Ancient and modern DNA reveal that the distribution and lack of genetic diversity among modern European beavers is largely due to hunting by humans.
The research provides important new insights into the genetic history of the Eurasian beaver Castor fiber. Crucially, it shows that expanding human populations have strongly affected the European beaver for many thousands of years.
The researchers say that centuries of hunting, rather than changing climate conditions since the beginning of the Holocene (or recent) period, account for the lack of genetic diversity, as well as the geographic distribution of genetic diversity, seen in modern European beavers.
Through DNA sequencing, the research team discovered that the Eurasian beaver can be divided into three distinct groups. The two main ones are in western and eastern Europe, with a now extinct, and previously unknown, third group in the Danube basin. This population existed at least 6,000 years ago but went extinct during the transition to modern times.
“While beaver populations have been growing rapidly since the late 19th century when conservation efforts began, genetic diversity within modern beaver populations remains considerably reduced to what was present prior to the period of human hunting and habitat reduction,” says Professor Michi Hofreiter of the University of York biology department.
“In addition, the rapid loss of diversity prior to conservation efforts appears to have established a very strong pattern for the geographic distribution of genetic diversity among present-day beaver populations.”
Beavers have long been an important resource for human populations across the northern continents. Their fur is of exceptional quality, and has been a highly traded commodity. Beavers have also been hunted for meat and for castoreum, an anal gland secretion often used in traditional medicine. Stone engravings at Lake Onega in northern Europe indicate that beavers played a role in ancient human societies from around 3,000-4,000 years ago.
After centuries of human hunting, the Eurasian beaver had disappeared from most of its original range by the end of the 19th century, with only an estimated 1,200 beavers remaining.
The research team set out to discover whether the lack of genetic diversity and strong phylogeography (geographic distribution of genetic diversity) seen today are the result of its near extinction, or already existed prior to the reduction in its range.
To do this, they examined DNA from 48 ancient beaver samples, ranging in age from several hundred to around 11,000 years old, and 152 modern DNA sequences.
Corresponding author Susanne Horn, from the Max Planck Institute for Evolutionary Anthropology, Leipzig, says: “We found that overall there was more genetic diversity in the past. Apparently, already in ancient times an ancient contact zone existed between the eastern and western populations of beavers in the Oder River area. This is close to a present-day contact zone in Germany and Poland.”
Hofreiter adds: “The present-day contact zone was assisted by conservation management and members of the eastern and western population groups meet there today as they did in the past. This suggests that conservation management may, in the long run, help to restore the pre-human impact population structure of threatened species.”
The experimental work took place in Leipzig, Germany. The Max Planck Society and the Volkswagen Foundation supported the study, which appears in Molecular Ecology.
Source: University of York