Extreme Sexual Dimorphism Research Articles

First genome assembly of the order Strepsiptera using PacBio HiFi reads reveals a miniature genome

Twisted-wing insects (Strepsiptera) are an enigmatic order of parasites with unusual life histories and striking sexual dimorphism. Males emerge from hosts as free-living winged adults, while females from most species remain as endoparasites that retain larval traits. Due to scarce genomic data and phylogenetic controversies, Strepsiptera was only recently placed as the closest living relative to beetles (Coleoptera). Here, we report the first PacBio HiFi genome assembly of the strepsipteran Xenos peckii (Xenidae). This de novo assembly size is 72.1 Mb, with a BUSCO score of 87.4%, N50 of 7.3 Mb, 23.4% GC content, and 38.41% repeat content. We identified 8 contigs that contain >75% of the assembly and reflect the haploid chromosome number reported from karyotypic data, and 3 contigs that exhibit sex chromosome coverage patterns. Additionally, the mitochondrial genome is 16,111 bp long and has 37 genes. This long-read assembly for Strepsiptera reveals a miniature genome and provides a unique tool to understand complex genome evolution associated with a parasitic lifestyle and extreme sexual dimorphism.

Induction of male-like mandibles in XX individuals of a stag beetle by gene knockdown of a feminizer gene transformer.

Males and females share most of the genome, but many animals show different phenotypes between the sexes, known as sexual dimorphism. Many insect species show extreme sexual dimorphism, including beetles with "weapon traits" represented by extremely developed horns and mandibles. Existing studies of sex-specific development of beetle weapon traits suggest that sex-specific gene expression plays an important role. On the other hand, contributions of the Y-chromosome, which may potentially carry genes necessary for male development, to weapon trait expression have not been examined. In holometabolous insects, including beetles, the feminizing gene transformer (tra) is roughly conserved in its feminizing function. Only females express a functional isoform of Tra, which causes female differentiation. Knocking down tra in females leads to male tissue differentiation, enabling us to analyze male phenotypes in individuals lacking a Y-chromosome (XX-males). In this study, we investigate whether the Y-chromosome is necessary for stag beetles to express male-specific weapon traits by comparing tra-knockdown-induced XX-males with natural XY males. We show that XX-males could express weapons (enlarged mandibles) as in XY-males. These results suggest that the Y-chromosome does not have a major role in weapon trait expression in this species.

Developmental asynchrony: A potential cost of extreme sexual size dimorphism in seasonal environments

Developmental asynchrony: A potential cost of extreme sexual size dimorphism in seasonal environments

Phylogenomic analysis of Stylops reveals the evolutionary history of a Holarctic Strepsiptera radiation parasitizing wild bees

Holarctic Stylops is the largest genus of the enigmatic insect order Strepsiptera, twisted winged parasites. Members of Stylops are obligate endoparasites of Andrena mining bees and exhibit extreme sexual dimorphism typical of Strepsiptera. So far, molecular studies on Stylops have focused on questions on species delimitation. Here, we utilize the power of whole genome sequencing to infer the phylogeny of this morphologically challenging genus from thousands of loci. We use a species tree method, concatenated maximum likelihood analysis and Bayesian analysis with a relaxed clock model to reconstruct the phylogeny of 46 Stylops species, estimate divergence times, evaluate topological consistency across methods and infer the root position. Furthermore, the biogeographical history and coevolutionary patterns with host species are assessed. All methods recovered a well resolved topology with close to all nodes maximally supported and only a handful of minor topological variations. Based on the result, we find that included species can be divided into 12 species groups, seven of them including only Palaearctic species, three Nearctic and two were geographically mixed. We find a strongly supported root position between a clade formed by the spreta, thwaitesi and gwynanae species groups and the remaining species and that the sister group of Stylops is Eurystylops or Eurystylops + Kinzelbachus. Our results indicate that Stylops originated in the Western Palaearctic or Western Palaearctic and Nearctic in the early Neogene or late Paleogene, with four independent dispersal events to the Nearctic. Cophylogenetic analyses indicate that the diversification of Stylops has been shaped by both significant coevolution with the mining bee hosts and host-shifting. The well resolved and strongly supported phylogeny will provide a valuable phylogenetic basis for further studies into the fascinating world of Strepsipterans.

