Friday, October 5, 2012

A Snail's Escape Response to Snake Predation


Snails that can shed their tails to escape much faster-moving predators and then regrow the amputated body section have been discovered living in sub-tropical Japan.

At left. The snail-eating snake Pareas iwasakii as it feeds on a snail. Bar= 10 mm. Photo credit: Masaki Hoso.

The ability to shed body parts, similar to that found in lizards, crabs and earthworms, has reportedly never before been seen in a mollusk.

Masaki Hoso, a Netherlands-based fellow with the Japan Society for the Promotion of Science, posted the findings on his website Wednesday, as his paper was published in the British science journal Proceedings of the Royal Society.

Hoso experimented with "isshikimaimai" snails (Satsuma caliginosa caliginosa) that live on the Okinawan islands of Ishigaki and Iriomote by feeding them to predator snakes, called Pareas iwasakii.

"It was found that isshikimaimai often escaped predation by detaching their own tails" before hiding themselves inside their shells, he said on his website, adding the cut-off sections were regenerated "a few weeks later".

Hoso also put the same kind of snakes together with a different type of snails from another Okinawan island, about 120 kilometres (75 miles) west of Ishigaki, where there are no snail-eating snakes.

"These snails do not cut off their tails at all and in the experiment they were easily eaten by Iwasaki's snail-eaters," he said.

"The autotomy of isshikimaimai is presumed to be a special case of adapting to counter snakes," said Hoso, a visiting researcher at the Naturalis Biodiversity Center in Leiden.

The tail shedding behaviour is frequently seen among the snails whose shell has yet to fully develop into an effective defence, the study said.

When the snails mature, the aperture of their shell becomes disfigured in a way that protects the creature when it retreats inside.

Hoso noted that while the tails of lizards are structured to be easily detached from the body trunks, no such special structure is present in the tail of isshikimaimai.

"The mechanism of the autotomy remains to be solved," he wrote.

Scientists have previously noted that Iwasaki's snail-eaters have asymmetrical jaws, with more teeth on the right side to allow for more efficient access to snail shells, which predominantly spiral clockwise.

Biologists in the US reported last month that the African spiny mouse, a desert rodent that has become an exotic pet, can shed up to 60 percent of the skin on its back and fully regrow the lost tissue.

The spiny mouse (Acomys) is well-known for eluding hunters by shedding its tail skin.

Understanding the trick could one day help burns victims in need of scar-free skin regeneration, scientists said.

The entire article is available on-line.

Citation
Hoso, M. 2012. Cost of autotomy drives ontogenetic switching of anti-predator mechanisms under developmental constraints in a land snail Proc. R. Soc. B , doi:10.1098/rspb.2012.1943 1471-2954

2 comments:

  1. Greetings,

    A minor correction, the Anadenidae slug genera Prophysaon from Western North America, "the tail dropping slugs" autotomize their tails in response to predation. This has been known for perhaps over 100 years.

    Warm Regards,
    Nick Waters

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  2. You may wish to examine this article as well. http://mollus.oxfordjournals.org/content/60/1/19.abstract

    I know from personal investigation that Prophysaon possesses a cleavage plane. It can drop the tail at will without tearing.

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