Final answer:
Traits with less genetic variation due to their association with reproduction are part of reproductive isolation mechanisms, which when producing less fit hybrids, lead to reinforcement, while in other cases, might lead to species stability or fusion.
Step-by-step explanation:
Traits that by logic should show less genetic variation because of their close association with reproduction fall into the category of reproductive isolation mechanisms. In evolution, reproductive isolation mechanisms ensure that genetic and phenotypic divergence between populations affects characters influencing reproduction. When closely related species produce hybrids that are less fit than the parent species, reproductive isolation is reinforced, a process known as reinforcement. Over time, such reproduction diminishes, leading to further divergence between species.
Conversely, if hybrids are as fit or more fit than the parent species, the potential outcome is the fusion of the two species back into one. This process shows the potential variability in the evolutionary fate of species interactions. However, in some cases, two species can remain distinct while still producing some hybrid individuals which indicates a state of stability with no significant evolutionary change.