Effects of physical impairments on fitness correlates of the white-footed mouse, Peromyscus leucopus

Physical impairments are widely assumed to reduce the viability of individual animals, but their impacts on individuals within natural populations of vertebrates are rarely quantified. By monitoring wild populations of white-footed mice over 26 years, we assessed whether missing or deformed limbs, tail or eyes influenced the survival, body mass, movement and ectoparasite burden of their bearers. Of the 27 244 individuals monitored, 543 (2%) had visible physical impairments. Persistence times (survival) were similar between mice with and without impairments. Mice with eye and tail impairments had 5% and 6% greater mass, respectively, than unimpaired mice. Mice with tail impairments had larger home ranges than did unimpaired mice. Burdens of black-legged ticks (Ixodes scapularis) were higher among mice with tail and limb impairments while burdens of bot fly larvae (Cuterebra) were higher among mice with cataracts compared to mice without impairments. Our findings do not support the presupposition that physical impairments reduce viability in their bearers and are inconsistent with the devaluation of impaired individuals that pervaded early thinking in evolutionary biology.


General interest: Is the paper of sufficient general interest? Good
Quality of the paper: Is the overall quality of the paper suitable? Excellent Is the length of the paper justified? Yes Should the paper be seen by a specialist statistical reviewer? No Do you have any concerns about statistical analyses in this paper? If so, please specify them explicitly in your report. Yes It is a condition of publication that authors make their supporting data, code and materials available -either as supplementary material or hosted in an external repository. Please rate, if applicable, the supporting data on the following criteria.

Do you have any ethical concerns with this paper? No
Comments to the Author Here, the authors use a powerful long-term dataset of wild Peromyscus to address a widespread convention that physical impairment impacts host fitness. They investigated limb, tail, and eye impairments on host survival, movement, weight, and ectoparasite infection and conclude that there is no support for impairments negatively impacting host movement & fitness save for moderate effects of increased bot fly infection. I found this manuscript enjoyable to read and a robust & thoughtful study. I have some comments which I feel should be clarified/ addressed before publication. I detail these below but feel they are all addressable with minor revisions and that this study is well-suited to Proceedings B.

Minor comments
Lines 23-25 in the abstract highlight results which were not supported by the models, particularly the effects on ticks and persistence. I think the phrasing in the discussion which presents the results as similar persistence times between the groups and no effect on ticks is more transparent and that these lines as they are slightly misleading for the model results.
Line 99 -It would be helpful here just to clarify/confirm whether the recording of impairments was standard recording for notes at each capture. It seems so but initially I wondered if there could be any missing impairments if this was not an aim of data collection throughout all years trapped.
Lines 106-108 -Given the small sample size this is not much of an issue, but I wondered if authors could have three columns for tail, eye, or limb impairments as binary variables rather than having one variable for impairments and having to assign mice to one category?
Line 122-123 -Was the assumption of uniform capture probability between these two groups tested in any way? It seems that several mechanisms being tested in this study could also affect capture probability (eg movement/ fitness).
Lined 128-130 -The N of mice for which a status change of unimpaired to impaired over the course of trapping would be informative here.
Lines 138-140 -Does 'selection criteria' here refer only to age and week of first capture as mentioned further down in this section? If so suggest explicitly stating when first mentioning selection criteria.
Line 201 -Some justification for why the interaction of sex and season was not tested in ectoparasite models but was for other metrics tested would be useful.
Lines 201-203 -It is not clear to me from this description why negative binomial models were used for all (?) ectoparasites and then botflies were singled out for Poisson models for mice with at least one botfly.
Lines 222-223 -Clarify here what it indicates that the impaired population correlates with overall mouse population. In space? In time? Something else? Lines 236-237 -As stated above this result comes as surprising based on the abstract. It is reasonable to present the raw data summaries throughout the results, in several instances it reads as a bit of an afterthought that there were no effects from the models accounting for other covariates, so would caution conservative phrasing of the raw data comparisons.
Lines 276-277 -This statement regarding selection bias is a bit lost on me in terms of conveying how this was determined, perhaps rephrase? Line 316 -How was zero-inflation ruled out?
Line 330 -The use of 'risk' here seems in contrast following results describing effects on bot fly number as that term should pertain to probability of infection and not load, while there was no effect on odds of botfly infestation.
Lines 336-337 -Incidence rate seems inappropriate to describe data that does not include zeroes, as it suggests information about the risk/rate of cases, which requires there to be uninfected and infected individuals. Some clarification on the 'at least one' criteria may be needed if this does not refer to only non-zero data.
Line 405-406 -Unclear what 'risk' is referring to in this sentence given this is discussing body mass.
Statistical models -I had a few queries about the treatment of terms in statistical models.

