| 总结: | Bacteria are capable of a wide range of cooperative behaviours. It has been suggested that horizontal gene transfer, which is common in bacteria, could help to stabilise cooperation and prevent the invasion of non-cooperative cheats. Research on this hypothesis has largely focused on plasmids: genetic sequences found across bacteria that can often transfer to other cells. Here, I test two key predictions of this hypothesis across 51 bacterial species. Contrary to these predictions, I find that genes for cooperation are not more likely to be carried on: (1) plasmids compared to chromosomes; (2) more mobile plasmids compared to less mobile plasmids. Next, I explore characteristics of plasmids themselves. First, I examine correlations between three potential ‘life-history’ traits of plasmids: size, mobility and range. Second, I find that plasmid sequences are consistently enriched with A and T nucleotide bases compared to chromosomes, and explore two hypotheses for why this is the case. Finally, horizontal gene transfer can impact the content of bacterial genomes. To explore these impacts, I test whether bacterial species’ genomes become more variable with increasing environmental variability. Overall, in this thesis I consider the evolution of cooperation and horizontal gene transfer in bacteria, and how they may interact.
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