Abstract
Parasitism is a life strategy that has repeatedly evolved within the Florideophyceae. Until recently, the accepted paradigm of red algal parasite evolution was that parasites arise by first infecting a close relative and, either through host jumping or diversification, adapt to infect more distant relatives. The terms adelphoparasite and alloparasite have been used to distinguish parasites that are closely related to their hosts from those more distantly related to their hosts, respectively. Phylogenetic studies have cast doubt on the utility of these terms as data show that even alloparasites predominately infect with the same family. All adelphoparasites that have been investigated have lost a native plastid and instead hijack and incorporate a copy of their hosts’ plastid when packaging spores. In contrast, a highly reduced plastid that has lost all genes involved with photosynthesis was sequenced from the alloparasite Choreocolax polysiphoniae, which indicates that it did not pass through an adelphoparasite stage. In this study we investigate whether other species in the Choreocolacaceae, a family of alloparasites, also retains its native plastid, as well as test the hypothesis that alloparasites can arise and subsequently speciate to form monophyletic clades that infect a range of hosts. We present the plastid genome for Harveyella mirabilis which, similar to that of C. polysiphoniae, has lost genes involved in photosynthesis. The H. mirabilis plastid shares more synteny with free-living red algal plastids than that of C. polysiphoniae Phylogenetic analysis identifies a well-supported monophyletic clade of parasites in the Choreocolacaceae, which retain their own plastid genomes, within the Rhodomelaceae. We therefore transfer genera in the Choreocolacaceae to the Rhodomelaceae.