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Ferreira VHB, Lansade L, Calandreau L, Cunha F, Jensen P. Are domesticated animals dumber than their wild relatives? A comprehensive review on the domestication effects on animal cognitive performance. Neurosci Biobehav Rev 2023; 154:105407. [PMID: 37769929 DOI: 10.1016/j.neubiorev.2023.105407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 10/03/2023]
Abstract
Animal domestication leads to diverse behavioral, physiological, and neurocognitive changes in domesticated species compared to their wild relatives. However, the widely held belief that domesticated species are inherently less "intelligent" (i.e., have lower cognitive performance) than their wild counterparts requires further investigation. To investigate potential cognitive disparities, we undertook a thorough review of 88 studies comparing the cognitive performance of domesticated and wild animals. Approximately 30% of these studies showed superior cognitive abilities in wild animals, while another 30% highlighted superior cognitive abilities in domesticated animals. The remaining 40% of studies found similar cognitive performance between the two groups. Therefore, the question regarding the presumed intelligence of wild animals and the diminished cognitive ability of domesticated animals remains unresolved. We discuss important factors/limitations for interpreting past and future research, including environmental influences, diverse objectives of domestication (such as breed development), developmental windows, and methodological issues impacting cognitive comparisons. Rather than perceiving these limitations as constraints, future researchers should embrace them as opportunities to expand our understanding of the complex relationship between domestication and animal cognition.
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Affiliation(s)
- Vitor Hugo Bessa Ferreira
- IFM Biology, AVIAN Behavioural Genomics and Physiology group, Linköping University, 581 83 Linköping, Sweden; INRAE, CNRS, IFCE, Université de Tours, Centre Val de Loire UMR Physiologie de la Reproduction et des Comportements, 37380 Nouzilly, France.
| | - Léa Lansade
- INRAE, CNRS, IFCE, Université de Tours, Centre Val de Loire UMR Physiologie de la Reproduction et des Comportements, 37380 Nouzilly, France
| | - Ludovic Calandreau
- INRAE, CNRS, IFCE, Université de Tours, Centre Val de Loire UMR Physiologie de la Reproduction et des Comportements, 37380 Nouzilly, France
| | - Felipe Cunha
- IFM Biology, AVIAN Behavioural Genomics and Physiology group, Linköping University, 581 83 Linköping, Sweden
| | - Per Jensen
- IFM Biology, AVIAN Behavioural Genomics and Physiology group, Linköping University, 581 83 Linköping, Sweden.
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Camerlink I, Farish M, Arnott G, Turner SP. Sexual dimorphism in ritualized agonistic behaviour, fighting ability and contest costs of Sus scrofa. Front Zool 2022; 19:13. [PMID: 35279172 PMCID: PMC8917762 DOI: 10.1186/s12983-022-00458-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Accepted: 03/02/2022] [Indexed: 11/24/2022] Open
Abstract
Background Sexual selection has driven sexual dimorphism in agonistic behaviour in many species. Agonistic behaviour is fundamentally altered by domestication and captivity, but it is unclear whether ancestral sex differences remain. We aimed to evaluate the effect of sex on agonistic behaviour, fighting ability and contest costs. We studied this in domestic pigs (Sus scrofa) where aggression compromises welfare, and sexual dimorphism in aggression has been inconclusively demonstrated. Behaviour and physiology of 827 male and female juvenile pigs were studied during resident-intruder tests and dyadic contests at various ages, while accounting for the relative body weight difference between the opponents. Results Males won in 79% of contests against females, even when at a large weight disadvantage. The effect of sex increased with age, with males having a 138 times higher likelihood of winning than females when 13 weeks old. In dyadic contests, males invested more time in non-damaging agonistic display behaviour and took longer before escalating into damaging aggression. Males showed ritualized display that included foaming from the mouth and piloerection of the neck hair, which was nearly always absent in females. Contest costs in terms of contest duration, blood lactate and skin lesions where higher for males, especially when fighting another male. Conclusions Profound sex differences were present for agonistic behaviour, fighting ability and contest costs, and became more pronounced as animals got older. Males invested more in ritualized display before escalating into costly fights, whereas females attacked sooner but also terminated contests more rapidly and with fewer costs. The sexual dimorphism in agonistic behaviour in juvenile domestic pigs is in line with the evolutionary relevance for females’ maternal defence and males’ competition for females.
