Horn Formation Research Articles

Dyke emplacement under mixed loading conditions: Insights from the Dharwar Craton, India

Dykes are intrusive igneous bodies that play crucial role in the supply and ascent of magma to the Earth’s crust. Magma can intrude along pre-existing anisotropies such as fractures or foliations present within the host rock or it may create its own path by fracturing the host rock. In the latter scenario, when fractures are formed by the pressure exerted by the invading magma, a dyke’s outcrop shape and geometry are diagnostic of the conditions under which it evolved. Here, we report mafic dykes emplaced within the younger granites of Dharwar Craton, peninsular India. Outcrop attributes of these dykes are characteristic of emplacement under conditions of mixed mode loading. We discuss different discrete modes of fracture formation and their possible combinations to understand the generation and eventual emplacement of dykes under mixed mode loading. This leads to the development of a comprehensive sequence of progressive dyke evolution under mixed mode I-III loading and thereby distinguishing incremental orders of dyke horn formation. We further apply this knowledge along with collected field evidence on dyke body geometries to propose an evolutionary model of dyke formation and emplacement within the Chitradurga granite under varying regional stress fields of the Chitradurga Schist Belt, Western Dharwar Craton, India. We infer, that the dykes initiated as extensional fractures within an earlier NE-SW directed compressive stress field and were subsequently sheared sinistrally by the effect of the adjacent Chitradurga Shear Zone on account of a later E-W to ESE-WNW directed compression.

Eye development influences horn size but not patterning in horned beetles.

Understanding the origin of novel morphological traits is a long-standing objective in evolutionary developmental biology. We explored the developmental genetic mechanisms that underpin the formation of a textbook example of evolutionary novelties, the cephalic horns of beetles. Previous work has implicated the gene regulatory networks associated with compound eye and ocellar development in horn formation and suggested that horns and compound eyes may influence each other's sizes. Therefore, we investigated the functional significance of genes central to visual system formation in the initiation, patterning, and size determination of head horns across three horned beetle species. We find that while the downregulation of canonical eye patterning genes reliably reduces or eliminates compound eye formation, it does not alter the position or shape of head horns yet does result in an increase in relative horn length. We discuss the implications of our results for our understanding of the genesis of cephalic horns in particular and evolutionary novelties in general.

Histological characterisation of the horn bud region in 58 day old bovine fetuses.

The presence of horns in domestic ruminants, such as cattle, sheep and goats, has financial and welfare implications. The genetic interactions that lead to horn development are not known. Hornless, or polled, cattle occur naturally. The known causative DNA variants (Celtic, Friesian, Mongolian and Guarani) are in intergenic regions on bovine chromosome 1, but their functions are not known. It is thought that horns may be derived from cranial neural crest stem cells and the POLLED variants disrupt the migration or proliferation of these cells. Relaxin family peptide receptor 2 (RXFP2) is more highly expressed in developing horns in cattle compared to nearby skin and has been shown to play a role in horn development in sheep. However, the role of RXFP2 in horn formation is not understood. Histological analyses of cranial tissues from homozygous horned and polled cattle fetuses at day 58 of development was carried out to determine the differences in the structure of the horn bud region. Condensed cells were only observed in the horn bud mesenchyme of horned fetuses and could be the progenitor horn cells. The distribution of neural crest markers (SOX10 and NGFR) and RXFP2 between horned and polled tissues by immunohistochemistry was also analysed. However, SOX10 and NGFR were not detected in the condensed cells, and therefore, these cells are either not derived from the neural crest, or have differentiated and no longer express neural crest markers. SOX10 and NGFR were detected in the peripheral nerves, while RXFP2 was detected in peripheral nerves and in the horn bud epidermis. Previous research has shown that RXFP2 variants are associated with horn phenotypes in cattle an sheep. Therefore, the RXFP2 variants may affect the development of the epidermis or peripheral nerves in the horn bud.