1.
Given the number of levels in the variable, it seems more suitable for year to be considered as a random effect.

2.
It was unclear to me why grid was considered a random effect for some models but was a fixed effect for tick and movement models.

3.
Was there a reason the intercept level for year changes between models for mass and movement?
Discussion -Just a general comment that I felt the authors handled the discussion very nicely and logically. I found the hypotheses regarding vertical movement and future directions very interesting and thought-provoking, particularly potentially implications of social interactions affected by impairments.

15-Jun-2021
Dear Ms Rubino: I am writing to inform you that your manuscript RSPB-2021-0886 entitled "Effects of Physical Impairments on Fitness Correlates of the White-footed Mouse, Peromyscus leucopus" has, in its current form, been rejected for publication in Proceedings B.
This action has been taken on the advice of referees, who are generally positive about the work but have also recommended that revisions are necessary. With this in mind we would be happy to consider a resubmission, provided the comments of the referees are fully addressed. However please note that this is not a provisional acceptance.
The resubmission will be treated as a new manuscript. However, we will approach the same reviewers if they are available and it is deemed appropriate to do so by the Editor. Please note that resubmissions must be submitted within six months of the date of this email. In exceptional circumstances, extensions may be possible if agreed with the Editorial Office. Manuscripts submitted after this date will be automatically rejected.
Please find below the comments made by the referees, not including confidential reports to the Editor, which I hope you will find useful. If you do choose to resubmit your manuscript, please upload the following: 1) A 'response to referees' document including details of how you have responded to the comments, and the adjustments you have made. 2) A clean copy of the manuscript and one with 'tracked changes' indicating your 'response to referees' comments document. 3) Line numbers in your main document. 4) Data -please see our policies on data sharing to ensure that you are complying (https://royalsociety.org/journals/authors/author-guidelines/#data).
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Sincerely, Professor Hans Heesterbeek mailto: proceedingsb@royalsociety.org Associate Editor Comments to Author: Following two expert reviews there is considerable enthusiasm that the manuscript submitted by Rubino et al will make a significant contribution to understanding how physical impairment affects fitness in wildlife. The reviewers raise a few issues that should be addressed in any revision. One reviewer raises the point that the comparison to the human eugenics movement, while an interesting hook for the article, is a bit of a stretch and therefore the manuscript should focus on physical impairment in wildlife as the motivating framework for the research. Additionally, an interesting point is raised concerning cause and effect: do individuals with impairments have larger home ranges because of impairment, or would unimpaired individuals be more likely to become impaired due to having larger home ranges? Minor concerns also were raised about the heavy reliance on supplementary tables, which most readers are unlikely to read, and the need for more detailed statistical reporting in the main text. The authors should address all of the points raised by the reviewers in preparing a revision of their manuscript.
Reviewer(s)' Comments to Author: Referee: 1 Comments to the Author(s) This paper is well written, and is generally a contribution to the literature, but needs some work.
Line 24: need to include Latin binomial or at least genus for "tick and bot fly" Line 36: "Natural Selection" need not be capitalized Line 41: comma after "thus" Lines 36-46: The title and abstract mention and specifically speak about mice. I think when talking about "individuals" in these opening lines, you need to make clear you are talking about humans. Lines 41 and 44, change "individuals" to "humans." Lines 47-48: Do you really think, and expect the readership to believe, that the role impairments play in humans can be better understood by looking at those in a single mouse population found on Cary Institute property? I would say this is a bit of stretch. And you are assuming that mice are born with these impairments and not sustaining them from predator encounters or from human sampling events to be able to compare to human birth defects? This opening paragraph is impossibly broad, comparing human eugenics to a mouse who may have lost its tail which saved its life in an attack from a barred owl. Your Abstract is spot on, using these data to attribute survival of the fittest within species is an addition to the literature base; pulling from and comparing to human eugenics is an enormous over-reach. Line 92: oak and maple should at least have the genus identified Lines 94-95: I know this is a brief description and you reference more specific methods, but your description here seems to indicate you trapped mice every 3-4 weeks since 1991. I am guessing you were not trapping in January, so might want to include that you were trapping every 3-4 weeks from May -October, or whatever the range of months that might be. Line 159: Likely not many mice under 11 grams existed in the data set because mice below that mass were unlikely to trigger Sherman traps. 