Advantages of social skills for contest resolution

Animal contests are natural interactions that occur to obtain or defend resources such as food and territory. Selection should favour individuals that can win contests with minimal costs in terms of energy expenditure or injuries. We hypothesized that social skills contribute to animals' assessment abilities in a contest situation and thereby will shorten contest duration. Animals were either raised in early life conditions stimulating the development of social skills, termed socialization or not (control). Contests between 342 pigs at eight weeks old (171 dyads) were studied for opponent assessment ability (using a game theoretical approach), examining duration and escalation, social behaviours performed, injuries and outcome. Contesting dyads were from the same treatment group and varied in body weight, a validated measure of resource holding potential (RHP). Socialized animals had shorter contests that were resolved with fewer injuries and they showed more ritualized display behaviour, consistent with mutual assessment. Furthermore, there was evidence of a novel form of opponent assessment in the socialized group revealed by a positive relationship between winner RHP and fight duration. In conclusion, social skills enabled more rapid establishment of dominance relationships at lower cost. Besides its evolutionary relevance, these findings may also contribute towards improving animal welfare.


INTRODUCTION
I found the structure of the introduction a little unusual, specifically with the hypothesis of the study being presented in the second paragraph! However, all the information is there to set up the study so unless the editor has a problem with this I think it's OK albeit unconventional.
Line 75 and others: I think you need to be specific when you talk about 'contest costs'. Traditionally when examining assessment rules, one would inspect the relationship between contestant RHP and contest duration (as a proxy of cost) but you also explore injury here (which is very cool). I think it would be worthwhile for you to be explicit throughout the manuscript when talking about costs to make it clear to the reader specifically which proxy of cost you are referring to.

METHODS
Line 8: Why was the barrier replaced if the piglets were still able to mingle? Was this to prevent aggression between the sows? Line 91 and others: Be more specific about which animals. Say piglets or pigs depending on which you are referring to.
Line 100: Are pigs still classed as piglets at 8 weeks old? Please specify.
Line 117: Were pre-fight lesions the result of play-fighting between siblings or were they only present on SOC piglets? Did you look at the effect the presence of these pre-fight lesions had on contest behaviour? Could be quite interesting to see if pigs with these lesions were more or less aggressive regardless of socialisation treatment?
Line 125-126: Table 1 only gives a definition of 'mutual fighting' not 'fighting'. I find the use of fight to mean something different to contest very confusing throughout the manuscript and recommend that you are explicit about the difference between these two terms when you first being to use them. I also recommend that you are consistent with using 'mutual fight' rather than just 'fight' to avoid confusion. It also might be worth writing a brief description of how a pig fight plays out in this section so the reader understands all that comes next.
Line 138: Again be specific about what you mean when you say 'contest costs' here.
Line 150: What is 'batch'? : "… shorter contest duration was therefore due to the accumulation of nonsignificant time differences" -I don't understand this sentence.

Review form: Reviewer 3
Is the manuscript scientifically sound in its present form? Yes

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
This study looked at whether socialization influences the aggressive behavior of pigs. The study design is straightforward and the authors bring in tests from contest theory to see not only whether overall levels of aggression differed but also whether the way that individuals assess one another may depend on socialization. And indeed it seems that socialization affects both things, and importantly reduces contest duration and costs, which has potentially very important welfare implications. I found the study design and write-up very well done, and I only have a few minor comments related to the interpretation of the data. It's a bit difficult to tell what's going on here in terms of assessment, which the authors acknowledge, but I think the possibilities are even broader than what they discuss.

Specific comments:
Line 72: Just to be clear here, is the hypothesis that socialized pigs should show mutual assessment and other pigs should do something else (self assessment?)? Or rather that both types should do mutual assessment, but socialized pigs do it better. Line 185: Although Table 1 is cited above when the definition of fights is brought up, it would probably help to alert the reader to the fact that all these other behaviors were also being measured, sometime in the Methods section. This result on parallel walking comes as a surprise otherwise because we wouldn't have known that was looked at.
Line 191: Which "shorter contest duration" is being referred to here? Same comment for next sentence.
Line 200: They were shorter contests, but presumably the fight is the most costly part of the contest? If they're both fighting equally often and for equal amounts of time, what does this say about differences in aggression and assessment in these species? (granted, the trend for less biting does of course suggest lower costs for socialized pigs) Line 214: Would this strategy be based on absolute winner size, or winner size relative to loser size? In the latter case, then wouldn't you also expect a negative relationship between loser size and contest duration? Did the larger pig always win?
Line 225: The results on overall contest duration are consistent with pigs being better at resolving encounters, but it's not clear if that's because of improved assessment. Isn't one interpretation of the results that the individuals were actually doing a worse job of assessing one another, assuming mutual assessment? That is, shouldn't large socialized winners, if they were good mutual assessors, been especially good at defeating their opponent, and shouldn't small socialized losers have been very good at giving up right away when facing a larger opponent? Instead, large socialized winners seemed to take an especially long time to win for some reason, which didn't happen in the control group. On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-181456 entitled "Advantages of social skills for contest resolution" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
The reviewers and handling editors have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
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If your manuscript is newly submitted and subsequently accepted for publication, you will be asked to pay the article processing charge, unless you request a waiver and this is approved by Comments to the Author(s) Review note on RSOS-181456 "Advantages of social skills for contest resolution" General comments This is a well written and well-structured manuscript. The study has a good design, is clearly presented and the conclusions reflects the results. I have some minor specific comments and some questions related to the statistical analyses (see below).

