Research led by Bangor University challenges assumptions about how snake venoms evolve.
For many people, the fear of venomous snakes is linked to one thing: pain.
Yet new research led by scientists at Bangor University suggests that, for Europe's vipers at least, causing pain may never have been a driving force in the evolution of their venom.
The study, published in the journal Functional Ecology by an international team of researchers from across Europe and Australia, examined the venoms of multiple European viper species to investigate a long-standing question in evolutionary biology: how are snake venoms shaped by the competing demands of catching prey and defending against predators?
The answer came as a surprise.
Professor Wolfgang Wüster, a venom evolution expert at Bangor University and senior author of the study explained
"We expected to find evidence that some vipers had evolved venom components specifically to cause rapid pain as a defensive mechanism.
"Instead, we found no evidence that the venoms directly activate pain-sensing nerve cells. This suggests that, in European vipers, venom evolution is driven overwhelmingly by the need to subdue prey."
A biological balancing act
Venom is one of nature's most sophisticated weapons. Snakes rely on it to immobilise and kill prey, but it can also help deter predators.
However, these dual roles present an evolutionary challenge. Venom glands contain a finite chemical cocktail, meaning different venom functions may compete for space and resources.
The researchers set out to test whether vipers that feed on relatively defenceless prey (insects) have more opportunity to evolve pain-inducing toxins for defence than species that regularly hunt tougher, more dangerous prey such as rodents.
To investigate, the team analysed venom samples collected from European vipers across the continent and tested their effects on specialised nerve receptors involved in sensing pain.
The scientists predicted that at least some species would show evidence of evolving toxins that trigger immediate pain, helping them fend off predators.
But that is not what they found.
No gain from pain
Despite considerable differences in venom composition between species, none of the venoms directly activated the pain-sensing receptors tested in the study, regardless of their diet.
The findings suggest that natural selection has prioritised hunting efficiency over defensive pain production during the evolution of European viper venoms.
In other words, venom appears to be optimised for securing a meal rather than delivering a warning.
Lead author Dr Bálint Üveges, a research fellow, who conducted the research as part of his work with Bangor University's Molecular Ecology and Evolution group and the Centre for Ecological Research of the Hungarian Research Network said:
"This challenges the idea that defensive and predatory functions drive venom evolution in different directions in snakes. Our results indicate that prey capture is the dominant force shaping venom composition in these species."
Why it matters
Understanding how and why snake venoms evolve is far more than an academic question.
According to the World Health Organisation, snakebite is a neglected tropical disease that kills more than 100,000 people every year and leaves hundreds of thousands more with permanent injuries or disabilities.
One of the biggest challenges in developing effective antivenoms is the enormous variation in venom composition, even within individual snake species.
By revealing the evolutionary forces that shape venom, scientists hope to better understand why these differences occur and how they may affect medical treatment.
Professor Wüster said: "To improve treatments for snakebite, we first need to understand what drives venom diversity. Studies like this help us uncover the evolutionary processes behind the venoms that cause so many medically important bites around the world."
An international effort
The research brought together scientists from institutions across the UK, Europe and Australia, combining expertise in venom biology, ecology, evolutionary science and neurobiology.
