The Acquisition of a Plastid by Haptophytes, Cryptophytes, and Photosynthetic Heterokonts

Abstract

Red algae and green plants are known to have obtained their photosynthetic organelles, or plastids, through the endosymbiotic adoption of cyanobacteria. It is still widely debated as to how other eukaryotic alga such as haptophytes, cryptophytes, and photosynthetic heterokonts obtained their plastids, although all are believed to be descended from a red alga. In this thesis, genome-level regressions, analyses of residuals, and Fisher's exact tests were used to determine how these three eukaryotic algal groups obtained their plastids. A phylogeny also was constructed using 11 plastid genes from various red algae, green plants, haptophytes, cryptophytes, and photosynthetic heterokonts. The results from these collective analyses indicate that multiple endosymbiosis events occurred. Furthermore, they show that a plastid was passed from a red alga, first to cryptophytes, then to photosynthetic heterokonts, and finally to haptophytes in a series of endosymbioses.