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Scaia MF, Trudeau VL, Somoza GM, Pandolfi M. Fighting cichlids: An integrated multimodal analysis to understand female and male aggression in Cichlasoma dimerus. Horm Behav 2023; 148:105301. [PMID: 36623433 DOI: 10.1016/j.yhbeh.2022.105301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2022] [Revised: 12/17/2022] [Accepted: 12/22/2022] [Indexed: 01/08/2023]
Abstract
Aggression has been historically linked to males and androgen levels and, even if females from different species also display aggressive behavior, female aggression is still widely understudied. The aim of the present work is to disentangle how sex differences in social plasticity can be explained by sex steroid hormone levels, gonadal state and/or morphometric characteristics. In this context, we performed intrasexual dyadic encounters to identify social plasticity after acquiring a winner or loser status in males and females of Cichlasoma dimerus. This integral analysis suggests that the reproductive and hormonal variables analyzed explain the behavioral variation among winner and loser males and females, and that there are significant differences between sexes and contest outcome when individual morphometric variables are excluded from the analysis. Interestingly, there are no sex differences in aggressive and submissive behaviors, and clustering into winners and losers is mainly explained by specific behavioral displays, such as bites, chases, approaches, passive copings, and escapes. Correlation heatmaps show a positive correlation between estradiol with aggression and a negative correlation with submission, suggesting estrogens may have a dual role regulating agonistic behavior. Finally, these results suggest that size difference can help to understand aggression in females but not in males, and that assessment of the opponent's body size is important to understand aggression also before the initiation of the contest in both sexes. Overall, this study constitutes an integral approach adding insights into the importance of reproductive and hormonal variables to understand social plasticity in males and females.
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Affiliation(s)
- María Florencia Scaia
- Instituto de Biodiversidad y Biología Experimental y Aplicada, CONICET, Ciudad Autónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina.
| | - Vance L Trudeau
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Gustavo Manuel Somoza
- Instituto Tecnológico de Chascomús (CONICET-UNSAM), Chascomús, Argentina; Escuela de Bio y Nanotecnologías (UNSAM). Argentina
| | - Matías Pandolfi
- Instituto de Biodiversidad y Biología Experimental y Aplicada, CONICET, Ciudad Autónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
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2
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Ito K, Doebeli M. The joint evolution of cooperation and competition. J Theor Biol 2019; 480:1-12. [PMID: 31323234 DOI: 10.1016/j.jtbi.2019.07.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 07/04/2019] [Accepted: 07/15/2019] [Indexed: 01/27/2023]
Abstract
In nature, cooperation among individuals is often accompanied by competition among the same individuals for the cooperatively produced rewards. In such a situation, the evolution of cooperative and competitive investments influences each other, but previous theoretical studies mostly focused on either cooperation or competition. Here we consider a generic situation in which individuals cooperatively produce rewards according to the continuous snowdrift game, and then rewards are divided among cooperating individuals according to a generalized tug-of-war game. Using adaptive dynamics and numerical simulations, we investigated the joint evolution of two continuous traits, the investment in cooperation and in competition, respectively. We found that competition for the division of rewards promotes evolutionary branching, and hence polymorphism in both the cooperative and the competitive traits. In polymorphic populations, cooperation levels are positively correlated with competition levels among strains, so that cooperators tend to benefit disproportionately from the benefits produced. We also found that the mean cooperation level within the population is promoted by the competition. Our results show that coevolution of cooperation and competition has qualitatively different outcomes compared to the evolution of only cooperation or only competition, and suggest that it is important to simultaneously consider multiple aspects of social interactions.
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Affiliation(s)
- Koichi Ito
- Department of Zoology, University of British Columbia, 4200-6270 University Blvd. Vancouver, B.C., V6T 1Z4, Canada.
