The vomeronasal organ of wild canids: the fox (Vulpes vulpes) as a model

Abstract

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.

Morphological and Histological Features of the Vomeronasal Organ in African Pygmy Hedgehog (Atelerix albiventris)

“…The vomeronasal capsule consists of cartilage in most mammalian species, including carnivores [15][16][17], ungulates [19,[33][34][35], bats [31], primates [20], rabbits [27,29], elephants [21,22], hyraxes [23], armadillos [30], marsupials [24,25], and hedgehogs (revealed in the present study). However, the capsule is bony in some rodents, for example, rats, mice [27], hamsters [36], and caudal third in capybaras [37], although it is partly or mostly cartilaginous in mole rats [38].…”

“…The hedgehog VNO connects to the incisive duct just before the nasal cavity. The VNO of most carnivores [14][15][16][17], ungulates [18,19], primates [20], elephants [21,22], hyraxes [23], and marsupials [24,25] is connected around the center of the incisive duct. The VNO in all these animals takes up substances through both the nasal and oral cavities, except in horses, in which the incisive ducts do not open to the oral cavity.…”

Volatile scent chemicals in the urine of the red fox, Vulpes vulpes

“…Olfaction in most mammals involves two complementary systems, the main olfactory system and the vomeronasal system (VNS), which is particularly associated with reproductive behaviours and maternal recognition [ 28 , 29 ]. Recently the anatomy and function of the fox VNS has been found to be well-developed and suited to assess the reception and recognition of semiochemicals [ 30 ]. In further evidence of their chemical signalling, foxes exhibit marking behaviour with urine [ 31 – 33 ] and faeces [ 34 ], and have an aromatic supracaudal tail gland [ 35 ] whose scent chemicals have recently been described [ 36 ].…”

A comprehensive structural, lectin and immunohistochemical characterization of the zebrafish olfactory system

“…The olfactory subsystems play a fundamental role in the daily life of all animal species 1 , having been extensively studied in mammals, with a fundamental difference between a main olfactory system (MOS) and a vomeronasal or accessory olfactory system (AOS) 2 . While the first one is known for its role in associative behaviours mediated by odorants sensed in the olfactory mucosa 3 , the AOS process innate capabilities mediated by pheromones detected by the vomeronasal organ 4 .…”