MBE Advance Access published online on October 17, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn239
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Research Article |
Horse Domestication and Conservation Genetics of the Przewalski's Horse Inferred from Sex Chromosomal and Autosomal Sequences
1 Department of Biology, The Pennsylvania State University, University Park, PA 16802
2 Conservation and Research for Endangered Species, San Diego Zoological Society
* Corresponding author 305 Wartik Lab, Penn State University, University Park, PA 16802, Tel: (814)863-1619, Fax: (814)865-9131, E-mail: kdm16{at}psu.edu.
Received for publication June 11, 2008. Revision received October 6, 2008. Revision received October 13, 2008. Accepted for publication October 13, 2008.
Despite their ability to interbreed and produce fertile offspring, there is continued disagreement about the genetic relationship of domestic horse (Equus caballus) to its endangered wild relative, the Przewalski's horse (Equus przewalskii). Analyses have differed as to whether or not Przewalski's horse is placed phylogenetically as a separate sister group to domestic horses. Because Przewalski's horse and domestic horse are so closely related, genetic data can also be used to infer domestication-specific differences between the two. To investigate the genetic relationship of Przewalski's horse to domestic horse and to address whether evolution of domestic horse is driven by males or females, five homologous introns (a total of 
3 kb) were sequenced on the X and Y chromosomes in two Przewalski's horses and three breeds of domestic horses: Arabian horse, Mongolian domestic horse, and Dartmoor pony. Five autosomal introns (a total of 6 kb) were sequenced for these horses as well. The sequences of sex chromosomal and autosomal introns were used to determine nucleotide diversity and the forces driving evolution in these species. As a result, X chromosomal and autosomal data do not place the Przewalski's horses in a separate clade within phylogenetic trees for horses, suggesting a close relationship between domestic and Przewalski's horses. It was also found that there was a lack of nucleotide diversity on the Y chromosome and higher nucleotide diversity than expected on the X chromosome in domestic horses as compared to the Y chromosome and autosomes. This supports the hypothesis that very few male horses along with numerous female horses founded the various domestic horse breeds. Patterns of nucleotide diversity among different types of chromosomes were distinct for Przewalski's in contrast to domestic horses, supporting unique evolutionary histories of the two species.
Key Words: Przewalski's horse • horse domestication • nucleotide diversity • conservation genetics
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