Sheep with Partial RXFP2 Knockout Exhibit Normal Horn Phenotype but Unilateral Cryptorchidism1

Comprehending the genetic basis of economically important traits is of significant importance to enhance livestock breeding. In domestic ruminants, hornlessness is becoming a more desirable trait since horns could lead to accidental injuries to animals and producers. Recent studies have identified the relaxin family peptide receptor 2 (RXFP2) as a primary candidate gene associated with the presence and absence of horns in sheep. However, no sufficient molecular biology-based analyses were performed to validate the association and function of RXFP2 in sheep. Noticeably, previous studies in both humans and mice have provided evidence supporting the involvement of RXFP2 in testicular descent. To validate the potential function of the RXFP2 gene in sheep, we used the CRISPR/Cas9 technology to obtain RXFP2-disrupted sheep individuals. Initially, highly efficient sgRNAs, targeting RXFP2, were screening through in vitro cleavage assays and cellular assessments. Then, two RXFP2-disrupted lambs were generated by intracytoplasmic microinjection of CRISPR/Cas9-sg1 ribonucleoprotein, with an efficiency of 81.84 and 37.17%, respectively. No potential off-target events were detected. Western blot analysis showed that RXFP2 expression was significantly reduced in the pedicle skin of edited lambs (P=0.034). Intriguingly, although the partial disruption of RXFP2 did not affect the horn phenotype in sheep, it led to an obvious unilateral cryptorchidism. These results provide evidence for a hitherto ambiguous link between both horn and testicular development. In conclusion, this study represents the first successful generation of cryptorchid sheep models via the disruption of RXFP2 using CRISPR/Cas9. These findings provide new insights into the roles of RXFP2, whose partial disruption is associated with testicular descent rather than horn formation.

A method for the prevention of pathologies of the distal extremities in cattle

Animal husbandry, aimed at obtaining dairy products, is an important link in the economy of the agro-industrial complex of the country. This industry makes it possible to provide the population with especially valuable food products. Modern conditions for the successful development of the industry are high dairy productivity of cattle and high-quality products. The requirements for the safety and quality of milk are constantly increasing, which also depends on the health of the livestock. Cows with limb pathologies have a decrease in milk productivity and a deterioration in its quality. One of the key points in preventive measures is orthopedic trimming of the hoof horn, which should be carried out at least once every 6 months. Recently, the use of hoof baths with various preparations has become very popular. HOOF Liquid F2 is an innovative hoof treatment and care product. "HOOF Liquid F2" is a concentrated multicompositional agent that has strong disinfecting, bactericidal and drying properties, promotes the process of normal horn formation. Carrying out these preventive measures made it possible to reduce the spread of pathologies of the distal extremities in 8 months to 25.0%, which indicates high efficiency. The use of hoof baths with HOOF Liquid F2 in a complex of therapeutic measures allows you to achieve a more pronounced therapeutic effect in a shorter period of time.

The draft genome sequence of the Japanese rhinoceros beetle Trypoxylus dichotomus septentrionalis towards an understanding of horn formation

The Japanese rhinoceros beetle Trypoxylus dichotomus is a giant beetle with distinctive exaggerated horns present on the head and prothoracic regions of the male. T. dichotomus has been used as a research model in various fields such as evolutionary developmental biology, ecology, ethology, biomimetics, and drug discovery. In this study, de novo assembly of 615 Mb, representing 80% of the genome estimated by flow cytometry, was obtained using the 10 × Chromium platform. The scaffold N50 length of the genome assembly was 8.02 Mb, with repetitive elements predicted to comprise 49.5% of the assembly. In total, 23,987 protein-coding genes were predicted in the genome. In addition, de novo assembly of the mitochondrial genome yielded a contig of 20,217 bp. We also analyzed the transcriptome by generating 16 RNA-seq libraries from a variety of tissues of both sexes and developmental stages, which allowed us to identify 13 co-expressed gene modules. We focused on the genes related to horn formation and obtained new insights into the evolution of the gene repertoire and sexual dimorphism as exemplified by the sex-specific splicing pattern of the doublesex gene. This genomic information will be an excellent resource for further functional and evolutionary analyses, including the evolutionary origin and genetic regulation of beetle horns and the molecular mechanisms underlying sexual dimorphism.