202,213,318,320,321,325,327,328,334,336,340,350,371,375,378,382: need to specify they were parasitized by bot fly larvae, not bot flies Line 202: why is "botfly" one word here and two words everywhere else? Line 238: "3" should be "3.0" Line 243: "3096" should be "3,096" to remain consistent with previous usage Line 247: comma after "average" Line 247: "lighter" is a reference to weight. Here you are measuring mass. "On average, adult mice without impairments had less mass . . ." Line 248: delete the comma and insert "mass" after "observed" Lines 249-250: don't you need to swap the order of limb impaired mice and eye impaired mice if you are reporting those cohorts in descending order of average mass?
Lines 251-261: You keep saying/implying that various impairments caused an increase in mass, but that is really not the case. Mice with these impairments had more mass, generally. Semantics, I know. And this is not surprising as elder mice (with more mass) will have had more intraspecific and interspecific conflicts than younger mice merely as a function of age. Lines 262-263: You had multiple leucopus with 30-50 grams of mass in your study? In the thousands we have trapped over 15 years, we seldom have had one over 30 grams, and usually they were gravid females. Based on personal experience, I would have to agree with this site on the physical description of leucopus, including their mass of between 15-25 grams (https://animaldiversity.org/accounts/Peromyscus_leucopus/). I would double check these figures before publishing. They seem like they could be data errors in the "Absent, Missing Tail, and Partial Tail" box and whisker plots. Those are BIG leucopus that I have never seen reported in the literature previously. People in the know are going to question the veracity of your data if these data are published as is and are not addressed. Lines 307-308: if you are going to include the mean ectoparasite burden for mice without impairments, you need to include it for impaired mice as well instead of just referring the to supplemental table. Do you have any statistical proof that mean burdens on impaired mice were significantly higher than without impairments? If so, here is where you need to include that in text. Otherwise, this is meaningless. Line 310: comma after "average" Lines 312-314 and 314-316: even if there was no significance, you need to include statistical outputs here Lines 318-319: need to include mean burdens in text here as well instead of referencing a supplemental table Line 319-320, 321-323: need to include statistical output showing lack of significant differences Lines 356-365: You have this exactly backwards. The mice do not have larger home ranges because they had a tail impairment, they have tail impairments because they had larger home ranges. These mice prior to becoming impaired, were pre-programmed to wander and have larger home ranges, placing them further away from the safety of their dens than their counterparts. As a result, these mice were more exposed and more likely to encounter a predator attack, thus causing said tail impairment. Most mice with larger home ranges without tail impairments were dead as the result of predation and were not available to be trapped. This entire paragraph needs to be omitted and re-written because it is wrong and will fall completely flat if published as is. Line 367-369: Yes!!! Omit the vertical habitat usage altogether and focus on this. Mice with larger home ranges are more exposed and thus, more at risk. This is the focus of this paragraph (not a closing example) and not that they cannot climb because of a damaged tail. Line 372: period after "al" Line 377: "…may come into more frequent contact with bot fly eggs." Line 381: delete second "in" Line 383: In lines 20 and 89, you mention you monitored a single wild population of white-footed mice. Why here then are you suggesting you monitored multiple populations? Line 391: It is likely you saw higher parasitism on impaired mice because of their propensity to travel further than other mice, thus increasing their susceptibility to encountering both predators and parasites. Line 395: "et al." need not be in italics here to remain consistent with the rest of the text Line 398: comma after "study" and delete "on," or reword the sentence as I find it difficult to understand what you are trying to say. Line 432: "developed" Referee: 2 Comments to the Author(s) Here, the authors use a powerful long-term dataset of wild Peromyscus to address a widespread convention that physical impairment impacts host fitness. They investigated limb, tail, and eye impairments on host survival, movement, weight, and ectoparasite infection and conclude that there is no support for impairments negatively impacting host movement & fitness save for moderate effects of increased bot fly infection. I found this manuscript enjoyable to read and a robust & thoughtful study. I have some comments which I feel should be clarified/ addressed before publication. I detail these below but feel they are all addressable with minor revisions and that this study is well-suited to Proceedings B.

