Venom increases diversity of fish and insect species, research suggests

Venom has played an important role in helping the diversity of fish and insect species to flourish, according to new research.

Fish and insects are by far the most diverse groups of vertebrates and invertebrates, respectively – with the more than a million known types of insects accounting for three-quarters of the invertebrate species discovered on Earth. The 31,000 species of fish account for nearly half of all known vertebrates.

While biologists have long examined what drives biodiversity, the role of venom in relation to these most diverse groups of all had not previously been fully considered.

But a new study, published in the BMC Ecology and Evolution journal, has found that venomous fishes and insects diversify around twice as fast as their non-venomous counterparts.

With venom providing an effective means of repelling predators or catching prey, this may allow species to exploit more opportunities in their environment, potentially leading to the formation of new species as they diversify in their ecology.

Furthermore, the research showed that venom itself has independently evolved at least 19-20 times in fish, and at least 28 times in insects across their evolutionary history.

Animals have not always been venomous. Venoms started off as genes with other functions in animals’ bodies, such as immune system proteins or digestive enzymes.

Commonly, these genes then mutated – appearing instead in a part of the body where they could be weaponised against prey or predators and eventually natural selection ensured the survival and proliferation of those animals with this advantageous mutation, with the venom likely mutating further over generations to become more toxic.

Today, some 10 per cent of fish families and 16 per cent of insect families contain venomous species – from stingrays and catfish, to wasps and mosquitoes.

“Our results provide evidence that venom has played a part in generating the diversity of insects and fishes, which have the largest number of species amongst invertebrates and vertebrates respectively,” said lead researcher, Dr Kevin Arbuckle.

“Venom is not the only factor driving species richness in these animal groups, but we show that it has played an important but previously unrecognised role in generating the amazing diversity we see today amongst insects and fishes.”

Although tentative, the pattern of timing in the origins of different venomous fish, traced during the research, suggested tantalising clues as to what may have driven the evolution of their venom.

Unlike insects, where venom evolved fairly evenly throughout their history, most origins of fish venom were concentrated in the Late Cretaceous and Eocene periods.

Dr Arbuckle offered a possible explanation for this, saying: “Mosasaurs – the aquatic behemoths made famous in the Jurassic World series – originated and peaked in diversity in the Late Cretaceous, at a time when other large marine predator groups were declining.

“Similarly, whales originated and peaked in diversity in the Eocene, when most other large marine predators had gone extinct at the end-Cretaceous mass extinction, which killed off the dinosaurs. Both early whales and mosasaurs are thought to have been active predators with similar styles of movement.

“As a result, we cautiously speculate that most origins of fish venom were linked to similar predation pressures imposed by mosasaurs in the Late Cretaceous and early whales in the Eocene.”