Venom isn’t just a feature of some animals; it’s found across the living world, from plants and fungi to bacteria and viruses, says a new study.
Lead author William Hayes, an ecologist at Loma Linda University, U.S., has long studied venomous rattlesnakes. It was while teaching a course on the biology of venom that he and his students began thinking about the various definitions of venom and examples of non-animals that satisfied those definitions.
“The deeper we dug into those examples, the more convinced we became that venom wasn’t invented solely by animals. It’s a remarkable adaptation that is far, far more widespread and ubiquitous than currently recognized,” Hayes told Mongabay.
All venomous animals have one thing in common, the authors write: They introduce toxins into another organism using structures like fangs or spines. However, different animals acquire, store, deliver and use venom in different ways.
Some like jellyfish and anemones make toxins inside specialized stinging cells. Scorpions and snakes produce venom inside special glands, delivering it through stingers or fangs. Others borrow toxins: boxer crabs (Lybia tessellate), for instance, carry venomous sea anemones on their claws like boxing gloves for defense, while the anemones likely get food in return. Some marine worms store bacteria-produced toxins in glands, which they inject into their prey or predators through a wound.
The non-animal world has analogous examples, the authors found. For instance, tiny, single-celled organisms called ciliates contain toxin-filled, harpoon-like structures that can inject toxins into larger, single-celled prey, causing paralysis or death, Hayes said.
Among plants, the parasitic mistletoe uses a specialized root structure to penetrate another plant’s tissues, before delivering venom-like toxins that allow it to extract nutrients from its host.
Like boxing crabs co-opting anemones, a group of plants called ant-plants host stinging ant colonies that defend the plants while receiving food and shelter in return. “Why expend energy synthesizing, storing, and producing structures to defend yourself with venom when you can just as readily use someone else’s investment instead?” Hayes said.
Ant-plants can even manipulate the size of their ant colonies in response to threats, like snakes or scorpions controlling how much venom they deliver during a bite or sting, a trait researchers call “venom-metering,” Hayes added.
Timothy Jackson, co-head of the Australian Venom Research Unit at the University of Melbourne, who wasn’t involved in the study, told Mongabay by email that the paper “does the field a service” by cataloguing examples of toxin delivery across a wide range of non-animal organisms. “Some of us have been discussing non-animal (including microbial) ‘venoms’ for a number of years, so I welcome this survey.”
Jackson added that some toxin researchers “may resist the inclusion of plants, fungi, microbes, and viruses, within the function class of venomous organisms”. But “nature is exceptionally complex, and rather messy, and we must allow our definitions to evolve along with our understanding,” he said.
Banner image: acacia with stinging ants by Ryan Somma via Flickr (CCBY-SA2.0).
This story first appeared on Mongabay
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