| | - Michael Doebeli
- Department of Zoology, University of British Columbia, 4200-6270 University Blvd. Vancouver, B.C., V6T 1Z4, Canada
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3
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Černý D, Lee K, Medal J, Blumstein DT. Applying Lanchester’s laws to the interspecific competition of coral reef fish. Behav Ecol 2018. [DOI: 10.1093/beheco/ary182] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- David Černý
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
- Department of Geophysical Sciences, University of Chicago, Chicago, IL, USA
| | - Kristen Lee
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
| | - Jocelyn Medal
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
| | - Daniel T Blumstein
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
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4
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Scaia MF, Morandini L, Noguera CA, Ramallo MR, Somoza GM, Pandolfi M. Fighting cichlids: Dynamic of intrasexual aggression in dyadic agonistic encounters. Behav Processes 2017; 147:61-69. [PMID: 29273550 DOI: 10.1016/j.beproc.2017.12.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 12/18/2017] [Accepted: 12/18/2017] [Indexed: 01/09/2023]
Abstract
Aggression is an extremely complex behaviour and female aggression is understudied when compared to males. Despite the fact that it has been suggested that conflict among females may be more frequently resolved peacefully, in many species females show high levels of aggression. We used Cichlasoma dimerus to describe dynamics and conflict outcome in intrasexual agonistic encounters. We performed encounters of two sex-matched animals in a neutral arena and we recorded agonistic interactions during one hour. All aggressive and submissive behaviours were described and quantified to perform the ethogram. Encounters followed three phases: pre-contest, contest and post-resolution. Latency, time of resolution and frequency of aggressive displays did not differ between sexes. Relative variations in size between female opponents better explained aggression outcome in each contest, since higher levels of aggression occurred in dyads of more similar fish. However, this was not observed in males, suggesting that probably morphological characteristics could be less relevant in male conflict resolution. Altogether these results suggest that in this ethological context, C. dimerus females are as aggressive as males and that they have similar motivation towards territorial aggression, emphasizing the need of deepening the study of aggression in females and not only in males.
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Affiliation(s)
- María Florencia Scaia
- Instituto de Biodiversidad y Biología Experimental y Aplicada - CONICET, Ciudad Auntónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina.
| | - Leonel Morandini
- Instituto de Biodiversidad y Biología Experimental y Aplicada - CONICET, Ciudad Auntónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Cristobal Alejandro Noguera
- Instituto de Biodiversidad y Biología Experimental y Aplicada - CONICET, Ciudad Auntónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Martín Roberto Ramallo
- Instituto de Biodiversidad y Biología Experimental y Aplicada - CONICET, Ciudad Auntónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Gustavo Manuel Somoza
- Laboratorio de Ictiofisiología y Acuicultura, Instituto de Investigaciones Biotecnológicas- Instituto Tecnológico de Chascomús (IIB-INTECH. CONICET-UNSAM), Chascomús, Argentina
| | - Matías Pandolfi
- Instituto de Biodiversidad y Biología Experimental y Aplicada - CONICET, Ciudad Auntónoma de Buenos Aires, Argentina; Laboratorio de Neuroendocrinología y Comportamiento, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina.
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5
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Phillips T. The concepts of asymmetric and symmetric power can help resolve the puzzle of altruistic and cooperative behaviour. Biol Rev Camb Philos Soc 2017; 93:457-468. [PMID: 28699275 DOI: 10.1111/brv.12352] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/14/2017] [Accepted: 06/19/2017] [Indexed: 12/25/2022]
Abstract
Evolutionary theory predicts competition in nature yet altruistic and cooperative behaviour appears to reduce the ability to compete in order to help others compete better. This evolutionary puzzle is usually explained by kin selection where close relatives perform altruistic and cooperative acts to help each other and by reciprocity theory (i.e. direct, indirect and generalized reciprocity) among non-kin. Here, it is proposed that the concepts of asymmetry and symmetry in power and dominance are critical if we are ever to resolve the puzzle of altruism and cooperation towards non-kin. Asymmetry in power and dominance is likely to emerge under competition in nature as individuals strive to gain greater access to the scarce resources needed to survive and reproduce successfully. Yet asymmetric power presents serious problems for reciprocity theory in that a dominant individual faces a temptation to cheat in interactions with subordinates that is likely to far outweigh any individual selective benefits gained through reciprocal mechanisms. Furthermore, action taken by subordinates to deter non-reciprocation by dominants is likely to prove prohibitively costly to their fitness, making successful enforcement of reciprocal mechanisms unlikely. It is also argued here that many apparently puzzling forms of cooperation observed in nature (e.g. cooperative breeding in which unrelated subordinates help dominants to breed) might be best explained by asymmetry in power and dominance. Once it is recognized that individuals in these cooperative interactions are subject to the constraints and opportunities imposed on them by asymmetric power then they can be seen as pursuing a 'least bad' strategy to promote individual fitness - one that is nevertheless consistent with evolutionary theory. The concept of symmetric power also provides important insights. It can inhibit reciprocal mechanisms in the sense that symmetric power makes it easier for a cheat to appropriate common resources while incurring fewer penalties. Nevertheless under certain restrictive conditions, symmetric power is seen as likely to promote direct reciprocity through 'tit for tat'.
