Members of a species can recognize mates using

Behavior

Explanation:

There are many ways by which individuals of the same species recognize mates to copulate. Individuals usually recognize other individuals of the same species by morphology. However, the recognition of individuals of the same species can be complex when there is great similarity between different species, as it happens, for example, in flies.  In these cases the recognition of specific behaviors can be essential. Behaviors can include movement, vocalizations, sounds etc.

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.