Marine gregarines: evolutionary prelude to the apicomplexan radiation?
Gregarine apicomplexans inhabit the intestines, coeloms and reproductive vesicles of invertebrates. An emphasis on specific ancestral characteristics in marine gregarines has given the group a reputation of being 'primitive.' Although some lineages have retained characteristics inferred to be ancestral for the group, and perhaps apicomplexans as a whole, most gregarines represent highly derived parasites with novel ultrastructural and behavioral adaptations. Many marine gregarines have become giants among single-celled organisms and have evolved ornate surface structures. A comparison of gregarine morphology, placed in a modern phylogenetic context, helps clarify the earliest stages of apicomplexan evolution, the origin of Cryptosporidium, and specific cases of convergent evolution within the group and beyond.
Leander
Brian S
BS
Canadian Institute for Advanced Research, Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada. bleander@interchange.ubc.ca
D000818:Animals; D016782:Apicomplexa / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure; D005075:Biological Evolution; D007422:Intestines / Q000469:parasitology; D007448:Invertebrates / Q000469:parasitology; D008018:Life Cycle Stages; D008855:Microscopy, Electron, Scanning; D010802:Phylogeny; D011077:Polychaeta / Q000469:parasitology; D012623:Seawater / Q000469:parasitology*