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Smith JE, Jaeggi AV, Holmes RK, Silk JB. Sex differences in cooperative coalitions: a mammalian perspective. Philos Trans R Soc Lond B Biol Sci 2023; 378:20210426. [PMID: 36440559 PMCID: PMC9703251 DOI: 10.1098/rstb.2021.0426] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 08/09/2022] [Indexed: 11/29/2022] Open
Abstract
In group-living species, cooperative tactics can offset asymmetries in resource-holding potential between individuals and alter the outcome of intragroup conflicts. Differences in the kinds of competitive pressures that males and females face might influence the benefits they gain from forming intragroup coalitions. We predicted that there would be a female bias in intragroup coalitions because females (1) are more like to live with kin than males are, and (2) compete over resources that are more readily shared than resources males compete over. We tested this main prediction using information about coalition formation across mammalian species and phylogenetic comparative analyses. We found that for nearly all species in which intragroup coalitions occur, members of both sexes participate, making this the typical mammalian pattern. The presence and frequency of female or male coalitions were not strongly associated with key socio-ecological factors like resource defensibility, sexual dimorphism or philopatry. This suggests that once the ability to form intragroup coalitions emerges in one sex, it is likely to emerge in the other sex as well and that there is no strong phylogenetic legacy of sex differences in this form of cooperation. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.
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Affiliation(s)
- Jennifer E. Smith
- Biology Department, University of Wisconsin Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54702, USA
- Biology Department, Mills College, 5000 MacArthur Boulevard, Oakland, CA 94631, USA
| | - Adrian V. Jaeggi
- Institute of Evolutionary Medicine, University of Zurich, Zurich 8057, Switzerland
| | - Rose K. Holmes
- Biology Department, University of Wisconsin Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54702, USA
| | - Joan B. Silk
- School of Human Evolution and Social Change, Institute of Human Origins, Arizona State University, Tempe, AZ 85287-2402, USA
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2
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McGuire KM, Sauther ML. Characterizing group and individual engagement in intergroup encounters between small groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, USA. Primates 2023; 64:161-176. [PMID: 36418748 DOI: 10.1007/s10329-022-01036-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 11/02/2022] [Indexed: 11/25/2022]
Abstract
Primate species exhibit considerable variation in behavior and outcomes during intergroup encounters (IGEs). Social group characteristics, like group size, and individual traits, such as sex, rank, and reproductive status, within those groups can influence both IGE engagement and outcomes. To better understand the impact of group heterogeneity on IGEs, we must examine individual strategies to elucidate individual costs and benefits of engaging in these interactions. Here, we present a descriptive study of the IGEs between two small social groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, GA, USA. We distinguish between dyadic and multiple-individual interactions between groups to compare collective and individual agonistic engagement. All encounters occurred when the East Road group (N = 7 individuals) traveled from the center of their home range to the boundary with Windmill group's (N = 5 individuals) home range, indicating that East Road might have been actively testing this boundary for access to food resources, sleeping trees, and mating opportunities. We also found notable individual variation in participation during IGEs. The daughters of the highest-ranking females were the most-engaged in dyadic intergroup and intragroup aggression, had high "win" rates during intergroup dyadic encounters, and engaged in intergroup multiple-individual interactions at high levels. These findings indicate that they might value their home range more as "potential alphas" compared to other group members. Dominant females were the most engaged in multiple-individual interactions, suggesting that they contribute heavily to collective action that might result in a gain or loss of access to resources. Finally, these two small groups might be equally matched despite the two-individual group size disparity due to individual free-riding strategies. Future research should focus on individual strategies during IGEs to characterize the complex decisions and trade-offs that influence participation.
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Affiliation(s)
- Kathleen M McGuire
- Department of Anthropology, University of Colorado Boulder, Boulder, CO, 80302, USA.
| | - Michelle L Sauther
- Department of Anthropology, University of Colorado Boulder, Boulder, CO, 80302, USA
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3
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Fighting force and experience combine to determine contest success in a warlike mammal. Proc Natl Acad Sci U S A 2022; 119:e2119176119. [PMID: 35700363 PMCID: PMC9231503 DOI: 10.1073/pnas.2119176119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Intergroup conflict has been proposed as a major influence in social evolution. Understanding how intergroup contests exert selection on group living requires determining what properties of groups and their members drive contest success. We analyzed 19 y of data on intergroup fighting in wild banded mongooses to disentangle the factors that determine victory. Two factors, the number of males in the group and the age of the oldest “senior” male, most strongly influence the probability of victory. Senior males may be a benefit because of their disproportionate fighting experience. As in human societies, strength in numbers and the presence of key individuals are critical for success in violent intergroup contests, perhaps influencing selection on individual life history and social behavior. Conflicts between social groups or “intergroup contests” are proposed to play a major role in the evolution of cooperation and social organization in humans and some nonhuman animal societies. In humans, success in warfare and other collective conflicts depends on both fighting group size and the presence and actions of key individuals, such as leaders or talismanic warriors. Understanding the determinants of intergroup contest success in other warlike animals may help to reveal the role of these contests in social evolution. Using 19 y of data on intergroup encounters in a particularly violent social mammal, the banded mongoose (Mungos mungo), we show that two factors, the number of adult males and the age of the oldest male (the “senior” male), have the strongest impacts on the probability of group victory. The advantage conferred by senior males appears to stem from their fighting experience. However, the galvanizing effect of senior males declines as they grow old until, at very advanced ages, senior males become a liability rather than an asset and can be evicted. As in human conflict, strength in numbers and the experience of key individuals combine to determine intergroup contest success in this animal society. We discuss how selection arising from intergroup contests may explain a suite of features of individual life history and social organization, including male eviction, sex-assortative alloparental care, and adult sex ratio.
