Question

What is ‘Brood parasitism’? Give an example.

Answer 1

Brood parasitism is the phenomenon in which one species takes help of other species to raise their young ones. They show egg mimicry. Eggs of parasites resemble the eggs of the hosts. It is commonly observed in cuckoo birds.

Complete answer:
Brood parasites are the organisms that raise their young ones with the help of other organisms. They manipulate the host, either of the same or of another species. They use brood mimicry or egg mimicry in which the eggs resemble the eggs of the host. The organisms which show brood parasitism spend their time on other activities when other organisms are feeding their young ones. It gives them relief from investing their time on rearing young ones or building nests for them. They distribute their eggs amongst a number of different hosts in order to reduce the risk of egg loss. It results in an evolutionary arms race between parasite and host as the pair of species co evolved.
The ability of species to evolve depends on the strength of defenses and counter-adaptation of hosts and Parasites. Parasites should have close mimicry to the host as the hosts have evolved very strong rejection defences. It occurs only in some species, in other species hosts do not show rejection defenses and as a result, the parasitic species will show no evolved trait.
For example: cuckoo bird (parasite) leaves its eggs in the crow’s (host) nest. This cuckoo egg performs its early development activities like hatching into the crow’s nest and after maturation, it flies away. Brood parasitism is observed in many birds such as honey guides in Africa, cowbirds, old world cuckoos, black-headed ducks, and some new world cuckoos in America.

Note: Brood parasitism involves many mechanisms such as nest-site hypothesis, parental-care parasitism, harm to the hosts, hosts reject offspring, cost to the parasites, hosts raise offspring. Brood parasitism is also observed in fishes such as mochokidae catfish of Lake Tanganyika, Synodontis multipunctatus. Catfish eggs are incubated in the mouth of hosts. Cuckoo bees also show this phenomenon.