Question

Mention the changes Koel must have undergone in order to achieve brood parasitism, during the course of evolution.

Answer 1

The real koels, Eudynamys, is a genus of cuckoos native to Asia, Australia, and the Pacific. Brood parasites manipulate the host's behavior so that the host nourishes the offspring of the parasite. A well-known example of this phenomenon in birds is the cuckoo. To successfully complete its life cycle and maintain reproduction, the parasite must be in harmony with the rhythm of the host.

Complete answer:
Parasitism: Relationship between two organisms of the same or different species, one of which lives in the other's body or receives food and nutrients that harm that organism is called parasitism.
Due to the parasite's lifestyle, parasites undergo various adaptations in order to survive. The environment also plays an important role when it comes to hosting parasites.
Brood parasitism in Koel: Cuckoos lay their eggs in a host's nest. These eggs are similar to crows. the host hatches eggs and takes care of them.
Adaptation in Koel for brood parasitism:

Mimetic eggs: Among the specific parasites of birds, mimic eggs represent an almost universal adaptation. Size is also important for the culture and survival of the parasite species. This can be beneficial if the eggs of the parasite are the same size as the eggs of the host species.
Thick eggshell: The shell of the egg of brood parasites is often thicker than the shell of the host.
Short incubation period of eggs: Most brood parasites have very short hatching times and fast growth of chicks. In many brood parasites, such as cuckoos and copper conductors, the short hatching time of eggs is associated with an internal hatching time, which is twenty-four hours longer for the cuckoo than for the host. Some non-parasitic cuckoos have a longer internal hatching time, so this long internal hatching period is not an adaptation to the brood parasites, but rather causes the birds to parasitize on the chicks. This can be made easier by adding thick yolk inside the egg to provide more nutrients.
Getting taller than the host is an additional amendment for the brood parasite.

Note:
The common cuckoo is an interesting example in which individual females specialize in one species, although the entire species parasitize different hosts, including reeds and eardrums. Females are usually parasites in the nests of the species they raise. Male cuckoos fertilize females of all strains, maintaining sufficient gene flow between different maternal lines to prevent species from emerging.
Nesting hypothesis: According to this hypothesis, the female cuckoo chooses a group of host species that have similar nesting positions and egg characteristics. Observe this potential host population and select nests from this group.