A team of University of Queensland researchers has revealed why male funnelweb spiders develop much deadlier venom than their female counterparts.
Led by UQ’s Associate Professor Bryan Fry, the team has spent 20 yearsinvestigating delta-hexatoxins, the venom peptides that make funnel web spidervenom so dangerous.
“Australian funnel-web spiders are infamous for causing human fatalities withthis particular range of toxins,” Dr Fry said.
“Delta-hexatoxins exert fatal neurotoxic effects in humans by keeping nervesturned on, so that they keep firing over and over again.
“It has puzzled scientists why these toxins are so deadly to humans, when theyand other primates, haven’t featured as either prey or predator during thespider’s evolution.
“And we couldn’t understand why most human deaths were being caused by malefunnel web spiders, which seemingly had much deadlier venom than females.”
Using molecular analysis of the venom, Dr Fry and the team decided to take acloser look.
Although 35 species of funnel-web spiders had previously been described, onlyeight delta-hexatoxins from five species had been analysed.
Dr Fry and his team almost tripled the data – profiling 22 novel delta-hexatoxins from the venom of 10 funnel-web species.
“Having much more data helped paint a much clearer picture, revealing anincredibly interesting evolutionary story – one that had been hypothesised,but we’ve now proven,” he said.
“These toxins had originally evolved to kill insects such as cockroaches andflies.
“But, when male funnel web spiders become sexually mature, they leave thesafety of their burrow and wander quite considerable distances in search offemales.
“This can be quite treacherous, and these male funnel web spiders started toencounter dangerous vertebrate predators, such as the dunnart, a smallnocturnal mouse-like marsupial.
“The data shows that natural selection put the necessary pressure on to switchan insect-specific venom into a vertebrate-specific defensive venom.
“And, unluckily for us, we’re a vertebrate species which copped it in theprocess.”
With a stronger evolutionary understanding of delta-hexatoxins, Dr Fry and histeam are now endeavouring to put this new knowledge to use.
“We’re hoping this research will give us a better understanding of exactlywhat funnel web spider venom does to the human body,” he said.
“And – medically speaking – this could be critical for the design of evidence-based treatment strategies for bite victims.
“We’re also hoping it will help researchers discover novel insecticides,finding better sources for insect-specific toxins.
“They’re dangerous as hell, but male funnel web spiders offer us some realopportunities.”
The research has been published in the Proceedings of the National Academy ofScience (DOI: 10.1073/pnas.2004516117).
Image above: Research team member Dr David Wilson milking venom samples froma funnel web spider (Credit: Paul Dymond).
Featured Image: the deadly funnel web spider (Credit: Dr David Wilson).
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