ScienceDaily (Aug. 23, 2011) — An international team of researchers has used ancient DNA to produce compelling evidence that the lack of genetic diversity in modern stallions is the result of the domestication process.
The team, which was led by Professor Michi Hofreiter from the University of York, UK, has carried out the first study on Y chromosomal DNA sequences from extinct ancient wild horses and found an abundance of diversity.
The results, which are published in Nature Communications, suggest the almost complete absence of genetic diversity in modern male horses is not based on properties intrinsic to wild horses, but on the domestication process itself.
Professor Hofreiter said: "Unlike modern female domestic horses where there is plenty of diversity, genetic diversity in male horses is practically zero.
"One hypothesis to explain this suggests modern horses have little Y chromosome diversity because the wild horses from which they were domesticated were also not diverse, due in part to the harem mating system in horses, implying skewed reproductive success of males. Our results reject this hypothesis as the Y chromosome diversity in ancient wild horses is high. Instead our results suggest that the lack of genetic diversity in modern horses is a direct consequence of the domestication process itself."
The Y chromosome is a valuable tool in population genetics, providing a means of directly assessing evolutionary processes that only affect the paternal lineage. So far mitochondrial DNA studies have failed to discover the origin of domestic horses. However, these new Y chromosomal markers now open the possibility of solving this issue in detail.
As part of the study, researchers sequenced Y chromosomal DNA from eight ancient wild horses dating back from around 15,000 to more than 47,000 years and a 2,800-year-old domesticated horse. The results were compared to DNA sequences from Przewalski horses -- the only surviving wild horse population -- and 52 domestic horses, representing 15 modern breeds, which had been sequenced previously.
Domestication of horses dates back approximately 5,500 years. DNA from the skeletal remains of a 2,800-year-old domesticated stallion from Siberia showed that in contrast to modern horses, Y chromosomal diversity still existed several thousand years after the initial domestication event for horses.
Professor Hofreiter said: "This suggests some level of Y chromosomal diversity still existed in domestic horses several thousand years after domestication, although the lineage identified was closely related to the modern domestic lineage."
The study was carried out in Germany by Sebastian Lippold, from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. The results were then independently replicated at the Centre for GeoGenetics at Copenhagen University, Denmark.
Sebastian Lippold said: "Working on ancient Y chromosomal DNA was especially challenging but the only opportunity to investigate Y chromosomal diversity in wild horses. For now we have a first idea of ancestral diversity and therefore a better impression of how much diversity has been lost. Basically this was an important first step and points to the potential the Y chromosomal marker could have in order to further investigate domestication history in horses."
Beth Shapiro, an Assistant Professor in the Department of Biology at the Pennsylvania State University, USA, carried out the analysis and interpretation.
She said: "Most ancient DNA research until now has focused on a different part of the genome -- the mitochondrion -- which is much more abundant in cells and therefore much easier to work with when the DNA is degraded. This has been a serious limitation in ancient DNA research, because we generally only have a good idea what happened along the maternal line. Here, we've been able to look at what happened along the paternal lineage, and, probably unsurprisingly, we see something different going on in males than in females.
"This is exciting stuff, and means we can start getting a much better picture of how events like domestication and climate change have shaped the diversity of organisms alive today."
Researchers had found that Przewalski's horse displays DNA haplotypes not present in modern domestic horses, suggesting they are not ancestral to modern domestic horses. However, while the Y chromosome data supported historic isolation, it also suggests a close evolutionary relationship between the domestic horse and the Przewalski's horse, since the Przewalski Y chromosomal haplotype is more similar to the two domestic ones than any of the ancient wild horse haplotypes.
http://www.sciencedaily.com/releases/2011/08/110823115145.htm
Showing posts with label genetic diversity. Show all posts
Showing posts with label genetic diversity. Show all posts
Wednesday, August 24, 2011
Tuesday, August 16, 2011
Bolstering Genetic Diversity Among Cheetahs
ScienceDaily (Aug. 12, 2011) — Researchers at the Smithsonian Conservation Biology Institute have discovered why older females are rarely able to reproduce -- and hope to use this information to introduce vital new genes into the pool. SCBI scientists and collaborating researchers analyzed hormones, eggs and the uteri of 34 cheetahs at eight institutions, and determined that while the hormones and eggs of cheetahs older than 8 years appear normal, the animals' uterine tracks tend to suffer from abnormal cell growth, infections and cysts that prevent pregnancy.
"Those of us who work with cheetahs have anecdotally noted that it's hard to reproduce older cheetahs, but this is the first time anyone has documented how aging affects the physiology of reproduction in this species," said Adrienne Crosier, SCBI cheetah biologist and lead author of the study in which these results were published. "We were relieved to find that, unlike in other older mammals, the eggs in older cheetahs can produce viable-appearing and growing embryos, which means we may be able to transfer them to younger cheetahs and preserve genetic diversity. If we had found that the eggs were abnormal, we were facing losing genes in an already depleted population."
The researchers' findings were published in a paper titled "Increasing Age Influences Uterine Integrity, But Not Ovarian Function or Oocyte Quality, in the Cheetah (Acinonyx jubatus)" in the online version of the Biology of Reproduction in May and in final form this month. According to the study, approximately 80 percent of adult female cheetahs in North American institutions have never reproduced and the death rate for cheetahs has exceeded the birth rate in 13 of the last 16 years. Lack of genetics can lead to cub mortality and lower cheetahs' resistance to disease.
