“The main difference from eukaryotes is that prokaryotic reproduction is independent of DNA acquisition and recombination. Instead, DNA is obtained from fragmented chromosomes obtained via parasexual means (that is, without reproduction). These mechanisms of DNA exchange are not restricted to gene exchange within species, and therefore traits can and do come from highly divergent organisms. For example, imagine that acacia trees could exchange DNA with lions and that the resulting new tree developed “limbs” that allowed them to attack grazing giraffes. This is in a sense what prokaryotes do all the time.”
I am fascinated by horizontal gene transfer, whereby microbes from different species share genetic information. Species, as we all learn, are defined by not being able to exchange genetic information and produce fertile offspring.
Of course, microbes flaunt this rule.
The prevalence of gene transfer, where bacteria of different species exchange genetic information, blurs the boundaries between “species”. I remember listening to Penny Chisholm talk to Ira Flatow about Parachlorococcus and redefining what we call a species of microbes, which she called “genomic variants.”
The quote above is from a review of an article in Science that examines speciation in marine bacteria. It discusses how the investigators found prevalent horizontal gene transfer. But the cool thing, as I understand it, was that many of the same genes were being captured by bacteria in the same ecological niche.
In short, the environment is selecting for horizontally transferred genes to be conserved. These genes are not transmitted through organisms in the same species, but all of the bacteria are being selected to keep these transferred genes. In short, many of the genes from a population do not have a common ancestor (as in, cells dividing and propagating genes that way).
Even cooler, an analogue has been seen in prokaryotes, in a sense. Darwin’s finches all share genetic information through the usual repeated back-crossing between species, but ” the characters defining their ecological niche appear to be maintained through selection.”
So I guess we are talking about genomic variants, but not necessarily variants with the same ancestor – the ecological niche selects for that genomic variant, which has a collection of genes from the mother cell (ancestor) and from other cells (horizontal gene transfer)
That’s so cool.
