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Adult-young ratio, a major factor regulating social behaviour of young: a horse study.

Bourjade M, de Boyer des Roches A, Hausberger M - PLoS ONE (2009)

Bottom Line: We found striking variations of aggression rates and spatial relationships related to the adult-young ratio: the lower this ratio, the more the young were aggressive, the more young and adults segregated and the tighter the young bonded to other young.The increase of aggression and the emergence of social segregation in groups with lower proportions of adults could reflect a related decrease of the influence of adults as regulators of the behaviour of young.This social regulation has both theoretical and practical implications for understanding the modalities of the influence of adults during ontogeny and for recommending optimal settings, as for instance, for schooling or animal group management.

View Article: PubMed Central - PubMed

Affiliation: Université de Rennes 1, Laboratoire d'Ethologie Animale et Humaine, Centre National de la Recherche Scientifique, Rennes, France. marie.bourjade@gmail.com

ABSTRACT

Background: Adults play an important role in regulating the social behaviour of young individuals. However, a few pioneer studies suggest that, more than the mere presence of adults, their proportions in social groups affect the social development of young. Here, we hypothesized that aggression rates and social cohesion were correlated to adult-young ratios. Our biological model was naturally-formed groups of Przewalski horses, Equus f. przewalskii, varying in composition.

Methodology/principal findings: We investigated the social interactions and spatial relationships of 12 one- and two-year-old Przewalski horses belonging to five families with adult-young ratios (AYR) ranging from 0.67 to 1.33. We found striking variations of aggression rates and spatial relationships related to the adult-young ratio: the lower this ratio, the more the young were aggressive, the more young and adults segregated and the tighter the young bonded to other young.

Conclusion/significance: This is the first study demonstrating a correlation between adult-young ratios and aggression rates and social cohesion of young individuals in a naturalistic setting. The increase of aggression and the emergence of social segregation in groups with lower proportions of adults could reflect a related decrease of the influence of adults as regulators of the behaviour of young. This social regulation has both theoretical and practical implications for understanding the modalities of the influence of adults during ontogeny and for recommending optimal settings, as for instance, for schooling or animal group management.

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Related in: MedlinePlus

Spatial relationships of young Przewalski horses with their nearest neighbour in relation to adult-young ratios.a- Time spent with either a young neighbour or an adult neighbour, in relation to the adult-young ratio, b- Time spent close to or far from the nearest neighbour, in relation to the adult-young ratio. Time is expressed in percentage of scan-samples recorded in the field. Black triangles: adults; white circles: young; white squares: far from nearest neighbour (farther than 3.5 Horse Body-Length); stars: close to nearest neighbour (less than 0.5 Horse Body-Length). Categories “close” and “far” are not exclusive alternatives. Kendall partial coefficient correlation: * p<0.05, *** p<0.01.
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pone-0004888-g002: Spatial relationships of young Przewalski horses with their nearest neighbour in relation to adult-young ratios.a- Time spent with either a young neighbour or an adult neighbour, in relation to the adult-young ratio, b- Time spent close to or far from the nearest neighbour, in relation to the adult-young ratio. Time is expressed in percentage of scan-samples recorded in the field. Black triangles: adults; white circles: young; white squares: far from nearest neighbour (farther than 3.5 Horse Body-Length); stars: close to nearest neighbour (less than 0.5 Horse Body-Length). Categories “close” and “far” are not exclusive alternatives. Kendall partial coefficient correlation: * p<0.05, *** p<0.01.

Mentions: Adult-young ratios were also negatively correlated to time spent close to young nearest neighbours: the higher the proportion of young, the longer young remained close to their nearest neighbours, especially young neighbours to the detriment of adults (Fig. 2ab; Kendall partial coefficients: time spent at less than 0.5 horse body-length from nearest neighbour, T = −0.44, p<0.05; time spent with a nearest young neighbour, T = −0.44, p<0.05; time spent at more than 3.5 horse body-length from nearest neighbour, T = 0.66, p<0.01; time spent with a nearest adult neighbour, T = 0.44, p<0.05).


