Review of “Experimental demonstration of allometric invariance of plant response to density over the course of wheat domestication”, manuscript ID RSPB-2024-2696.
This paper presents a set of experiments looking into the allometric relationships between above-ground vegetative structures and reproductive output in emmer wheat. The working hypotheses are that these may have changed as a result of “artificial” selection across stages of domestication, from wild ancestors to modern elite breeds. Furthermore, domestication may have also changed the plants’ response to growth in dense, conspecific stands. The results are largely negative. In spite of clear morphological variation among the genotypes classified in the different stages of domestication (or breeding), the experiments did not detect any change in allometry or plasticity to density. Consequently, the paper is built around this lack of detectable effects.
This is always a difficult exercise, the causes can be manifold (absence of evidence is not evidence of absence, etc.). In this case, the authors’ take on their own results is plausible, but consideration of further causes should be given more room, or at least, some room. Maybe the “breeding stages” are not truly different form one another, maybe the effects of density are not manifest because of some experimental limitation, maybe plants were too far apart and fertiliser too readily available, etc..
This problem is further compounded by the lack of background information. It is impossible to ascertain whether the accessions have been correctly assigned to the different “breeding history” stages. Where were the wild accessions collected? How can the authors now that the first domesticated accessions are truly “first domesticates” and not landraces? Is this some sort of archaeological material? How have landraces been maintained? What is their geographical origin? How were the elite lines developed? By whom? Of course, one could always take the trouble to look up every single International genotype number in Table S1, but that would make for extremely demanding and tedious reading, not to mention that it would not explain why the authors chose those particular genotypes and how had they been maintained before the experiment begun.
The experimental design also needs further explanation. To begin with, the densities are strikingly low, durum wheat is usually cultivated at around ~300 plants/m2. Why did the authors deem 20 to 200 plants/m2 as biologically meaningful? In the same vein, some justification for the fertilisation levels is required. How were the specific amounts chosen? If plants are far apart and nutrients and water plentiful, what sort of interaction is driving the responses?
Or maybe the response is just not manifest in the aerial parts. A lot, if not all of plant-plant interactions take place underground. Consequently, root growth is very sensitive to population density. Moreover, breeding has had a very strong effect on root architecture and shoot/root allocation. It seems doubtful that any conclusion can be derived from this kind of experiment if roots are not considered.
Of course, all of the above does not preclude the possibility that the authors’ are correct and that allometry has not been affected by breeding. In fact, a recent paper has described something along these lines in legumes (de Casas, R. R., Martín‐Brull, I., Milla, R., & Ocaña‐Calahorro, F. J. (2024). “Selection for domestication favored taxa characterized by fast growth and tolerance of high intraspecific density.” Plants, People, Planet). Unfortunately, it is impossible to ascertain whether that is the case with the information provided.

Minor comments
L. 20-21: What are the “unexplored constraints”? Either specify or use something more informative, specially for the closing lines of the Abstract.
L. 39-40: Please explain what “invariance in parameters in the cross-species relationships” means, ideally without jargon.
L. 59-60: “a large amount of seeds…” this contention needs to be properly justified.
Plant material
This section lacks a lot of crucial information, such as: geographic origin of the accessions, maintenance information, breeding history, etc. Also, were the lines grown in the same common garden for at least one generation to homogenise environmental maternal effects?
L. 144: Why use growing degree days?
L. 191: Please provide citation info for the ‘emmeans’ package.
L. 309: “We might thus have expected…” However, the authors did not consider realistic sowing densities...
L. 337: male guppies? The authors are advised to look for more comparable biological systems.
L. 349-350: Unclear. Do the authors mean that ancestral farmers selected for increased allocation to reproduction and that further selection has had no effect?