Explain parasitism and co-evolution with the help of one example of each.
Many parasites have evolved to be host-specific. They can live as parasite only in a single species of host. These organisms parasitize in such a way that both the host and the parasite tend to co-evolve; that is if the host evolves a special mechanism for rejecting or resisting the parasite, in such conditions parasite has to evolve a mechanism to counteract and neutralise them, in order to be successful with the same host species. In accordance with their mode of living, parasites evolve special adaptations such as loss of unnecessary sense organs, presence of adhesive organs or sucker so as to cling to the host. It also loses the digestive system. Parasites have a high reproductive capacity. The human liver fluke depends on the intermediate host (a snail and a fish ) to complete the life cycle. The malarial parasite needs a female anopheles mosquito as a vector to spread to other hosts.
