PONE-D-20-07291

Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats

PLOS ONE

Dear Dr Gall,

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The Manuscript entitled “Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats” represents an interesting attempt to describe how environmental changes may shape sociality and vocal behavior in a wild population of meerkats.

A lot of work has been done on this wild population, but this MS provides new insights about meerkats’ adaptability to their unpredictable natural environment.

The Manuscript is overall well written and structured, but an improvement is necessary before publication. For this reasons I suggested the Editor to consider this MS for publication, after a revision.

Introduction

All the first part of the Introduction section is centered around the difference between “direct” and “indirect” impacts on signal transmission. Nevertheless the difference between the two is somewhat misleading, as presented differently in consecutive sentences (LL. 22-29).

I suggest to rewrite the first paragraph (from line 22 to 37), by focusing on the main idea that is expressed in lines 19-20. I strongly recommend to strengthen the idea that environmental characteristics may directly impact the nature of the acoustic signal itself (in both acoustic and temporal features), or indirectly impact the signaler’s vocal production (e.g. inter-individual spacing, cohesion calls, etc.).

I suggest to insert a paragraph focusing on the role of contact and cohesion calls in primates.

L.57 I think the Authors should better explain here the differences between dry and drought season.

LL. 59-61 According to Wyman et al. 2017 [26] pups begging calls may mask the adult contact calls, so that meerkats reduce their calling rate to avoid information redundancy. For the aim of this Manuscript, I think it would be important to tell the reader if pups (and how many) were present in all the sampled groups and in all the periods. As suggested by Mausbach et al. 2017, if I am not wrong, the season between October and February should be characterized by the presence of pups (<3 months old), and I would like to understand if not only the presence/absence of pups but also the number of pups/group may influence the calling rate. Have you tested for this factor too?

I also suggest to cite here the results from Mausbach et al. 2017, according to the relationship between call rate and environmental windy condition.

I think that Authors’ hypotheses are consistent with the literature and well organized according to the logic of the Introduction section.

Methods

The Method section is well organized and detailed. Here my detailed comments:

L. 87 A number in brackets should be provided for the Clutton-Brock et al. 1998 citation.

I would suggest to the Authors to switch between Table 1 and Table S1 (Supplement1). In my opinion, the readers would be more interested in visualizing the details of the data composition for this study. Environmental details for the study period may be more appropriate in the Supplemental Materials.

LL. 121-123 The authors should be more clear here. How did they estimate the nearest neighbor identity and distances through sound recordings?

LL133-141 The Authors well explained what a group splitting is (mixed-sex sub-groups being further than 100 m apart for at least 15 minutes). It is not clear, nevertheless, how the number of group split is reported in Table S1. In Table S1 the number of groups in the Group Split column is equal to the Total number of groups (except for Dry season 2013/2014, that is dropped of one unit: this means that one group did not split in 2013/2014?). If I am not wrong, the Authors tested the frequency of group splits in the different seasons, as the % of the observation days in which the splits were observed. I think that the number of days of split over the total number of days of observation should be provided in the table or in the text.

When there were group splits did you implement the number of groups tested in the models, considering the both the group and the sub-group as separate units, or still considered the group of origin as a single group? The fact that animals are more likely to split in the drought season, consequently being further than 100 m apart for longer periods, should emerge also from the analysis of the time spent in each distance category. This is not apparently emerging from the results. Did you consider split groups as different groups in the Dirichlet regression?

Results

I suggest to pay attention to the way in which the Authors called the Supplementary Materials. Table S1 is present in both Supplement 1 and Supplement 2, thus being confounding for the reader.

I found Figure 1 very helpful for the reader. I suggest to modifying the Figure, by insert two more graphs: one for the relationship between the call rate and the presence/absence of pups (and eventually the correlation between the call rate and the number of pups) and the Figure S1.

Models provided results for the differences between Wet and Dry conditions and Wet and Drought conditions. I suggest the Authors to test the differences between Dry and Drought conditions in the different models, for example by using the multcomp package in R, to test whether significative differences emerge also for the factors in the two different conditions.

Discussion

I think that the Authors well discussed the results at the light of their hypothesis and that they should focus more on the direct (on call rate) and indirect (on group cohesion) effects of the environment on acoustic signals.

