Could future humans evolve to have venom glands? In new research, scientists close a long-open door by causally linking early salivary glands with what eventually became venom glands in many animals.
Because saliva is the common thread, that means anyone with salivary glands could eventually develop venom—from mice in the new experiment all the way up to humans.
First, the facts. In this study, scientists from the Okinawa Institute of Science and Technology Graduate University (OIST) and the Australian National University sought to answer an old question in evolutionary biology: how did venom glands evolve in animals?
“Oral venom systems evolved multiple times in numerous vertebrates enabling the exploitation of unique predatory niches. Yet how and when they evolved remains poorly understood,” the researchers explain.
To narrow down the field of possible answers, the scientists studied the group of several thousand genes that are found to be expressed in tandem with venom release in animals with venom glands. They found the same genes and physical mechanisms were at work in plain old saliva glands in other animals:
Basically, the saliva glands are serving up empty bowls, and venom glands are serving up bowls full of poison. The missing piece isn’t in genes or mechanism, but in the contents of what is being released from the glands: special proteins.
Why is venom such a mystery? It’s mostly just that scientists haven’t studied it en masse, and part of that is because venom is perplexingly common and eclectic. “While many snakes employ an oral venom system for securing prey, there are also mammals, such as shrews, and solenodons, that have evolved oral venom systems (based on salivary glands) for prey capture or defense,” the scientists say. There are thousands of venomous animal species.
That widespread nature is one reason why a common genetic ancestor is so exciting. In this case, researchers highlighted the shared link between, specifically, mammals and reptiles. There are only a handful of venomous mammals, and the actual venom they secret is different. The researchers explain:
All of this helps to explain why the link hasn’t previously been explored—the pool of venomous animals was just too big for a link to suggest itself at first glance.
“In venomous snakes, gene families have undergone greater expansions, and have evolved at a significantly higher rate than in other lineages like mammals,” the scientists say, which is why these snakes are spitting out high-octane venom compared with the watery venom of mammals with the same genetic pattern for expression.
But knowing that it all goes back to early salivary glands means there’s a better place to start exploring the commonalities, as well as the differences.
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