EU-funded research sheds light on evolution and selection of pigs and wild boars
Brussels, 14 November 2012
What changes have accumulated in the genome of the pig during its speciation in Eurasia and during its subsequent domestication and selection by humans? An international team of researchers from 12 countries – led by researchers at Wageningen University in The Netherlands, the University of Illinois, and the University of Edinburgh – has sequenced the genomes of several pigs and wild boars and discovered new details of Sus scrofa evolution after the ancestors of the domestic pig, which most resembled today’s wild boars, first emerged in Southeast Asia and gradually migrated across Eurasia. Following this migration, humans independently domesticated the pig in Asia as well as Europe some 10,000 years ago and humans have interacted with pigs since then. This interaction and selection of animals with specific characteristics, has resulted in the wide variety of different breeds seen in Europe and Asia today. This research, funded by a variety of grants including the advanced ERC Grant SelSweep, and European collaborative projects SABRE (FP6) and Quantomics (FP7), is published in the scientific journal Nature on 15 November.
The researchers compared the genome of a common farm pig, Sus scrofa domesticus, with those of ten wild boars – all from different parts of Europe and Asia. They also compared the pig genome with those of the human, mouse, dog, horse and cow. The team reveals some new, unexpected and potentially beneficial similarities between pigs and humans, along with a few distinct differences. Comparisons of Asian and European wild boars revealed significant genetic differences, the result of their separating from one another roughly one million years ago. “They have been separated so long that the Asian and European lineages are almost sub-species now,” says Larry Schook from the University of Illinois and one of the principal investigators of the study. The European and Asian wild boars lost a lot of genetic diversity about 20,000 years ago, likely as a result of a global glaciation event. “We had evidence from previous studies, but those studies focused on the mitochondrial DNA, a small DNA molecule only inherited from the mother,” said Wageningen University professor and ERC grantee Martien Groenen, also a principal investigator on the study. “With the complete genome sequence of multiple wild boars we now have a much clearer picture about these events.”
Some gene families are undergoing relatively fast evolution in the pig, with immune genes and (perhaps not surprisingly) olfactory genes quickly expanding. The pig has more unique olfactory genes than humans, mice or dogs, the researchers report. And while pigs can smell a world of things humans and many other animals can’t (think truffles), their sense of taste is somewhat impaired. Pigs have significantly fewer bitter taste receptor genes than humans, for example, and genes involved in perception of sweet and umami (which humans perceive as meaty) flavours are also different in pigs and humans.
The new analysis also supports the use of the pig in studies of human diseases. “In total, we found 112 positions where the porcine protein has the same amino acid that is implicated in a disease in humans,” the researchers wrote. “By also sequencing the genomes of another 48 pigs, we identified many more gene variants implicated in human disease, further supporting the pig as a valuable biomedical model,” Groenen said. Some of the protein aberrations pigs share with humans are associated with obesity, diabetes, dyslexia, Parkinson’s disease and Alzheimer’s disease, the researchers report.
The new analysis also has important implications for agriculture, particularly since the domestic pig still has an ancestor-like wild cousin on the loose, the researchers said. Unlike the domestic cow, whose ancestors, the aurochs, are now extinct, the porcine lineage has a lot of genetic diversity remaining. “This understanding of the genetic origins of modern pigs is important as we breed pigs to meet growing demand more efficiently and to resist old and emerging diseases,” said Alan Archibald, a professor of The Roslin Institute at the University of Edinburgh and a principal investigator on the study.
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