni Quicke, Loncle & Butcher, sp. nov., T.rafaelnadali Quicke, Loncle & Butcher, sp. nov., and T.rogerfedereri Quicke, Loncle & Butcher, sp. nov. from Thailand, and T.anamikae Ranjith, sp. nov. from India are described and illustrated photographically, bringing the total number of species of the genus known from the Indo-Malayan Region to 19. Troporhogas is recorded for the first time from India. A key is included to differentiate Troporhogas species. A four-gene ML tree based on COI, Cytb, 16S and 28S is reconstructed, representing the six new species. Troporhogascontrastus Long, 2014, originally described from Vietnam, is recorded from Thailand for the first time. The holotypes of the type species, Troporhogastricolor Cameron, 1905 and that of its junior synonym Iporhogas are illustrated, and photographs are presented of all the species known only from China and Sri Lanka. Sexual colour dimorphism of males of several species is described for the first time. Drawings summarising the different patterns of black marks on the metasoma that aid species recognition are presented.

An integrative taxonomic approach to the Atlantic Hansarsia (formerly Nematoscelis) yields new krill taxa (Crustacea: Euphausiidae)

A recent molecular phylogenetic and biogeographic study on the krill genus Hansarsia revealed undescribed cryptic diversity in the Atlantic. Each of four species analysed encompassed robust molecular clades that were linked to dimorphic males in H. microps, H. atlantica and H. tenella. We tested the robustness and divergence of the observed clades using an integrative approach including (1) three independent species delimitation methods for the mitochondrial COI gene (ASAP, GMYC, bPTP), (2) variability of two nuclear genes (H3 and ITS1) and (3) morphological analysis (MDS and PCA) with a dataset of 22 characters scored for 131 specimens. Both molecular and morphological analyses resulted in at least six distinct clades within the Atlantic Hansarsia. The strongest divergence was revealed between the two clades of H. tenella, one of which we diagnosed as a new species. Two clades of H. megalops also showed significant divergence but in the absence of males, we were reluctant to designate new species. Different clades linked to male forms in H. microps and H. atlantica are suggested as an incipient species. We also hypothesise an unusual trend in the evolution of euphausiids, in which visual recognition enhances tactile interaction during mating. Our results show that analyses of ostensibly well studied groups may yet yield taxonomic surprises. ZooBank: urn:lsid:zoobank.org:pub:AE045636-50EF-450A-B9B3-9231E8B91522

Manipulation of male display traits has minimal effects on reproductive outcome in a jumping spider with dimorphic males

Manipulation of male display traits has minimal effects on reproductive outcome in a jumping spider with dimorphic males

New Benthopelagic Calanoids (Copepoda: Clausocalanoidea) of the deep Japan Sea

Two new species of benthopelagic calanoid copepod Bradfordian genera Pseudophaenna japonica sp. nov. and Xantharus dubius sp. nov. are described from collections of the Russian-German deep-sea expedition (SoJaBio) to the Sea of Japan onboard of the R/V Akademik Lavrentyev, 51st cruise taken close to the sea bed. The rare calanoid copepod genera Pseudophaenna Sars, 1902 and Xantharus Andronov, 1981 and a rare aetideid species Bradyidius rakuma (Zvereva, 1977) are recorded for the first time from the Japan Sea; the male of B. rakuma is described for the first time. Pseudophaenna japonica sp. nov. is the second species described for the genus Pseudophaenna and is distinguished by biramous rostrum, antennule ancestral segment XXII without seta, details of oral parts setation in females and in P5 structure in dimorphic males. Xantharus dubius sp. nov. is described from males and is distinguished from congeners in the antennule ancestral segments XXII and XXIII not comparatively small relative to the segment XXI and in the large and robust uniramous P5. In the collections of the expedition SoJaBio in 2010 from the Japan Sea the near-bottom benthopelgic fauna of Calanoida have been represented by these species only and they all belong to the calanoid superfamily Clausocalanoidea.

Differences in the Diets of Female and Male Red Deer: The Meaning for Sexual Segregation.