Rediscovery and systematics of the enigmatic genus Helicostoa reveals a new species of sessile freshwater snail with remarkable sexual dimorphism.

Helicostoa sinensis E. Lamy, 1926 is a unique freshwater gastropod species with a sessile habit. This enigmatic species was first found cemented on river limestones from China about 120 years ago and described together with the genus. It was never collected again and has been considered monotypic. Here, we report the rediscovery of Helicostoa from several rivers in China, and describe a second species of this genus based on a comprehensive study. In addition to the unique sessile habit of both species, the new Helicostoa species presents one of the most remarkable cases of sexual dimorphism within molluscs. Only the adult female is sessile and the original aperture of the female is sealed by shell matter or rock, while an opening on the body whorl takes the function of the original aperture. The male is vagile, with a normal aperture. Our results confirm the recently suggested placement of Helicostoa within the family Bithyniidae. The sessility of Helicostoa species is considered as an adaption to the limestone habitat in large rivers. The extreme sexual dimorphism and secondary aperture of females are considered as adaptations to overcome the obstacles for mating and feeding that come with a sessile life style.

DNA Barcoding Unveils New Species of the Sexually Dimorphic Genus Anteon Jurine (Hymenoptera, Dryinidae) from China.

Species of Anteon Jurine, 1807 are a large group of parasitoids attacking leafhoppers, which are important insect pests. Despite their great potential in pest biological control, the taxonomy and biology of these parasitoids are far from clear. Sexual dimorphism is extreme in Anteon species and has hampered the taxonomy of these parasitoids, resulting in many species described based on a single sex. In this paper, we employed an integrated taxonomic approach for delimitating species, combining morphological examinations with DNA barcoding, to investigate Anteon species from China. In total, 53 COI sequences representing 29 species of Anteon were obtained and analyzed. On the basis of both morphology and DNA barcoding, five new species of Anteon were discovered and described: A. clariclypeum sp. nov., A. maguanense sp. nov., A. parafidum sp. nov., A. shaanxianum sp. nov., and A. shandonganum sp. nov. The neotype of A. claricolle Kieffer is designated. The sexual association of six species was confirmed by DNA barcoding, which led to the synonymy of Anteon liui Xu, Olmi & He 2010, new syn., under Anteon meifenganum Olmi, 1991. Keys to species of Anteon from the Oriental and Eastern Palaearctic are updated to contain the five new species. Our study demonstrates that DNA barcoding is a potent tool for tackling the taxonomic challenges in parasitoids with extreme sexual dimorphism.

Anatomical, phenological and genetic aspects of the host-parasite relationship between Andrena vaga (Hymenoptera) and Stylops ater (Strepsiptera).

Stylops ater is an endoparasite of the mining bee Andrena vaga with extreme sexual dimorphism and hypermetamorphosis. Its population structure, parasitization mode, genetic diversity and impact on host morphology were examined in nesting sites in Germany to better understand this highly specialized host–parasite interaction. The shift in host emergence due to stylopization was proven to be especially strong in A. vaga. Around 10% of bees hosted more than 1 Stylops, with at maximum 4. A trend in Stylops' preference for hosts of their own sex and a sex-specific position of extrusion from the host abdomen was found. Invasion of Andrena eggs by Stylops primary larvae was depicted for the first time. Cephalothoraces of female Stylops were smaller in male and pluristylopized hosts, likely due to lower nutrient supply. The genes H3, 18S and cytochrome c oxidase subunit 1 were highly conserved, revealing near-absence of local variation within Stylops. Ovaries of hosts with male Stylops contained poorly developed eggs while those of hosts with female Stylops were devoid of visible eggs, which might be due to a higher protein demand of female Stylops. Male Stylops, which might have a more energy-consuming development, led to a reduction in head width of their hosts. Host masculinization was present in the leaner shape of the metabasitarsus of stylopized females and is interpreted as a by-product of manipulation of the host's endocrine system to shift its emergence. Stylopization intensified tergal hairiness, most strongly in hosts with female Stylops, near the point of parasite extrusion, hinting towards substance-induced host manipulation.

