Which type of selection tends to increase genetic variation?

Disruptive selection

Explanation:

In disruptive selection individual with traits having the extreme values are selected over the individuals having intermediate trait values. This increases the genetic variance because the variance of trait increases and the population gets divided into two separate groups.

For example, there is a population of moth in an area in which trees with black color bark and white color bark are present and the genotype BB gives rise to black color moth and bb give rise to white color moth but genotype Bb which is intermediate trait give rise to blue color moth.

So, in this case, white and black color moth can camouflage on tree having white color bark and black color bark but the blue color moth will not be able to camouflage so it will be hunted more by predators which is an example of disruptive selection.