Identification of Critical Genes for Ovine Horn Development Based on Transcriptome during the Embryonic Period.

Horns, also known as headgear, are a unique structure of ruminants. As ruminants are globally distributed, the study of horn formation is critical not only for increasing our understanding of natural and sexual selection but also for the breeding of polled sheep breeds to facilitate modern sheep farming. Despite this, a significant number of the underlying genetic pathways in sheep horn remain unclear. In this study, to clarify the gene expression profile of horn buds and investigate the key genes in horn bud formation, RNA-sequencing (RNA-seq) technology was utilized to investigate differential gene expression in the horn buds and adjacent forehead skin of Altay sheep fetuses. There were only 68 differentially expressed genes (DEGs) identified, consisting of 58 up-regulated genes and 10 down-regulated genes. RXFP2 was differentially up-regulated in the horn buds and had the highest significance (p-value = 7.42 × 10-14). In addition, 32 DEGs were horn-related genes identified in previous studies, such as RXFP2, FOXL2, SFRP4, SFRP2, KRT1, KRT10, WNT7B, and WNT3. Further, Gene Ontology (GO) analysis showed that the DEGs were mainly enriched with regard to growth, development, and cell differentiation. Pathway analysis revealed that the Wnt signaling pathway may be responsible for horn development. Further, through combining the protein-protein interaction networks of the DEGs, it was found that the top five hub genes, namely, ACAN, SFRP2, SFRP4, WNT3, and WNT7B, were also associated with horn development. Our results suggest that only a few key genes, including RXFP2, are involved in bud formation. This study not only validates the expression of candidate genes identified at the transcriptome level in previous studies but also provides new possible marker genes for horn development, which may promote our understanding of the genetic mechanisms of horn formation.

Penile Cutaneous Horn Mimicking Carcinoma: A Rare Case

Cutaneous horns are cornified hyperkeratotic lesions on the skin, usually present on photo-exposed areas such as the face and scalp. Its presence on the penis is very rare and represents the most unusual site. The role of chronic irritation, phimosis, surgical trauma, and radiotherapy have been implicated in penile horn formation. Penile horns present as elongated, keratinous, white or yellowish projections that range from a few millimeters to centimeters in size arising from the glans penis. Histopathology of the keratotic mass reveals nothing but keratin. One-third of cases of penile horns are associated with underlying malignancies. The standard treatment is electrosurgical excision with the removal of a broad base.

Numerical investigation of the unsteady effect owing to oscillation on airfoil icing

Modeling the unsteadiness owing to body motion is essential for accurately simulating ice accretion on a moving object. For an oscillating airfoil, high-frequency oscillations have been assumed to occur in slow motion to apply a quasi-steady approach to numerical analysis. The method raised arbitrariness in the number of data exchanges and the initial angle of attack. Simultaneously, the oscillation owing to a change in the angle of attack was considered for each step. Subsequently, the quasi-unsteady approach was proposed, the results from which exhibited good agreement for a few ice shapes, unlike that of the extended quasi-steady approach. However, whether a quasi-unsteady approach is sufficiently accurate for simulating ice accretion on a two-dimensional oscillating airfoil under various conditions still remains unknown. This study analyzed the unsteady effect on collection efficiency and convective heat transfer using the quasi-unsteady approach. Furthermore, as the static case, this approach demonstrated that the roughness and laminar-turbulent transition model for the oscillating airfoil can improve the prediction of the ice shape. The results obtained from this approach using the improved model exhibited good agreement with previously reported experimental results.Fig. 11 compared predicted ice shape with different roughness height. Fig. 11(a) is Run 61 with a reduced frequency of 0.044 at an LWC = 1 g/m3, and Fig. 11(b) is Run 50 with a reduced frequency of 0.027 at an LWC =.55 g/m3 The dotted line indicates the experimental ice shape and the dashed line indicates the numerical results applied to the empirical roughness model. The solid line indicates ice shape with the roughness size when the direction and size of the ice horn closely match the experimental values. When an empirical roughness model is applied, the ice horns are usually concentrated near the leading edge. Roughness increases convective heat transfer and premature laminar turbulence in ice accretion. The convective heat transfer peaks near the leading edge with a high roughness value; therefore, the ice horn gathers near the leading edge. Low roughness delayed the formation of the ice horn due to the decreased heat transfer rate, which balances the latent heat of icing, thereby allowing the droplets to freeze before moving to the trailing edge. In Run 61, the ice shape was predicted accurately at 20 % of the empirical roughness and 40 % roughness height of Run 55. When the roughness height was reduced, such as in the case of Run 61 with 10 % empirical roughness, the primary horn reduced, whereas the secondary horns increased.

Recent advances in understanding horn formation in the Japanese rhinoceros beetle Trypoxylus dichotomus using next-generation sequencing technology.

The exaggerated horns of beetles are attractive models for studying the origin of novel traits and morphological evolution. Closely related species often differ profoundly in the size, number, and shape of their horns, and in the body region from which they extend. In addition, beetle horns exhibit exquisite nutrition-dependent phenotypic plasticity, leading to disproportionate growth of the horns in the largest, best-condition individuals and much smaller - even stunted - horn sizes in poor-condition individuals. These exciting phenomena in beetle horns have recently been revealed at the molecular level with the advent of next-generation sequencing. This section reviews the latest research on a horned beetle, the Japanese rhinoceros beetle Trypoxylus dichotomus, whose genome was recently sequenced.

Ungulomycosis of cattle: treatment and preventive measures

Of the total number of animal diseases, 70–80 % are non-communicable diseases, and more than 50 % are surgical diseases, which cause significant economic damage to the livestock industry due to reduced productivity and premature culling of livestock. Irrational, unbalanced in terms of macro- and microelements, vitamins, carbohydrates feeding leads to metabolic disorders. At the same time, deep destructive-degenerative changes in bones, joints, ligaments and tendons are registered, horn formation in the hooves is disturbed and a less stable horn is produced. Omission in feeding unsatisfactory housing conditions and inadequate care of animals. When such conditions are often supplemented, the outer cover of animals, in particular the hooves, is affected first of all. In the event of inflammatory and dystrophic processes at the base of the skin of the hooves there is a violation of tissue (tubular) and cellular structure. The horn of such hooves undergoes changes in the form of parakeratosis and deformation; this contributes to the spread and accumulation of fungal flora, which shows its pathogenic action mainly due to enzymatic activity and toxic products, which characterizes these microorganisms as a factor in the destructive processes of the hoof horn. With reduced mechanical stability and destroyed by microscopic fungi of hoof horn is more likely to develop aseptic or purulent pododermatitis. Here, the fungal flora is not only a contributing factor in the occurrence of diseases, but also as one of the factors complicating the course of the disease. That is why timely detection and effective treatment of ungulomycosis prevents the complication of the pathological process, which can even lead to culling of animals. The essence of treatment of superficial ungulomycosis is reduced to functional cleaning of hooves and their antiseptic treatment in the form of fungicidal powders, sprays, hoof baths. In deep ungulomycosis, and, moreover, in combination with purulent pododermatitis, treatment includes local anesthesia, orthopedic treatment, antiseptic treatment with isolation, pathogenetic therapy. Prevention of ungulomycosis is based on knowledge of the etiology of the disease and the pathogenetic mechanisms of its development. Its essence is to form in animals a strong hoof horn, prevent its destruction and eliminate favorable conditions for the reproduction of keratomycetes. This includes proper feeding, proper housing conditions and appropriate animal care.

Disease of the island of Meleda or keratoderma of Meleda

Keratoderma is a group of dermatoses characterized by a violation of keratinization processes, excessive horn formation mainly in the area of the palms and soles. Under our supervision in the Tashkent regional skin and venereal clinic in the Department of dermatology was a patient Z. born in 2007, who was undergoing inpatient treatment for Meleda island disease. The rash is localized in the area of the palm and soles, changes and dystrophy of the nails. As a result of inpatient treatment (12 days), the Horny layers on the palms and soles decreased, especially in the Central part. All the cracks have fused, no new ones have been found. The severity of inflammatory phenomena, hyperkeratotic layers decreased, the area of the lesion and the intensity of itching decreased. The patient was discharged from the hospital with clinical improvement. This case is of particular interest to practical dermatovenerologists as a rare dermatosis

Rising temperature accelerates the responses of inducible anti-predator morphological defenses of Ceriodaphnia cornuta but decreases the responsive intensity

Cladocerans can recognize predation risk by sensing the chemical cues released by their predators, and adopt effective anti-predator defensive strategies to avoid being predated. In nature waters, temperature, as one of the key abiotic factors, fluctuates with day-night and seasons, especially under climate warming, which may impact the inducible anti-predator defenses of cladocerans. To investigate the effects of rising temperatures on the inducible anti-predator defenses of cladocerans, we cultured a common species Ceriodaphnia cornuta at presence or absence of Chaoborus sp. larvae kairomone at 15, 20, 25, and 30 °C for 15 days. Results showed that both the inducible anti-predator morphological responses and all the life history traits of C. cornuta were significantly affected by temperature changes. Specifically, rising temperature accelerated the inducible defense responses of the horn formation, but reduced the expression intensity of this morphological defense trait. With increasing temperature, the body size was increased, the time to first reproduction was decreased, and the reproduction was enhanced, indicating that C. cornuta tends to adopt K-selective strategy with maturity at relatively larger size and r-selective strategy with relatively earlier reproductive time and more offspring under warming conditions. These data demonstrated that the inducible anti-predator responses and the life history traits of C. cornuta can be shifted by temperature changes, which may indirectly affect top-down species interactions. Our study highlights the importance of incorporating species interactions when estimating the impact of rising temperature on species.

Notch signaling patterns head horn shape in the bull-headed dung beetle Onthophagus taurus.

Size and shape constitute fundamental aspects in the description of morphology. Yet while the developmental-genetic underpinnings of trait size, in particular with regard to scaling relationships, are increasingly well understood, those of shape remain largely elusive. Here we investigate the potential function of the Notch signaling pathway in instructing the shape of beetle horns, a highly diversified and evolutionarily novel morphological structure. We focused on the bull-headed dung beetle Onthophagus taurus due to the wide range of horn sizes and shapes present among males in this species, in order to assess the potential function of Notch signaling in the specification of horn shape alongside the regulation of shape changes with allometry. Using RNA interference-mediated transcript depletion of Notch and its ligands, we document a highly conserved role of Notch signaling in general appendage formation. By integrating our functional genetic approach with a geometric morphometric analysis, we find that Notch signaling moderately but consistently affects horn shape, and does so differently for the horns of minor, intermediate-sized, and major males. Our results suggest that the function of Notch signaling during head horn formation may vary in a complex manner across male morphs, and highlights the power of integrating functional genetic and geometric morphometric approaches in analyzing subtle but nevertheless biologically important phenotypes in the face of significant allometric variation.

Precise staging of beetle horn formation in Trypoxylus dichotomus reveals the pleiotropic roles of doublesex depending on the spatiotemporal developmental contexts.

