"selective pressure" or "selection pressure"? Editing a manuscript of mine, a co-author changes "selection pressure" to "selective pressure". Are those two terms interchangeable? Or are there subtle differences that I'm not aware of? The sentence under consideration: "In contrast, gene expression changes during development and tissue formation are under high selection/selective pressure." FWIW, "selection pressure" is a bit more popular in the literature.

As far as online references are concerned, they should be equivalent (as "selective" becomes "making a selection"). The important difference in my understanding is that speaking in terms of biology, "selection" triggers associations with evolutionary terminology, whereas "selective" doesn't. Thus, as far as I am concerned, "selective pressure" could be referring to some machine that has a method of applying pressure to one thing but not another, whereas "selection pressure" immediately makes me think of factors benefitting the proliferation of one thing over another. Hence I would personally prefer "selection pressure".

Given the ambiguity, you probably won't be able to make all readers happy with either of the two. Thus, it might be best just to use a different phrasing as suggested e.g. by rg255 ("subject to selection").