Final answer:
Coevolutionary alteration is most likely in a situation where a parasite invades a population of asexually reproducing snails, as this reflects the negative frequency-dependent selection exerted by parasites on their hosts, illustrating the Red Queen Hypothesis of coevolving species.
Step-by-step explanation:
Coevolutionary alteration is most likely to occur in scenarios where two or more species have close ecological interactions that place reciprocal selection pressures on one another. This can be seen in scenarios where interactions are mutualistic or in the relationship between parasites and their hosts. One of the key concepts that illustrate this continual evolutionary arms race is the Red Queen Hypothesis. It posits that organisms must constantly adapt and evolve, not just for reproductive advantage but also to maintain their existence in response to the evolving threats from other coevolving organisms, be it predators, parasites, prey, or competitors.
An example of a likely scenario that supports the Red Queen Hypothesis is choice B, "Individuals of a snail population that reproduces asexually die out after a parasite invades its territory." In this situation, the parasites and the asexually reproducing snail population exert negative frequency-dependent selection on each other. The snails lack genetic variation due to asexual reproduction, which makes it difficult for them to coevolve and adapt rapidly to the selective pressure imposed by the parasites, leading to their potential demise.