Final answer:
The gene patristacin being repurposed for male pipefish's brood pouch development from its original function in liver and kidney activities is an example of co-option. The multiple-choice option is (A) co-option.
Step-by-step explanation:
The phenomenon where the gene patristacin, which is involved in liver and kidney function in all other fish, plays a major role in the formation and function of the brood pouch in male pipefish can be described as co-option. Co-option, also known as exaptation, is an evolutionary process where a gene or structure takes on a new function in addition to or instead of its original role. In the case of pipefish, the gene that originally participated in vital organ functions has been co-opted to help develop the brood pouch where the males carry and protect developing embryos, exhibiting an adaptive feature related to their polyandrous mating systems, where one female mates with multiple males.