Which of the following is most closely associated with speciation?

Disruptive selection is closely associated with speciation because it favors extreme phenotypes at both ends of the spectrum, rather than the average phenotype. This type of selection can lead to increased variability within a population, making it more likely for different subpopulations to adapt to differing environmental conditions and potentially lead to reproductive isolation. Over time, these changes can result in the emergence of new species as the extremes diverge from one another, reducing gene flow between the groups.

In contrast, stabilizing selection tends to favor intermediate phenotypes and reduces variation, which may inhibit the process of speciation. Directional selection favors one extreme phenotype over others, which can lead to adaptation in a single direction but does not necessarily promote divergence necessary for speciation. Sexual selection focuses on traits that improve mating success, which may influence reproductive isolation and mating preferences but does not directly contribute to speciation as strongly as disruptive selection does.