However, the discussion lacks a comment on the relationship between call rate and the presence of pups, also at the light of the findings of previous works on the same population, explaining why meerkats may cope with environmental as social factors affecting vocal emission.

LL 263-267 I think that the differences between dry and drought conditions affecting the frequency of group splits are not well discussed here.

The Authors stated that individuals are less able to maintain cohesion when signal perception is directly affected by the amount of individual spacing between group members, thus expecting a gradual increase in call rate and in inter-individual distance from the wet to the dry and drought seasons. The results are only partially in line with this scenario. How do the Authors explain the different trend observed in the dry season? By providing the results of the comparison between dry and drought season, as suggested before, the Author could also provide more explanation about the observed variation. The hypothesis that fission-fusion dynamics may explain the Authors observations is, in fact, interesting, but it is not completely clear how to read the emerging differences in the group split in relation to the dry or drought condition. Are the Authors stating (LL274-275) that in the dry condition the groups are more dispersed that in the wet condition, while in the drought season they split, and form smaller sub-groups in which the individuals disperse over longer distances? Why this dispersion did not emerge from the distance analysis?

Reviewer #2: Review of MS: Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats

I have reviewed the paper by Toni et al.

I thought this was a well written and interesting MS that investigated the extent to which meerkats can flexibly modify their group coordination behaviour when faced with both direct and indirect environmental effects on signal perception.

I found the analyses to be solid and the results convincing. My comments are therefore mainly aimed at the discussion of the results which I feel could be broadened slightly.

Specifically, I found the discussion to be very meerkat-centric and hence would encourage the authors to zoom out slightly in the discussion and contextualise the results more broadly. How do their results compare and contrast with similar findings in other species and what are the implications of this? I don’t envisage an extensive re-writing here, just a paragraph or two would be useful in understanding how the meerkat results fit in to what is generally known about vocal mitigation of environmental effects on signal perception in animals.

In line with this, it might also be useful to comment on what light these findings may be able to shed on the ongoing discussion surrounding mammalian vocal flexibility. I appreciate this is not the focus of the paper, but nevertheless such results provide further support against the notion that mammal vocal production is hardwired and confirms that relatively dynamic changes in the social or ecological environment are responded to with equally dynamic changes in vocal production.

Lastly, perhaps some discussion regarding the correlational nature of the findings and the potential drawbacks of this could be important. Furthermore, if the authors have considered following up their observational results with experiments it might be worthwhile outlining what form such experiments might take.

Minor points:

1) Why did the authors not also include “group” as a random factor when investigating what factors influence group split propensity?

2) L186: Can you elaborate exactly what you compared in the LRT tests when assessing the significance of each of the fixed effects in the final model.

3) L203: Can you provide some quantification of variability around the mean for the differences in call rate when pups were present and absent?

4) L34-36: This is an oddly phrased sentence, perhaps consider revising

5) L35-37: You use “thus” twice in quick succession.

6) L198: Change to “Increasing dryness substantially affected…”

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Reviewer #1: No

Reviewer #2: No

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Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats

PONE-D-20-07291R1

Dear Dr. Gall,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The Authors have adequately addressed my previous comments. I thank the Authors for the text integrations and for replying to my comments with clear and precise explanations, that completely fulfill my requirements. I feel that this manuscript is now acceptable for publication.

Reviewer #2: I have re-reviewed the MS by Toni et al.

My previous issues and concerns have been adequately addressed and I am therefore happy to recommend publication.

Upon second reading I found some additional changes that could be made to aid clarification and readability.

L24: Change “with” to “including”

L31: Change “he” to “they”

L217: Change “did” to “implemented” or something similar.

320 – commas not needed.

L345: Reference here?

Plus change to: “sympatric-living”

L349: I would put this clause at the end of the sentence, rather than the middle to aid readability.

L355-357: you have “indicating” twice in quick succession. Consider using a different word.

L362: rather than highlighting about different “causes” maybe use the term “causal mechanism”?

L363: “dynamics”

L384-385: I found this sentence a little difficult to follow. It needs to be explicitly stated what your findings confirm.

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Reviewer #1: No

Reviewer #2: No