Dinobryon is a species of protozoa that reproduce asexually. How can this

asexual reproduction be harmful to the species?

Asexual reproduction is speedy, but it doesn't provide for genetic variation. When a cell reproduces asexually, it makes an exact copy of itself. This doesn't allow for much selective alleles because all alleles are the same, and it doesn't allow for too much evolution because of this selfsame reason. No phenotypes are more or less fit because they're all the same.