The next step for SCBI researchers is to extract eggs from a cheetah older than 8 years that has not reproduced and to fertilize the eggs and transfer them to a younger female. Crosier estimates that SCBI will try an embryo transfer within the next two years and said that if it works, it is feasible that someday researchers could do this with wild cheetahs to continue to infuse the population in human care with new genes.
Paper co-author, Pierre Comizzoli, a vertebrate cryobiologist at SCBI, has been collecting and freezing immature eggs and ovarian tissues from felids for the SCBI's Genome Resource Bank, a frozen repository of biological materials that includes sperm and embryos, tissues, blood products and DNA. Researchers are currently able to produce embryos from fresh eggs, but aim to do the same with frozen eggs.
"The work on freezing eggs and ovarian tissues will offer yet another option to preserve the fertility of females, especially long after they are dead," Comizzoli said. "These approaches also allow us to to boost the number of offspring that can be produced from a single individual."
SCBI is one of five centers participating in research to boost the cheetah population in human care as part of the Conservation Centers for Species Survival, also known as C2S2. All five centers collectively manage more than 25,000 acres of land devoted to the survival of threatened species with special needs (including those requiring large land areas, natural group sizes and minimal public disturbance). All five centers maintain a cheetah breeding facility as part of their long-term commitment to cheetah breeding and research. The Smithsonian's National Zoo's Front Royal facility currently houses 10 adult cheetahs and seven cubs. The National Zoo houses three adults.
Cheetahs, the fastest animals on land, are struggling to outpace threats to their survival in the wild. As the result of human conflict, hunting and habitat loss, there are only an estimated 7,500 to 10,000 cheetahs left in the wild. The International Union for Conservation of Nature considers cheetahs a vulnerable species.
The study's authors from the Smithsonian Conservation Biology Institute are Crosier, Comizzoli, David E. Wildt and JoGayle Howard. The other authors are Autumn Davidson, Tom Baker and Linda Munson from the School of Veterinary Medicine, University of California at Davis, and Laurie L. Marker from the Cheetah Conservation Fund.
http://www.sciencedaily.com/releases/2011/08/110812153221.htm
"Those of us who work with cheetahs have anecdotally noted that it's hard to reproduce older cheetahs, but this is the first time anyone has documented how aging affects the physiology of reproduction in this species," said Adrienne Crosier, SCBI cheetah biologist and lead author of the study in which these results were published. "We were relieved to find that, unlike in other older mammals, the eggs in older cheetahs can produce viable-appearing and growing embryos, which means we may be able to transfer them to younger cheetahs and preserve genetic diversity. If we had found that the eggs were abnormal, we were facing losing genes in an already depleted population."
The researchers' findings were published in a paper titled "Increasing Age Influences Uterine Integrity, But Not Ovarian Function or Oocyte Quality, in the Cheetah (Acinonyx jubatus)" in the online version of the Biology of Reproduction in May and in final form this month. According to the study, approximately 80 percent of adult female cheetahs in North American institutions have never reproduced and the death rate for cheetahs has exceeded the birth rate in 13 of the last 16 years. Lack of genetics can lead to cub mortality and lower cheetahs' resistance to disease.
The next step for SCBI researchers is to extract eggs from a cheetah older than 8 years that has not reproduced and to fertilize the eggs and transfer them to a younger female. Crosier estimates that SCBI will try an embryo transfer within the next two years and said that if it works, it is feasible that someday researchers could do this with wild cheetahs to continue to infuse the population in human care with new genes.
Paper co-author, Pierre Comizzoli, a vertebrate cryobiologist at SCBI, has been collecting and freezing immature eggs and ovarian tissues from felids for the SCBI's Genome Resource Bank, a frozen repository of biological materials that includes sperm and embryos, tissues, blood products and DNA. Researchers are currently able to produce embryos from fresh eggs, but aim to do the same with frozen eggs.
"The work on freezing eggs and ovarian tissues will offer yet another option to preserve the fertility of females, especially long after they are dead," Comizzoli said. "These approaches also allow us to to boost the number of offspring that can be produced from a single individual."
SCBI is one of five centers participating in research to boost the cheetah population in human care as part of the Conservation Centers for Species Survival, also known as C2S2. All five centers collectively manage more than 25,000 acres of land devoted to the survival of threatened species with special needs (including those requiring large land areas, natural group sizes and minimal public disturbance). All five centers maintain a cheetah breeding facility as part of their long-term commitment to cheetah breeding and research. The Smithsonian's National Zoo's Front Royal facility currently houses 10 adult cheetahs and seven cubs. The National Zoo houses three adults.
Cheetahs, the fastest animals on land, are struggling to outpace threats to their survival in the wild. As the result of human conflict, hunting and habitat loss, there are only an estimated 7,500 to 10,000 cheetahs left in the wild. The International Union for Conservation of Nature considers cheetahs a vulnerable species.
The study's authors from the Smithsonian Conservation Biology Institute are Crosier, Comizzoli, David E. Wildt and JoGayle Howard. The other authors are Autumn Davidson, Tom Baker and Linda Munson from the School of Veterinary Medicine, University of California at Davis, and Laurie L. Marker from the Cheetah Conservation Fund.
http://www.sciencedaily.com/releases/2011/08/110812153221.htm
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