Question

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from the air-breathing organ (a simple lung) of an ancestral fish is an example of

(A) exaptation.

(B) changes in Hox gene expression.

(C) paedomorphosis.

(D) adaptive radiation

Short answer

1. The option “exaptation” istrue.

2. The option “changes in Hox gene expression” isfalse.

3. The option “paedomorphosis” is false.

4. The option “adaptive radiation” is false.

Step-by-step solution

Swim bladder

The aquatic organisms need to respire for the exchange of gases. The aquatic animals make use of dissolved oxygen present in their environment.

The swim bladder is the gas-filled structure that enables buoyancy for aquatic animals such as fishes. The swim bladder inflates and deflates depending on the external fluid pressure and helps fish.

Explanation of option ‘(A)’

The swim bladder or gas bladder evolved from the air-breathing organ. Exaptation refers to the situation where an organ or part develops but eventually functions differently than its desired role.

Thus, the swim bladder assists in buoyancy rather than breathing; it refers to exaptation.

Therefore, the given option is true.

Explanation of option ‘(B)’

The hox genes did not express differently. In the conversion of air-breathing organ, lungs, the swim bladder does not provide respiratory functions rather allow buoyancy; this is not related to hox genes.

Thus, the hox genes were not responsible for the event.

Therefore, the given option is false.

Explanation of option ‘(C)’

Paedomorphosis is a term that explains the retention of certain traits which appear in younger phases of any organism’s life cycle till their adult stages.

Thus, the development of the swim bladder from air-breathing organs is not an event occurring due to paedomorphosis.

Therefore, the given option is false.

Explanation of option ‘(D)’

Adaptive radiation occurs when the organisms make changes in their behavioral and morphological attributes. The swim bladder evolved from an air-breathing organ but does not assist fishes in breathing. Hence it is an example of exaptation instead of adaptive radiation.

Thus, the swim bladder development is not an example of adaptive radiation.

Therefore, the given option is false.