This is excellent news that an international team announced on April 26, 2021 in the review Nature Communications. The last populations of Sumatran rhinoceros (Dicerorhinus sumatrensis) suffer only from a low level of inbreeding.
A critically endangered species
The International Union for Conservation of Nature counts only 30 mature Sumatran rhinos in the world. The species is also critically endangered and it is one of the most endangered mammal species in the world. “The population size (…) is estimated to have declined by around 70% over the past 20 years due to poaching and habitat change“, says the study. Recent reports also highlighted health problems in these animals and fertility. Scientists feared that these phenomena were the result of high inbreeding in populations still present. In this new study , the researchers sequenced the genome of 21 modern rhinos or “historic” specimens from museums over 100 years old. 16 specimens represented contemporary populations of Borneo, Sumatra and the Malay Peninsula (a recently extinct population) In this way, the authors were able to assess the consanguinity which affects populations, but also the frequency of certain mutations which could prove to be deleterious for the survival of the species.
No inbreeding … for the moment
The researchers were pleasantly surprised by some of the results obtained.
“To our surprise, we found relatively low levels of inbreeding and great genetic diversity in the current populations of Borneo and Sumatra.“, noted in a press release Johanna von Seth, one of the main authors of the study. This phenomenon could be explained by the relatively recent decline of these populations. Inbreeding has not yet had time to settle in According to the authors of this study, this is good news: there is still time to save the species by preserving its genetic diversity. And we must act quickly and not claim victory too quickly: “the population of the Malay Peninsula experienced an increase in inbreeding shortly before their demise“The study reveals. In addition, genomic analyzes have provided disturbing news: potentially harmful mutations have been found in the DNA of some animals.”Unless populations start to increase in size, there is a high risk that inbreeding levels will start to rise and, as a result, genetic diseases will become more common.“, warns Nicolas Dussex, co-author of this study.
Two sub-populations treated as one set?
An increase in the size of these populations would be the ideal solution to save the populations of Borneo and Sumatra without any problem, but the challenge is considerable. Transfers of rhinos between populations and the use of artificial insemination can also be solutions to save the entire species which consists of two subspecies: Sumatra (DsSumatrensis) and Borneo (Ds harrissoni). “Given the high risk of Sumatran rhino extinction, one could argue that the remaining populations should be managed as a metapopulation (a set, editor’s note), because increasing the evolutionary potential and chances of survival of the species through genetic rescue may outweigh the value of maintaining evolutionary lines“, explain the scientists.”With less than 100 individuals remaining, there have been recent proposals to manage the species as a single unit and to increase gene flow through translocation or exchange of gametes from different populations.“, also underlines the study. But precautions will have to be taken anyway if the species were indeed to be managed as a single group: the transferred individuals must not present mutations which could threaten the host population.
“With little evidence of recent inbreeding in the two surviving populations and with few fixed deleterious alleles, the long-term survival of the Sumatran rhino does not appear to be immediately threatened by damaging genetic factors characteristic of small populations, rejoice the authors of this new study. However, given the extremely small size of the surviving populations in Borneo and Sumatra, it seems inevitable that inbreeding will increase in the near future.“if the situation does not improve.