Ancient ground squirrels prove to belong to a present-day species
Members of the Faculty of Biology of the Lomonosov Moscow State University have studied arctic ground squirrels, inhabiting the Indigirka river basin, and found out that their relatives now inhabit Kamchatka. The scientists have shared with the research results in an article, published in Scientific Reports journal.
Beringian ground squirrels are model organisms, used by scientists for studies of trans-Beringian connections (namely, connections between the Old and New Worlds, established at existence time of the terrestrial Bering Land Bridge at the site of the Bering Strait). Studies of so called arctic ground squirrels, inhabiting the Indigirka river basin, Urocitellus glacialis, have revealed new data, concerning trans-Beringian connections. This fossil species was described by Boris Vinogradov, a Soviet zoologist. The description was made on the basis of three carcasses, found in 1946 by unnamed prisoners of GULAG in vertical excavations (shafts) at a depth of 12.5 meters. Preservation of the mummified carcasses of ground squirrels was so good that even ectoparasites (lice) were found in their hair. It's a unique case as actually no hair coat is usually preserved.
Later on a biologist named Igor Gromov, paid attention to the fact that fossils of Citellus glacialis resemble Beringian ground squirrels, inhabiting Alaska, but not northeastern Asia. It became a step up towards studying the glacialis form with the help of molecular genetic methods. The scientists were interested in conducting this research even in the 90-s, however, lack of any experience of operating with ancient DNA among Russian scientists at that time was a formidable obstacle on this way. The complexity of such DNA sequence lies in the fact that DNA degradates with time as a result of dehydration of carcasses, low temperatures or strong salt content. That's why special processing of ancient DNA before its studying is necessary. Marina Faerman-Arkchangelskaya, who graduated from the Anthropology Department of the Lomonosov Moscow State University, currently working at the Hebrew University of Jerusalem, helped the scientists to solve this problem. She showed the Moscow colleagues how to work with ancient DNA and sequenced cytochrome b gene in the U. glacialis paratype. The substance has been extracted from tissue samples of a ground squirrel, so that one could estimate degree of relationship with present-day representatives, basing on this gene. She also organized dating the sample on the new device – AMS (Accelerator mass spectrometer), started working in Novosibirsk. It allows to date, basing on tissue microsamples, what prevents destroying the sample. In usual devices you need a sample at the rate of 5 grams of carbon, what means a whole skull of a ground squirrel or a dog shoulder bone. Consequently, in cases of small animals you take the larger half of a sample for dating. The analysis results show that the U. glacialis form is three times older than supposed to be – it's 30 000-year-old.
The scientists have conducted extraction and sequence of all present-day and another three fossil samples in Russia. The U. Glacialis species has proved to be very near to present-day Beringian ground squirrels (Urocitellus parryii), however, at that moment specialists knew its closest relatives only from the New World, from the Alaska Peninsula. The scientists have also established that Beringian ground squirrels colonized Eurasia at least twice. It was likely connected with glaciation, before which ground squirrels managed to distribute in Asia from America. Later they became extinct in Asia cause of cooling, and after warming a new part of ground squirrels came from Alaska.
Nikolai Formozov, a Leading researcher in the Laboratory of Vertebrate Behavior, existing at the Department of Vertebrate Zoology of the Faculty of Biology at the Lomonosov Moscow State University and the article author shares: "In the course of the work we ask ourselves if there are somewhere descendants of the first colonization wave in Eurasia. Kamchatka was the most appropriate region from this point of view but we didn't have substances from there at that time. But suddenly we got unexpected support. Igor Shpilenok, a famous blogger and photographer, was busy with months-long photographic surveying of animals in the Kronotsky Nature Reserve. Once the Moscow researchers reached out to him and asked to assist in gathering tissue samples of ground squirrels, then a fox, named Alisa, inhabited nearby Igor, began to bring ground squirrels to the doorstep of his lodge. Already first samples, gathered by Alisa, precisely proved the hypothesis – ground squirrels from Kamchatka appeared to be close relatives of the glacialis form. The fox was wilde bur quite closely communicated with people and sometimes brought ground squirrels as they are an easy target in that places. Probably, it's a trust mark, like when cats bring caught mice to their masters and get surprised that they are reluctant to eat mice."
The scientists notice that their project substantially contributes to understanding trans-Beringian connections and dispersal routes of various animals in the Pleistocene in northeastern Asia.
The project has been done in cooperation with the scientists from the Ministry of Healthcare of the Russian Federation; I.D. Papanin Institute for Biology of Inland Water, Russian Academy of Sciences; Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences; Zoological Institute, Russian Academy of Sciences; Institute of Biological Problems of the North, Far-East Branch of the Russian Academy of Sciences; Diamond and Precious Metals Geology Institute of the Siberian Branch of the Russian Academy of Sciences; Penza State University, Weizmann Institute of Science and Hebrew University of Jerusalem, Israil.