Minor comments
Lines 23-25 in the abstract highlight results which were not supported by the models, particularly the effects on ticks and persistence. I think the phrasing in the discussion which presents the results as similar persistence times between the groups and no effect on ticks is more transparent and that these lines as they are slightly misleading for the model results.
Line 99 -It would be helpful here just to clarify/confirm whether the recording of impairments was standard recording for notes at each capture. It seems so but initially I wondered if there could be any missing impairments if this was not an aim of data collection throughout all years trapped.
Lines 106-108 -Given the small sample size this is not much of an issue, but I wondered if authors could have three columns for tail, eye, or limb impairments as binary variables rather than having one variable for impairments and having to assign mice to one category?
Line 122-123 -Was the assumption of uniform capture probability between these two groups tested in any way? It seems that several mechanisms being tested in this study could also affect capture probability (eg movement/ fitness).
Lined 128-130 -The N of mice for which a status change of unimpaired to impaired over the course of trapping would be informative here.
Lines 138-140 -Does 'selection criteria' here refer only to age and week of first capture as mentioned further down in this section? If so suggest explicitly stating when first mentioning selection criteria.
Line 201 -Some justification for why the interaction of sex and season was not tested in ectoparasite models but was for other metrics tested would be useful.
Lines 201-203 -It is not clear to me from this description why negative binomial models were used for all (?) ectoparasites and then botflies were singled out for Poisson models for mice with at least one botfly.
Lines 222-223 -Clarify here what it indicates that the impaired population correlates with overall mouse population. In space? In time? Something else? Lines 236-237 -As stated above this result comes as surprising based on the abstract. It is reasonable to present the raw data summaries throughout the results, in several instances it reads as a bit of an afterthought that there were no effects from the models accounting for other covariates, so would caution conservative phrasing of the raw data comparisons.
Lines 276-277 -This statement regarding selection bias is a bit lost on me in terms of conveying how this was determined, perhaps rephrase?
Line 316 -How was zero-inflation ruled out?
Line 330 -The use of 'risk' here seems in contrast following results describing effects on bot fly number as that term should pertain to probability of infection and not load, while there was no effect on odds of botfly infestation.
Lines 336-337 -Incidence rate seems inappropriate to describe data that does not include zeroes, as it suggests information about the risk/rate of cases, which requires there to be uninfected and infected individuals. Some clarification on the 'at least one' criteria may be needed if this does not refer to only non-zero data.
Line 405-406 -Unclear what 'risk' is referring to in this sentence given this is discussing body mass.
Statistical models -I had a few queries about the treatment of terms in statistical models. 1. Given the number of levels in the variable, it seems more suitable for year to be considered as a random effect. 2. It was unclear to me why grid was considered a random effect for some models but was a fixed effect for tick and movement models. 3. Was there a reason the intercept level for year changes between models for mass and movement?
Discussion -Just a general comment that I felt the authors handled the discussion very nicely and logically. I found the hypotheses regarding vertical movement and future directions very interesting and thought-provoking, particularly potentially implications of social interactions affected by impairments.

