Shape variation and modularity of skull and teeth in domesticated horses and wild equids.
Abstract: In horses, the morphological changes induced by the process of domestication are reportedly less pronounced than in other species, such as dogs or pigs - although the horses' disparity has rarely been empirically tested. We investigated shape differences and modularity of domesticated horses, Przewalski's horses, donkeys and zebras. Mandibular and tooth shape have been shown to be valuable features for differentiating wild and domesticated forms in some mammals. Results: Both mandible and teeth, show a pattern of shape space occupation analogous to that of the cranium, with domesticated horses occupying a similar extension in shape space to that of wild equids. Only cranial shape data exhibit a tendency to separate domesticated horses and Przewalski's horses from donkeys and zebras. Maximum likelihood model-based tests confirm the horse cranium is composed of six developmental modules, as reported for placental mammals in general. The magnitude of integration in domesticated horse skull was lower than in wild equids across all six cranial modules, and lower values of integration were associated with higher disparity values across all modules. Conclusions: This is the first study that combines different skeletal features for the description and comparison of shape changes in all living equid groups using geometric morphometrics. We support Darwin's hypothesis that the shape variation in the skull of domesticated horses is similar to the shape variation of all wild equid species existing today. Lower magnitudes of module integration are recovered in domesticated horses compared to their wild relatives.
Publication Date: 2018-04-19 PubMed ID: 29713365PubMed Central: PMC5907714DOI: 10.1186/s12983-018-0258-9Google Scholar: Lookup
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Summary
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This research reveals that the changes in the shape of skulls and teeth brought about by domestication are less pronounced in horses as compared to other species, like dogs or pigs. By comparing domesticated horses, Przewalski’s horses, donkeys, and zebras, the study found similarities in the mandible and tooth shapes of both domesticated and wild horses. It confirmed that the horse cranium comprises six developmental modules, and domesticated horses exhibit lower levels of integration in skull development, which are linked to higher disparity values.
Skull and Tooth Shape Analysis
- The research challenges the notion by scientifically testing the disparity in shape variations between domesticated horses and wild equids such as Przewalski’s horses, donkeys, and zebras.
- It was found that both the mandible (lower jaw) and teeth exhibit a similar pattern in domesticated horses as they do in wild equids. This signifies that domestication has not significantly altered these features in horses as might be expected.
Modularity of Horse Cranium
- The study discovered that the horse cranium, like other placental mammals, is composed of six developmental modules. This means that the skull of horses develops in six distinct sections.
- Interestingly, domesticated horses had lower levels of integration across all six cranial modules compared to their wild counterparts. Integration in this context refers to how much the development of one section depends on the development of other sections. Lower levels of integration mean these sections are more independent in their development.
Implications and Findings
- The practical significance of this study lies in its unique combination of different skeletal features to analyze and compare shape differences in all living equid groups using geometric morphometrics – a method in biological anthropology that quantitively analyzes the form of living organisms.
- This research extends support to Darwin’s hypothesis about the similarity in shape variation between the skull of domesticated horses and that of all present-day wild equid species.
- The discovery of lower magnitudes of module integration in domesticated horses compared to wild equids offers valuable insights into the impacts of domestication on horses.
Cite This Article
APA
Heck L, Wilson LAB, Evin A, Stange M, Sánchez-Villagra MR.
(2018).
Shape variation and modularity of skull and teeth in domesticated horses and wild equids.
Front Zool, 15, 14.
https://doi.org/10.1186/s12983-018-0258-9 Publication
Researcher Affiliations
- 1Palaeontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
- 2Palaeontology, Geobiology and Earth Archives Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052 Australia.
- 3Institut des Sciences de l'Evolution - Montpellier, CNRS UMR 5554, Université de Montpellier, IRD, EPHE, 2 place Eugène Bataillon, 34095 Montpellier, France.
- 4Department of Archaeology, Classics and Egyptology, University of Liverpool, Liverpool, UK.
- 1Palaeontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
- 1Palaeontological Institute and Museum, University of Zurich, 8006 Zurich, Switzerland.
Conflict of Interest Statement
Not applicable.Not applicableThe authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
This article includes 65 references
Citations
This article has been cited 15 times.- Geiger M, Sánchez-Villagra MR, Sherratt E. Cranial shape variation in domestication: A pilot study on the case of rabbits.. J Exp Zool B Mol Dev Evol 2022 Dec;338(8):532-541.
- Salamanca-Carreño A, Parés-Casanova PM, Rangel-Pachón DE, Bentez-Molano J, Vélez-Terranova OM. No Morphological Integration of Dorsal Profiles in the Araucanian Horse (Colombia).. Animals (Basel) 2022 Jul 5;12(13).
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- Clauss M, Heck L, Veitschegger K, Geiger M. Teeth out of proportion: Smaller horse and cattle breeds have comparatively larger teeth.. J Exp Zool B Mol Dev Evol 2022 Dec;338(8):561-574.
- Balcarcel AM, Geiger M, Clauss M, Sánchez-Villagra MR. The mammalian brain under domestication: Discovering patterns after a century of old and new analyses.. J Exp Zool B Mol Dev Evol 2022 Dec;338(8):460-483.
- Hanot P, Bayarsaikhan J, Guintard C, Haruda A, Mijiddorj E, Schafberg R, Taylor W. Cranial shape diversification in horses: variation and covariation patterns under the impact of artificial selection.. BMC Ecol Evol 2021 Sep 21;21(1):178.
- Wilson LAB, Balcarcel A, Geiger M, Heck L, Sánchez-Villagra MR. Modularity patterns in mammalian domestication: Assessing developmental hypotheses for diversification.. Evol Lett 2021 Aug;5(4):385-396.
- Balcarcel AM, Veitschegger K, Clauss M, Sánchez-Villagra MR. Intensive human contact correlates with smaller brains: differential brain size reduction in cattle types.. Proc Biol Sci 2021 Jun 9;288(1952):20210813.
- Cirilli O, Pandolfi L, Rook L, Bernor RL. Evolution of Old World Equus and origin of the zebra-ass clade.. Sci Rep 2021 May 12;11(1):10156.
- White HE, Goswami A, Tucker AS. The Intertwined Evolution and Development of Sutures and Cranial Morphology.. Front Cell Dev Biol 2021;9:653579.
- Köhler L, Schulz-Kornas E, Vervuert I, Gittel C, Winter K, Berner D, Gerlach K. Volumetric measurements of paranasal sinuses and examination of sinonasal communication in healthy Shetland ponies: anatomical and morphometric characteristics using computed tomography.. BMC Vet Res 2021 Jan 21;17(1):41.
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- Parés-Casanova PM, Salamanca-Carreño A, Crosby-Granados RA, Bentez-Molano J. A Comparison of Traditional and Geometric Morphometric Techniques for the Study of Basicranial Morphology in Horses: A Case Study of the Araucanian Horse from Colombia.. Animals (Basel) 2020 Jan 10;10(1).
- Stange M, Núñez-León D, Sánchez-Villagra MR, Jensen P, Wilson LAB. Morphological variation under domestication: how variable are chickens?. R Soc Open Sci 2018 Aug;5(8):180993.
- Geiger M, Sánchez-Villagra MR. Similar rates of morphological evolution in domesticated and wild pigs and dogs.. Front Zool 2018;15:23.
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