Snakes are one of the most feared species on the planet.
They are widely distributed throughout most continents and are known for being
extremely deadly. This stems from the large amount of snake species that are
venomous. These snake species have evolved special apparatuses to inject venom
and complex venom glands that produce the toxins. The structure of venom glands
are not similar with every snake family though and only share a commonality in that
they are encased by a fibrous sheath of connective tissue allowing muscle
attachment . The family's Viperidae, Elapidae, and Atractaspididae have the
most highly developed venom glands and are mostly what I will be focusing on in
this blog. The Colubridae family is known to have a type of venom gland, but is
said to be less developed than other venom glands and is called a Duvernoy's
gland (Jackson 2003).
The viperid family venom gland is large with a triangular
shape that has the longest side along the upper lip. The main gland is a
complex tubular structure divided into smaller sections by in-foldings. Large
quantities of venom are stored in a structure called the lumen and is the
primary duct to the mucous accessory gland that extends to the fangs (Jackson
2003).
The Elapid family venom gland is an oval shape. The main
gland is made up of simple tubules and the lumen is narrow, but the venom is
stored within cells than in the lumen. The mucous accessory gland surrounds the
entire lumen and continues to the fangs
(Jackson 2003).
The Atractaspidid venom gland is cylindrical and extends
back along the body well behind the head. The lumen extends the length of the main
gland with tubules radiating outward. There is no accessory gland, but mucous
cells line the lumen (Jackson 2003).
These are the main differences between the venom glands and they
have evolved differentially over time. It is believed that the Viperidae,
Elapidae, and Atractadpididae family lineages evolved their venom glands from
the Duvernoy's gland. The venom glands for the family's are hypothesized to
have had three separate evolutions and the Duvernoys gland only had one at an
early point in time (Jackson 2003).
Jackson, K. (2003) 'The evolution of venom-delivery systems
in snakes', Zoological Journal of the
Linnean Society, Vol. 137, Iss. 3, Pgs. 337-354
Awesome post! I was just wondering if the difference in venom glands can relate to how venomous the snake is? i.e. the more venomous the snake is, the more complex or simpler the venom gland is?
ReplyDeleteVery interesting. It’s so easy to forget that, just because species show similar structures and similar systems, it doesn’t mean that the underlying morphology and physiology will be the same! What type of snakes do you find in the family Atractaspididae? Which of these groups would be considered to more evolutionarily ancient? Fascinating post!
ReplyDeleteRhyannon I have tried to find mention of any article on whether the difference in the venom glands relates to its toxicity, but I was not able to find anything. The structure is most correlated to the fang structure and the venom gland structure could just be a correlation with it. The viperids can store more venom in their glands than the other two families which could allow it to secrete more venom, but not necessarily that it is more toxic.
ReplyDeleteTasmin the Atractaspididae family is known for the type of fangs within the family. The species in it generally have no fangs, rear fangs, or fixed fangs. The Colubroid family, which I did not talk about in this article, is known to be the oldest family from 25 million years ago. Viperids and Elapids are known to come much later due to their advanced venom apparatuses.
ReplyDeleteFascinating blog! Snakes are just amazing! I have heard people say that young snakes are more dangerous than adults, is that right? And if this is the case, is it because young snakes have more concentrated venom, or because they can't control how much they inject, or is there another reason?
ReplyDeleteMarthe: You know what your talking about! It is a little of both depending on the species your talking about :) Many venomous Juvenile snakes are more lethal due to them not being able to control the amount of venom they inject and slowly learn how to meter their venom. Juvenile snakes in certain species have more concentrated venom than adults for protection.
ReplyDelete