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6
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Rodrigues AMM, Kokko H. Models of social evolution: can we do better to predict 'who helps whom to achieve what'? Philos Trans R Soc Lond B Biol Sci 2016; 371:20150088. [PMID: 26729928 DOI: 10.1098/rstb.2015.0088] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Models of social evolution and the evolution of helping have been classified in numerous ways. Two categorical differences have, however, escaped attention in the field. Models tend not to justify why they use a particular assumption structure about who helps whom: a large number of authors model peer-to-peer cooperation of essentially identical individuals, probably for reasons of mathematical convenience; others are inspired by particular cooperatively breeding species, and tend to assume unidirectional help where subordinates help a dominant breed more efficiently. Choices regarding what the help achieves (i.e. which life-history trait of the helped individual is improved) are similarly made without much comment: fecundity benefits are much more commonly modelled than survival enhancements, despite evidence that these may interact when the helped individual can perform life-history reallocations (load-lightening and related phenomena). We review our current theoretical understanding of effects revealed when explicitly asking 'who helps whom to achieve what', from models of mutual aid in partnerships to the very few models that explicitly contrast the strength of selection to help enhance another individual's fecundity or survival. As a result of idiosyncratic modelling choices in contemporary literature, including the varying degree to which demographic consequences are made explicit, there is surprisingly little agreement on what types of help are predicted to evolve most easily. We outline promising future directions to fill this gap.
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Affiliation(s)
- António M M Rodrigues
- Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK Wolfson College, Barton Road, Cambridge CB3 9BB, UK
| | - Hanna Kokko
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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7
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Abstract
Why should organisms incur a cost in order to inflict a (usually greater) cost on others? Such costly harming behavior may be favored when competition for resources occurs locally, because it increases individuals' fitness relative to close competitors. However, there is no explicit experimental evidence supporting the prediction that people are more willing to harm others under local versus global competition. We illustrate this prediction with a game theoretic model, and then test it in a series of economic games. In these experiments, players could spend money to make others lose more. We manipulated the scale of competition by awarding cash prizes to the players with the highest payoffs per set of social partners (local competition) or in all the participants in a session (global competition). We found that, as predicted, people were more harmful to others when competition was local (Study 1). This result still held when people "earned" (rather than were simply given) their money (Study 2). In addition, when competition was local, people were more willing to harm ingroup members than outgroup members (Study 3), because ingroup members were the relevant competitive targets. Together, our results suggest that local competition in human groups not only promotes willingness to harm others in general, but also causes ingroup hostility.
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Powers ST, Lehmann L. When is bigger better? The effects of group size on the evolution of helping behaviours. Biol Rev Camb Philos Soc 2016; 92:902-920. [PMID: 26989856 DOI: 10.1111/brv.12260] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Revised: 02/03/2016] [Accepted: 02/11/2016] [Indexed: 11/30/2022]
Abstract
Understanding the evolution of sociality in humans and other species requires understanding how selection on social behaviour varies with group size. However, the effects of group size are frequently obscured in the theoretical literature, which often makes assumptions that are at odds with empirical findings. In particular, mechanisms are suggested as supporting large-scale cooperation when they would in fact rapidly become ineffective with increasing group size. Here we review the literature on the evolution of helping behaviours (cooperation and altruism), and frame it using a simple synthetic model that allows us to delineate how the three main components of the selection pressure on helping must vary with increasing group size. The first component is the marginal benefit of helping to group members, which determines both direct fitness benefits to the actor and indirect fitness benefits to recipients. While this is often assumed to be independent of group size, marginal benefits are in practice likely to be maximal at intermediate group sizes for many types of collective action problems, and will eventually become very small in large groups due to the law of decreasing marginal returns. The second component is the response of social partners on the past play of an actor, which underlies conditional behaviour under repeated social interactions. We argue that under realistic conditions on the transmission of information in a population, this response on past play decreases rapidly with increasing group size so that reciprocity alone (whether direct, indirect, or generalised) cannot sustain cooperation in very large groups. The final component is the relatedness between actor and recipient, which, according to the rules of inheritance, again decreases rapidly with increasing group size. These results explain why helping behaviours in very large social groups are limited to cases where the number of reproducing individuals is small, as in social insects, or where there are social institutions that can promote (possibly through sanctioning) large-scale cooperation, as in human societies. Finally, we discuss how individually devised institutions can foster the transition from small-scale to large-scale cooperative groups in human evolution.