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Nawroth C, Rosenberger K, Keil NM, Langbein J. Goats ( Capra hircus) From Different Selection Lines Differ in Their Behavioural Flexibility. Front Psychol 2022; 12:796464. [PMID: 35178010 PMCID: PMC8844551 DOI: 10.3389/fpsyg.2021.796464] [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] [Received: 10/16/2021] [Accepted: 12/27/2021] [Indexed: 11/22/2022] Open
Abstract
Given that domestication provided animals with more stable environmental conditions, artificial selection by humans has likely affected animals' ability to learn novel contingencies and their ability to adapt to changing environments. In addition, the selection for specific traits in domestic animals might have an additional impact on subjects' behavioural flexibility, but also their general learning performance, due to a re-allocation of resources towards parameters of productivity. To test whether animals bred for high productivity would experience a shift towards lower learning performance, we compared the performance of dwarf goats (not selected for production, 15 subjects) and dairy goats (selected for high milk yield, 18 subjects) in a visual discrimination learning and reversal learning task. Goats were tested individually in a test compartment and were rewarded by choosing either a white or a black cup presented by the experimenter on a sliding board behind a crate. Once they reached a designated learning criterion in the initial learning task, they were transferred to the reversal learning task. To increase the heterogeneity of our test sample, data was collected by two experimenters at two research stations following a similar protocol. Goats of both selection lines did not differ in the initial discrimination learning task in contrast to the subsequent reversal learning task. Dairy goats reached the learning criterion slower compared to dwarf goats (dairy goats = 9.18 sessions; dwarf goats = 7.74 sessions; P = 0.016). Our results may indicate that the selection for milk production might have affected behavioural flexibility in goats. These differences in adapting to changing environmental stimuli might have an impact on animal welfare e.g., when subjects have to adapt to new environments or changes in housing and management routines.
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Affiliation(s)
- Christian Nawroth
- Research Institute for Farm Animal Biology, Institute of Behavioural Physiology, Dummerstorf, Germany
| | - Katrina Rosenberger
- Swiss Food Safety and Veterinary Office, Centre for Proper Housing of Ruminants and Pigs, Agroscope Tanikon, Ettenhausen, Switzerland
| | - Nina M Keil
- Swiss Food Safety and Veterinary Office, Centre for Proper Housing of Ruminants and Pigs, Agroscope Tanikon, Ettenhausen, Switzerland
| | - Jan Langbein
- Research Institute for Farm Animal Biology, Institute of Behavioural Physiology, Dummerstorf, Germany
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Niego A, Benítez-Burraco A. Are feralization and domestication truly mirror processes? ETHOL ECOL EVOL 2021. [DOI: 10.1080/03949370.2021.1975314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Amy Niego
- PhD Program, Faculty of Philology, University of Seville, C/Palos de la Frontera s/n, 41004 Sevilla, Spain
| | - Antonio Benítez-Burraco
- Department of Spanish, Linguistics, and Theory of Literature (Linguistics), Faculty of Philology, University of Seville, C/Palos de la Frontera s/n, 41004 Sevilla, Spain (E-mail: )
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Rasolofoniaina B, Kappeler PM, Fichtel C. Wild narrow‐striped mongooses use social information to enhance behavioural flexibility. Ethology 2020. [DOI: 10.1111/eth.13123] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Bako Rasolofoniaina
- Dept. Sociobiology/Anthropology Johann‐Friedrich‐Blumenbach Institute of Zoology and Anthropology University of Göttingen Göttingen Germany
| | - Peter M. Kappeler
- Dept. Sociobiology/Anthropology Johann‐Friedrich‐Blumenbach Institute of Zoology and Anthropology University of Göttingen Göttingen Germany
- Behavioral Ecology and Sociobiology Unit German Primate Center Leibniz Institute for Primate Research Göttingen Germany
| | - Claudia Fichtel
- Behavioral Ecology and Sociobiology Unit German Primate Center Leibniz Institute for Primate Research Göttingen Germany
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Sorato E, Zidar J, Garnham L, Wilson A, Løvlie H. Heritabilities and co-variation among cognitive traits in red junglefowl. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2017.0285. [PMID: 30104430 DOI: 10.1098/rstb.2017.0285] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 06/20/2018] [Indexed: 12/15/2022] Open
Abstract
Natural selection can act on between-individual variation in cognitive abilities, yet evolutionary responses depend on the presence of underlying genetic variation. It is, therefore, crucial to determine the relative extent of genetic versus environmental control of these among-individual differences in cognitive traits to understand their causes and evolutionary potential. We investigated heritability of associative learning performance and of a cognitive judgement bias (optimism), as well as their covariation, in a captive pedigree-bred population of red junglefowl (Gallus gallus, n > 300 chicks over 5 years). We analysed performance in discriminative and reversal learning (two facets of associative learning), and cognitive judgement bias, by conducting animal models to disentangle genetic from environmental contributions. We demonstrate moderate heritability for reversal learning, and weak to no heritability for optimism and discriminative learning, respectively. The two facets of associative learning were weakly negatively correlated, consistent with hypothesized trade-offs underpinning individual cognitive styles. Reversal, but not discriminative learning performance, was associated with judgement bias; less optimistic individuals reversed a previously learnt association faster. Together these results indicate that genetic and environmental contributions differ among traits. While modular models of cognitive abilities predict a lack of common genetic control for different cognitive traits, further investigation is required to fully ascertain the degree of covariation between a broader range of cognitive traits and the extent of any shared genetic control.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.