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Glowacki L, McDermott R. Key individuals catalyse intergroup violence. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210141. [PMID: 35369758 DOI: 10.1098/rstb.2021.0141] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Intergroup violence is challenging to understand: why do individuals cooperate to harm members of other groups when they themselves may be killed or injured? Despite progress in understanding the evolutionary and proximate mechanisms that underlie violence, we still have little insight into the processes that lead to the emergence of coalitionary aggression. We argue that an overlooked component is the presence of individuals who have a crucial role in initiating violence. In instigating intergroup violence, these key individuals may expect to face lower costs, receive greater benefits, or garner benefits that have a greater value to them than others. Alternatively, key individuals may be motivated by individual traits such as increased boldness, propensity for aggression or exploratory behaviour. Key individuals catalyse the emergence of coalitionary violence through one of several processes including altering the costs and benefits that accrue to others, paying a greater share of the startup costs, signalling privileged knowledge, or providing coordination, among other factors. Here we integrate diverse lines of empirical research from humans and non-human animals demonstrating that inter-individual variation is an important factor in the emergence of intergroup violence. Focusing on the role of key individuals provides new insights into how and why violence emerges. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
| | - Rose McDermott
- Political Science, Brown University, Providence, RI, USA
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Smith JE, Fichtel C, Holmes RK, Kappeler PM, van Vugt M, Jaeggi AV. Sex bias in intergroup conflict and collective movements among social mammals: male warriors and female guides. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210142. [PMID: 35369756 DOI: 10.1098/rstb.2021.0142] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Intergroup conflict is a major evolutionary force shaping animal and human societies. Males and females should, on average, experience different costs and benefits for participating in collective action. Specifically, among mammals, male fitness is generally limited by access to mates whereas females are limited by access to food and safety. Here we analyse sex biases among 72 species of group-living mammals in two contexts: intergroup conflict and collective movements. Our comparative phylogenetic analyses show that the modal mammalian pattern is male-biased participation in intergroup conflict and female-biased leadership in collective movements. However, the probability of male-biased participation in intergroup conflicts decreased and female-biased participation increased with female-biased leadership in movements. Thus, female-biased participation in intergroup conflict only emerged in species with female-biased leadership in collective movements, such as in spotted hyenas and some lemurs. Sex differences are probably attributable to costs and benefits of participating in collective movements (e.g. towards food, water, safety) and intergroup conflict (e.g. access to mates or resources, risk of injury). Our comparative review offers new insights into the factors shaping sex bias in leadership across social mammals and is consistent with the 'male warrior hypothesis' which posits evolved sex differences in human intergroup psychology. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
- Jennifer E Smith
- Biology Department, Mills College, 5000 MacArthur Boulevard, Oakland, CA 94631, USA
| | - Claudia Fichtel
- Behavioral Ecology and Sociobiology Unit, German Primate Center, Leibniz Institute for Primate Research, Göttingen, Germany
| | - Rose K Holmes
- Biology Department, Mills College, 5000 MacArthur Boulevard, Oakland, CA 94631, USA
| | - Peter M Kappeler
- Behavioral Ecology and Sociobiology Unit, German Primate Center, Leibniz Institute for Primate Research, Göttingen, Germany.,Department Anthropology/Sociobiology, University of Göttingen, Göttingen, Germany
| | - Mark van Vugt
- Department of Experimental and Applied Psychology, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Adrian V Jaeggi
- Institute of Evolutionary Medicine, University of Zurich, Zurich, Switzerland
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Morris-Drake A, Kennedy P, Braga Goncalves I, Radford AN. Variation between species, populations, groups and individuals in the fitness consequences of out-group conflict. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210148. [PMID: 35369741 PMCID: PMC8977661 DOI: 10.1098/rstb.2021.0148] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Out-group conflict is rife in the natural world, occurring from primates to ants. Traditionally, research on this aspect of sociality has focused on the interactions between groups and their conspecific rivals, investigating contest function and characteristics, which group members participate and what determines who wins. In recent years, however, there has been increasing interest in the consequences of out-group conflict. In this review, we first set the scene by outlining the fitness consequences that can arise immediately to contest participants, as well as a broader range of delayed, cumulative and third-party effects of out-group conflict on survival and reproductive success. For the majority of the review, we then focus on variation in these fitness consequences of out-group conflict, describing known examples both between species and between populations, groups and individuals of the same species. Throughout, we suggest possible reasons for the variation, provide examples from a diverse array of taxa, and suggest what is needed to advance this burgeoning area of social evolution. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
