The fate of the Sumatran rhinoceros is uncertain

A new genetic study from the the Centre for Palaeogenetics at Stockholm University shows that the last remaining populations of the Sumatran rhinoceros display surprisingly low levels of inbreeding. However, unless their populations start to increase, the researchers expect rates of inbreeding to rise among the rhinos.  

The Sumatran rhinoceros is one of the most endangered mammal species in the world, with less than 100 individuals remaining. Health issues and low fertility have raised concerns about a potentially high rate of inbreeding.

To investigate, the researchers analyzed the genomes of 16 individuals on Borneo and Sumatra, as well as five specimens from a population on the Malaysian Peninsula that recently went extinct. 

The experts estimated inbreeding levels, genetic variation, and the frequency of harmful mutations for each of the three populations. Furthermore, the researchers used the historical genetic data to explore the genetic consequences of the severe population decline of the past 100 years.

“To our surprise, we found relatively low inbreeding levels and high genetic diversity in the present-day populations on Borneo and Sumatra,” said study co-lead author and PhD student Johanna von Seth.

The researchers theorize that low inbreeding levels found in the present-day rhinos can be attributed to the fact that the substantial decline in population size occurred recently. In other words, inbreeding has not yet caught up with the small population size.

While this indicates that there is still time to preserve the species’ genetic diversity, the researchers also found that there are many potentially harmful mutations hidden in the genomes of the Sumatran rhinos. 

“Unless the populations start increasing in size, there is a high risk that inbreeding levels will start rising, and consequently that genetic diseases will become more common,” said study co-lead author Nicolas Dussex.

The recently extinct Sumatran rhinoceros population on the Malaysian Peninsula serves as a warning of what could soon happen to the remaining populations in Borneo and Sumatra.

According to the study, the Malaysian population experienced a rapid increase in inbreeding levels before it went extinct. The researchers also found changes in the frequency of potentially harmful mutations that are consistent with inbreeding depression, where closely related parents produce offspring that suffer from genetic disease. 

“The Sumatran rhino is by no means out of the woods. But at least our findings provide a path forward, where we might still be able to rescue a large part of the species’ genetic diversity,” said Professor Love Dalén.

The study authors said it is imperative that the population size increases in order to minimize the risk of extinction. They also recommend the exchange of genes between Borneo and Sumatra, either through translocation or artificial insemination. 

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer