The vomeronasal system (VNS) has been extensively studied within specific animal families, such as Rodentia. However, the study of the VNS in other families, such as Canidae, has long been neglected. Among canids, the vomeronasal organ (VNO) has only been studied in detail in the dog, and no studies have examined the morphofunctional or immunohistochemical characteristics of the VNS in wild canids, which is surprising, given the well-known importance of chemical senses for the dog and fox and the likelihood that the VNS plays roles in the socio-reproductive physiology and behaviours of these species. In addition, characterising the fox VNS could contribute to a better understanding of the domestication process that occurred in the dog, as the fox would represent the first wild canid to be studied in depth. Therefore, the aim of this study was to analyze the morphological and immunohistochemical characteristics of the fox VNO. Tissue dissection and microdissection techniques were employed, followed by general and specific histological staining techniques, including with immunohistochemical and lectin-histochemical labelling strategies, using antibodies against olfactory marker protein (OMP), growth-associated protein 43 (GAP-43), calbindin (CB), calretinin (CR), α-tubulin, Gαo, and Gαi2 proteins, to highlight the specific features of the VNO in the fox. This study found significant differences in the VNS between the fox and the dog, particularly concerning the expression of Gαi2 and Gαo proteins, which were associated with the expression of the type 1 vomeronasal receptors (V1R) and type 2 vomeronasal receptors (V2R), respectively, in the vomeronasal epithelium. Both are immunopositive in foxes, as opposed to the dog, which only expresses Gαi2. This finding suggests that the fox possesses a welldeveloped VNO and supports the hypothesis that a profound transformation in the VNS is associated with domestication in the canid family. Furthermore, the unique features identified in the fox VNO confirm the necessity of studying the VNS system in different species to better comprehend specific phylogenetic aspects of the VNS.

The characterization of the rabbit mammary pheromone, which is sensed by the main olfactory system, has made this species a unique model for the study of pheromonal communication in mammals. This discovery has brought attention to the global understanding of chemosensory communication in this species. Chemocommunication is mediated by two distinct organs located in the nasal cavity, the main olfactory epithelium and the vomeronasal organ (VNO). However, there is a lack of knowledge about the vomeronasal system in rabbits. To understand the role of this system, an exhaustive anatomical and histological study of the rabbit VNO was performed. The rabbit VNO was studied macroscopically by light microscopy, and by histochemical and immunohistochemical techniques. We employed specific histological staining techniques (periodic acid‐Schiff, Alcian blue, Gallego's trichrome), confocal autofluorescence, histochemical labelling with the lectin Ulex europaeus agglutinin (UEA‐I), and immunohistochemical studies of the expression of the Gαi2 and Gαo proteins and olfactory marker protein. The opening of the vomeronasal duct into the nasal cavity and its indirect communication with the oral cavity through a functional nasopalatine duct was demonstrated by classical dissection and microdissection. In a series of transverse histological sections, special attention was paid to the general distribution of the various soft‐tissue components of this organ (duct, glands, connective tissue, blood vessels and nerves) and to the nature of the capsule of the organ. Among the main morphological features that distinguish the rabbit VNO, the presence of a double envelope, which is bony externally and cartilaginous internally, and highly developed venous sinuses stand out. This observation indicates the crucial role played in this species by the pumping mechanism that introduces chemical signals into the vomeronasal duct. The functional properties of the organ are also confirmed by the presence of a well‐developed neuroepithelium and profuse glandular tissue that is positive for neutral mucopolysaccharides. The role of glycoconjugates was assessed by the identification of the α1‐2 fucose glycan system in the neuroepithelium of the VNO employing UEA‐I lectin. The pattern of labelling, which was concentrated around the commissures of the sensory epithelium and more diffuse in the central segments, is different from that found in most mammals studied. According to the expression of G‐proteins, two pathways have been described in the VNOs of mammals: neuroreceptor cells expressing the Gαi2 protein (associated with vomeronasal receptor type 1); and cells expressing Gαo (associated with vomeronasal receptor type 2). The latter pathway is absent in most mammals studied. The expression of both G‐protein families in the rabbit VNO places Lagomorpha together with rodents and insectivores in a small group of mammals belonging to the two‐path model. These findings support the notion that the rabbit possesses a highly developed VNO, with many spe...

the vomeronasal system (VnS) is responsible for the perception mainly of pheromones and kairomones. primarily studied in laboratory rodents, it plays a crucial role in their socio-sexual behaviour. As a wild rodent, the capybara offers a more objective and representative perspective to understand the significance of the system in the Rodentia, avoiding the risk of extrapolating from laboratory rodent strains, exposed to high levels of artificial selection pressure. We have studied the main morphological and immunohistochemical features of the capybara vomeronasal organ (Vno) and accessory olfactory bulb (AoB). the study was done in newborn individuals to investigate the maturity of the system at this early stage. We used techniques such as histological stains, lectinslabelling and immunohistochemical characterization of a range of proteins, including G proteins (Gαi2, Gαo) and olfactory marking protein. As a result, we conclude that the VNS of the capybara at birth is capable of establishing the same function as that of the adult, and that it presents unique features as the high degree of differentiation of the AOB and the active cellular migration in the vomeronasal epithelium. All together makes the capybara a promising model for the study of chemical communication in the first days of life. The vomeronasal system (VNS) is the sensorial system responsible in most vertebrates for the detection of chemosensory signals linked to innate socio-sexual behaviours 1,2. In mammals, the VNS presents a high morphofunctional 3 and genomic 4 diversity among different species. The vomeronasal organ (VNO) specialises in detecting pheromones for the purpose of reproductive behaviours such as maternal aggression and sexual attraction 5. The VNS is also involved in the recognition of major histocompatibility complex (MHC) associated peptides 6 , kairomones 7 and aversive molecules 8. By performing an in-depth study of the macroscopic and microscopic morphological characteristics of the vomeronasal system in the newborn capybara, we aimed to achieve two objectives. On the one hand, we aimed to obtain general information regarding the vomeronasal system in a rodent model that is distinct from most studied laboratory rodents. On the other hand, because the capybara is a precocial animal species, we aimed to determine the degree to which the capybara vomeronasal system morphology at birth has adapted to the requirements of a demanding socio-cognitive environment. Most studies of the VNS have been done on laboratory rodent strains, exposed to artificial selection pressure that do not reflect the selection pressure present in the wild. Therefore, these laboratory strains present significant genetic and behavioural differences compared with wild rodent models 9. The laboratory mouse (Mus musculus) and rat (Rattus norvegicus) may not be representative of all animals that make up this family. A remarkable differential feature among rodents is the altricial character of mice and rats, compared with the precocial character presented by hys...

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We wish to thank Mark Evans and Rosie Sammons for help with 3D tracing in Fiji, Annisa Chand for instructions on nose plug manufacture, and Maxim Volgushev for Matlab code. Venki Murthy and all members of the Grubb, Murthy and Galliano laboratories provided helpful discussions, while Juan Burrone and Sue Jones made invaluable comments on the manuscript.