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Affiliation(s)
- Enrico Sorato
- Department of Physics, Chemistry and Biology, IFM Biology, Linköping University, Linköping 581 83, Sweden
| | - Josefina Zidar
- Department of Physics, Chemistry and Biology, IFM Biology, Linköping University, Linköping 581 83, Sweden
| | - Laura Garnham
- Department of Physics, Chemistry and Biology, IFM Biology, Linköping University, Linköping 581 83, Sweden
| | - Alastair Wilson
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK
| | - Hanne Løvlie
- Department of Physics, Chemistry and Biology, IFM Biology, Linköping University, Linköping 581 83, Sweden
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Dougherty LR, Guillette LM. Linking personality and cognition: a meta-analysis. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2017.0282. [PMID: 30104427 DOI: 10.1098/rstb.2017.0282] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/02/2018] [Indexed: 12/21/2022] Open
Abstract
In the past decade, several conceptual papers have linked variation in animal personality to variation in cognition, and recent years have seen a flood of empirical studies testing this link. However, these results have not been synthesized in a quantitative way. Here, we systematically search the literature and conduct a phylogenetically controlled meta-analysis of empirical papers that have tested the relationship between animal personality (exploration, boldness, activity, aggression and sociability) and cognition (initial learning/reversal speed, number of correct choices/errors after standard training). We find evidence for a small but significant relationship between variation in personality and variation in learning across species in the absolute scale; however, the direction of this relationship is highly variable and when both positive and negative effect sizes are considered, the average effect size does not differ significantly from zero. Importantly, this variation among studies is not explained by differences in personality or learning measure, or taxonomic grouping. Further, these results do not support current hypotheses suggesting that that fast-explorers are fast-learners or that slow-explorers perform better on tests of reversal learning. Rather, we find evidence that bold animals are faster learners, but only when boldness is measured in response to a predator (or simulated predator) and not when boldness is measured by exposure to a novel object (or novel food). Further, although only a small sub-sample of papers reported results separately for males and females, sex explained a significant amount of variation in effect size. These results, therefore, suggest that, while personality and learning are indeed related across a range of species, the direction of this relationship is highly variable. Thus further empirical work is needed to determine whether there are important moderators of this relationship.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.
