|
Some parasites and parasitoids cause changes in the behavior of their hosts by directly affecting the hosts' decision-making and behavior control mechanisms. The acquired or modified behaviors assist in parasite transmission, and often result in the host's demise. == Types of behavioral change == Parasites may alter hosts' behaviors in ways that enhance the likelihood of parasite transmission from host to host (eg. by host predation); result in parasite release at appropriate sites (eg. by changes in the host's preferences for habitat selection); increase parasite survival or increase the host’s likelihood of colonization by suitable mates for the parasite. The protozoan ''Toxoplasma gondii'' infects animals from the ''Felidae'' family (its ''definitive host''), and its oocysts are shed with the host's feces. When a rodent consumes the fecal matter it gets infected with the parasite (becoming its ''intermediate host''). The rodent subsequently becomes more extroverted and less fearful of felines, increasing its chance of predation and the parasite's chance of completing its lifecycle. There is some evidence that ''T. gondii'', when infecting humans, alters their behavior in similar ways to rodents; it has also been linked to cases of schizophrenia. Other parasites that increase their host's risk of predation include ''Euhaplorchis californiensis'', ''Dicrocoelium dendriticum'' and ''Myrmeconema neotropicum''. ''Plasmodium falciparum'', carried by the ''Anopheles gambiae'' mosquito, changes its host's attraction to sources of nectar in order to increase its sugar intake and enhance the parasite's chance of survival. The Emerald cockroach wasp (''Ampulex compressa'') parasitises its host, the American cockroach (''Periplaneta americana'') as a food source and for its growing larvae. Unlike other parasites, the wasp induces the behavioral change ''prior'' to infecting the host, putting it into a state of hypokinesia - "a reversible long-term lethargy characterized by lack of spontaneous movement or response to external stimuli".〔.〕 The cockroach remains alive but motionless, and after dragging it to a burrow the wasp deposits an egg into its carcass and buries it for the growing larva to feed on. The adult wasp emerges after 6 weeks, leaving behind nothing but a hard outer cockroach "shell".〔 The parasitic wasp ''Hymenoepimecis argyraphaga'' grows its larvae on spiders of the species ''Leucauge argyra''. Shortly before killing its host the larva induces changes in the spider's weaving behavior, causing it to weave a strong, cocoon-like structure. The larva then kills, enters the cocoon and pupates. ''Strepsiptera'' of the ''Myrmecolacidae'' family can cause their ant host to linger on the tips of grass leaves, increasing the chance of being found by the parasite's males (in case of females) and putting them in a good position for male emergence (in case of males). A similar, but much more intricate behavior is exhibited by ants infected with the fungus ''Ophiocordyceps unilateralis'': irregularly-timed body convulsions cause the ant to drop to the forest floor, from which it climbs a plant up to a certain height〔 〕 before locking its jaws into the vein of one of its leaves answering a certain criteria of direction, temperature and humidity. After several days the fruiting body of the fungus grows from the ant's head and ruptures, releasing the fungus's spores. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Behavior-altering parasites and parasitoids」の詳細全文を読む スポンサード リンク
|