Ontogenetic Development of Sexual Dimorphism in Body Mass of Wild Black-and-White Snub-Nosed Monkey (Rhinopithecus bieti).

Sexual dimorphism exists widely in animals, manifesting in different forms, such as body size, color, shape, unique characteristics, behavior, and sound. Of these, body mass dimorphism is the most obvious. Studies of evolutionary and ontogenetic development and adaptation mechanisms of animals' sexual dimorphism in body mass (SDBM), allow us to understand how environment, social group size, diet, and other external factors have driven the selection of sexual dimorphism. There are fewer reports of the ontogenetic development of sexual dimorphism in body mass in Rhinopithecus. This study explores the ontogenetic development pattern of SDBM in wild black-and-white snub-nosed monkeys (R. bieti), and the causes resulting in extreme sexual dimorphism compared to other colobines. A significant dimorphism with a ratio of 1.27 (p < 0.001) appears when females enter the reproductive period around six years old, reaching a peak (1.85, p < 0.001) when males become sexually mature. After the age of eight, the SDBM falls to 1.78, but is still significant (p < 0.001). The results also indicate that males had a longer body mass growth period than females (8 years vs. 5 years); females in larger breeding units had a significantly higher SDBM than those in smaller ones (2.12 vs. 1.93, p < 0.01). A comparative analysis with other colobines further clarifies that Rhinopithecus and Nasalis, which both have multilevel social organization, have the highest degree of SDBM among all colobines. The large SDBM in R. bieti can be explained through Bergman's and Rensch's rules. Overall, environmental adaptation, a distinctive alimentary system, and a complex social structure contribute to R. bieti having such a remarkable SDBM compared to other colobines. In addition, we found that females' choice for males may not be significantly related to the development of SDBM.

Phylogenomic inference of the higher classification of velvet ants (Hymenoptera: Mutillidae)

AbstractThe family Mutillidae (Hymenoptera) is a species‐rich group of aculeate wasps that occur worldwide. The higher‐level classification of the family has historically been controversial due, in part, to the extreme sexual dimorphism exhibited by these insects and their morphological similarity to other wasp taxa that also have apterous females. Modern hypotheses on the internal higher classification of Mutillidae have been exclusively based on morphology and, further, they include Myrmosinae as a mutillid subfamily. In contrast, several molecular‐based family‐level studies of Aculeata recovered Myrmosinae as a nonmutillid taxon. To test the validity of these morphology‐based classifications and the phylogenetic placement of the controversial taxon Myrmosinae, a phylogenomic study of Mutillidae was conducted using ultraconserved elements (UCEs). All currently recognized subfamilies and tribes of Mutillidae were represented in this study using 140 ingroup taxa. The maximum likelihood criterion (ML) and the maximum parsimony criterion (MP) were used to infer the phylogenetic relationships within the family and related taxa using an aligned data set of 238,764 characters; the topologies of these respective analyses were largely congruent. The modern higher classification of Mutillidae, based on morphology, is largely congruent with the phylogenomic results of this study at the subfamily level, whereas the tribal classification is poorly supported. The subfamily Myrmosinae was recovered as sister to Sapygidae in the ML analysis and sister to Sapygidae + Pompilidae in the MP analysis; it is consequently raised to the family level, Myrmosidae, stat.nov. The two constituent tribes of Myrmosidae are raised to the subfamily level, Kudakrumiinae, stat.nov., and Myrmosinae, stat.nov. All four recognized tribes of Mutillinae were found to be non‐monophyletic; three additional mutilline clades were recovered in addition to Ctenotillini, Mutillini, Smicromyrmini, and Trogaspidiini sensu stricto. Three new tribes are erected for members of these clades: Pristomutillini Waldren, trib.nov., Psammothermini Waldren, trib.nov., and Zeugomutillini Waldren, trib.nov. All three recognized tribes of Sphaeropthalminae were found to be non‐monophyletic; six additional sphaeropthalmine clades were recovered in addition to Dasymutillini, Pseudomethocini, and Sphaeropthalmini sensu stricto. The subtribe Ephutina of Mutillinae: Mutillini was found to be polyphyletic, with the Ephuta genus‐group recovered within Sphaeropthalminae and the Odontomutilla genus‐group recovered as sister to Myrmillinae + Mutillinae. Consequently, the subtribe Ephutina is transferred from Mutillinae: Mutillini and is raised to a tribe within Sphaeropthalminae, Ephutini, stat.nov. Further, the taxon Odontomutillinae, stat.nov., is raised from a synonym of Ephutina to the subfamily level. The sphaeropthalmine tribe Pseudomethocini was found to be polyphyletic, with the subtribe Euspinoliina recovered as a separate clade in Sphaeropthalminae; consequently, Euspinoliina is raised to a tribe, Euspinoliini, stat.nov., in Sphaeropthalminae. The dasylabrine tribe Apteromutillini was recovered within Dasylabrini and is proposed as a new synonym of Dasylabrinae. Finally, dating analyses were conducted to infer the ages of the Pompiloidea families (Mutillidae, Myrmosidae, Pompilidae, and Sapygidae) and the ages of the Mutillidae subfamilies and tribes.

