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Yabbies share sharks' 'sixth sense' |
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A yabby explores a bubblewrap wall using its expert abilities in touch, smell and electrical fields.
Photo: David Paul
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Defense response posture in a yabby which researchers observed among behavioural changes seen when yabbies sense electrical signals.
Photo: David Paul
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Most good Aussies know the yabby. A small aquatic crayfish which is as much a part of the Australian psyche as a prawn on the barbie. For years children have been captivated by this little creature, spending hours catching the critters using meat attached to a long piece of string. But the poor old yabby is dying out. These days it is listed by the World Conservation Union as vulnerable and in grave danger of disappearing.
In a natural population, with limits to space and food, only a few of the 500 to 1000 young produced by each mature female in a breeding season can survive to two or three years of age. A juvenile yabby has only one chance in 1,000 of surviving to old age. Studies also show that the chance of a yabby getting this far increases as it grows, but unfortunately about 95% die during their first year, about 50-80% of the survivors die in their second year and further decreasing during the third year.
As if the yabby didn't have enough problems, it also has a plethora of natural predators including fish, birds, insects, humans, and more shockingly, other yabbies. Yabbies are commonly found with legs or claws missing, usually as a result of fights with mates or a close encounter with one of their many predators.
Then there is disease. For yabbies, porcelain disease, a common problem which can only be detected in advanced stages, is usually fatal. All these threats so it's no wonder the yabby population is declining, threatening to unbalance the Australian eco-system.
But there is hope! A group of scientists at the University of Melbourne have been closely studying yabbies, and more curiously the signals they use to detect predators - their 'sixth sense'.
Australian yabbies share this special 'sixth sense' with the senior predator of the oceans, sharks. According to new University of Melbourne research, it is the ability to listen to electrical signals, called electroreception, that alert them to prey or predators.
Study team researcher Mr Blair Patullo said that like the great white shark "one of the biggest predators on the planet", yabbies use electroreception to hunt prey.
"We have provided the first evidence that yabbies 'listen' to electrical fields for their survival," Blair said.
"All animals make small electrical signals when they swim but to detect them is a powerful ability because it enables animals to 'hear' predators and prey, before they are seen or even smelt.
"It makes sense that yabbies would also listen to these signals, but despite much evidence in vertebrate species, until now there was no evidence in the simpler invertebrate animals."
Blair explained that listening to electrical signals could help the yabby detect a nearby tadpole to capture a meal; a predatory fish for a fast getaway; and a fellow yabby for companionship.
The study was conducted by playing electrical signals through electrodes placed in the water near a yabby in total darkness. Darkness was maintained to ensure that the only sensory cue changing in the tank was the electrical field. The researchers then studied how yabbies responded when they heard the signals.
The research, funded largely by an Australian Research Council grant and led by Professor David Macmillan and a team of dedicated students, was published in the international journal Current Biology.
Blair said the research not only reveals more information about the survival techniques of yabbies, it has further applications in the management and preservation of other animal species.
"As with many new discoveries we have raised more questions than we started with and some of those relate to the management, fishing and culture of yabbies, other crustaceans, and the species they interact with.
"We know of electrical fields used to enhance fishing or to prevent species dispersing and this new finding could be valuable in developing new techniques in farming and preserving animal species," Blair concluded.
So for the little yabby it's a case of "watch this space", yet it seems that all is not lost.
This story was adapted from The University of Melbourne's Research Review magazine. The original source article can be found here:
http://uninews.unimelb.edu.au/articleid_4530.html
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The common yabby's biological name is cherax destructor.
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The common Australian yabby is listed as a vulnerable species by the World Conservation Union.
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Yabbies are very hardy and can tolerate poor water conditions and long periods of drought by burrowing deep into the river bed or dam wall to stay moist.
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Porcelain disease is a freshwater fungal infection, Aphanomyces astaci, which affects all members of the crustacean family. It can be identified by brown or blackening spots on the shell of the crustacean and is usually fatal.
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