Some of you may remember my post on chemical warfare in the insect world. In that post, I mentioned:
Chrysomeline (Leaf) beetles, for example, have chemical defense glands. Originally, they synthesized the chemicals themselves. During the course of their evolution, however, the became dependent on plant hosts to acquire the chemicals they use for defense (in other words, they incorporate the host plants toxins into their own defense system).
Fireflies illustrate another, creepy, way insects can acquire chemical defenses. Female fireflies of the genus Photuris imitate females of the genus Photinus. Once they attract a male of the genus Photinus they eat him! Photinus species have a chemical called lucibufagin (similar to a chemical found in the chinese toad) which are extremely noxius to the insects that prey on fireflies (mainly jumping spiders). So female Photuris acquire the chemical by ingesting male Photinus. Then when attacked they engage in what is called reflexive bleeding and the chemical in their blood drives the predator away. They also incorporate the chemical into eggs when they lay them so their offspring is protected.
Today I have another example of both these phenomena, this time among vertebrates.
According to an article that will be appearing in the Proceedings of the National Academy of Sciences a species of snake called Rhabdophis tigrinus does much the same thing. The article is reported on by National Geographic:
But the Asian snake Rhabdophis tigrinus has evolved a way to cosume the toxic meal safely.
Instead, the snake stores the toad toxins in glands in its neck, making it too poisonous to eat.
These snakes even taunt enemies to attack, according to the new research…
The snakes also pass the toxins on to their offspring to protect them while they are too young to eat toads themselves.
There are two other interesting aspects to the story. First:
This Asian snake is the first vertebrate known to eat another vertebrate’s toxin and save it to use in its own defense.
Another population of the same species of snake lives on toad-free islands, which separated more than 10,000 years ago when sea levels rose at the end of the last Ice Age.
Since then, the toxin-deprived snakes have evolved into scaredy cats.
Rather than taunting predators, these snakes flee, the researchers show.
Back to the ability of the mother to pass the toxins on to her offspring:
In addition, while a mother snake is carrying eggs in her body, she can pass toxins on to her offspring, the study demonstrates.
This gives the young enough of a protective dose of the toxin to last them until they can start eating toads on their own.
“That’s the coolest part of the study,” said Edmund Brodie III, an evolutionary biologist at the University of Virginia.
Instead of having to pass on genes to the hatchlings, mother snakes can give them toxins directly, a system that in theory is simpler to evolve, Brodie said.
“It makes it a lot easier to evolve toxicity when you’ve got a maternal effect.”
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