- Amy Morris-Drake
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Patrick Kennedy
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Ines Braga Goncalves
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Andrew N Radford
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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García MG, de Guinea M, Bshary R, van de Waal E. Drivers and outcomes of between-group conflict in vervet monkeys. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210145. [PMID: 35369750 PMCID: PMC8977665 DOI: 10.1098/rstb.2021.0145] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Neighbouring groups compete over access to resources and territories in between-group encounters, which can escalate into between-group conflicts (BGCs). Both the ecological characteristics of a territory and the rival's fighting ability shape the occurrence and outcome of such contests. What remains poorly understood, however, is how seasonal variability in the ecological value of a territory together with fighting ability related to the likelihood of between-group encounters and the extent to which these escalate into conflicts. To test this, we observed and followed four vervet monkey groups in the wild, and recorded the group structure (i.e. size, composition), the locations and the outcomes of 515 BGCs. We then assessed key ecological measures at these locations, such as vegetation availability (estimated from Copernicus Sentinel 2 satellite images) and the intensity of usage of these locations. We tested to what extent these factors together influenced the occurrence and outcomes of BGCs. We found that the occurrence of BGCs increased at locations with higher vegetation availability relative to the annual vegetation availability within the group's home territory. Also, groups engaging in a BGC at locations far away from their home territory were less likely to win a BGC. Regarding group structure, we found that smaller groups systematically won BGCs against larger groups, which can be explained by potentially higher rates of individual free-riding occurring in larger groups. This study sheds light on how the ecology of encounter locations in combination with a group's social characteristics can critically impact the dynamics of BGCs in a non-human primate species. This article is part of the theme issue ‘Intergroup conflict across taxa’.
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Affiliation(s)
- Miguel Gareta García
- Inkawu Vervet Project, Mawana Game Reserve, KwaZulu Natal 3115, South Africa.,Department of Eco-Ethology, Faculty of Biology, University of Neuchâtel, Rue Emile Argand 11, Neuchâtel 2000, Switzerland
| | - Miguel de Guinea
- Movement Ecology Laboratory, Alexander Silverman Institute of Life Sciences, Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Redouan Bshary
- Inkawu Vervet Project, Mawana Game Reserve, KwaZulu Natal 3115, South Africa.,Department of Eco-Ethology, Faculty of Biology, University of Neuchâtel, Rue Emile Argand 11, Neuchâtel 2000, Switzerland
| | - Erica van de Waal
- Inkawu Vervet Project, Mawana Game Reserve, KwaZulu Natal 3115, South Africa.,Department of Ecology and Evolution, Faculty of Biology and Medicine, University of Lausanne, Lausanne 1015, Switzerland
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Green PA, Briffa M, Cant MA. Assessment during Intergroup Contests. Trends Ecol Evol 2020; 36:139-150. [PMID: 33187729 DOI: 10.1016/j.tree.2020.09.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 09/24/2020] [Accepted: 09/25/2020] [Indexed: 12/11/2022]
Abstract
Research on how competitors assess (i.e., gather information on) fighting ability and contested resources, as well as how assessment impacts on contest processes and outcomes, has been fundamental to the field of dyadic (one-on-one) contests. Despite recent growth in studies of contests between social-living groups, there is limited understanding of assessment during these intergroup contests. We adapt current knowledge of dyadic contest assessment to the intergroup case, describing what traits of groups, group members, and resources are assessed, and how assessment is manifested in contest processes (e.g., behaviors) and outcomes. This synthesis helps to explain the role of individual heterogeneity in assessment and how groups are shaped by the selective pressure of contests.
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Affiliation(s)
- P A Green
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn TR10 9FE, UK.
| | - M Briffa
- School of Biological and Marine Sciences, Plymouth University, Drake Circus, Plymouth PL3 8AA, UK
| | - M A Cant
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn TR10 9FE, UK
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Van Belle S, Grueter CC, Furuichi T. Dynamics of Intergroup Relationships in Primates: Introduction to the Special Issue. INT J PRIMATOL 2020. [DOI: 10.1007/s10764-020-00159-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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