Sexual segregation is a common phenomenon among animals, particularly dimorphic ones. Although widely addressed, the reasons and consequences of sexual segregation are still an important topic in need of better understanding. In this study, we mainly evaluate the diet composition and feeding behaviour of animals, which are related to the use of different habitats by the sexes, a special case of sexual segregation also termed habitat segregation. Sexually size dimorphic males and females often have different energetic and nutritional needs and, thus, different diets. We collected fresh faecal samples from wild Iberian red deer (Cervus elaphus L.) in Portugal. Samples were analysed in terms of diet composition and quality. As expected, both sexes differed in their diet composition, with males eating more arboreous species than females, but this difference was affected by sampling periods. Diet composition of both sexes had the biggest differences (and the lowest overlap) in spring, which corresponds to the end of gestation and beginning of birth. These differences might be a consequence of the sexual body size dimorphism characteristic of this species, as well as of different needs due to different reproductive costs. No differences regarding the quality of the excreted diet were observed. Our results may help to understand some patterns of sexual segregation observed in this red deer population. However, besides foraging ecology, other factors may also be contributing to sexual segregation in this Mediterranean population of red deer, and further studies focusing on sexual differences regarding feeding behaviour and digestibility are needed.

Individual reflectance of solar radiation confers a thermoregulatory benefit to dimorphic males bees (Centris pallida) using distinct microclimates.

Incoming solar radiation (wavelengths 290-2500 nm) significantly affects an organism's thermal balance via radiative heat gain. Species adapted to different environments can differ in solar reflectance profiles. We hypothesized that conspecific individuals using thermally distinct microhabitats to engage in fitness-relevant behaviors would show intraspecific differences in reflectance: we predicted individuals that use hot microclimates (where radiative heat gain represents a greater thermoregulatory challenge) would be more reflective across the entire solar spectrum than those using cooler microclimates. Differences in near-infrared (NIR) reflectance (700-2500 nm) are strongly indicative of thermoregulatory adaptation as, unlike differences in visible reflectance (400-700 nm), they are not perceived by ecological or social partners. We tested these predictions in male Centris pallida (Hymenoptera: Apidae) bees from the Sonoran Desert. Male C. pallida use alternative reproductive tactics that are associated with distinct microclimates: Large-morph males, with paler visible coloration, behave in an extremely hot microclimate close to the ground, while small-morph males, with a dark brown dorsal coloration, frequently use cooler microclimates above the ground near vegetation. We found that large-morph males had higher reflectance of solar radiation (UV through NIR) resulting in lower solar absorption coefficients. This thermoregulatory adaptation was specific to the dorsal surface, and produced by differences in hair, not cuticle, characteristics. Our results showed that intraspecific variation in behavior, particular in relation to microclimate use, can generate unique thermal adaptations that changes the reflectance of shortwave radiation among individuals within the same population.

Heterogeneities in infection outcomes across species: sex and tissue differences in virus susceptibility.

Species vary in their susceptibility to pathogens, and this can alter the ability of a pathogen to infect a novel host. However, many factors can generate heterogeneity in infection outcomes, obscuring our ability to understand pathogen emergence. Such heterogeneities can alter the consistency of responses across individuals and host species. For example, sexual dimorphism in susceptibility means males are often intrinsically more susceptible than females (although this can vary by host and pathogen). Further, we know little about whether the tissues infected by a pathogen in one host are the same in another species, and how this relates to the harm a pathogen does to its host. Here, we first take a comparative approach to examine sex differences in susceptibility across 31 species of Drosophilidae infected with Drosophila C Virus (DCV). We found a strong positive inter-specific correlation in viral load between males and females, with a close to 1:1 relationship, suggesting that susceptibility to DCV across species is not sex specific. Next, we made comparisons of the tissue tropism of DCV across seven species of fly. We found differences in viral load between the tissues of the seven host species, but no evidence of tissues showing different patterns of susceptibility in different host species. We conclude that, in this system, patterns of viral infectivity across host species are robust between males and females, and susceptibility in a given host is general across tissue types.

Reticulated evolution marks the rapid diversification of the Delphinoidae

Species vary in their susceptibility to pathogens, and this can alter the ability of a pathogen to infect a novel host. However, many factors can generate heterogeneity in infection outcomes, obscuring our ability to understand pathogen emergence. Such heterogeneities can alter the consistency of responses across individuals and host species. For example, sexual dimorphism in susceptibility means males are often intrinsically more susceptible than females (although this can vary by host and pathogen). Further, we know little about whether the tissues infected by a pathogen in one host are the same in another species, and how this relates to the harm a pathogen does to its host. Here, we first take a comparative approach to examine sex differences in susceptibility across 31 species of Drosophilidae infected with Drosophila C Virus (DCV). We found a strong positive inter-specific correlation in viral load between males and females, with a close to 1:1 relationship, suggesting that susceptibility to DCV across species is not sex specific. Next, we made comparisons of the tissue tropism of DCV across seven species of fly. We found differences in viral load between the tissues of the seven host species, but no evidence of tissues showing different patterns of susceptibility in different host species. We conclude that, in this system, patterns of viral infectivity across host species are robust between males and females, and susceptibility in a given host is general across tissue types.

