Nothing in Biology Makes Sense: For species delimitation, size matters

Shewanella Scanning electron micrograph of Shewanella putrefaciens. Photo by EMSL.

This week at Nothing in Biology Makes Sense!, Sarah Hird explains a new theoretical study proposing that species concepts are hard to define for microorganisms not because just because they reproduce asexually and trade genetic code like playing cards … but simply because they’re small and numerous.

Specifically, the product of mutation rate and carrying capacity (uK) needs to be below a certain threshold for species to form. This is because there needs to be a small amount of variation relative to the amount of niche space available or no clear “best” type will emerge that can outcompete all the other types quickly enough to become established. If mutation rate is high, there are too many available types. If carrying capacity is high, there is no way to limit who’s there at all. Many other things are happening with this paper, but their big conclusion, put plainly, is that if there is too much variation, differentiation cannot occur.

If that sounds as freaky to you as it does to me, you’ll want to go read the whole thing.◼