As the aim of the PREreview Journal Club is to support the authors by providing constructive feedback, the reviewer(s) should also include positive remarks to encourage future posting of preprints. Remember, the authors are human too! To help guide you, here are a few questions you might ask yourself after reading the preprint:

WHY IS THIS STUDY RELEVANT? WHAT WHERE THE INTERESTING POINTS?

This idea of compensation is known in unicellular organisms, now done on multicellular ones, which makes it interesting.

It shows the importance of evolutionary compensation in general (should be explained in more detail in discussion)

The experimental design and work done (massive amount of lab work) was very well designed to answer their question.

Figure 1 shows interesting and surprising results since the deleterious trait does not “come back” to its “normal” value under natural selection, but COULD return, as shown very clearly by artificial selection

Figure 3. presents very interesting results on how males have higher fitness without having “normal” wings

A few points that are very important and interesting but that would need to be discussed more / made clearer in the ms (in intro or discussion)

1-the ms gives a mechanism by which deleterious mutations can be found at low frequency in a natural population, and this is generalizable to other systems

2-the results explain why closely related species have diverged in a trait but are both still there: one species (species 1) has lost it but persists while in the other species (species 2) it is a “necessary” trait. In systems like these, one can look for the traits that “compensate” for the “missing” trait in species 1 and if it comes from standing genetic variation. It is an interesting observation for the study of speciation and rapid evolution.

3-It answers the question as to whether genetic constraints or selection will control evolutionary trajectory, and shows that both factors act.