Environmental transitions in microbial eukaryotes: a phylogenetic analysis of publicly available short-read metabarcodes

Sammanfattning

Major environmental transitions such as crossing the “Salty Divide” are thought to be rare across the tree of life, yet this has not been extensively investigated in microbial eukaryotes. High-throughput, next-generation sequencing technologies such as Illumina are producing vast amounts of data from environmental DNA, yet these short sequences lack the phylogenetic signal to infer broad patterns across the eukaryotic tree of life. This work uses a combination of publicly available short-read and curated long-read sequences to overcome this issue, by means of a multilevel placement method. Transition patterns across the salinity barrier are inferred and found to differ across protistan groups, both in their rate and directionality. Contrary to expectations, transitions are found to occur both towards marine and terrestrial environments. These differences are hypothesized to be correlated with major biological traits, such as trophic mode, morphology, and/or physiology in different groups. Future work should test further potential environmental barriers than those presented in this work.