Do you have any ethical concerns with this paper? No
Comments to the Author You nailed it. Much much improved over the previous submission. This one was a pleasure to read. I have no further modifications.

Do you have any concerns about statistical analyses in this paper? If so, please specify them explicitly in your report. No
It is a condition of publication that authors make their supporting data, code and materials available -either as supplementary material or hosted in an external repository. Please rate, if applicable, the supporting data on the following criteria.

Do you have any ethical concerns with this paper? No
Comments to the Author I would like to commend the authors for their thorough response to reviews. They have carefully responded to all comments raised in my previous review, and I particularly appreciate the revision of the statistical models to address any concerns as I know this is time-consuming. I have no remaining issues and think this will make a very interesting contribution to the literature.

04-Oct-2021
Dear Ms Rubino I am pleased to inform you that your manuscript RSPB-2021-1942 entitled "Effects of Physical Impairments on Fitness Correlates of the White-footed Mouse, Peromyscus leucopus" has been accepted for publication in Proceedings B.
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Sincerely, Professor Hans Heesterbeek mailto: proceedingsb@royalsociety.org Associate Editor Board Member Comments to Author: The authors have performed a thorough revision of their manuscript in response to two expert reviews. As a result the manuscript is much improved and the authors deserve credit for their careful consideration of all concerns raised previously by the reviewers. A few small issues remain. 1) It appears that the authors may have accidentally deleted the abstract and keywords from the submitted version of the revised manuscript? At least these are missing from the version available through the submission portal. 2) In their revisions to the abstract in response to reviewer 2, if the new statement "Mice with impairments were roughly 5% heavier and had comparable persistence times as well as burdens of black-legged ticks (Ixodes scapularis) and bot fly larvae (Cuterebra) compared to mice without impairments" refers to mass and not weight, please see the comment from reviewer 1 to use the terms "greater mass" and "less mass" instead of "lighter" and "heavier" throughout the manuscript.
Reviewer(s)' Comments to Author: Referee: 1 Comments to the Author(s). You nailed it. Much much improved over the previous submission. This one was a pleasure to read. I have no further modifications.
Referee: 2 Comments to the Author(s). I would like to commend the authors for their thorough response to reviews. They have carefully responded to all comments raised in my previous review, and I particularly appreciate the revision of the statistical models to address any concerns as I know this is time-consuming. I have no remaining issues and think this will make a very interesting contribution to the literature.

11-Oct-2021
Dear Ms Rubino I am pleased to inform you that your manuscript entitled "Effects of Physical Impairments on Fitness Correlates of the White-footed Mouse, Peromyscus leucopus" has been accepted for publication in Proceedings B.
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Response to Referees for Manuscript: RSPB-2021-0886
Associate Editor Comments to Author: Following two expert reviews there is considerable enthusiasm that the manuscript submitted by Rubino et al will make a significant contribution to understanding how physical impairment affects fitness in wildlife. The reviewers raise a few issues that should be addressed in any revision. One reviewer raises the point that the comparison to the human eugenics movement, while an interesting hook for the article, is a bit of a stretch and therefore the manuscript should focus on physical impairment in wildlife as the motivating framework for the research. Additionally, an interesting point is raised concerning cause and effect: do individuals with impairments have larger home ranges because of impairment, or would unimpaired individuals be more likely to become impaired due to having larger home ranges? Minor concerns also were raised about the heavy reliance on supplementary tables, which most readers are unlikely to read, and the need for more detailed statistical reporting in the main text. The authors should address all of the points raised by the reviewers in preparing a revision of their manuscript. Response: We thank the Associate Editor for these comments. As we detail below in responses to specific reviewer comments and suggestions, we have carefully revised the manuscript to address these two major comments, regarding the comparison to human eugenics theory and the potential for reverse causality in the case of impairments and home range size. In addition, we have changed the balance of supplementary tables and the main text as repositories of the results, and addressed all other concerns raised in the reviews.

