The "detoxification" channels of venomous snakes that we commonly see and are known can be divided into three categories: tube teeth (Viper family), anterior groove teeth (Cobra family), and posterior groove teeth (some zoonotic species).
So did you know that the "neck groove snake" has a gland in addition to the Duvernoy gland that is also capable of storing toxins? That's what we're going to talk about today as the Nuchal gland.
The Kowloon neck slot snake secretes cervical gland fluid forgives the author's landline pixels
But in fact, the term "cervical gland" is still controversial, mainly for two reasons:
First, the word "neck", whether the snake has a neck, where the specific neck should be, and there is still no clear definition of the location so far;
The second is the word "gland", which we define as a gland that is capable of producing special substances in the animal body, and the special substances secreted by the cervical glands are not produced by themselves, but are closely related to their prey (I am not the generator of glandular fluid, I am only the porter of glandular fluid. Specifically mentioned below).
Therefore, whether this organ can be called a "gland" is still controversial.
However, as far as the current naming results are concerned, the name "cervical gland" is still used later, waiting for the revision of future research.
In addition, some species with cervical glands also have derivatives of the cervical glands, which are called dorsal glands, which are often referred to as "dorsal glands" or "Nucho-dorsal glands" (nucho-dorsal glands).
In addition to the special instructions in the following article, the "cervical glands" and "dorsal glands" are collectively referred to as "cervical glands" in other places.
(Takeuchi et al., 2018)
Discovery of the cervical gland: Nakamura conducted anatomical studies of the species in 1935 after the species was burned by liquid splashed from its neck during the execution of the tabby-necked snake, and found that there were many white vesicle-like structures under the skin of its neck, like glands, and the term "Nuchal gland" was first proposed [1].
The study found that when the tabby-necked snake itself presses against the cell membrane of the neck and ruptures the glandular connective tissue sac, a pale yellow opaque liquid with an unpleasant odor will squirt out, and the discharge liquid is rich in small particles, glandular cell independent nuclei, blood, lymphocytes and pigment cells.
It is worth mentioning that this type of cell is limited, that is, each cell can only be used once in a snake's lifetime or is renewable, and it is still inconclusive [2]. Akizawa (1986) discovered that the tabby-necked snake's neck secretion is actually the same as that of the skin glands on the surface of the toad, a cardiac steroid called Toaddienoolactone (Bufadienolide)[3].
In other words, this amazing species can actually turn the toxins of its own food into its own use! This is also what I said earlier, "I am not the generator of glandular fluid, I am only the porter of glandular fluid".
However, the specific physiological mechanism of transformation has not been reported in the literature.
(Mori et al., 2016)
Toxicity of the cervical glands: Wu Found in the study that deinagkistrodon acutus rolled on the ground after preying on a tabby-necked snake and died in shock, he studied the toxicity of tabby-necked cloister hydrangea secretions in mice as a test model, and the study showed that half of the lethal amounts (LD50) per kg of mice were (crude poison): subcutaneous injection was 82mg, intraperitoneal injection was 100mg, intravenous injection was 26mg, Anatomical analysis indicates that the toxin is a mixed toxin with a predominance of hematoxins [4].
The Heqi First Class (2007) study also showed that the toxicity of cervical gland secretions to intraperitoneal injection in mice was 97.99 mg/kg, and the results showed that mice would have convulsions, spasms, quadriplegia and other symptoms, suggesting a strong neurotoxin [5].
Mori et al. reported that the venom of the dorsal gland of the tabby-necked snake Rhabdophis tigrinus has a strong stimulating effect on the mucous membrane [6]. Chen et al. conducted a study on the toxicity of cervical gland secretions to the eyes, and the results showed that the cervical gland secretions of Rhabdophis formosanus of the Taiwan tabbyneck snake had foreign body sensation, progressive burning pain and blurred vision after entering the eyes, and ophthalmic examination found diffuse superficial punctate keratitis, corneal interstitial edema with ligament folds, and conjunctival hyperemia. Patients respond well to topical treatment with corticosteroids, antihistamines, and antibiotics, with a good clinical course and efficacy [7].
Cervical glands
Behavior of the neck glands: Hutchinson et al. have studied the neck glands of the tabby neck snake that preys on toads and uncatchers toads, and concluded that only the neck glands of the toad-eating tabby neck snake will have defensive secretions, and this defense mechanism can be passed on from the mother line to the offspring through vertical transmission, so when approaching production, the female snake will look for toads in large quantities to meet her own needs.
The authors speculate that this may be due to the difference in the breeding season between predators and predators, that juvenile snakes born around the end of August have no way to swallow toads that are already large enough, resulting in them having to reselect only in food, and in order to avoid predators, they can only use a defense system from maternal inheritance, we often say that parent-to-off feeding is often reflected in mammals, and this parenting method related to the "neck gland" may also reflect the unique parent-to-off parenting method that exists on reptiles (ah! O great motherly love! ）。
Offspring of mothers who do not have the conditions to prey on toads are born without secretions in the cervical glands, but secretions occur in the cervical glands of acquired predatory toads [8].
Mori and Burghardt (2000) found that the defense mechanism of the tabby-necked snake fed frogs or fish was very different from that of the tabby-necked snake that preyed on toads, and that tabby-necked snakes on toad-free islands had far lower neck arches when encountering danger than tabby-necked snakes that normally prey on toads, that is, tabby-necked snakes that do not prey on toads evade more quickly when encountering predators, precisely because they lack secretions for defense against predators. [9] He had to move as quickly as a normal snake to avoid predators.
