The explosive evolutionary tactics of snakes

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The writer is a science commentator

There is something otherworldly about snakes. The slithering creatures feature heavily in religion, folklore and mythology: the serpent in the Garden of Eden that tempts Eve to eat forbidden fruit; Medusa, a snake-haired Gorgon cursed with a gaze that turns observers to stone; the Nagas, the half-human, half-cobra beings of Hinduism, Jainism and Buddhism, who dwell in underground palaces.

The serpentine presence across global cultures may reflect their extraordinary variety in the real world. There are around 4,000 snake species, living in oceans, lakes, deserts, forests and even underground. The longest species, reticulated pythons, regularly exceed six metres; the shortest, the 10cm Barbados threadsnake, looks like a curl of brown string.

In February, herpetologists from the US, UK, Australia, Brazil and Finland revealed the most comprehensive family tree of snakes and lizards to date — and found it contained a “macroevolutionary singularity”, or a relatively sudden, unexplained shift in the rate of snake evolution that began more than 100mn years ago and is still ongoing. The twists and turns of their evolutionary backstory are emerging just as other scientists are touting snakes as the new superfood.

This evolutionary burst, called adaptive radiation, saw snakes evolving up to three times faster than other lizards, which allowed them to prosper after the asteroid impact that wiped out the dinosaurs 66mn years ago. The process also produced the eye-catching characteristics seen today: multiple hunting strategies, including venom and constriction; the ability to consume toxic prey such as scorpions; flexible skulls for devouring large animals; the capacity to “smell” chemicals with the tongue; and the ability to glide, burrow, climb and swim.

University of Michigan biologist Daniel Rabosky, senior author, described the serpentine pace of evolution in Scientific American: “Lizards are puttering around on a moped, while snakes are on a bullet train.”

Together, snakes and lizards belong to the order of scaly reptiles known as squamates, containing about 11,000 species and making up about a third of all terrestrial vertebrates. To complicate matters, there are limbless lizards, such as slow worms, that are not snakes (unlike snakes, they have eyelids, ear openings and notched, rather than forked, tongues). While many lizard species have barely changed since the time of the dinosaurs, snakes have since been able to colonise new niches by evolving different ways of moving, eating and sensing the environment.

The researchers used, appropriately, a two-pronged method to examine snake evolution: first, sequencing the genomes of around a thousand squamate species to build a backbone of the family tree and using this to position other squamate species; and second, studying their diets. There are few direct observations of the animals dining in the wild, so the researchers also examined the stomach contents of more than 60,000 preserved snake and lizard specimens stored in museums around the world.

Crunching the genomic and dietary data suggested that three broad changes occurred relatively close together in snake evolution, resulting in a split from other lizards: bodies lengthened and lost limbs; skulls became flexible; and chemical sensing became more refined. It seems to have been this trio of changes, rather than any single innovation, that triggered evolutionary success. The research, published in Science, highlights the value of collecting and preserving natural specimens — scientific practices that can feel antiquated in the digital age.

Charles Darwin noted a similar singularity in the fossil record with the sudden appearance and diversification of flowering plants. Darwin was frustrated by the puzzle, describing it in 1879 to his eminent botanist friend Joseph Hooker as “an abominable mystery”.

The propensity of snakes to adapt quickly to changing environments makes them, for some observers, the perfect food source for a climatically unstable world. Snake meat is high in protein and low in fat, and already a delicacy in south-east Asia and China.

Farmed pythons can be fed on wild rodents and waste protein from agricultural processes; the animals can reach weights of more than 100kg. One study published this year found that, in terms of converting feed to protein, “pythons outperform all mainstream agricultural species studied to date”.

Still, with half the UK population reporting anxiety about snakes and about one in 50 harbouring a phobia, the idea of snakes as the new livestock of choice might not have legs.

Via

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