Ядовитые млекопитающие: состав, эволюция и распространение

Venom producing animals of the class Mammalia

Venomous mammals are animals of the class Mammalia that produce venom, which they use to kill or disable prey, to defend themselves from predators or conspecifics or in agonistic encounters. Mammalian venoms form a heterogeneous group with different compositions and modes of action, from four orders of mammals: Eulipotyphla, Monotremata, Primates, and Chiroptera. To explain the rarity of venom delivery in Mammalia, Mark Dufton of the University of Strathclyde has suggested that modern mammalian predators do not need venom because they are able to kill quickly with their teeth or claws, whereas venom, no matter how sophisticated, requires time to disable prey. In spite of the rarity of venom among extant mammals, venom may be an ancestral feature among mammals, as venomous spurs akin to those of the modern platypus are found in most non therian Mammaliaformes groups. Venom is much more common among other vertebrates; there are many more species of venomous reptiles (e. g. venomous snakes) and fish (e. g. stonefish). Some birds are poisonous to eat or touch (e. g. hooded pitohui) though no bird species is known to be venomous. There are only a few species of venomous amphibians; certain salamandrid salamanders can extrude sharp venom tipped ribs.

Several definitions of venomous animals have been proposed. Bücherl states that venomous animals must possess at least one venom gland, a mechanism for excretion or extrusion of the venom, and apparatus with which to inflict wounds. Mebs writes that venomous animals produce venom in a group of cells or gland, and have a tool, the venom apparatus, which delivers the venom by injection during a bite or sting. The venom apparatus in this definition encompasses both the gland and the injection device, which must be directly connected. Fry et al. found that a venom is a secretion produced in a specialized gland in one animal and delivered to a target animal through the infliction of a wound. This secretion must contain molecules that disrupt normal physiological processes so as to facilitate feeding or defense by the producing animal. Additionally, the feeding secretion of hematophagous specialists (e. g. vampire bats) may be regarded as a specialized subtype of venom.

Venomous mammals may have been more common in the past. Extratarsal spurs observed in extinct Mesozoic mammals are homologous with those seen in extant monotremes, and this feature was widespread. Whether or not these extratarsal spurs served as a venom delivery system is up for debate. While species such as Gobiconodon and Zhangeotherium possessed an extratarsal spur, they are hypothesized to be nonvenomous due to the lack of the spur being hollow or channeled, as seen in modern venomous Ornithorhyncus. Whether or not the lack of venom is due to the loss of a basal trait is difficult to determine with current fossil records. These specimens were reexamined and rejected on the basis that the evidence provided may not be enough to prove the presence of venom in these species. Fox and Scott found no fossa that would be indicative of the presence of a venom gland. Also, grooved teeth are a feature of many species of nonvenomous mammals, so the presence of grooved teeth alone is not indicative of venom. There is no phylogenetic support for the presence of venom in B. browni. The genus Beremendia may have featured individuals with a venom delivery system. The first lower incisor of several species exhibited a groove that may have served as a canal for venom to travel from a venom gland to the tip of the tooth. Support for a venom gland is seen in the fossa in the mandibular symphysis. Also, Beremendia is phylogenetically close to Solenodon, which has extant members that are venomous. Euchambersia is an example of a fossil therapsid (a relative of mammals) with grooved teeth, and maxillary fossa to match, indicating the presence of venom glands. Euchambersia differs in that the upper canines are the teeth that are grooved, and the grooves are almost enclosed, forming a tube.

With the exception of vampire bats, the Eulipotyphla are the only mammals so far observed to produce toxic saliva. These species have significantly enlarged and granular submaxillary salivary glands from which the toxic saliva is produced. The Cuban solenodon (Atopogale cubana) and Hispaniolan solenodon (Solenodon paradoxus) look similar to large shrews. They both have venomous bites; the venom is delivered from modified salivary glands via grooves in their second lower incisors. Recent study has identified the gene regulatory network responsible for the development of venom delivery systems in these small mammals. Due to the overexpression of kallikreins in their saliva, solenodon bites cause vasodilation and may result in circulatory shock. The European mole (Talpa europaea), and possibly other species of mole, have toxins in their saliva that can paralyze earthworms, allowing the moles to store them alive for later consumption.

Both male and female platypuses (Ornithorhyncus anatinus) hatch with keratinised spurs on the hind limbs, although the females lose these during development. The spurs are connected to the venom producing crural glands, forming the crural system. During the mating season these glands become highly active, producing venom to be delivered by the channeled spur. Echidnas, the other monotremes, have spurs but no functional venom glands. Although not potent enough to be lethal to humans, platypus venom is nevertheless so excruciating that victims may sometimes be temporarily incapacitated. Platypus envenomation was fairly common when the animal was still hunted for its fur. Nowadays any close contact with the animal is rare and restricted to biologists, zookeepers and anglers (who occasionally catch them in fishing lines or nets). The spurs have enough strength to support the weight of the platypus, which often hangs from the victim, requiring assistance for removal. Most of the evidence now supports the proposition that the venom system is used by males on one another as a weapon when competing for females, taking part in sexual selection. During this season, males become more aggressive and are found with punctures in their bodies, especially in the tail region. Adult male platypuses largely avoid each other, outside of this mating rivalry. It has been hypothesized that venom spurs were once used for defense against predators.

The definition of venom by Fry et al. (see Definitions) regards the feeding secretions of hematophagous (blood eating) specialists as a particular subtype of venom. In this context, the subfamily Desmodontinae represents the venomous mammals from the order Chiroptera. This group comprises the most well known venomous bat, the common vampire bat (Desmodus rotundus) and two other rare species, the hairy legged vampire bat (Diphylla ecaudata) and the white winged vampire bat (Diaemus youngi). These bats produce toxic saliva with anticoagulant properties and have a series of anatomical and physiological adaptations to allow nourishment based solely on blood. The majority of their prey do not perish from the attack or contact with the venom.

Slow lorises (of the genera Nycticebus and Xanthonycticebus) are accepted as the only known venomous primate. They possess a dual composite venom consisting of saliva and brachial gland exudate, a malodourous fluid forming from an apocrine sweat gland on the animal's forearm. Both fluids have been demonstrated as being venomous individually and creating a more potent venom when mixed. and communication. Slow loris saliva has been shown to be cytotoxic to human skin cells in laboratory experiments without the administration of BGE. The venom is administered through morphologically distinct dentition in the form of an adapted toothcomb. often resulting in festering and necrotic wounds. Slow loris envenomation in humans is rare, but can result in near fatal anaphylactic shock. A suite of additional effects of the venom have been documented including mild to permanent disfigurement and mobility loss. The study of slow loris venom was brought to the public attention in 2012 by the research of the primatologist Prof. K. A. I Nekaris and in her BBC documentary The Jungle Gremlins of Java.

Hedgehogs (Erinaceinae) anoint their spines with a range of toxic and irritating substances. They will sometimes kill toads (Bufo sp. ), bite into the toads' poison glands and smear the toxic mixture on their spines.

Skunks (Mustelidae) can eject a noxious fluid from glands near their anus. It is not only foul smelling, but can cause skin irritation and, if it gets in the eyes, temporary blindness. Some members of the mustelid family, such as the striped polecat (Ictonyx striatus), also have this capacity to an extent. Pangolins can also emit a noxious smelling fluid from glands near the anus. The greater long nosed armadillo can release a disagreeable musky odor when threatened.