Specific comments
Abstract LN 22: It would help the reader if you add the age of the pigs at the contest. LN 28: Write out what RHP stands for, this is the first time the reader meats this abbreviation.
Materials and methods LN 110-111: Please specify which fear behaviors you refer to. LN 121-129: Please clarify how the individuals were identified on the films (i.e. how they were marked). LN 131 and onwards: Statistical analyses: • The treatments (SOC and CON) were allocated to sows (specified in line 84 and 85), thus the analyses should be done on averages per litter (sow) and not on individual piglet level (as sow/litter is the experimental unit). • Specify which effects in the model are fixed and which are random. • Even though the correct way to analyses this data is on litter/sow level and not piglet level. If analyzed on piglet level (given that this is well justified in the statistical analyses section), the random effect of litter(or sow if each sow only have one litter in the experiment) should be included as a random effect in the model.

Results
Throughout the results section: Give one more decimal for SE than for the least square mean, now you give the same number of decimals for both LSM and SE.

Reviewer: 2
Comments to the Author(s) In this study, the authors test the effects of early life socialisation on contest dynamics and intensity in pigs. They hypothesise that socialised pigs will be less aggressive than non-socialised pigs due to an increased ability to assess their opponent. The authors find that socialised pigs are indeed less aggressive during fights, being able to resolve conflict in a less costly manner than non-socialised pigs. However, they find mixed evidence as to whether or not this is due to an increased assessment ability.
Overall this is a neat study with interesting results. I have only minor comments for the authors to consider before publication can be recommended.

INTRODUCTION
I found the structure of the introduction a little unusual, specifically with the hypothesis of the study being presented in the second paragraph! However, all the information is there to set up the study so unless the editor has a problem with this I think it's OK albeit unconventional.
Line 75 and others: I think you need to be specific when you talk about 'contest costs'. Traditionally when examining assessment rules, one would inspect the relationship between contestant RHP and contest duration (as a proxy of cost) but you also explore injury here (which is very cool). I think it would be worthwhile for you to be explicit throughout the manuscript when talking about costs to make it clear to the reader specifically which proxy of cost you are referring to.

METHODS
Line 8: Why was the barrier replaced if the piglets were still able to mingle? Was this to prevent aggression between the sows? Line 91 and others: Be more specific about which animals. Say piglets or pigs depending on which you are referring to.
Line 100: Are pigs still classed as piglets at 8 weeks old? Please specify.
Line 117: Were pre-fight lesions the result of play-fighting between siblings or were they only present on SOC piglets? Did you look at the effect the presence of these pre-fight lesions had on contest behaviour? Could be quite interesting to see if pigs with these lesions were more or less aggressive regardless of socialisation treatment?
Line 125-126: Table 1 only gives a definition of 'mutual fighting' not 'fighting'. I find the use of fight to mean something different to contest very confusing throughout the manuscript and recommend that you are explicit about the difference between these two terms when you first being to use them. I also recommend that you are consistent with using 'mutual fight' rather than just 'fight' to avoid confusion. It also might be worth writing a brief description of how a pig fight plays out in this section so the reader understands all that comes next.
Line 138: Again be specific about what you mean when you say 'contest costs' here.
Line 150: What is 'batch'? : "… shorter contest duration was therefore due to the accumulation of nonsignificant time differences" -I don't understand this sentence.

Reviewer: 3
Comments to the Author(s) This study looked at whether socialization influences the aggressive behavior of pigs. The study design is straightforward and the authors bring in tests from contest theory to see not only whether overall levels of aggression differed but also whether the way that individuals assess one another may depend on socialization. And indeed it seems that socialization affects both things, and importantly reduces contest duration and costs, which has potentially very important welfare implications. I found the study design and write-up very well done, and I only have a few minor comments related to the interpretation of the data. It's a bit difficult to tell what's going on here in terms of assessment, which the authors acknowledge, but I think the possibilities are even broader than what they discuss.

Specific comments:
Line 72: Just to be clear here, is the hypothesis that socialized pigs should show mutual assessment and other pigs should do something else (self assessment?)? Or rather that both types should do mutual assessment, but socialized pigs do it better.
Line 185: Although Table 1 is cited above when the definition of fights is brought up, it would probably help to alert the reader to the fact that all these other behaviors were also being measured, sometime in the Methods section. This result on parallel walking comes as a surprise otherwise because we wouldn't have known that was looked at.
Line 191: Which "shorter contest duration" is being referred to here? Same comment for next sentence.
Line 200: They were shorter contests, but presumably the fight is the most costly part of the contest? If they're both fighting equally often and for equal amounts of time, what does this say about differences in aggression and assessment in these species? (granted, the trend for less biting does of course suggest lower costs for socialized pigs) Line 214: Would this strategy be based on absolute winner size, or winner size relative to loser size? In the latter case, then wouldn't you also expect a negative relationship between loser size and contest duration? Did the larger pig always win?
Line 225: The results on overall contest duration are consistent with pigs being better at resolving encounters, but it's not clear if that's because of improved assessment. Isn't one interpretation of the results that the individuals were actually doing a worse job of assessing one another, assuming mutual assessment? That is, shouldn't large socialized winners, if they were good mutual assessors, been especially good at defeating their opponent, and shouldn't small socialized losers have been very good at giving up right away when facing a larger opponent? Instead, large socialized winners seemed to take an especially long time to win for some reason, which didn't happen in the control group. Dear Dr Camerlink, I am pleased to inform you that your manuscript entitled "Advantages of social skills for contest resolution" is now accepted for publication in Royal Society Open Science.
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