Social bonds between unrelated females increase reproductive success in feral horses
Open accessAbstract
In many mammals, females form close social bonds with members of their group, usually between kin. Studies of social bonds and their fitness benefits have not been investigated outside primates, and are confounded by the relatedness between individuals in primate groups. Bonds may arise from kin selection and inclusive fitness rather than through direct benefits of association. However, female equids live in long-term social groups with unrelated members. We present 4 years of behavioral data, which demonstrate that social integration between unrelated females increases both foal birth rates and survival, independent of maternal habitat quality, social group type, dominance status, and age. Also, we show that such social integration reduces harassment by males. Consequently, social integration has strong direct fitness consequences between nonrelatives, suggesting that social bonds can evolve based on these direct benefits alone. Our results support recent studies highlighting the importance of direct benefits in maintaining cooperative behavior, while controlling for the confounding influence of kinship.
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Individuals who maintain long-lasting cooperative relationships have more offspring than those who do not.
“Crucially, there is evidence that individuals who maintain such cooperative relationships have more offspring than those who do not [8,10 -12].”
From Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees (2014) · cites this paper as [10]
Other social mammals form cooperative relationships between unrelated adults that can last over months or years.
“Recent studies show that, in addition to humans, other social mammals form cooperative relationships between unrelated adults, which can last over months or years (chimpanzees [7], baboons [8,9] and feral horses [10]).”
From Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees (2014) · cites this paper as [10]
Individuals who maintain bonds between same-sex adults compared with those who do not, have more offspring, live longer and are healthier.
“Individuals who maintain bonds between same-sex adults compared with those who do not, have more offspring, live longer and are healthier (monkeys: Schülke et al., 2010; feral horses: Cameron et al., 2009; humans: Holt-Lunstad et al., 2010).”
From Endogenous peripheral oxytocin measures can give insight into the dynamics of social relationships: a review (2014) · cites this paper as Cameron et al., 2009
Beneficial bonded relationships can be with kin or between non-kin.
“In some cases these beneficial bonded relationships are with kin, such as between sisters (Silk et al., 2003, 2010), but in some cases they are between non-kin (Cameron et al., 2009; Schülke et al., 2010; humans: Holt-Lunstad et al., 2010).”
From Endogenous peripheral oxytocin measures can give insight into the dynamics of social relationships: a review (2014) · cites this paper as Cameron et al., 2009
Network size and relationship quality are known to have significant impacts on reproduction and fitness in primates and other mammals.
“network size and relationship quality are known to have significant impacts on reproduction and fitness in primates and other mammals (8 -10)”
From Variation in the β-endorphin, oxytocin, and dopamine receptor genes is associated with different dimensions of human sociality (2017) · cites this paper as [10]
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- Authors
- Cameron, E. Z., Setsaas, T. H., & Linklater, W. L.
- Affiliations
- Massey University (NZ)
- University of Pretoria (ZA)
- Victoria University of Wellington (NZ)
- Venue
- Proceedings of the National Academy of Sciences
- Publisher
- National Academy of Sciences
- Published
- 2009-08-18
- Volume
- 106
- Issue
- 33
- Pages
- 13850-13853
- ISSN
- 0027-8424 (ISSN-L)
- 1091-6490
- PMC
- PMC2728983
- OpenAlex
- W2033687430
- Cited by
- 547
- References
- 56
- Citations by year
- 2026: 23 · 2025: 36 · 2024: 28 · 2023: 32 · 2022: 45 · 2021: 52 · 2020: 53 · 2019: 41 · 2018: 27 · 2017: 39 · 2016: 32 · 2015: 28 · 2014: 27 · 2013: 30 · 2012: 28
- FWCI
- 18.73
- Type
- journal article
- Language
- en
- Open access
- green
- www.ncbi.nlm.nih.gov
- Locations
- Proceedings of the National Academy of Sciences (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- eCite Digital Repository (University of Tasmania) (submittedVersion)
- Figshare (submittedVersion, cc-by)
- Topics
- Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
- Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
- Social Sciences › Sociology and Political Science › Evolutionary Game Theory and Cooperation
- Keywords
- social bonds, feral horses, horses, reproductive success, foal survival, direct benefits, kin selection, inclusive fitness, cooperative behavior, male harassment, social integration
- MeSH terms
- Animals, Behavior, Animal, Birth Rate, Cooperative Behavior, Female, Horses, Male, Reproduction, Risk, Sexual Behavior, Animal, Time Factors
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