A new species of spiny Rineloricaria (Siluriformes: Loricariidae) from the Rio Paraba do Sul basin and costal rivers from Rio de Janeiro State.

Although the genus Rineloricaria is widely distributed in the Neotropical region, its species usually occupy single drainages with high habitat fidelity. Rineloricaria species show evident sexual dimorphism with hypertrophied odontodes in sexually mature males. Here, we describe a new species of Rineloricaria present in the Rio Paraiba do Sul basin and coastal rivers in Rio de Janeiro State. The new species has extreme sexual dimorphism making possible to differentiate it from all congeners. The new species can also be separated from other sympatric species by morphometric characteristics and dermal plates pattern.

Mitogenomes resolve the phylogeography and divergence times within the endemic New Zealand Callaeidae (Aves: Passerida)

AbstractThe biogeographical origins of the endemic birds of New Zealand (Aotearoa) are of great interest, particularly Palaeogene lineages such as Callaeidae, a passerine family characterized by brightly coloured wattles behind the beak and, in some cases, extreme sexual dimorphism in bill size and shape. Ancestral representatives of Callaeidae are thought to have split from their closest relatives outside New Zealand in the Oligocene, but little is known about the timing of divergences within the family. We present a fully dated molecular phylogeny of Callaeidae mitogenomes and discuss the biogeographical implications. Our results suggest that formation of Pliocene marine seaways, such as the Manawatu Strait, are likely to have played a significant role in the differentiation of North Island and South Island kōkako (Callaeas spp.) and saddlebacks/tīeke (Philesturnus spp.).

Recent evolution of extreme sexual dimorphism in the huia (Heteralocha acutirostris; Callaeidae)

The New Zealand wattlebirds (Callaeidae) are an endemic New Zealand passerine family whose species show extreme variation in bill morphology. In particular, the extinct huia (Heteralocha acutirostris) has attracted considerable attention because it exhibited extreme sexual dimorphism in bill morphology. However, the phylogenetic relationships within the Callaeidae, crucial for understanding bill evolution in the family, have not been resolved to date. Here we present phylogenies based on complete mitochondrial genome sequences and nuclear ultraconserved elements. Kōkako (Callaeas spp.) is strongly supported as sister taxon to saddleback/tīeke (Philesturnus spp.) and huia, diverging around 6.8 Ma. Saddleback and huia are estimated to have split from each other 5 Ma, indicating that the extreme sexual bill dimorphism in huia has evolved within this time frame. Our estimates for the divergences within the Callaetidae are similar to, or younger than, those of most other endemic New Zealand avian families, therefore the observed bill variation is not a consequence of a longer divergence time. Instead, the expansion of the huia into the wood-foraging niche, combined with the sexual dimorphism it evolved in order to optimise feeding on this resource, has been the main contributor to the large variation of bill morphologies within this family.

