Symbiosis and its impact on eukaryote evolution

Abstract

Endosymbiosis has had a significant impact on eukaryotic evolution, from various coevolving partnerships to the origin of mitochondria and plastids. Cryptophytes are a lineage of unicellular algae that harbor a red-algal plastid derived from secondary endosymbiosis and belong to a phylum (Cryptista) thought (by some) to be ancestrally non-photosynthetic. Furthermore, Cryptista has traditionally been difficult to place in the eukaryotic tree of life. To investigate Cryptista’s relationship to other eukaryotes and the evolution of red-algal complex plastids, I searched for an algal footprint in genomic data from Goniomonas avonlea, a close heterotrophic relative of cryptophytes. Overall, a close association of Cryptista to Archaeplastida was revealed – specifically to green/glaucophyte algae – and little evidence supporting red-algal plastid ancestry in G. avonlea was found. Additionally, I investigated a novel, recently established, eukaryote-eukaryote endosymbiosis not involving photosynthesis. Characterization of novel isolates and comprehensive phylogenetic analyses on Paramoeba-Perkinsela revealed a strong signal for co-evolution.