Multimale breeding aggregations by “many-friends” snakes: courtship behaviours by Malagasy Pseudoxyrhophiine snakes, Dromicodryas bernieri and D. quadrilineatus, and their sexual size dimorphism

When several male snakes dispute over one female in the breeding season, two major male-male rivalries are known to occur: male-male combat and multimale breeding aggregation. The roles of male body size and the degree of sexual size dimorphism are different between these rivalries. We report field observations of mating behaviour including a multimale breeding aggregation of pseudoxyrhophiins, Dromicodryas bernieri and D. quadrilineatus, in northwestern Madagascar, which have a local name, “Maro longo”, meaning “many friends”. To examine the relationships between sexual size dimorphism and mating strategies of males, we also analysed the body size of the two species of Dromicodryas and two other pseudoxyrhophiins, Leioheterodon madagascariensis and L. modestus, which are known to exhibit the male-male combat. Our data obtained during a long-term field study showed that D. bernieri and D. quadrilineatus have female-biased sexual size dimorphism, whereas L. madagascariensis and L. modestus have male-biased sexual size dimorphism. This result conforms to the general tendency of the relationship between body size and male-male rivalry in snakes.

Estimation of Stature from Index Finger Length and Sexual Dimorphism in Adult Chakma Males and Females

Background: Estimation of stature from index finger length in adult Chakma males and females and also to observe gender difference was the main purpose of this study. Materials and methods: It was a cross-sectional analytical study conducted over 104 adult healthy Chakma males and females (52 males and 52 females) residents of Chattogram Hill Tracts area in the year 2016 and 2017. Subject selection was done by convenience sampling technique and stature and index finger length were measured and data were documented in SPSS version 19. Results: A highly significant (p<0.001) gender difference was found in index fingers length. Mean Multiplication Factor (M.F.) to estimate stature in males was 25.1239 and 25.1149 for right and left index finger respectively and in female was 25.2505 and 25.2135 for right and left index finger respectively. A highly significant (p<0.001) positive correlation was found between stature and right index finger length 0.571 and left index finger length 0.576 in Chakma males. The stature and right index finger length 0.630 and left index finger length 0.679 in Chakma females respectively. Conclusion: This study found multiplication factors for right and left index finger length to estimate stature in a correct way and found a linear correlation between stature and index fingers length. There was significant gender difference present between index fingers length in between adult Chakma males and females. IAHS Medical Journal Vol 5(1), June 2022; 22-26

A new brackish tanaidacean, Sinelobus kisui sp. nov. (Crustacea, Peracarida, Tanaidacea), from Japan, with a key to Sinelobus species and barcode information from two loci

We describe the new brackish tanaidid species Sinelobus kisuisp. nov. from Hagi, Yamaguchi, Japan. Sinelobus kisui is similar to S. barretti and S. vanhaareni in having antennal article 2 with one outer distal seta, the dorsodistal crotchet on pereopods 2 and 3 carpi shorter than half propodus length, and pereopodal carpi 2–6 with five distal crotchets, but differs from them in having (1) the inner of two ventro-subdistal circumplumose setae on the maxillipedal endite longer than the outer; (2) the maxillipedal endite with one mid-inner spiniform seta; (3) the pereopod-1 propodus with one middle setulate seta; and (4) the pleopod-1 protopod lacking inner plumose setae. Our study confirmed that character states of the chelipeds in strongly dimorphic males are useful in Sinelobus taxonomy. We determined partial sequences for the cytochrome c oxidase subunit I (COI; cox1) and 18S rRNA (18S) genes in S. kisui for future DNA barcoding and phylogenetic analyses. Morphological and/or molecular data reveal that S. kisui also occurs in Kagawa and Osaka, Japan. A key to species in Sinelobus is provided.

Enigmatic male dimorphism in the Phlaeothripinae (Thysanoptera, Phlaeothripidae), with description of a new genus and species

Nazonothrips toshifumii gen. et sp. n. is described from unidentified fungus in Taiwan. This fungus-feeding species probably belongs to the tribe Plectrothripini of the subfamily Phlaeothripinae. The males of the new species exhibit a strange allometric growth that appears to involve two patterns of variation, but it is not possible to be certain due to the small number of available specimens.

