The paper “Sexual selection in Bacteria?” with Angus Buckling and Bram Kuijper has now been published in Trends in Microbiology. This was a tough, but ultimately very rewarding paper to write. I knew a bit about sexual selection, but must admit that I did not fully appreciate the decades (centuries even) of intricate theory developed by many clever evolutionary biologists and at times it was difficult trying to wrap my head around it. As last author Bram says: ‘the more you know about sexual selection, the less you know about it’. To then apply this theory to bacteria was even harder.
In our paper, we used sexual selection in its broadest sense, namely as ‘any competition between bacterial cells for access to conspecifics assisting in the reproduction of genetic information’. We describe four distinct sexual selection scenario’s that could apply to bacteria (or could not, but at least they are testable, which is what science is ultimately about). Essentially, the main reasons put forward to explain horizontal gene transfer in bacteria, sex-like benefits of gene shuffling, DNA as food or as a template for repair, or selfish genetic elements hopping around, are based on ‘conventional’ natural selection. We thought it worth exploring whether sexual selection theory, which has been highly succesful in explaining many behaviours and morphologies relating in animals (and plants, and even fungi) could explain some of the substantial diversity in DNA release and uptake processes in bacteria. Anyway, as the paper is open access, you can have a look and make up your own mind!
Click here for the Open Access paper at the Trends in Microbiology website.
Bacteria that take up DNA (recipient cells) are red; bacteria that donate DNA (donor cells) are blue or green. DNA strands are the same colour as the cell they originate from. (A) Competition through DNA release. A green and blue cell release a small and large amount of DNA, respectively, leading primarily to the uptake of blue DNA by the recipient cell. This can be viewed as being analogous to sexual conflict, specifically sperm competition where males invest in increased sperm number to enhance fertilization success. (B) Biased DNA uptake. A recipient cell has a random bias uptake towards donor DNA containing uptake sequences (yellow circles), resulting in uptake sequences accumulating in the recipient genome and in the extracellular DNA pool as the result of subsequent DNA release by the recipient cell. This can be viewed as mate choice, specifically where females choose males based on an arbitrary characteristic (Fisherian sexual selection). (C) Competence manipulation. A blue cell releases DNA and a pheromone (blue circles), inducing competence in a recipient cell with a matching receptor (left) but not in a potential recipient cell with an altered receptor (right). This can be viewed as mate choice, specifically where males coerce females to mate. (D) Active DNA acquisition via predation. A recipient cell produces a toxin (red triangles) lysing a related, but genetically different, strain (blue), thus providing DNA for uptake by the toxin producer, whereas unrelated cells (green) (as well as related cells that produce immunity factors) are not lysed. This can be viewed as mate choice, specifically where females coerce males to mate.