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Home / Equine Research Bank / Mamm Biol / Insular dwarfism in horses from the Aegean Sea and the Japan...
Mammalian biology = Zeitschrift fur Saugetierkunde2024; 104(4); 345-361; doi: 10.1007/s42991-024-00408-4

Insular dwarfism in horses from the Aegean Sea and the Japanese archipelago.

Abstract: The horse () varieties from Skyros and Rhodes islands (Greece) in the Aegean archipelago are extremely small, reaching shoulder heights of only about 1 m. Furthermore, the Japanese archipelago is home to eight small, native horse breeds. We investigated the evolutionary morphology and provided a review of historical documentations of these horses of cultural interest in Greece and Japan, thus providing a comparison of the independent evolution of small size in islands. We integrate cranial data from historical literature with data from newly gathered and curated skulls and analyse a measurement dataset featuring various domestic and mainland horse breeds and varieties. We use non-invasive imaging to study and measure 3D models of the bony labyrinth, housing the inner ear, and the braincase endocast. When considering the effects of allometry by regressing each PC1 scores (for each set of measurements) with the cranial geometric mean from linear measurements as a body size proxy, we show that size explains a large amount of the shape variation in horse crania, the bony labyrinths and brain endocasts. We found high intrabreed variation in all the analysed datasets. Globally, there are at least 30 distinct horse populations on islands, offering the chance to further study processes of convergence in morphological divergence and evaluate the effect of drift and the environment. Unassigned: The online version contains supplementary material available at 10.1007/s42991-024-00408-4.
© The Author(s) 2024.
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Publication Date: 2024-03-29 PubMed ID: 39070961PubMed Central: PMC11281976DOI: 10.1007/s42991-024-00408-4Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Insular dwarfism has led to extremely small horse varieties in the Aegean Sea islands of Skyros and Rhodes in Greece and in several native breeds in the Japanese archipelago. This study compares the evolutionary morphology of these island horses, investigating how their small sizes evolved independently in different island environments.

Background and Purpose of the Study

  • Some horse populations living on islands, such as Skyros and Rhodes in Greece and multiple breeds in Japan, are notably smaller than mainland horses, a phenomenon known as insular dwarfism.
  • The study aims to explore the evolutionary changes in morphology associated with this size reduction.
  • It also compares horses from two geographically and culturally distinct island groups to understand their independent evolutionary paths.

Methods and Data Collection

  • The research integrates data from historical literature with new, curated skull specimens to provide a comprehensive dataset.
  • Measurements were gathered from various domestic horse breeds and mainland varieties for comparison.
  • Non-invasive imaging techniques were employed to generate 3D models of the bony labyrinth (inner ear structure) and braincase endocasts, which help assess morphological characteristics beyond just external skull shape.
  • The study analyzed cranial data using principal component analyses (PCA) to assess shape variation and to account for allometric effects (changes correlated with size differences).
  • Linear measurements were used to calculate a geometric mean as a proxy for body size, allowing regression of shape variables against size to ascertain how much shape variation is explained by size differences.

Findings and Key Results

  • Size was found to explain a significant amount of cranial shape variation, as well as variation in the structure of the inner ear and braincase, indicating strong allometric effects.
  • Despite being small, horses from these island populations showed high variation within their breeds, indicating diverse morphological traits even among dwarfed individuals.
  • The analysis suggests that insular dwarfism evolved independently in these geographically separate populations, demonstrating convergence driven by island environments.

Broader Implications and Future Directions

  • There are at least 30 known distinct island horse populations worldwide, providing extensive opportunities to study evolutionary processes like morphological convergence (similar evolutionary changes in separate populations) and divergence caused by genetic drift or environmental pressures.
  • This comparative approach can shed light on how island isolation and environmental constraints influence the evolution of mammalian morphology.
  • The research highlights the cultural and biological importance of maintaining and studying these unique island horse populations.
  • Supplementary material accompanying the online paper may provide further detailed data or methods for interested researchers.

Cite This Article

APA
Ming KM, Le Verger K, Geiger M, Schmelzle T, Georgalis GL, Shimbo G, Sasaki M, Ohdachi SD, Sánchez-Villagra MR. (2024). Insular dwarfism in horses from the Aegean Sea and the Japanese archipelago. Mamm Biol, 104(4), 345-361. https://doi.org/10.1007/s42991-024-00408-4

Publication

Mammalian biology = Zeitschrift fur Saugetierkunde
ISSN: 1616-5047
NlmUniqueID: 101242502
Country: Switzerland
Language: English
Volume: 104
Issue: 4
Pages: 345-361

Researcher Affiliations

Ming, Keesha M
  • Department of Paleontology, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland.
Le Verger, Kévin
  • Department of Paleontology, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland.
Geiger, Madeleine
  • Naturmuseum St. Gallen, Rorschacher Strasse 263, 9016 St. Gallen, Switzerland.
Schmelzle, Thomas
  • Department of Paleontology, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland.
Georgalis, Georgios L
  • Department of Paleontology, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland.
  • Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31-016 Kraków, Poland.
Shimbo, Genya
  • Institute of Veterinary Medicine, Hokkaido University, Kita-19, Nishi-8, Kita-Ku, Sapporo, 060-0819 Japan.
Sasaki, Motoki
  • Department of Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Inada-Cho, Obihiro, Hokkaido 080-8555 Japan.
Ohdachi, Satoshi D
  • Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-Ku, Sapporo, 060-0819 Japan.
Sánchez-Villagra, Marcelo R
  • Department of Paleontology, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland.

Conflict of Interest Statement

Conflict of interestThe second author (KLV) is part of the editorial board of Mammalian Biology as an Associate Editor. The remaining authors have no competing interests.

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