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Lecture 13

Lecture 13 - Parasitism

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Biology 2483A
Hugh Henry

LECTURE 13 PARASITISMIntroductionSymbiontsorganisms that live in or on other organisms o Not all symbionts are parasites However more than half of Earths species are symbiontsOur own bodies can be a home to many other speciesA parasite consumes the tissues or body fluids of the organism on which it lives the hostPathogens are parasites that cause diseases an abnormal condition affecting the body of an organismParasites typically harm but dont immediately kill the organisms they eat unlike predatorsDegree of harm varies widely Compare The fungus that causes athletes foot and Yersinia pestis the bacterium that causes the plague Parasite Natural HistoryParasites typically feed on only one or a few host individualsIncludes herbivores such as aphids or nematodes that feed on one or a few host plantsParasitoidsinsects whose larvae feed on a single host and almost always kill itMacroparasiteslarge species such as arthropods and wormsMicroparasitesmicroscopic such as bacteriaMost species are attacked by more than one kind of parasite even parasites have parasitesMany parasites are closely adapted to particular host speciesThis specialization helps explain why there are so many species of parasitesEctoparasites live on the outer body surface of the hostEndoparasites live inside their hosts within cells or tissues or in the alimentary canalMany fungi are ectoparasites More than 5000 species of fungi attack crop plantsMildews rusts and smuts grow on the surface and extend their hyphae fungal filaments into the plant to extract nutrients from its tissuesPlants are also attacked by animals o Ectoparasites Aphids whiteflies scale insects nematodes beetles and juvenile cicadas o They can be thought of as both herbivores and parasitesAnimals also have many ectoparasites o Examples Athletes foot fungus fleas mites lice and ticks o Some of these parasites also transmit disease organismsMany disease organisms are endoparasites o The alimentary canal is excellent habitat for many parasites Most do not eat host tissue but rob the host of nutrients o Tapeworms attach to the hosts intestinal wall and absorb digested foodMany endoparasites live in the hosts tissuescellsExampleso Yersinia pestis the bacterium that causes the plague o Mycobacterium tuberculosis the bacterium that causes tuberculosisPlants also have endoparasitesBacterial pathogens cause soft rot fungi can rot various plant parts from the inside outSome bacteria invade vascular tissues disrupting the flow of water and nutrients causing wilting and often deathEctoparasites can disperse more easily than endoparasitesEndoparasites have evolved various mechanisms for dispersal including complex life cycles and enslaver parasitesSome parasites of the alimentary canal are dispersed in feces
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