Studies by Mori and Burghardt (2008) have shown that tabby-necked snakes that normally prey on toads exhibit four behaviors when encountering predators: the neck is arched and the neck is in contact with the irritant; the back of the neck is arched to contact the irritant; the neck is flattened; and the entire body is flattened, all of which are aimed at rubbing the gland into the predator's body.[10]
Mori et al. divided the entire body segment of the Kowloon neck snake into five parts: neck, front half of the body, middle body, back of the body and tail to explore the frequency of corresponding reactions caused by different body parts when invaded by predators, and the results showed that all individuals had neck reactions, and as the trunk moved backwards, the number of responding individuals gradually decreased, and all individuals did not respond accordingly at the tail.
I suspect that this may be related to the fact that the neck is the site where predators first choose to invade, or it may be related to the gradual degeneration of the dorsal glands from the tail as they evolve [11].
(Mori et al., 2016b)
Taxonomy of the cervical gland: The cervical gland as a special defense organ is found in only 17 species belonging to the genus Rhabdophis of the genus Rhabdophis, the genus Macropisthodon of the genus Macropisthodon, and the genus Balanophis, so does this particular organ taxonomically suggest a special taxonomic orientation?
Takeuchi et al. performed phylogenetic analysis of most species in the Asian aquatic snake subfamily Natricinae [12].
The study explored the phylogenetic relationship based on the three genera of the genus Protochthral Snake, the Genus Naper and the Genus Serpentine, and reclassified the species with both cervical glands and no cervical glands in the same genus, and the phylogenetic analysis showed that species with cervical glands formed an effective branch, they named this branch NGC (Nuchal Glande), while species without cervical glands in the genus Znaeucarpus and Zygomatica appeared outside NGC.
Red-necked slot snake
Due to the lack of sample size, it was impossible to verify the species without molecular data in the genus Serpentinus, and finally the authors retained the genera names of all species in the genus Proto-Cervical Serpentinae, and merged the two species of the genus Crater spp.M. flaviceps and M. Plumbicolor and the proto-sycamore genus B. Ceylonensis is classified into the genus Zolofts changed to: R. ceylonensis, R. flaviceps and R. plumbicolor。 In addition, Takeuchi argues that the necked snake M. Rudis is a separate branch that proposes to restore the pseudo-pit viper genus Pseudagkistrodon, established by Van Denburgh in 1909, with the scientific name corrected to Pseudagkistrodon rudis.
bibliography
[1] Nakamura K. 1935. On a new integumental poison gland found in the nuchal region of a snake, Natrix tigrina. Mem College Sci Kyoto Imperial Univ Ser B 10:229-240.
[2] Mori A , Burghardt G M , Savitzky A H , et al. Nuchal glands: a novel defensive system in snakes[J]. Chemoecology, 2012, 22(3):187-198.
[3] Akizawa T. 1986. Studies on the activities of chemicals in the nuchal glands of Rhabdophis tigrinus. Ochanomizu Med J 34:85 97 (in Japanese).
WU Jiaobin. Study on the cervical glands of tabby-necked snakes[J]. Journal of Wildlife, 1996(2):34-35.
He 71, Yu Xiaodong, Liu Jianping. Study on the venom of the neck-dorsal glands of the tabby-necked trough snake Chinese mainland subspecies[J]. Sichuan Zoology, 2007, 26(2):255-257.
[6] Mori A, Layne G, Burghardt GM. 1996. Descrip tion and p relim inary anal2 ysis of anti2p redator behavior ofRhabdophis tigrinus tigrinus, a colu2 brid snake with nuchal glands[ J ]. Japanese J Herpetology, 16 (3) : 94~1071.
[7] Chen Y C , Yen H T , Chen Y W , et al. Toxin ophthalmia caused by nuchal gland secretion of the Taiwan tiger keelback (Rhabdophis tigrinus formosanus)[J]. Journal of the Formosan Medical Association, 2014, 113(10):750-753.
[8] Hutchinson D A , Mori A , Savitzky A H , et al. Dietary sequestration of defensive steroids in nuchal glands of the Asian snake Rhabdophis tigrinus[J]. Proceedings of the National Academy of Sciences, 2007, 104(7):2265-2270.
[9] Mori A, Burghardt GM. 2000. Does prey matter? Geographic variation in antipredator responses of hatchlings of a Japanese natricine snake, Rhabdophis tigrinus. J Comp Psychol 114:408-413.
[10] Mori A, Burghardt GM. 2008. Comparative experimental tests of natricine antipredator displays, with special reference to the apparently unique displays in the Asian genus, Rhabdophis. J Ethol 26:61-68.
[11] Mori A , Jono T , Takeuchi H , et al. Morphology of the nucho‐dorsal glands and related defensive displays in three species of Asian natricine snakes[J]. Journal of Zoology, 2016, 300(1):18-26.
[12] Takeuchi H, Savitzky AH, Ding L, et al. Evolution of nuchal glands, unusual defensive organs of Asian natricine snakes (Serpentes: Colubridae), inferred from a molecular phylogeny. Ecol Evol. 2018;8( 20):10219-10232.
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Author: Yang Shijun; Article from: Crawling Boundary; Follow me to take you to learn more about reptile knowledge.