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Affiliation(s)
- Simon T Powers
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Lausanne, Switzerland.,School of Computing, Edinburgh Napier University, Edinburgh, EH10 5DT, U.K
| | - Laurent Lehmann
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Lausanne, Switzerland
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9
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Barker JL, Loope KJ, Reeve HK. Asymmetry within social groups: division of labour and intergroup competition. J Evol Biol 2015; 29:560-71. [PMID: 26663312 PMCID: PMC4784174 DOI: 10.1111/jeb.12805] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Revised: 10/22/2015] [Accepted: 12/01/2015] [Indexed: 11/28/2022]
Abstract
Social animals vary in their ability to compete with group members over shared resources and also vary in their cooperative efforts to produce these resources. Competition among groups can promote within-group cooperation, but many existing models of intergroup cooperation do not explicitly account for observations that group members invest differentially in cooperation and that there are often within-group competitive or power asymmetries. We present a game theoretic model of intergroup competition that investigates how such asymmetries affect within-group cooperation. In this model, group members adopt one of two roles, with relative competitive efficiency and the number of individuals varying between roles. Players in each role make simultaneous, coevolving decisions. The model predicts that although intergroup competition increases cooperative contributions to group resources by both roles, contributions are predominantly from individuals in the less competitively efficient role, whereas individuals in the more competitively efficient role generally gain the larger share of these resources. When asymmetry in relative competitive efficiency is greater, a group's per capita cooperation (averaged across both roles) is higher, due to increased cooperation from the competitively inferior individuals. For extreme asymmetry in relative competitive efficiency, per capita cooperation is highest in groups with a single competitively superior individual and many competitively inferior individuals, because the latter acquiesce and invest in cooperation rather than within-group competition. These predictions are consistent with observed features of many societies, such as monogynous Hymenoptera with many workers and caste dimorphism.
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Affiliation(s)
- J L Barker
- Department of Neurobiology & Behavior, Cornell University, Ithaca, NY, USA
| | - K J Loope
- Department of Neurobiology & Behavior, Cornell University, Ithaca, NY, USA
| | - H K Reeve
- Department of Neurobiology & Behavior, Cornell University, Ithaca, NY, USA
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10
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Suppressing subordinate reproduction provides benefits to dominants in cooperative societies of meerkats. Nat Commun 2014; 5:4499. [PMID: 25047446 PMCID: PMC4109011 DOI: 10.1038/ncomms5499] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 06/25/2014] [Indexed: 11/08/2022] Open
Abstract
In many animal societies, a small proportion of dominant females monopolize reproduction by actively suppressing subordinates. Theory assumes that this is because subordinate reproduction depresses the fitness of dominants, yet the effect of subordinate reproduction on dominant behaviour and reproductive success has never been directly assessed. Here, we describe the consequences of experimentally preventing subordinate breeding in 12 groups of wild meerkats (Suricata suricatta) for three breeding attempts, using contraceptive injections. When subordinates are prevented from breeding, dominants are less aggressive towards subordinates and evict them less often, leading to a higher ratio of helpers to dependent pups, and increased provisioning of the dominant's pups by subordinate females. When subordinate breeding is suppressed, dominants also show improved foraging efficiency, gain more weight during pregnancy and produce heavier pups, which grow faster. These results confirm the benefits of suppression to dominants, and help explain the evolution of singular breeding in vertebrate societies.
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11
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Port M, Cant MA. Reproductive Competition Among Males in Multimale Groups of Primates: Modeling the Costs and Effectiveness of Conflict. INT J PRIMATOL 2013. [DOI: 10.1007/s10764-013-9744-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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12
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Shen SF, Akçay E, Rubenstein DR. Group size and social conflict in complex societies. Am Nat 2013; 183:301-10. [PMID: 24464203 DOI: 10.1086/674378] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Conflicts of interest over resources or reproduction among individuals in a social group have long been considered to result in automatic and universal costs to group living. However, exploring how social conflict varies with group size has produced mixed empirical results. Here we develop a model that generates alternative predictions for how social conflict should vary with group size depending on the type of benefits gained from being in a social group. We show that a positive relationship between social conflict and group size is favored when groups form primarily for the benefits of sociality but not when groups form mainly for accessing group-defended resources. Thus, increased social conflict in animal societies should not be viewed as an automatic cost of larger social groups. Instead, studying the relationship between social conflict and the types of grouping benefits will be crucial for understanding the evolution of complex societies.