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Affiliation(s)
- Liam R Dougherty
- Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7RB, UK
| | - Lauren M Guillette
- School of Biology, University of St Andrews, St Andrews, Fife KY16 9TH, UK .,Department of Psychology, University of Alberta, Edmonton, Canada AB T6G 2R3
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Assessing spatial learning and working memory in plateau zokors in comparison with plateau pikas and laboratory rats. Acta Ethol 2019. [DOI: 10.1007/s10211-019-00320-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Dudde A, Krause ET, Matthews LR, Schrader L. More Than Eggs - Relationship Between Productivity and Learning in Laying Hens. Front Psychol 2018; 9:2000. [PMID: 30416464 PMCID: PMC6212530 DOI: 10.3389/fpsyg.2018.02000] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 09/28/2018] [Indexed: 12/24/2022] Open
Abstract
The intense selection of chickens for production traits, such as egg laying, is thought to cause undesirable side effects and changes in behavior. Trade-offs resulting from energy expenditure in productivity may influence other traits: in order to sustain energetic costs for high egg production, energy expenditure may be redirected away from specific behavioral traits. For example, such energetic trade-offs may change the hens' cognitive abilities. Therefore, we hypothesized highly productive laying hens to show reduced learning performance in comparison to moderate productive lines. We examined the learning ability of four chicken lines that differed in laying performance (200 versus 300 eggs/year) and phylogenetic origin (brown/white layer; respectively, within performance). In total 61 hens were tested in semi-automated Skinner boxes in a three-phase learning paradigm (initial learning, reversal learning, extinction). To measure the hens' learning performance within each phase, we compared the number of active decisions needed to fulfill a learning criteria (80% correct choices for learning, 70% no responses at extinction) using linear models. Differences between the proportions of hens per line that reached criterion on each phase of the learning tasks were analyzed by using a Kaplan-Meier (KM) survival analysis. A greater proportion of high productive hens achieved the learning criteria on each phase compared to less productive hens (Chi2 3 = 8.25, p = 0.041). Furthermore, high productive hens accomplished the learning criteria after fewer active decisions in the initial phase (p = 0.012) and in extinction (p = 0.004) compared to the less selected lines. Phylogenetic origin was associated with differences in learning in extinction. Our results contradict our hypothesis and indicate that the selection for productivity traits has led to changes in learning behavior and the high productive laying hens possessed a better learning strategy compared to moderate productive hens in a feeding-rewarding context. This better performance may be a response to constraints resulting from high selection as it may enable these hens to efficiently acquire additional energy resources. Underlying mechanisms for this may be directly related to differences in neuronal structure or indirectly to foraging strategies and changes in personality traits such as fearfulness and sociality.
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Affiliation(s)
- Anissa Dudde
- Institute of Animal Welfare and Animal Husbandry, Friedrich-Loeffler-Institut, Celle, Germany
- Department of Animal Behaviour, Bielefeld University, Bielefeld, Germany
| | - E. Tobias Krause
- Institute of Animal Welfare and Animal Husbandry, Friedrich-Loeffler-Institut, Celle, Germany
| | - Lindsay R. Matthews
- School of Psychology, The University of Auckland, Auckland, New Zealand
- Lindsay Matthews Research International, Hamilton, New Zealand
| | - Lars Schrader
- Institute of Animal Welfare and Animal Husbandry, Friedrich-Loeffler-Institut, Celle, Germany
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Guenther A, Brust V. Individual consistency in multiple cognitive performance: behavioural versus cognitive syndromes. Anim Behav 2017. [DOI: 10.1016/j.anbehav.2017.06.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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Houslay TM, Wilson AJ. Avoiding the misuse of BLUP in behavioural ecology. Behav Ecol 2017; 28:948-952. [PMID: 29622923 PMCID: PMC5873244 DOI: 10.1093/beheco/arx023] [Citation(s) in RCA: 185] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/23/2017] [Accepted: 02/10/2017] [Indexed: 12/21/2022] Open
Abstract
Having recognized that variation around the population-level "Golden Mean" of labile traits contains biologically meaningful information, behavioural ecologists have focused increasingly on exploring the causes and consequences of individual variation in behaviour. These are exciting new directions for the field, assisted in no small part by the adoption of mixed-effects modelling techniques that enable the partitioning of among- and within-individual behavioural variation. It has become commonplace to extract predictions of individual random effects from such models for use in subsequent analyses (for example, between a personality trait and other individual traits such as cognition, physiology, or fitness-related measures). However, these predictions are made with large amounts of error that is not carried forward, rendering further tests susceptible to spurious P values from these individual-level point estimates. We briefly summarize the problems with such statistical methods that are used regularly by behavioural ecologists, and highlight the robust solutions that exist within the mixed model framework, providing tutorials to aid in their implementation.
