Some snails evolved ‘counter-coil’ to evade predators’ uneven bite

December 8th, 2010 - 6:00 pm ICT by ANI  

London, Dec 8 (ANI): Evolutionary benefit often makes for show-stopping stuff - for instance, a cheetah’s speed or a moth’s almost perfect mimicry of tree bark. In case of some snails, it’s simply down to a poor fit with a snake’s jaw.

A new study has revealed that some species of Satsuma snail have shells that coil to the left, which probably evolved to evade predators’ uneven bite.

The snakes that prey on them have jaws specialized for feeding on the molluscs’ right-coiling ancestors.

Snail genera tend to be either dextral (right-coiling) or sinistral (left-coiling) but the genus Satsuma contains both dextral and sinistral species, reports Nature.

In most land snails, a single gene controls the switch between dextrality and sinistrality, meaning that reversals are likely to occur frequently.

The study suggested that common snake predators that can easily eat dextral snails struggle to consume the sinistral ones.

This survival advantage allows sinistrality to spread throughout previously dextral populations. Sinistrality also prevented mating with dextral ancestors, leading to reproductive isolation and the evolution of entirely new species.

“This could change the general view of evolutionary genetics,” said Masaki Hoso, an ecologist at Tohoku University in Japan who led the study.

“We’ve found that a single gene can have major effects on speciation and adaptation simultaneously,” he added.

To investigate the effect that living alongside snake predators might have had on the evolution of sinistral species, Hoso and his colleagues first looked at how effectively the snake Pareas iwasakii preys on Satsuma snails.

They found that the snakes, which have more teeth on the right side of their jaws than the left, were able to eat all of the dextral snails fed to them, but only 12.5 percent of the sinistral snails.

Comparing the global distributions of both snakes and snails, the researchers found that sinistral snail species have evolved more often in areas in which predator and prey coexist.

And a DNA-based family tree of the snail genus showed that sinistrality has arisen independently at least six times in Satsuma, more than would be expected were there not some driving force behind its evolution.

“We knew the snakes had trouble picking up sinistral snails,” said Menno Schilthuizen, an evolutionary ecologist at the National Museum of Natural History of the Netherlands in Leiden, who specializes in snail evolution.

“But Masaki has shown the snake might actually speed up the fixation of sinistrality, suggesting this is a very plausible speciation mechanism,” he added. (ANI)

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