Reviewer(s)' Comments to Author:
Referee: 1 Comments to the Author(s) This paper is well written, and is generally a contribution to the literature, but needs some work. Response: We thank the reviewer for this assessment and have undertaken considerable work to improve the manuscript.
Line 24: need to include Latin binomial or at least genus for "tick and bot fly" Response: We have added the Latin binomial for the tick and the genus for the bot fly [line 27]. In the case of the latter, a species identification could not be confirmed on the basis on morphological characteristics.
Line 36: "Natural Selection" need not be capitalized Response: We have removed this sentence.
Line 41: comma after "thus" Response: We have removed this sentence.
Lines 36-46: The title and abstract mention and specifically speak about mice. I think when talking about "individuals" in these opening lines, you need to make clear you are talking about humans. Lines 41 and 44, change "individuals" to "humans." Response: We have modified this section to make use of the word "individuals" clearer. As noted below, we have strongly de-emphasized the focus on humans, resulting in a rewrite of these lines [lines 38-42].
Lines 47-48: Do you really think, and expect the readership to believe, that the role impairments play in humans can be better understood by looking at those in a single mouse population found on Cary Institute property? I would say this is a bit of stretch. And you are assuming that mice are born with these impairments and not sustaining them from predator encounters or from human sampling events to be able to compare to human birth defects? This opening paragraph is impossibly broad, comparing human eugenics to a mouse who may have lost its tail which saved its life in an attack from a barred owl. Your Abstract is spot on, using these data to attribute survival of the fittest within species is an addition to the literature base; pulling from and comparing to human eugenics is an enormous over-reach. Response: We appreciate the perspective provided by the reviewer and agree that greater care is required in applying these results from six mouse populations to humans. We have revised the paragraph to narrow the focus and removed discussion of the theory of natural selection and its influence on the devaluation of individuals to better focus on the specific implications of impairment in wild mice, which is the focus of the paper. We retained only one clause in the second sentence that mentions eugenic movements, providing citations. The context here is the broad impact arising from perceptions of the consequences of impairments in animals. We hope this revision will be considered more suitable.
Line 92: oak and maple should at least have the genus identified Response: We have added the scientific names here [line 89].
Lines 94-95: I know this is a brief description and you reference more specific methods, but your description here seems to indicate you trapped mice every 3-4 weeks since 1991. I am guessing you were not trapping in January, so might want to include that you were trapping every 3-4 weeks from May -October, or whatever the range of months that might be.

Response: We appreciate this suggestion and have changed sentence [lines 91-92] to: "In brief, trapping was conducted every 3-4 weeks over 2-3 consecutive days between May and November using Sherman live traps baited with oats."
Line 159: Likely not many mice under 11 grams existed in the data set because mice below that mass were unlikely to trigger Sherman traps. Response: In fact, there were 2,387 entries within our dataset recording mice that were below 11 grams. But these were clearly juvenile animals and we excluded them from analyses focusing on adults [line 159].
Lines 251-261: You keep saying/implying that various impairments caused an increase in mass, but that is really not the case. Mice with these impairments had more mass, generally. Semantics, I know. And this is not surprising as elder mice (with more mass) will have had more intraspecific and interspecific conflicts than younger mice merely as a function of age. Response: We appreciate these comments. In these descriptive sections of the results, we were not attempting to infer causality, but simply trying to state the nature of the association between impairment and mass (as well as the various other response variables). To clarify this, we have changed the language [lines: 246-256] from <x impairment was associated with y increase> to having <x impairment was associated with having on average y grams more mass>. For example: "tail impairments were significantly associated with having on average 1.43g more mass".
Lines 262-263: You had multiple leucopus with 30-50 grams of mass in your study? In the thousands we have trapped over 15 years, we seldom have had one over 30 grams, and usually they were gravid females. Based on personal experience, I would have to agree with this site on the physical description of leucopus, including their mass of between 15-25 grams (https://animaldiversity.org/accounts/Peromyscus_leucopus/). I would double check these figures before publishing. They seem like they could be data errors in the "Absent, Missing Tail, and Partial Tail" box and whisker plots. Those are BIG leucopus that I have never seen reported in the literature previously. People in the know are going to question the veracity of your data if these data are published as is and are not addressed.