Despite the benefits of phototrophy, many algae have lost photosynthesis and have converted back to heterotrophy. Parasitism is a heterotrophic strategy, with apicomplexans being among the most devastating parasites for humans. The presence of a nonphotosynthetic plastid in apicomplexan parasites suggests their phototrophic ancestry. The discovery of related phototrophic chromerids has unlocked the possibility to study the transition between phototrophy and parasitism in the Apicomplexa. The chromerid Chromera velia can live as an intracellular parasite in coral larvae as well as a free-living phototroph, combining phototrophy and parasitism in what I call photoparasitism. Since early-branching apicomplexans live extracellularly, their evolution from an intracellular symbiont is unlikely. In this opinion article I discuss possible evolutionary trajectories from an extracellular photoparasite to an obligatory apicomplexan parasite.

Institute of Parasitology Biology Centre Czech Academy of Sciences Branišovská 31 37005 České Budějovice Czech Republic; Faculty of Science University of South Bohemia Branišovská 31 37005 České Budějovice Czech Republic

References provided by Crossref.org

Circadian rhythms and circadian clock gene homologs of complex alga Chromera velia

Organellar Evolution: A Path from Benefit to Dependence

Editorial: Mixotrophic, Secondary Heterotrophic, and Parasitic Algae

Using Diatom and Apicomplexan Models to Study the Heme Pathway of Chromera velia