Many scarab beetles have sexually dimorphic exaggerated horns that are an evolutionary novelty. Since the shape, number, size, and location of horns are highly diverged within Scarabaeidae, beetle horns are an attractive model for studying the evolution of sexually dimorphic and novel traits. In beetles including the Japanese rhinoceros beetle Trypoxylus dichotomus, the sex differentiation gene doublesex (dsx) plays a crucial role in sexually dimorphic horn formation during larval-pupal development. However, knowledge of when and how dsx drives the gene regulatory network (GRN) for horn formation to form sexually dimorphic horns during development remains elusive. To address this issue, we identified a Trypoxylus-ortholog of the sex determination gene, transformer (tra), that regulates sex-specific splicing of the dsx pre-mRNA, and whose loss of function results in sex transformation. By knocking down tra function at multiple developmental timepoints during larval-pupal development, we estimated the onset when the sex-specific GRN for horn formation is driven. In addition, we also revealed that dsx regulates different aspects of morphogenetic activities during the prepupal and pupal developmental stages to form appropriate morphologies of pupal head and thoracic horn primordia as well as those of adult horns. Based on these findings, we discuss the evolutionary developmental background of sexually dimorphic trait growth in horned beetles.

Northern Cedar Mountains Red Beds, Tooele County

Recent mapping for the Tooele 30' x 60' quadrangle geologic map revealed more information about interesting exposures of red beds cropping out in an 11-mile (18-km) swath along the northwestern flank of the Cedar Mountains (Clark and others, 2017, 2019 in review). They are unusual because such rocks are seldom preserved in northwestern Utah, an area known for thick thrust sheets of Paleozoic marine carbonate and sandstone. These rocks were first mapped by Robert Maurer for his Ph.D. dissertation on the geology of the Cedar Mountains (Maurer, 1970). He called them North Horn (?) Formation and noted the presence of fresh-water snails (Gyraulus sp.) that a paleontologist said were probably of late Paleocene or Eocene age. The North Horn Formation is considered Late Cretaceous (Maastrichtian age) to Paleocene or Eocene (~70 to 60 Ma) in age. However, recent detrital zircon analysis from sandstone in the unit suggest a much older age, with the youngest grains (maximum depositional age) of 117 Ma, or Early Cretaceous, Aptian (UGS and O’Sullivan, 2017). Two samples of gray mudstone taken for fossil pollen in the unit did not produce any usable material. Inspection of these rocks by Don DeBlieux (Utah Geological Survey paleontologist) revealed no bone or other biological material at this location.

Rhinoceros beetle horn development reveals deep parallels with dung beetles.

Beetle horns are attractive models for studying the evolution of novel traits, as they display diverse shapes, sizes, and numbers among closely related species within the family Scarabaeidae. Horns radiated prolifically and independently in two distant subfamilies of scarabs, the dung beetles (Scarabaeinae), and the rhinoceros beetles (Dynastinae). However, current knowledge of the mechanisms underlying horn diversification remains limited to a single genus of dung beetles, Onthophagus. Here we unveil 11 horn formation genes in a rhinoceros beetle, Trypoxylus dichotomus. These 11 genes are mostly categorized as larval head- and appendage-patterning genes that also are involved in Onthophagus horn formation, suggesting the same suite of genes was recruited in each lineage during horn evolution. Although our RNAi analyses reveal interesting differences in the functions of a few of these genes, the overwhelming conclusion is that both head and thoracic horns develop similarly in Trypoxylus and Onthophagus, originating in the same developmental regions and deploying similar portions of appendage patterning networks during their growth. Our findings highlight deep parallels in the development of rhinoceros and dung beetle horns, suggesting either that both horn types arose in the common ancestor of all scarabs, a surprising reconstruction of horn evolution that would mean the majority of scarab species (~35,000) actively repress horn growth, or that parallel origins of these extravagant structures resulted from repeated co-option of the same underlying developmental processes.

