Introduction: definitions; principles and concept Parasitic relationships -Phoresis, commensalism, mutualism, symbiosis, parasitism Parasitism: definition, types of parasites, types of hosts Types of life cycles direct and indirect effects of parasites on their hosts- Immunity-immune response against parasites Introduction: definitions; principles and concept Definitions Parasites are often occupying the 3rd great environment (aquatic-terrestrial-parasitic) *Traditionally, only considered to be protists, worms, and arthropods. Parasite . A parasite is an organism that lives on or inside another organism to the detriment of the host organism . Traditionally parasite referred to organisms with life stages that needed more than one host Parasitism . A form of symbiosis in which one organism (called parasite) benefits at the expense of another organism usually of different species(called host). Organismal Associations Any association more or less permanent is called a symbiosis, with each member a symbiont. Symbiosis is used as a n umbrella term for organisms that live together Symbiosis Commensalism Mutualism Parasitism Phoresis Basic Definitions Symbiosis • Term was first coined by the German de Bary in 1879 to mean “living together.” • It was originally coined to refer to all cases where dissimilar organisms or species (e.g., heterogenetic associations) live together in an intimate association. Types of Associations 1-Phoresis • Phoresis means a type of symbiotic relationship in which one organism (the smaller phoront) is mechanically carried on or in another species (host). Two organisms simply travel together Neither organism is helped or harmed Usually one is transporting the other 2-Commensalism • Means “eating at the same table” One benefits but the other isn’t harmed and receives no benefits Usually one feeds off the “wastes” of the other partner. Branchiobdelid worm attached to a crayfish Commensalism Examples Remoras and sharks *Feed on scraps left by shark Humans have many commensals *Intestinal protozoans and bacteri *Entamoeba Gingivalis Amoeba in the mouth *Eyelash mites 3- Mutualism • Occurs when each member of the association benefits the other Both organisms benefit from the relationship Usually obligatory Both partners realy on the relationship and can’t live without the other. Mutualism Examples Coral and Zooxanthelle Termites and bacteria Bacteria digest wood Cleaner fish and the fish they clean Leeches and bacteria Bacteria digest blood Humans and bacteria Bacteria make vitamins out of our wastes 4-Parasitism  Parasitism – involves one organism living on or inside another organism and harming it.  The organism that benefits is called a parasite.  The organism that the parasite lives on or in is known as the host. Anterior end of a hookworm  Common parasites are fleas, ticks and leeches.  These parasites have adaptation that enable them to attach to their host and feed on their blood.  Other parasites live inside the host’s body such as tapeworms, that live inside the digestive systems of dogs, wolves, and some other mammals. Parasites Parasites can be ecotoparasites or endoparasite. They can have intermediate hosts which may not have any negative consequences. They often move around using “vectors.” Relationships can be quite complex. Lyme disease is a bacterial parasite that is transmitted through tick bites Ticks carry Lyme disease. Deer carry ticks Parasites Many parasites/diseases of humans (and other animals) have very complex ecological relationships. Example: Malaria is a disease caused by a parasitic protozoan. The protozoan is transferred effectively by mosquitoes. (particularly Anopheles). Malaria infection kills ~ 1 million people/year. Type of parasites • Ectoparasite – a parasitic organism that lives on the outer surface of its host, • Endoparasites – parasites that live inside the body of their host, • Obligate Parasite - This lakhasly.com © ﺗﻢ ﺗﻠﺨﻴﺺ اﻟﻨﺺ ﺑﻮاﺳﻄﺔ ﻣﻮﻗﻊ ﻟﺨﺼﻠ parasite is completely dependent on the host during a segment or all of its life cycle, • Facultative parasite – an organism that exhibits both parasitic and non- parasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host. • .Accidental parasite – when a parasite attacks an unnatural host and survives

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