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Affiliation(s)
- Thomas M Houslay
- Centre of Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Conrwall, TR10 9FE, UK
| | - Alastair J Wilson
- Centre of Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Conrwall, TR10 9FE, UK
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Brust V, Guenther A. Stability of the guinea pigs personality – cognition – linkage over time. Behav Processes 2017; 134:4-11. [DOI: 10.1016/j.beproc.2016.06.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 06/07/2016] [Accepted: 06/13/2016] [Indexed: 12/27/2022]
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Dunston EJ, Abell J, Doyle RE, Evershed M, Freire R. Exploring African lion (Panthera leo) behavioural phenotypes: individual differences and correlations between sociality, boldness and behaviour. J ETHOL 2016. [DOI: 10.1007/s10164-016-0473-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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von Engelhardt N, Kowalski GJ, Guenther A. The maternal social environment shapes offspring growth, physiology, and behavioural phenotype in guinea pigs. Front Zool 2015; 12 Suppl 1:S13. [PMID: 26816513 PMCID: PMC4722343 DOI: 10.1186/1742-9994-12-s1-s13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Background Prenatal conditions influence offspring development in many species. In mammals, the effects of social density have traditionally been considered a detrimental form of maternal stress. Now their potential adaptive significance is receiving greater attention.Sex-specific effects of maternal social instability on offspring in guinea pigs (Cavia aperea f. porcellus) have been interpreted as adaptations to high social densities, while the effects of low social density are unknown. Hence, we compared morphological, behavioural and physiological development between offspring born to mothers housed either individually or in groups during the second half of pregnancy. Results Females housed individually and females housed in groups gave birth to litters of similar size and sex-ratios, and there were no differences in birth weight. Sons of individually-housed mothers grew faster than their sisters, whereas daughters ofgroup-housed females grew faster than their brothers, primarily due to an effect on growth of daughters. There were few effects on offspring behaviour. Baseline cortisol levels in saliva of pups on day 1 and day 7 were not affected, but we saw a blunted cortisol response to social separation on day 7 in sons of individually-housed females and daughters of group-housed females. The effects were consistent across two replicate experiments. Conclusions The observed effects only partially support the adaptive hypothesis. Increased growth of daughters may be adaptive under high densities due to increasedfemale competition, but it is unclear why growth of sons is not increased under low social densities when males face less competition from older, dominant males. The differences in growth may be causally linked to sex-specific effects on cortisol response, although individual cortisol response and growth were not correlated, and various other mechanisms are possible. The observed sex-specific effects on early development are intriguing, yet the potential adaptive benefits and physiological mechanisms require further study.
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Affiliation(s)
| | - Gabriele J Kowalski
- Animal Behaviour, Bielefeld University, Morgenbreede 45, 33615 Bielefeld, Germany
| | - Anja Guenther
- Animal Behaviour, Bielefeld University, Morgenbreede 45, 33615 Bielefeld, Germany
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Abstract
Domestication is an evolutionary process during which the biobehavioural profile (comprising e.g. social and emotional behaviour, cognitive abilities, as well as hormonal stress responses) is substantially reshaped. Using a comparative approach, and focusing mainly on the domestic and wild guinea pig, an established model system for the study of domestication, we review (a) how wild and domestic animals of the same species differ in behaviour, emotion, cognition, and hormonal stress responses, (b) during which phases of life differences in biobehavioural profiles emerge and (c) whether or not animal personalities exist in both the wild and domestic form. Concerning (a), typical changes with domestication include increased courtship, sociopositive and maternal behaviours as well as decreased aggression and attentive behaviour. In addition, domestic animals display more anxiety-like and less risk-taking and exploratory behaviour than the wild form and they show distinctly lower endocrine stress responsiveness. There are no indications, however, that domestic animals have diminished cognitive abilities relative to the wild form. The different biobehavioural profiles of the wild and domestic animals can be regarded as adaptations to the different environmental conditions under which they live, i.e., the natural habitat and artificial man-made housing conditions, respectively. Concerning (b), the comparison of infantile, adolescent and adult wild and domestic guinea pigs shows that the typical biobehavioural profile of the domestic form is already present during early phases of life, that is, during early adolescence and weaning. Thus, differences between the domestic and the wild form can be attributed to genetic alterations resulting from artificial selection, and likely to environmental influences during the pre- and perinatal phase. Interestingly, the frequency of play behaviour does not differ between the domestic and wild form early in life, but is significantly higher in domesticated guinea pigs at later ages. Concerning (c), there is some evidence that personalities occur in both wild and domestic animals. However, there may be differences in which behavioural domains – social and sexual behaviour, emotionality, stress-responsiveness – are consistent over time. These differences are probably due to changing selection pressures during domestication.
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