Genome-wide association study provides insights into genes related with horn development in Nelore beef cattle

The causal mutation for polledness in Nelore (Bos taurus indicus) breed seems to have appeared first in Brazil in 1957. The expression of the polled trait is known to be ruled by a few groups of alleles in taurine breeds; however, the genetic basis of this trait in indicine cattle is still unclear. The aim of this study was to identify genomic regions associated with the hornless trait in a commercial Nelore population. A total of 107,294 animals had phenotypes recorded and 2,238 were genotyped/imputed for 777k SNP. The weighted single-step approach for genome-wide association study (WssGWAS) was used to estimate the SNP effects and variances accounted for by 1 Mb sliding SNP windows. A centromeric region of chromosome 1 with 3.11 Mb size (BTA1: 878,631–3,987,104 bp) was found to be associated with hornless in the studied population. A total of 28 protein-coding genes are mapped in this region, including the taurine Polled locus and the IFNAR1, IFNAR2, IFNGR2, KRTAP11-1, MIS18A, OLIG1, OLIG2, and SOD1 genes, which expression can be related to the horn formation as described in literature. The functional enrichment analysis by DAVID tool revealed cytokine-cytokine receptor interaction, JAK-STAT signaling, natural killer cell mediated cytotoxicity, and osteoclast differentiation pathways as significant (P < 0.05). In addition, a runs of homozygosity (ROH) analysis identified a ROH island in polled animals with 2.47 Mb inside the region identified by WssGWAS. Polledness in Nelore cattle is associated with one region in the genome with 3.1 Mb size in chromosome 1. Several genes are harbored in this region, and they may act together in the determination of the polled/horned phenotype. Fine mapping the locus responsible for polled trait in Nelore breed and the identification of the molecular mechanisms regulating the horn growth deserve further investigation.

Complex furrows in a 2D epithelial sheet code the 3D structure of a beetle horn

The external organs of holometabolous insects are generated through two consecutive processes: the development of imaginal primordia and their subsequent transformation into the adult structures. During the latter process, many different phenomena at the cellular level (e.g. cell shape changes, cell migration, folding and unfolding of epithelial sheets) contribute to the drastic changes observed in size and shape. Because of this complexity, the logic behind the formation of the 3D structure of adult external organs remains largely unknown. In this report, we investigated the metamorphosis of the horn in the Japanese rhinoceros beetle Trypoxylus dichotomus. The horn primordia is essentially a 2D epithelial cell sheet with dense furrows. We experimentally unfolded these furrows using three different methods and found that the furrow pattern solely determines the 3D horn structure, indicating that horn formation in beetles occurs by two distinct processes: formation of the furrows and subsequently unfolding them. We postulate that this developmental simplicity offers an inherent advantage to understanding the principles that guide 3D morphogenesis in insects.

Doublesex alters aggressiveness as a function of social context and sex in the polyphenic beetle Onthophagus taurus

Despite sharing nearly the same genome, individuals within the same species can vary drastically in both morphology and behaviour as a function of developmental stage, sex or developmental plasticity. Thus, regulatory processes must exist that enable the stage-, sex- or environment-specific expression of traits and their integration during ontogeny, yet exactly how trait complexes are co-regulated and integrated is poorly understood. In this study, we explore the developmental genetic basis of the regulation and integration of environment-dependent sexual dimorphism in behaviour and morphology in the horn-polyphenic dung beetle Onthophagus taurus through the experimental manipulation of the transcription factor doublesex (dsx). The gene dsx plays a profound role in the developmental regulation of morphological differences between sexes as well as alternative male morphs by inhibiting horn formation in females but enabling nutrition-responsive horn growth in males. Specifically, we investigated whether experimental downregulation of dsx expression affects male and female aggressive and courtship behaviours in two social contexts: interactions between individuals of the same sex and interactions between males and females. We find that dsx downregulation significantly alters aggressiveness in both males and females, yet does so differently for both sexes as a function of social context: dsxRNAi males exhibited elevated aggression towards males but showed reduced aggression towards females, whereas dsxRNAi females became more aggressive towards males, while their aggressiveness towards other females was unaffected. Moreover, we document unexpectedly high levels of female aggression independent of dsx treatment in both wild-type and control-injected individuals. Lastly, we found no effects of dsxRNAi on courtship and mating behaviours. We discuss the role of dsx in the regulation of sex-specific and plastic behaviours, the unexpectedly high levels of aggression of hornless dsxRNAi males in relation to the well-established description of the hornless sneaker phenotype and the potential ecological function of high female aggression.