Associations of mutillid wasps (Hymenoptera, Mutillidae) with eusocial insects

Although disturbing, this scenario is common within the Mutillidae, as the most striking feature is undoubtedly their marked sexual dimorphism: all known females are wingless and most males are winged, although some species have winged males. Reduced (brachypterous) or apterous. This extreme sexual dimorphism has historically led to numerous descriptions of new species, and even genera, based on a single sex, causing the family to remain poorly studied throughout the world. The objective of this paper is to verify the association of mutillid wasps (Hymenoptera, Mutillidae) with eusocial insects. To this end, a bibliographic survey of Mutillidae was carried out in the years 1937 to 2021. Only complete articles published in scientific journals and expanded abstracts presented at national and international scientific events. Data were also obtained from platforms such as: Academia.edu, Frontiers, Qeios, Pubmed, Biological Abstract, Publons, Dialnet, World, Wide Science, Springer, RefSeek, Microsoft Academic, Science and ERIC.

From the Ethiopian Bale Mountains hotspotFilopalpinae subfam. nov., a new taxon of Laniatorean harvestmen based on external and genital morphology (Arachnida, Opiliones, Assamiidae).

Filopalpinae subfam. nov. is proposed as a new subfamily within family Assamiidae based on a new genus, Filopalpus gen. nov. and on five new species: F. joschmidti sp. nov., F. bale sp. nov., F. kakaensis sp. nov., F. altomontanus sp. nov. and F. niger sp. nov. All originate from the highlands of Ethiopia, namely the Bale Mountains and adjacent volcanoes in Oromia State. Species of the new subfamily are characterized by dense body cover with pointed tubercles causing a hedgehog appearance of the body (dorsal side, partly ventral side), extreme sexual dimorphism in pedipalps (in males thread-like long and thin surpassing body length by about four to six times, devoid of apophyses and thorns; in females short and stout about body length, with a distal grasping hand formed by apophyses and strong setae of tibia and tarsus, and tarsal claw). Male genital morphology is characterized by a hemolymph-pressure system of truncus penis and glans, a dorsal sub-distal tube-like glans with an inner prickly funnel, which is everted by hemolymph pressure during courtship. These male genital characters place the present species in Assamiidae, but external morphology points to a strongly different separate evolutionary unit within this family. The five species known to date were secured at altitudes between 2830 and 4100 m. At least two of the collecting areas are now devoid of forest due to human impact. To secure the present specimens at high-altitude localities was possible only by searching in remote microhabitats unavailable for cattle and man-made fire. A perspective on current subfamilies of Assamiidae and on pedipalpal morphology and evolution is presented.

A new genus of Australian orb-weaving spider with extreme sexual size dimorphism (Araneae, Araneidae)

The new Australian orb-weaving spider genusMangroviain the family Araneidae Clerck, 1757 is described. It is characterised by extreme sexual size-dimorphism (eSSD) with females (total length 8–10 mm) ca. 3 to 5 times larger than males (2.5–3 mm). WhilstMangroviashares with the informal Australian ‘backobourkiine’ clade a single seta on the male pedipalp patella, the genus is probably more closely related to the ‘zealaraneines’ or associated genera. In addition to eSSD and the single patellar spine, the genus is characterised by a distinct subterminal embolus branch in males. The new genus includes two species: the type speciesMangrovia albida(L. Koch, 1871)comb. nov.(=Epeira fastidiosaKeyserling, 1887,new syn.) from Queensland andMangrovia occidentalissp. nov.from Western Australia. Both species are apparently coastal and occur in mangroves, but also in riparian woodland. Spiders were found resting in rolled-up leaves adjacent to their orb-web.

