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Temporal fragmentation of speciation in bacteria
Adam C Retchless1, Jeffrey G Lawrence
1Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Science (New York, N.Y.)
|August 25, 2007
Summary
Bacterial speciation involves gradual genetic isolation, with niche-specific genes diverging first over millions of years. This process explains how distinct bacterial lineages like Escherichia coli and Salmonella enterica evolve unique traits before full chromosomal separation.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genetics
Background:
- Bacterial recombination facilitates gene transfer, potentially maintaining distinct gene sets within recombining populations.
- Speciation models suggest genetic isolation can occur progressively across a chromosome, not instantaneously.
Purpose of the Study:
- To investigate the temporal dynamics of genetic divergence and isolation in bacterial speciation.
- To test the hypothesis that niche-specific genes become genetically isolated earlier than other chromosomal regions.
Main Methods:
- Analysis of sequence divergence rates and times across different chromosomal regions of Escherichia coli and Salmonella enterica.
- Separation of sequence divergence into rate and time components to infer evolutionary timelines.
Main Results:
- Different chromosomal regions of Escherichia coli and Salmonella enterica diverged over an approximately 70-million-year period.
- Genetic isolation initiated earlier in regions containing species-specific genes.
- Physiological distinctiveness between nascent Escherichia and Salmonella lineages persisted for millions of years prior to complete chromosomal isolation.
Conclusions:
- Bacterial speciation is a protracted process with asynchronous genetic isolation across the chromosome.
- Niche-specific adaptations drive early genetic divergence, preceding the complete isolation of bacterial genomes.
- The findings support a model where gradual curtailment of recombination at key loci facilitates bacterial lineage diversification.
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