Effects of Parasitism

Parasites are not degenerate animals. They are on the contrary specialized species which show many remarkable and beautiful adaptations to the mode of life that they have adapted during evolution of parasitic life; important adaptations are described below.

1.                  Adaptations to feeding and attachment to host: Powerful and large buccal capsule with teeth in hookworms to affect blood sucking. Remarkable structural changes in the mouth parts of blood sucking insect to suck blood or tissue of birds. Loss of entire digestive system in tapeworm which have adopted in absorbing fluid food through body cuticle or incomplete intestine in trematodes which only can take liquid food through the mouth. Among other modifications which are primarily use for attachment to the host but also help in g4etting food are the suckers and hoods, characteristics of the flukes and tapeworm, the toothed proboscis of the acanthocephalan worms and the hypostome of ticks. Also the claw of such ectoparasites as the lice, sheep ked, and hippoboscid insects which enable them to cling to the external surface of the hosts.

2.            Reduction or loss of organs: Parasitism tends to cause simplification of structure.

Parasitic insects for instance such as lice and fleas have lost their wings but they can move about rapidly by insects for instance such as lice and fleas have lost their wings but they can move about rapidly by means of their limbs. The retention of locomotory organ-cilia by miracidium of trematodes until it has made contact with the snail host and the abandonment of cilia once contact has made is another example. Parasitic life may increase rather than decrease the complexity of the organization of the individual.

3.            Reproductive adaptations: Reproductive adaptation represents methods by which the parasite meets the risk of loss of relatively large numbers of its offspring. One method is to increase the number of eggs produced. This may be affected by (a) increased size of the number of eggs produced. This may be affected by (a) increased size of the ovary , e.g. tapeworms and trematodes when mature, contains ovaries occupying the whole body, (b) increased egg production by a single ovary, e.g. female of Ascaris lumbricoides may produce, 2,000,000 a day compared to Ancylostoma duodenale producing 25,000 a day.

Parasites which experience less risk of destruction of offspring may produce fewer eggs, e.g. female warble fly Hypoderma lineatea attaches its eggs to the hairs of its eggs to the hairs of its hosts, hence produce 500-800 eggs in her life time. Female sheep-ked, Malophagus ovinus produce only 10-15 larvae in her life time as the larvae are less likely to be destroyed by exposure. Important among adaptation of the reproductive processes are methods by which the parasite increases the number of individuals derived from each fertilized eggs, e.g. (i) A single Ocyst of Eimeria tenella by sexual multiplication may produce 1,800,000 individuals of the species in four of five days, (b) Each fertilized egg of a trematods Schistosma mansoni liverates a miracidium which through asexual multiplication in the snail (intermediate host) may produce 100,000 to 250,000 infective cercariae.