Unusual sexually dimorphic head morphology in Lauxaniidae (Diptera: Lauxanioidea)a new species of the genus Trivialia Malloch from Peru.

A new species of the New World genus Trivialia Malloch from Peru is described and illustrated, along with discussion of unusual head morphology in Lauxaniidae. This new species represents an odd case where only a single known species in an otherwise non-dimorphic genus displays extreme sexual dimorphism.

Exploring sperm whale population demographics in the northern Gulf of Mexico using passive acoustic monitoring

Sperm whales are a sexually dimorphic species widely distributed throughout the world’s oceans, with social units of mature females and young thought to inhabit tropical and temperate waters, while individual mature males travel to higher latitudes in small bachelor groups or alone. Seasonal population demographics, particularly sex distributions, and the group structures of sperm whales have not been closely analyzed for the Gulf of Mexico. Utilizing the unique multi-pulse structure of sperm whale echolocation clicks, their total body length can be estimated, and, as a result of their extreme sexual dimorphism, their sex can be determined. Continuous acoustic recordings from June 2018 through June 2020 by the Environmental Acoustic Recording System (EARS) buoys, deployed off the coast of Louisiana, were analyzed using CABLE software [Beslin et al., JASA (2018)]. The results suggest that the sperm whale population is dominated by females in both summer and winter seasons, although mature whales of both sexes were detected in both seasons. Additionally, for each year of study, respectively, the mean size and the total number of whales detected were greater in winter months. Further insights into group structures will be discussed in the presentation. [Research supported by NSF REU (Award No. 1659853) and BOEM.]

The Evolution of Social Behaviour

The Evolution of Social Behaviour

The Infraorder Coccomorpha (Insecta: Hemiptera).

The scale insects (infraorder Coccomorpha) are the most morphologically specialised members of the Hemiptera. They form a monophyletic group within the suborder Sternorrhyncha, having one-segmented tarsi and a single claw (all other hemipterans have a double claw). They show extreme sexual dimorphism: the more-or-less sessile adult females are wingless and larviform, whereas the motile adult males mostly are winged and lack mouthparts. Within the Coccomorpha, 54 families are currently recognised, of which 20 are known only from fossils and 34 are extant (García Morales et al. 2016).

Evolution of sexual dimorphism and polychromatism in a lineage of tiger moths (Lepidoptera: Erebidae): advancing knowledge of a taxonomically chaotic group.

Pericopina is divided into 36 genera, with the greatest diversity recorded in the Neotropics. Studies on the taxonomy and systematics of pericopines are scarce, and one of the few phylogenetic hypotheses available in the literature places some Afro-Indo-Malayan lineages among the Neotropical representatives. Through a survey of adult morphological characters, we analyzed the phylogenetic relationships in Pericopina including Nyctemera and other Afro-Indo-Malayan genera as putative members of this subtribe. Additionally, we tested the monophyly of Dysschema, a key genus to understanding the evolutionary patterns of the extreme sexual dimorphism and polychromatism in Pericopina. Our cladistic analysis, based on 162 morphological characters, suggests that Pericopina is a polyphyletic group. Xenosoma is the only genus among the Neotropical pericopines related to the Afro-Indo-Malayan species; Scearctia is closely related to Lithosiini, and Pteroodes shows morphological similarities with Phaegopterina. Additionally, Seileria is a new junior subjective synonym of Thyrgis. The monophyly of Dysschema is supported only if the monotypic genera Myserla and Are are included. These are herein designated new synonyms of Dysschema. Our findings suggest that intersexual polychromatism and intersexual polymorphism for wing characters have arisen multiple times in the evolutionary history of Pericopina. Intersexual polychromatism is also widely distributed within Dysschema, perhaps representing a derived feature with multiple origins in the genus.