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Written by Thomas Hesselberg
Tuesday, 04 March 2008
Navigation in animals has puzzled people for centuries and still provides challenges for scientists. How for instance can a Monarch butterfly with a brain weighing less than 0.02 grams find its way to its overwintering site more than 4,000 km away? Or how can the Arctic Tern circumnavigate the globe with a precision better than human navigators before the invention of the GPS system? We know now that one of the most widely used methods of navigation in the animal kingdom is to use the Earth’s magnetic field as a compass. This method is predominantly found in birds, fish and insects, but has also recently been demonstrated in bats. However, questions remain as to how the animals detect the magnetic field. Scientists from Princeton University and Caltech in the United States have investigated this in the Big Brown Bat (Eptesicus fuscus). Tag it: ? Be first to comment this article \| Add as favourites (37) \| Quote this article on your site \| Views: 1358 \| E-mail
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Sneaking behaviour is risky for spider males

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Written by Thomas Hesselberg
Sunday, 17 February 2008
The poisonous redback spider (Latrodectus hasselti) showing its characteristic red pattern on the abdomen. Photo from Wikipedia. In the mating game everything is allowed. A sneaking strategy can be observed in a wide range of species. It is usually smaller subdominant males that quickly seize opportunities to mate with unguarded females, for instance when dominant males are fighting among each other for access to the female. Such a strategy can be risky though as the dominant males, for obvious reasons, are not very tolerant towards sneaking males. However, scientists have discovered that for the redback spider (Latrodectus hasselti), the danger does not come from other males but from the female. Tag it: ? Be first to comment this article \| Add as favourites (27) \| Quote this article on your site \| Views: 932 \| E-mail
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Ultrasonic communication in rats

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Written by Thomas Hesselberg
Wednesday, 02 January 2008
Rats are (in)famous for their versatility and their ability to survive and thrive under many different conditions. An important reason for this is the rats advanced social behaviour and their ability to effectively communicate with conspecifics. Rats emit two different kinds of signals – low frequency calls in the 22 kHz range and high frequency 50 kHz calls. The low frequency calls are used as alarm cries and for instance emitted during exposure to predators, during male-male aggression and during social isolation. Thus they have a clear communicative aim. The high frequency ultrasonic calls, in contrast, are used during play, mating and food consumption. The communicative role of ultrasonic calls is not clear. However, now Markus Wöhr and Rainer Schwarting from the University of Magdeburg in Germany have shown that ultrasonic signals serve a communicative purpose. Tag it: ? Be first to comment this article \| Add as favourites (35) \| Quote this article on your site \| Views: 2598 \| E-mail
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Underwater chemical warfare in sea hares

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Written by Thomas Hesselberg
Wednesday, 19 December 2007
The sea hare (Aplysia californica) squirt a ink and opaline cloud when threatened. Photo from Wikepedia and taken by Genny Anderson. The battle between prey and predators is a bloody and savage one that has been ongoing for 1000 of millennia. In some cases the weapons are obvious like the mighty claws and sharp incisors in the lions and the impenetrable protection of the tortoises. However, the battle is also fought with more sophisticated weapons. The sea hares are underwater slugs. Unlike other gastropods they are not protected by a shell, but employ a host of chemical defences including deterrent compounds in the skin. However, the most striking defence mechanism in sea hares is the release of a purple cloud of ink and opaline. Like the ink from octopuses it reduces the visibility and increases the sea hares chances of making an unseen get away. Interestingly, the chemicals in the cloud also interact with the sensory system of predators and act surprisingly enough as feeding stimulants. This is not as stupid as it sounds though. In this way the sea hare lures the predator into believing that the cloud contains food, which attracts the predator towards the cloud and not towards the sea hare. Tag it: ? Be first to comment this article \| Add as favourites (35) \| Quote this article on your site \| Views: 1169 \| E-mail
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Worming its way through mud

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Written by Thomas Hesselberg
Tuesday, 04 December 2007
A ragworm with its pharynx (or jaws) extended as viewed under the microscope. For many of us, worms are long pink creatures found in the ground with no visible head and mainly good for attaching to hooks when we go fishing. However, the segmented worms in the phylum Annelida comprise other animals than just the earth worms. The ragworms for instance in the class Polychaeta have a distinct head region with eyes, palps and antenna as well as appendages on each of the body segments, which is used as leg during crawling or as paddles during swimming. But like the earth worm burrows in the soil, the ragworm burrows in the muddy sediment in the shallow coastal waters where it lives. Tag it: ? Be first to comment this article \| Add as favourites (27) \| Quote this article on your site \| Views: 1097 \| E-mail
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