Driven progressive evolution of genome sequence complexity in Cyanobacteria

Progressive evolution, or the tendency towards increasing complexity, is a controversial issue in biology, which resolution entails a proper measurement of complexity. Genomes are the best entities to address this challenge, as they encode the historical information of a species’ biotic and environmental interactions. As a case study, we have measured genome sequence complexity in the ancient phylum Cyanobacteria. To arrive at an appropriate measure of genome sequence complexity, we have chosen metrics that do not decipher biological functionality but that show strong phylogenetic signal. Using a ridge regression of those metrics against root-to-tip distance, we detected positive trends towards higher complexity in three of them. Lastly, we applied three standard tests to detect if progressive evolution is passive or driven—the minimum, ancestor–descendant, and sub-clade tests. These results provide evidence for driven progressive evolution at the genome-level in the phylum Cyanobacteria.Tis project was funded by grants from the Spanish Minister of Science, Innovation and Universities (former Spanish Minister of Economy and Competitiveness) to A.M. (Project SAF2015-65878-R), J.L.O. (Project AGL2017-88702-C2-2-R) and A.L. (Project PGC2018-099344-B-I00), grant from Generalitat Valenciana to A.M. (Project Prometeo/2018/A/133), and co-fnanced by the European Regional Development Fund (ERDF). Tis project was also supported by a Fulbright fellowship (Spanish Minister of Science, Innovation and Universities) to A.M. for a sabbatical leave at Harvard University. Te authors thank to Fernando Baquero, Mitchell Distin and Guillermo Ponz for critical reading of the manuscript