Researcher challenges conclusions of Danish sika deer study

DR reports that a researcher believes a study of sika deer and red deer in Denmark was not extensive enough to conclude that the species are not interbreeding.

The study examined 56 sika deer and 22 red deer. Senior adviser Morten Elmeros of Aarhus University, who has advised the Danish Agency for Green Land Transition and Water Environment on sika deer, says researchers should have tested more animals and looked further back in time.

“This study does not look far enough back in time and is not as thorough as some of the Scottish, Czech and Polish studies,” Elmeros said. Those countries have recorded hybrids between the two deer species.

Niels Tommerup, a senior researcher at the University of Copenhagen who led the study, rejects the criticism. He says the number of animals was large enough to conclude that an exchange of genetic material between sika deer and red deer is unlikely.

The 56 sika deer tested represent about 5 per cent of Denmark’s total population of approximately 2,100 animals, including deer living both in the wild and behind fences. According to the report, researchers would have had a 95 per cent probability of finding a hybrid among the animals tested if such mixing were occurring.

Could mixing have happened earlier?

None of the 22 red deer examined had a sika deer parent, according to the study. However, Elmeros says the researchers should also have tested whether the animals were descendants of an earlier hybrid.

Sika deer and red deer can produce fertile offspring, he said. Their descendants could then breed with either parent species, gradually diluting the genetic traces of the original hybrid. Such traces would not necessarily be visible in the study’s analysis.

Tommerup acknowledged that the study did not examine whether hybridisation had occurred in previous generations. He said this was not the purpose of the research because nothing could be done about any earlier mixing.

He also said that no hybrids had been reported in Denmark during the 125 years in which the two species have lived alongside each other in the country’s natural environment.

Study has not yet undergone peer review

Elmeros argues that the researchers should have searched the animals’ genetic material for signs of sika deer genes from earlier generations.

Tommerup published the results before they had undergone peer review because of the time pressure created by decisions concerning sika deer in Denmark. A political decision has been made to eradicate the invasive species from Danish deer parks.

“You cannot produce a scientific article in six months. It takes too long in relation to the decisions that are currently being made,” Tommerup said.

He said the lack of peer review did not affect the study’s conclusions and that the research would eventually undergo the process.