By comparing the effects of early-life exposure of female mice to different social partners, Wilkinson et al., provide important insights into the potential functions of early-life seminal fluid exposure in later-life fertility and reproductive physiology. The experiments, although occasionally restricted by sample sizes, are well-designed and decouple the functional effects of seminal fluid exposure from (i) the whole ejaculate and (ii) mechanical stimulation. The manuscript is also generally concise and well written. I do however have some comments that might help improve the manuscript.
Broad Comments:
1. Roughly a third of the results section talks about the effects of the different treatments on female growth but receives little attention in the discussion. I would suggest briefly contextualising these results in the discussion section.
2. In Fig 1., the plot stops at month 4, but month 5 is possibly the most meaningful comparison. I would suggest to re-plot to include month 5.
3. In multiple parts of the manuscript, the authors state that preconception seminal fluid exposure improves pregnancy outcomes. However, the authors find that this is conditional, with the effects being seen only in females with no prior history of pregnancy. Please amend to reflect this (Lines 30-32, Lines 188-191).
4. The authors observe that a significant number of pups from the Vas treatments die between birth and weaning. Could this be due to infanticide/early-life mortality because of differences in per-capita available resources to offspring? It might be helpful to mention if the food provisioned was adjusted based on litter size.
5. I think the manuscript could be improved by touching on potential future experiments in the discussion section. For instance, in the placental dissections, it would’ve helped to see what was happening in the intact male treatment, because in the male exposure experiment, we see that increased litter sizes were seen only in the Vas exposure treatment. It would be interesting to see how pregnancy with seminal fluid exposure modulates female reproductive physiology as a comparison.
Other Comments:
Introduction:
1. Lines 72-77 and lines 87-90 makes it read like these are 2 separate experiments when it’s the same experiment testing the effects of different kinds of male exposure on two different variables. I think restructuring to reflect this might help make reading easier?
2. Lines 78-80: The sentence “We also tested whether….. a female’s litters.” is confusingly worded. Please rephrase.
3. Line 26: might help to amend “postnatal loss” to “postnatal loss of offspring”
4. Line 61: comma after humans, Line 62: “woman” to “women”
5. Line 85: “stain” to “strain”
Results:
1. Does the comparison in Lines 113-118 include intact males? I presume for the first comparison, this comparison is excluded as pregnancy is a confounding factor.
2. Lines 142-145: “However, the …… seminal fluid exposure.”
This is correlational and one of several explanations. The differential mortality could also be due to: (i) mother committing infanticide because she doesn’t want future competition between a high-density of offspring and (ii) mother commits infanticide because per-capita available resources reduced due to increased number of pups.
Discussion:
1. Lines 217-219: “This could reflect ….. Y chromosome minor antigens.”
This is likely not the reason because the same effects were not observed in females mated with intact males.
2. Lines 231-233: “Another possibility …. earlier seminal fluid exposure.”
But work from this paper shows that what is more likely happening is remodelling of the reproductive tract during early-life pregnancy is overriding priming effects of just early-life seminal fluid exposure.
3. Lines 237-240: “On an evolutionary level …. stages of pregnancy and lactation”
Possibly a redundant comment, re: resource dependence of offspring mortality, but sexual conflict is one possibility and possibly not the most likely one because in the most “natural” treatment where the males were intact, litter sizes were lower than only seminal fluid exposure.
Methodology:
1. Lines 274-275: “estrus cycling ….. by daily vaginal cytology”
This is confusingly worded. Was vaginal cytology performed everyday from start of the experiment to when the mice were 3 months old or was it performed once when the mice were 3 months old?
2. Lines 285-287: This is quite confusingly worded and it takes a couple of reads to understand what the exposure group is, especially because it is directly following an experiment with more treatment groups. This could just be re-phrased to list what the treatment groups are.