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The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives.

ABSTRACT: Cyanobacteria have played a significant role in Earth history as primary producers and the ultimate source of atmospheric oxygen. To date, however, how and when the group diversified has remained unclear. Here, we combine molecular phylogenetic and paleontological studies to elucidate the pattern and timing of early cyanobacterial diversification. 16S rRNA, rbcL, and hetR genes were sequenced from 20 cyanobacterial strains distributed among 16 genera, with particular care taken to represent the known diversity of filamentous taxa. Unlike most other bacteria, some filamentous cyanobacteria evolved a degree of cell differentiation, producing both specialized cells for nitrogen fixation (heterocysts) and resting cells able to endure environmental stress (akinetes). Phylogenetic analyses support the hypothesis that cyanobacteria capable of cell differentiation are monophyletic, and the geological record provides both upper and lower bounds on the origin of this clade. Fossil akinetes have been identified in 1,650- to 1,400-mega-annum (Ma) cherts from Siberia, China, and Australia, and what may be the earliest known akinetes are preserved in approximately 2,100-Ma chert from West Africa. Geochemical evidence suggests that oxygen first reached levels that would compromise nitrogen fixation (and hence select for heterocyst differentiation) 2,450-2,320 Ma. Integrating phylogenetic analyses and geological data, we suggest that the clade of cyanobacteria marked by cell differentiation diverged once between 2,450 and 2,100 Ma, providing an internal bacterial calibration point for studies of molecular evolution in early organisms.

SUBMITTER: Tomitani A

PROVIDER: S-EPMC1459374 | biostudies-literature | 2006 Apr

REPOSITORIES: biostudies-literature

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The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives.

Tomitani Akiko A Knoll Andrew H AH Cavanaugh Colleen M CM Ohno Terufumi T

Proceedings of the National Academy of Sciences of the United States of America 20060328 14

Cyanobacteria have played a significant role in Earth history as primary producers and the ultimate source of atmospheric oxygen. To date, however, how and when the group diversified has remained unclear. Here, we combine molecular phylogenetic and paleontological studies to elucidate the pattern and timing of early cyanobacterial diversification. 16S rRNA, rbcL, and hetR genes were sequenced from 20 cyanobacterial strains distributed among 16 genera, with particular care taken to represent the ...[more]

PMID: 16569695

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Project description:BackgroundThe origin of turtles and crocodiles and their easily recognized body forms dates to the Triassic and Jurassic. Despite their long-term success, extant species diversity is low, and endangerment is extremely high compared to other terrestrial vertebrate groups, with ~ 65% of ~ 25 crocodilian and ~ 360 turtle species now threatened by exploitation and habitat loss. Here, we combine available molecular and morphological evidence with statistical and machine learning algorithms to present a phylogenetically informed, comprehensive assessment of diversification, threat status, and evolutionary distinctiveness of all extant species.ResultsIn contrast to other terrestrial vertebrates and their own diversity in the fossil record, the recent extant lineages of turtles and crocodilians have not experienced any global mass extinctions or lineage-wide shifts in diversification rate or body-size evolution over time. We predict threat statuses for 114 as-yet unassessed or data-deficient species and identify a concentration of threatened turtles and crocodilians in South and Southeast Asia, western Africa, and the eastern Amazon. We find that unlike other terrestrial vertebrate groups, extinction risk increases with evolutionary distinctiveness: a disproportionate amount of phylogenetic diversity is concentrated in evolutionarily isolated, at-risk taxa, particularly those with small geographic ranges. Our findings highlight the important role of geographic determinants of extinction risk, particularly those resulting from anthropogenic habitat-disturbance, which affect species across body sizes and ecologies.ConclusionsExtant turtles and crocodilians maintain unique, conserved morphologies which make them globally recognizable. Many species are threatened due to exploitation and global change. We use taxonomically complete, dated molecular phylogenies and various approaches to produce a comprehensive assessment of threat status and evolutionary distinctiveness of both groups. Neither group exhibits significant overall shifts in diversification rate or body-size evolution, or any signature of global mass extinctions in recent, extant lineages. However, the most evolutionarily distinct species tend to be the most threatened, and species richness and extinction risk are centered in areas of high anthropogenic disturbance, particularly South and Southeast Asia. Range size is the strongest predictor of threat, and a disproportionate amount of evolutionary diversity is at risk of imminent extinction.

Dataset Information

The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives.

Publications

The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives.

Similar Datasets

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