Fears that the limited genetic diversity in surviving Przewalski’s horses will worsen their chances of survival in the wild because of greater inbreeding are receding.
Genetic analyses reveal that the wild horses reintroduced into the wilderness since 1992 do not show a decreased genetic variability, despite the small breeding populations.
The findings, recently published in the Mongolian Journal of Biological Sciences, will buoy efforts by conservationists working to restore wild populations across the endangered species’ original habitat on the Mongolian steppe.
The Przewalski’s horse (Equus ferus przewalskii) provides one of the great survival stories.
The species was declared extinct in the wild in 1969. It has since been reintroduced to the wild, with about 746 individuals now surviving on the steppe.
However, that population arose from careful breeding decisions made in relation to just a dozen surviving individuals housed in captivity in the early 1900s.
The last small herd had been sighted in 1967, and no further horses were seen for 25 years, until their reintroduction.
Given this limited genetic diversity, there were fears that greater levels of inbreeding would arise among horses returned to the wild. This has not been the case, according to research carried out by scientists in Mongolia and with the Senckenberg Research Institute and Natural History Museum in Germany.
“The current population goes back to a mere 12 horses that produced offspring while kept in zoos – a genetic bottleneck that carries the risk of diseases caused by inbreeding, such as a reduced resistance or shortened life expectancy,” explains Professor Hermann Ansorge, who took part in the study.
“Under these conditions, attempts to reintroduce the Przewalski’s Horses into the wild pose a serious challenge. A species can only react to environmental changes if it has a high level of genetic variability.”
In 1992, the first successful attempts began to reintroduce the Przewalski’s horse to its former homeland.
Today, nearly 750 individual horses can be found there in the wild again.
In recent years, an international team took a closer look at the reintroduced Przewalski’s horses and at historic materials.
The researchers examined a total of 130 skulls covering a period of 110 years.
Comparisons revealed insights into the genetic variability.
“This involves defined manifestations on the skull whose appearance can be differentiated qualitatively,” Ansorge explains.
“For example, these can be small natural openings that serve as passageways for blood vessels or nerves. Differences in the appearance and symmetry of these characteristics allow us to draw conclusions regarding the genetic differences.”
Their work reveals that, contrary to previous assumptions, the reintroduced populations of Przewalski’s horse show a comparatively high genetic diversity.
The study’s lead author and head of the reintroduction program, Dorj Usukhjargal of Hustai National Park in Mongolia, expressed his surprise about the research results.
“We initially expected that, due to the long periods of inbreeding, the populations of Przewalski’s horses might be too closely related genetically to ensure their long-term survival in the wild.”
Usukhjargal says Przewalski’s horses now appear to have much better chances for survival in their natural environment with the animals’ carefully considered selection.
“The horses that are intended for release in the wild must generally have good genetic preconditions; in this regard, we already made a preliminary selection.
“In addition, in the past decades, the zoos and wild animal reserves have improved the genetic diversity of their stock by keeping strict breeding records and engaging in exchange programs.”
According to the study, no indications were found of reduced developmental stability in the reintroduced Przewalski’s horses.
“After the Przewalski’s horse practically went extinct 50 years ago, the chances for the long-term survival of this last wild horse species now look much better than expected,” Ansorge says.
Usukhjargal, Dorj et al. Epigenetic Variability of the Highly Endangered Przewalski’s Horses in Temporal and Geographical Populations. Mongolian Journal of Biological Sciences, [S.l.], v. 18, n. 1, p. 31-40, mar. 2020. ISSN 2225-4994. https://www.biotaxa.org/mjbs/article/view/60628/60358