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Affiliation(s)
- Sheng-Feng Shen
- Biodiversity Research Center, Academia Sinica, Taipei 115, Taiwan
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13
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Cant MA, Young AJ. Resolving social conflict among females without overt aggression. Philos Trans R Soc Lond B Biol Sci 2013; 368:20130076. [PMID: 24167306 PMCID: PMC3826205 DOI: 10.1098/rstb.2013.0076] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Members of animal societies compete over resources and reproduction, but the extent to which such conflicts of interest are resolved peacefully (without recourse to costly or wasteful acts of aggression) varies widely. Here, we describe two theoretical mechanisms that can help to understand variation in the incidence of overt behavioural conflict: (i) destruction competition and (ii) the use of threats. The two mechanisms make different assumptions about the degree to which competitors are socially sensitive (responsive to real-time changes in the behaviour of their social partners). In each case, we discuss how the model assumptions relate to biological reality and highlight the genetic, ecological and informational factors that are likely to promote peaceful conflict resolution, drawing on empirical examples. We suggest that, relative to males, reproductive conflict among females may be more frequently resolved peacefully through threats of punishment, rather than overt acts of punishment, because (i) offspring are more costly to produce for females and (ii) reproduction is more difficult to conceal. The main need now is for empirical work to test whether the mechanisms described here can indeed explain how social conflict can be resolved without overt aggression.
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Affiliation(s)
- Michael A Cant
- Centre for Ecology and Conservation, University of Exeter, , Tremough Campus, Penryn, Cornwall TR10 8BG, UK
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14
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Abstract
Models of social conflict in animal societies generally assume that within-group conflict reduces the value of a communal resource. For many animals, however, the primary cost of conflict is increased mortality. We develop a simple inclusive fitness model of social conflict that takes this cost into account. We show that longevity substantially reduces the level of within-group conflict, which can lead to the evolution of peaceful animal societies if relatedness among group members is high. By contrast, peaceful outcomes are never possible in models where the primary cost of social conflict is resource depletion. Incorporating mortality costs into models of social conflict can explain why many animal societies are so remarkably peaceful despite great potential for conflict.
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Affiliation(s)
- Markus Port
- CRC Evolution of Social Behavior, University of Göttingen, , Kellnerweg 6, 37077 Göttingen, Germany
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16
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Port M, Johnstone RA. Facing the crowd: intruder pressure, within-group competition, and the resolution of conflicts over group-membership. Ecol Evol 2013; 3:1209-18. [PMID: 23762508 PMCID: PMC3678476 DOI: 10.1002/ece3.533] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 02/20/2013] [Accepted: 02/20/2013] [Indexed: 11/09/2022] Open
Abstract
Recent theory in social evolution has been mainly concerned with competition and cooperation within social groups of animals and their impact on the stability of those groups. Much less attention has been paid to conflicts arising as a result of solitary floaters (outsiders) attempting to join groups of established residents (insiders). We model such conflicts over group-membership using a demographically explicit approach in which the rates of births and deaths in a population determine the availability of group-vacancies and the number of floaters competing over these vacancies. We find that the outcome of within-group competition, reflected in the partitioning of reproduction among group members, exerts surprisingly little influence on the resolution of insider-outsider conflict. The outcome of such conflict is also largely unaffected by differences in resource holding potential between insiders and outsiders. By contrast, whether or not groups form is mainly determined by demographic factors (variation in vital rates such as fecundity and mortality) and the resulting population dynamics. In particular, at high floater densities territory defense becomes too costly, and groups form because insiders give in to the intruder pressure imposed on them by outsiders. We emphasize the importance of insider-outsider conflicts in social evolution theory and highlight avenues for future research.
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Affiliation(s)
- Markus Port
- Courant Research Center Evolution of Social Behavior, Research Group Social Evolution in Primates, University of Göttingen Kellnerweg 6, 37077, Göttingen, Germany ; Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter Cornwall Campus, Penryn, TR10 9E, United Kingdom
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