lunes, 14 de marzo de 2011
A weaver spider rests at the center of its web orbicular. A wasp comes and gives you a pang. The spider is paralyzed for 10 to 15 minutes. Meanwhile, the wasp egg attaches to the abdomen. When the spider is recovered, resumed his normal activities and one or two weeks continuing to build normal orb webs to capture prey on which it feeds. But in his abdomen of the wasp egg ends up producing a larva which will remain attached to the spider, vampire feeding in miniature hemolymph of the spider, which will suck for a few small holes made in the abdominal cuticle of it.
And here comes the incident. One night, when the wasp larva reaches the stage of development in cuticle molting for the first time, induces the spider to build a web abnormal, consisting only of guidewires, the larvae use for their own purposes. Then, the larva moves back cuticle, the spider kills and devours. The next afternoon, the larva spins a cocoon and hangs it on the special web spider wove enslaved and who happens to be a structure particularly well designed to support the bud. The larvae pupate after about four days and seven other emerges already become adult wasps.
This is a story of real life. The drama occurs between the spider Plesiometa argyra (Walckenaer 1841) (Tetragnathidae) and the wasp Hymenoepimecis argyraphaga Gauld (Ichneumonidae). It is one of many examples of parasites that take over the behavior of their hosts and force them to perform actions necessary for the parasite to continue or complete their life cycle.
In several studies published last year, giving details of the domain that carries the fungus on its host unilateralis Ophiocordyceps, the carpenter ant Camponotus leonardi, which forces you to die ideal area for growth and reproduction of the parasite itself.
The bite of death
When the fungus infects the ant, it continues to live for a short time, but his behavior becomes suicidal. Foliage leaves high in the lives normally, more than 20 feet above the ground, and down the saplings and smaller plants, there are moves under a sheet hanging near the floor and attaches it to the jaws. It is well for weeks, his jaw locked in what has been called the bite of death. When the ants finally dies, the fungus is growing inside your body. After several days, the stroma of the fungus sprouts grotesquely behind the head of the ant, to shed one or two weeks later, a shower of spores capable of infecting each another unfortunate ant.
In photographs taken of the study (link) Maj-Britt Pontoppidan and other researchers cite the end of this note is (up) a sheet with a dead ant against the backdrop of forest and (bottom) with Ant stroma of the fungus coming out behind the head. The second picture was so up and down so that it can be more parasite and host.
Infection, "says researcher David P. Hughes, Harvard University, must occur on the forest floor, because the spores of O. unilateralis are too heavy to disperse over long distances. Rather, create an area of infection of about one square meter below the dead host.
Although this example has been known for nearly a century, recent studies reveal how accurate is the government that exercises the fungus over his victim. Almost invariably, researchers found the ants clinging to leaves located at about 25 inches off the ground and on the northwest side of the plant. Apparently, humidity, lighting and temperature are hence the ideal for the growth and reproduction of the fungus. When the researchers removed some infected ants in that area and highest ranked sites, the mushrooms did not develop properly.
It is also notable that grows in the dead ant, the fungus converts it into sugars entrails, with which it feeds, but never touches the muscles that move the jaws, so that they remain locked to the blade.
Recently discovered for the first time convincing evidence that the parasite has been operating in the same way for about 48 million years. Fossil leaves collected in Messel, Germany, presents the characteristics of the bite marks of death. This is probably the oldest evidence of such parasitism. In this note Smithsonian Science (link) you will find more information.
There are many other examples, as I noted above. One or two until it sounds funny. There is a nematode parasite of an ant, her abdomen swells and puts it bright red like a cherry. Then the ant does lie belly up including strawberries to wait to eat it the bird which is the definitive host of the nematode. And there is a protozoan, Toxoplasma gondii, which must pass an intermediate host, a rat, in its final host, a cat. To do so, reverses the rat's innate aversion to cat odor and makes them attracted to it, with consequences that are to be expected.
The big question is how the parasite manages to change so radical and yet so specifically, the behavior of its host. The answers will surely come of biochemistry. The parasite may secrete neuroactive substances or that in some way, directly or indirectly, alters the levels of certain hormones and neurotransmitters of the host. In several cases it has checked the profile modification of protein synthesis, the researchers already have his eye on several proteins that may be involved in modifying the behavior of victims. Obviously this is a very complex and fascinating field of study.
Pontoppidan MB, Himaman W, Hywel-Jones NL, Boomsma JJ, Hughes DP (2009) Graveyards on the Move: The Spatio-Temporal Distribution of Ophiocordyceps-Infected Dead Ants. PLoS ONE 4 (3): e4835. doi: 10.1371/journal.pone.0004835
Robert Poulin, Parasite Manipulation of Host Behavior: An Update and Frequently Asked Questions. In H. Jane Brockmann, editor: Advances in the Study of Behavior, Vol 41, Burlington: Academic Press, 2010, pp. 151-186.