Adult-young ratio, a major factor regulating social behaviour of young: a horse study.

Bourjade M, de Boyer des Roches A, Hausberger M - PLoS ONE (2009)

Spatial relationships of young Przewalski horses with their nearest neighbour in relation to adult-young ratios.a- Time spent with either a young neighbour or an adult neighbour, in relation to the adult-young ratio, b- Time spent close to or far from the nearest neighbour, in relation to the adult-young ratio. Time is expressed in percentage of scan-samples recorded in the field. Black triangles: adults; white circles: young; white squares: far from nearest neighbour (farther than 3.5 Horse Body-Length); stars: close to nearest neighbour (less than 0.5 Horse Body-Length). Categories “close” and “far” are not exclusive alternatives. Kendall partial coefficient correlation: * p<0.05, *** p<0.01.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2654111&req=5

pone-0004888-g002: Spatial relationships of young Przewalski horses with their nearest neighbour in relation to adult-young ratios.a- Time spent with either a young neighbour or an adult neighbour, in relation to the adult-young ratio, b- Time spent close to or far from the nearest neighbour, in relation to the adult-young ratio. Time is expressed in percentage of scan-samples recorded in the field. Black triangles: adults; white circles: young; white squares: far from nearest neighbour (farther than 3.5 Horse Body-Length); stars: close to nearest neighbour (less than 0.5 Horse Body-Length). Categories “close” and “far” are not exclusive alternatives. Kendall partial coefficient correlation: * p<0.05, *** p<0.01.
Mentions: Adult-young ratios were also negatively correlated to time spent close to young nearest neighbours: the higher the proportion of young, the longer young remained close to their nearest neighbours, especially young neighbours to the detriment of adults (Fig. 2ab; Kendall partial coefficients: time spent at less than 0.5 horse body-length from nearest neighbour, T = −0.44, p<0.05; time spent with a nearest young neighbour, T = −0.44, p<0.05; time spent at more than 3.5 horse body-length from nearest neighbour, T = 0.66, p<0.01; time spent with a nearest adult neighbour, T = 0.44, p<0.05).

Bottom Line: We found striking variations of aggression rates and spatial relationships related to the adult-young ratio: the lower this ratio, the more the young were aggressive, the more young and adults segregated and the tighter the young bonded to other young.The increase of aggression and the emergence of social segregation in groups with lower proportions of adults could reflect a related decrease of the influence of adults as regulators of the behaviour of young.This social regulation has both theoretical and practical implications for understanding the modalities of the influence of adults during ontogeny and for recommending optimal settings, as for instance, for schooling or animal group management.

View Article: PubMed Central - PubMed

Affiliation: Université de Rennes 1, Laboratoire d'Ethologie Animale et Humaine, Centre National de la Recherche Scientifique, Rennes, France. marie.bourjade@gmail.com

ABSTRACT

Background: Adults play an important role in regulating the social behaviour of young individuals. However, a few pioneer studies suggest that, more than the mere presence of adults, their proportions in social groups affect the social development of young. Here, we hypothesized that aggression rates and social cohesion were correlated to adult-young ratios. Our biological model was naturally-formed groups of Przewalski horses, Equus f. przewalskii, varying in composition.

Methodology/principal findings: We investigated the social interactions and spatial relationships of 12 one- and two-year-old Przewalski horses belonging to five families with adult-young ratios (AYR) ranging from 0.67 to 1.33. We found striking variations of aggression rates and spatial relationships related to the adult-young ratio: the lower this ratio, the more the young were aggressive, the more young and adults segregated and the tighter the young bonded to other young.

Conclusion/significance: This is the first study demonstrating a correlation between adult-young ratios and aggression rates and social cohesion of young individuals in a naturalistic setting. The increase of aggression and the emergence of social segregation in groups with lower proportions of adults could reflect a related decrease of the influence of adults as regulators of the behaviour of young. This social regulation has both theoretical and practical implications for understanding the modalities of the influence of adults during ontogeny and for recommending optimal settings, as for instance, for schooling or animal group management.

Show MeSH
Related in: MedlinePlus