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Chapter 4 : Speciation and Bacterial Phylospecies
This chapter begins by discussing animal and plant speciation followed by bacterial speciation. First, the species concept is important in understanding the speciation process in that it provides the constraint necessary for evaluating the fulfillment of the speciation event. Three different mechanisms of speciation are known in animals and plants: allopatric speciation, parapatric speciation, and sympatric speciation. This process is thought to be the most common speciation process for plants and animals. An important aspect of speciation in plants and animals is that it does not necessarily involve dramatic changes in the genome. The concept of the species is of paramount importance when considering the process of speciation as illustrated for plants and animals. Like plants and animals, a bacterial species has a monophyletic ancestry. Bacteriologists who are interested in speciation need to look at this process at the level of strains. The term phylospecies is coined to describe those microorganisms, in particular Bacteria and Archaea, that, according to the phylogenetic species concept, form a monophyletic clade at a fundamental level and that are occupying, living, and evolving in a specific niche. The chapter discusses the environmental factors that may drive the speciation of an organism, and then treats the intrinsic responses of the organism in its environment that affect a speciation event.