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PONE-D-23-31155The impact of size on middle-ear sound transmission in elephants, the largest terrestrial mammalPLOS ONE

Dear Dr. O'Connell-Rodwell,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that comprehensively addresses the points of both reviewers.

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Academic Editor

PLOS ONE

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3. Thank you for stating the following in the Acknowledgments Section of your manuscript:

“We thank Jeffrey Tao Cheng and John J. Rosowski for edits and comments. Elephant postmortem specimens were donated by the following zoos: Pittsburgh Zoo & Aquarium, National Zoo, St. Louis Zoo, Santa Barbara Zoo, Oakland Zoo, San Antonio Zoo, Dallas Zoo, and the White Oak Sanctuary. Work supported by K01 DC017812 from the NIDCD of NIH (to COR) and The Amelia Peabody Fund (to SP).”

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 “Work supported by K01 DC017812 from the NIDCD of the National Institute of Health (to CEO-R) and The Amelia Peabody Fund (to SP).

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6. We are unable to open your Supporting Information file [S1_Data.zip]. Please kindly revise as necessary and re-upload.

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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: Yes

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?

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

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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: This manuscript presents an interesting study to compare middle ear transfer function (i.e. velocities of the umbo and the ossicles in response to ear canal sound pressure) between elephant and human. The velocity was measured with modern Laser Doppler Vibrometry (LDV) technique across a broad frequency range between 7 and 13,000 Hz. The results suggest elephant has a lower middle ear resonance frequency of about 300 Hz than human around 1000 Hz, which may facilitate elephant long distance communication. Surprisingly, despite larger size and heavier mass of the elephant middle ear, sound transmission through elephant ear at high frequencies is boosted to the similar level of human ear (see Fig.2E and 2F, where despite umbo motions in Elephant above 2 kHz are lower than those in Human, stapes motions in Elephant are close to those in Human). This is surprising as it counteracts the mass effect at high frequencies. The authors attempted to explain this surprising finding through several unique morphological features of the elephant middle ear (such as “an incus pedicle resonance and/or ISJ”) as well as potential changes of its vibration modes (like those observed in chinchillas in a recent study) at high frequencies. Another surprising finding is the significantly larger group delay (phase accumulation) in elephant ears in comparison to human ears, “which may play a role in improved high-frequency hearing, especially when more mass is involved”, as being speculated in the manuscript by the authors.

Line 77: “whereas it was reported as 9.6x larger (454 vs. 68.3 mm2)”. It should be “6.6x” larger.

In Table 1, the TM surface areas between African and Asian Elephants are significantly different (606.3 vs. 403.6), suggesting species differences. Indeed the TM surface area of Asian Elephant is not that much different from Nummela et al.

How was the thickness of the TM quantified? Given the thickness of the human TM quantified in this study (223 um) is more than twice of the reported human TM thickness (80~100 um), please give more details and justify the results.

Is the density of elephant middle ear same as the density of human ear when calculating the mass?

In Table 3, some mean values do not seem to match with individual values listed there. For instance, in Human HF column, how could 25 and 24 yield mean of 9.5? Please double check all your calculations of means and SDs and revise text accordingly.

Given only a limited number of elephant ears were measured in this study, would it make more sense to look at individual ear rather than looking at the mean and SD? For example, in Table 3, in Elephant HF column, the umbo group delay from four elephant ears are 5, -2, 170, 62, which makes no sense to average them. Plots like those shown in S2_Fig are more meaningful.

Reviewer #2: The authors carefully evaluated and described the middle ear function of elephants and compared it to 4 human temporal bones. Although the number of human temporal bones is quite small, I only have minor comments:

-Line 384: “Fig. 2H” instead of “Fig. 3H”

- Can you transfer your findings to the real life of elephants and speculate on the evolutionary benefits of their hearing?

- Are the findings of the two species (African and Asian elephant) comparable? Are the differences species or more age related?

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Reviewer #1: No

Reviewer #2: No

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PONE-D-23-31155R1The impact of size on middle-ear sound transmission in elephants, the largest terrestrial mammalPLOS ONE

Dear Dr. O'Connell-Rodwell,

Thank you for submitting your manuscript to PLOS ONE. While the manuscript has been improved, one of the reviewers has requested additional minor modifications. Your paper is essentially provisionally accepted pending these final minor changes. 

Please submit your revised manuscript by Mar 03 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Andre van Wijnen

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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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: (No Response)

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

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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: Yes

Reviewer #2: Yes

**********

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: I appreciate the efforts the authors have made into their revisions. I only have a few minor suggestions.

Line 216-217: “Nummela [2] reported human, seal, and elephant ossicle densities between 2.0 and 2.3.” Please add the unit of density after the numbers.

Table 3: Thanks for clarifying that you subtracted 15us to calculate human means. Looks like you also subtracted different times (varying from specimen to specimen) when calculating elephant means. However, are the values listed in Table 3 in the elephant columns from “after subtraction”? While the values listed in Table 3 in the human columns are from “before subtraction”? This is confusing, and I suggest you also list the values for the humans after subtraction.

Reviewer #2: The authors responded to all the reviewer's comments. I do not have any further comment and I would like to congratulate the authors for their excellent work.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

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[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

The impact of size on middle-ear sound transmission in elephants, the largest terrestrial mammal

PONE-D-23-31155R2

Dear Dr. O'Connell-Rodwell,

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.

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Kind regards,

Andre van Wijnen

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Editorial Comments:

The authors have adequately addressed the final minor comments.

Reviewers' comments: