Tag: defence

Crickets forewarn their offspring about predators before they're born

By Ed Yong | February 9, 2010 9:30 am

Mothers can teach their children much about the world, but some mothers can do it without ever meeting their young. Take the field cricket Gryllus pennsylvanicus. A female cricket isn’t exactly a caring mother. Once she lays her eggs, she abandons them to their fate. But amazingly, she can also forewarn her young of the dangers they might face. If a pregnant female is exposed to a wolf spider, her experiences affect her unborn young. When they hatch, the baby crickets are more likely to freeze when they smell wolf spiders nearby.

If mothers sense a threat in their environment, there are clear advantages in being able to prepare her young to face those threats. Over the last decade or so, scientists have discovered that many animal and plant mothers do exactly this, even before their young are born. If pregnant water fleas are exposed to the smell of a predatory midge, they produce young that are armed with larger “crowns-of-thorn”, defensive spiky helmets that make them difficult mouthfuls. In the same way, aphids produce more winged offspring if they sense danger. Even the humble radish can generate a generation with sharp, spiky hairs.

In all of these examples, the adaptations are physical ones. The case of the crickets, documented by Jonathan Storm and Steven Lima at Indiana State University, is the clearest example yet of mothers preparing their young for life by influencing their behaviour. Physical defences wouldn’t do much good here, for even the largest of crickets are easy pickings for spiders.

Storm and Lima bred crickets that had never seen a wolf spider before. They placed pregnant females in cages with wolf spiders whose killing fangs had been disabled with wax. After a while, the females were removed and allowed to lay their eggs. Storm and Lima collected the hatchlings and placed them in plastic arenas lined in paper saturated with the faeces and silk lines of wolf spiders.

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Tiger moths jam the sonar of bats

By Ed Yong | July 17, 2009 9:30 am

Blogging on Peer-Reviewed Research
Bats view the world in echoes, timing the reflections of their own ultrasonic calls to navigate and hunt. This biological sonar, or echolocation, has made them masters of the night sky; it’s so sensitive that some species take moths and other insects on the wing, while others pluck spiders from their webs without entangling themselves in silk. But with such an efficient technology, it was only a matter of time before their quarry developed countermeasures.

Some insects gained ears; others simply rely on outmanoeuvring their attackers. But one group, the tiger moths, play bats at their own game. When attacked, they unleash ultrasonic clicks of their own to jam the calls of their pursuers, disrupting their ability to accurately gauge distances or even feigning echoes off non-existent objects.

This technique has been suggested ever since moths were first discovered to click several decades ago, but Aaron Corcoran from Wake Forest University has found the first conclusive evidence that moths actually do this. They pitted moths of the species Bertholdia trigon) against four big brown bats (Eptesicus fuscus) against each other over the course of three days, in gladiatorial arenas surveyed by high-speed infrared cameras and ultrasonic microphones.

When the three bats were pitted against moths in flight, they only managed to snag B.trigona on around one in five attempts. Even if the moths were tethered onto a stump, the bats still fumbled their approach at the last minute. A related moth species that doesn’t click fared much worse and almost always succumbed to the bats.

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Retrocyclins: a defence against HIV, reawakened after 7 million years

By Ed Yong | April 29, 2009 8:30 am

Blogging on Peer-Reviewed ResearchHIV is an elusive adversary. The virus is so good at fooling the immune system that the quest for an HIV vaccine, or even a countermeasure to resist infections, has spanned two fruitless decades. But maybe a defence has been lurking in our genomes all this time.

Nitya Venkataraman from the University of Central Florida has managed to reawaken a guardian gene that has been lying dormant in our genomes for 7 million years. These genes, known as retrocyclins, protect monkeys from HIV-like viruses. The hope is that by rousing them from their slumber, they could do the same for us. The technique is several safety tests and clinical trials away from actual use, but it’s promising nonetheless.

Retrocyclins are the only circular proteins in our bodies, and are formed from a ring of 18 amino acids. They belong to a group of proteins called defensins that, as their name suggests, defend the body against bacteria, viruses, fungi and other foreign invaders. There are three types: alpha-, beta- and theta-defensins. The last group is the one that retrocyclins belong to. They were the last to be discovered, and have only been found in the white blood cells of macaques, baboons and orang-utans.

In previous experiments, Venkataraman’s group, led by Alexander Cole, showed that retrocyclins were remarkably good at protecting cells from HIV infections. They are molecular bouncers that stop the virus from infiltrating a host cell. The trouble is that in humans, the genes that produce retrocyclins don’t work. Over the course of human evolution, these genes developed a mutation that forces the protein-producing machinery of our cells to stop early. The result is an abridged and useless retrocyclin.

But aside from this lone crippling mutation, the genes are intact and 90% identical to the monkey versions. Now, Venkataraman has awakened them. She found two ways to fix the fault in human white blood cells, one involving gene transfer and the other using a simple antibiotic. Either way, she restored the cells’ ability to manufacture the protective proteins. And the resurrected retrocyclins did their job well – they stopped HIV from infecting a variety of human immune cells.

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MORE ABOUT: defence, HIV, retrocyclin
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