In this article we will discuss about the host-parasite relationship and their evolution.
Of a few members in the animal kingdom, who can really be proud of themselves as the stumbling block to the mind of Zoologists—the claim and complexity from the standpoint of adaptation of the parasites, is in no way rejectable.
To successfully complete its life cycle and perpetuate its race the parasite must synchronize its rhythms with those of the host and thus this adaptation according to Herbert Spencer—”is the power of self-regulation, self-preparation, self-protection and self-preservation so as to survive better in many respects than free-swimming ones and so an array of modifications leading to diversity in nature”.
Parasitism is the relationship between two organisms of the same or different species in which one lives on or inside the body of the other and obtains food and nourishment causing harm to this organism.
The organism which is thus benefitted from such association is called parasite and the other which is harmed is known as host. Due to parasitic mode of life the parasite has undergone different kinds of adaptations for its survival. Again in host parasite relation the environment plays a key role.
In this connection the following sorts of relation are observed between a parasite and a host:
i. Incompatibility:
It makes the environment suitable for parasitic development and in its absence the parasite die.
ii. Resistance of host:
This is of two folds— firstly making the parasite itself immature to the host enzyme and secondly to have full capacity to reproduce.
iii. End of virulents:
Parasites when not well adapted may lead to virulents and both the parasite and the host try to develop reciprocity and immunity.
iv. Mutual help:
The reciprocal immunity on the other hand develops a sort of relationship which does not destroy any of the animals and thus makes “parasitism” perfect. So parasitism is a specialized mode of living within a broader ecological category—symbiosis.
In parasitism—the host and the parasite have a very intimate association where all the benefits are derived by the parasites from its prey—the host and the two systems constantly interacting with each other.
Thus the criticism of the story—”Host- parasite-interaction” is one of the compromise—a key (the parasite) to unlock the box (host) of an unrevelled mysterious entity in which the parasites making elaborate efforts to overcome the match against the host while the host making attempts to keep the ball in the goal of parasites—thus trying it to eradicate it.
In the evolution of parasitism it would be difficult, if not impossible, to explain step by step by which some of the highly specialised parasites reached their present condition. Parasitism at times has probably grown out of a harmless association of different kinds of organisms, one of the members of the association, by virtue, perhaps, of characteristics already possessed, developing power of living at the expense of the other, and ultimately becoming more and more dependent upon it.
The general mechanism by which parasites of the digestive canal were originated from free living organisms which were accidentally or purposely swallowed and which were able to survive in the environment in which they observe themselves, and to adopt themselves to it.
It is also easy to see how some of these parasites might eventually have developed further territorial ambitions and have extended their operations beyond the confines of the digestive canal.
The development of some parasitic protozoa of vertebrates, on the other hand, seems clearly to have taken place two steps: first, adaptation to life in the gut of insects, and, second, adaptation to life in vertebrates blood or tissues when inoculated by hosts with skin-piercing and blood sucking habits.