Evolution of parasitism in kinetoplastid flagellates

•The evolution of parasitism on Kinetoplastid protists is presented.•Parasitism has repeatedly emerged within this group of flagellates.•We demonstrate rather unlike origin of dixenous life cycle in various groups.•Parasite (pre)adaptations for their co-existing with the hosts are discussed.•The biodiversity of monoxenous (one host) trypanosomatids is introduced. Kinetoplastid protists offer a unique opportunity for studying the evolution of parasitism. While all their close relatives are either photo- or phagotrophic, a number of kinetoplastid species are facultative or obligatory parasites, supporting a hypothesis that parasitism has emerged within this group of flagellates. In this review we discuss origin and evolution of parasitism in bodonids and trypanosomatids and specific adaptations allowing these protozoa to co-exist with their hosts. We also explore the limits of biodiversity of monoxenous (one host) trypanosomatids and some features distinguishing them from their dixenous (two hosts) relatives.