Interactions Between Individuals and Sex Rather Than Morphological Traits Drive Intraspecific Dung Removal in Two Dung Beetle Species

Dung beetle functional ecology has traditionally focused on studying the relation between traits and ecosystem functions in multispecies assemblages, often ignoring the contribution of behavioral interactions and trait variability within species. Here we focus on the factors that affect dung removal at an intraspecific level in two horned dung beetle species with dimorphic males (Onthophagus taurus and Onthophagus verticicornis). By setting treatments for each species with single individuals (one female, F; one major male, M; one minor male, m) or with pairs of individuals (MF, mF, MM, mm, FF), we examined the effect on dung removal of morphological traits (head, pronotum, leg, horn), sex, and interactions between individuals. Our results showed that dung removal at an intraspecific level depended more on sex and behavioral interactions than on the underlying morphological traits, whose effects on dung removal were negligible. Single females generally removed more dung than single males, which suggests that females are more effective than males. In both species, pairs with at least one female (MF, mF, FF) showed high dung removal efficiency, but did not perform differently from the sum of single treatments (M + F, m + f, F + F). This suggests an additive effect: males and females (or two females) join their efforts when they are together. The pairs with only males (MM and mm) removed less dung than the sum of the single individuals (M + M and m + m), which indicates a mutual inhibition of males. In both species, male morphs performed similarly as they removed the same amount of dung. Despite our results are limited to two Onthophagus species, we suggest that the intraspecific functional ecology of dung beetles might be more influenced by behavioral interactions and sex rather than by morphological traits.

Bimodal frequency distribution as a criterion for dimorphism in male rhinoceros beetles (Coleoptera: Scarabaeidae: Dynastinae)

AbstractBateson & Brindley (1892) reported that males of the rhinoceros beetle Xylotrupes gideon are dimorphic (i.e. occurring in two distinct forms) with respect to size of the prominent cephalic horn. This claim was based on a comparison of frequency distributions for size of the horn (bimodal) and size of the body (unimodal). Bateson and Brindley did not realize, however, that a bivariate plot of horn length against body size follows a steep, S-shaped trajectory, or that steepness of such a curve—and not dimorphism—underlies the bimodal frequency distribution for size of the horn. The bivariate distribution for horn size vs. body size is continuous and without breaks or interruptions, so the beetles merely exhibit a pattern of allometric variation that went unrecognized at the time. Other species of dynastine beetle also display patterns of sigmoid allometry, but only those with the steepest slopes for the allometric curve also have bimodal frequency distributions for size of the horn. The concept of male dimorphism in X. gideon and other dynastine beetles needs to be reconsidered in the light of findings reported here and elsewhere.

A new sexually dimorphic Hyphessobrycon from the western Amazon basin (Characiformes: Characidae).

A new species of Hyphessobrycon presenting dimorphic males is described from the western Amazon basin in Brazil, Colombia, Ecuador, and Peru. The new species has been mistakenly identified in the literature with the non-congener Hemigrammus marginatus, with which shares a similar color pattern by presenting dark patches of dark pigmentation on caudal-fin lobes. It can be distinguished from the latter species, as well as from Hemigrammus durbinae, and two similar congeners, Hyphessobrycon diancistrus and Hy. otrynus, all of which sharing the same caudal fin color pattern, by the combination of presenting a dark patch of pigmentation on the dorsal fin, a single large anal-fin hook at the last unbranched anal-fin ray in mature males, and a moderately high body depth (22.432.5 % SL, mean 28.4 %). The new species is more similar to Hyphessobrycon diancistrus, which is putatively its closely related taxon. A putative close relationship with Hyphessobrycon otrynus, and with a non-congener presenting a distinct color pattern but sharing a similar sexual dimorphism on anal-fin hook morphology, Hemigrammus boesemani, is suggested.

A meta-analysis of the association between male dimorphism and fitness outcomes in humans.

Humans are sexually dimorphic: men and women differ in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone. Sexual selection hypotheses posit that, ancestrally, more 'masculine' men may have acquired more mates and/or sired more viable offspring. Thus far, however, evidence for either association is unclear. Here, we meta-analyze the relationships between six masculine traits and mating/reproductive outcomes (96 studies, 474 effects, N = 177,044). Voice pitch, height, and testosterone all predicted mating; however, strength/muscularity was the strongest and only consistent predictor of both mating and reproduction. Facial masculinity and digit ratios did not significantly predict either. There was no clear evidence for any effects of masculinity on offspring viability. Our findings support arguments that strength/muscularity may be sexually selected in humans, but cast doubt regarding selection for other forms of masculinity and highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.