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Inbreeding among white rhino is the enemy within (South Africa)

Tanya Farber, Times Live | January 17, 2020

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Poachers have killed almost 1,800 SA rhino in the past two years, but a first-of-its-kind study has uncovered a threat to the species that is just as deadly yet far more subtle.

German scientists say inbreeding is playing a major part in propelling the southern white rhino towards extinction as fenced reserves have reduced the range over which they roam.

Over 13 years, a team from the Leibniz Institute for Zoo and Wildlife Research collected genetic material from 104 offspring, 37 mothers and 13 males on a game farm near Thabazimbi in Limpopo.

They uncovered three problems that have severely reduced the gene pool:

• Many females stick to the same partner over several consecutive breeding periods, so all their offspring inherit the same genes.

• Rhinos do not avoid reproducing with family members and do not have the same innate inbreeding avoidance of many other species. “Females tended to mate more frequently with closely related males, and one daughter produced a child with her father,” said lead researcher Petra Kretzschmar.

• The reproductive success of males is very unequal, so a few males dominate the gene pool.

All of this was not problematic in the past, but now that all rhino live in fenced reserves, they cannot disperse far enough to avoid inbreeding.

This is the largest scientific study to date on the sexual preferences of white rhino and was published in the journal Evolutionary Applications. “During the colonial period, intense hunting decimated white rhinos to a few individuals. All currently living white rhinos originate from this small founder population,” say the researchers, so the gene pool was already severely compromised.

According to The Boucher Legacy, a rhino protection organisation started by new Proteas coach Mark Boucher, “in the early 1900s there were fewer than 50 white rhinos left in the wild. Today, however, the population numbers are up to about 18,000, but the poaching crisis caused the white rhino population to decline by 15% between 2012 and 2017.”

Now that inbreeding has been confirmed, it is not only poaching that will need to be tackled.

“We need to keep the white rhinos as genetically diverse as possible, if we want to give them a chance to adapt to anthropogenic challenges such as poaching, climate change or diseases,” said Kretzschmar. She and the team did not expect females to keep mating with the same male for several reproductive cycles because long-term bonds with mating partners were previously unknown for rhinos.

“They live on their own and only get together shortly before mating,” said Kretzschmar. “This is why it took us 13 years of field research to uncover the secrets of their mating behaviour.”

In the past, they would range far and wide – away from biological family members. According to the World Wildlife Fund, this behaviour is part of their complex social structures.

Groups of sometimes 14 rhinos may form, notably females with calves. Adult males defend territories of roughly 2.5km², which they mark with vigorously scraped dung piles,” said the WWF.

“The home range for adult females can be more than seven times larger, depending on habitat quality and population density. Males competing for a female may engage in serious conflict, using their horns and massive size to inflict wounds.”

But this complex social structure has been affected by changes in land use. “Today, all remaining rhinos live in modestly sized conservation areas and private game reserves surrounded by fences or human settlements. They cannot disperse far enough,” said Alexandre Courtiol, a senior author of the new study.

So where to from here?

The researchers said SA national parks had been less successful in mitigating the effect of poaching than private game reserves and that the reserves could become “the last refuges for the species”.

They hold a third of the worldwide rhino population and have higher budgets than state-owned conservation areas. According to the researchers, however, “game farmers often pay little attention to genetic diversity”. They “remove or introduce new rhinoceros into their population according to the size of the horns or the origins of the new animals”, without taking the genetic makeup of an individual into account.

The researchers, therefore, recommend permanent monitoring of offspring and their genetic relatedness to rhinos nearby and a regular exchange of unrelated animals between protected areas.

“This is the only way to preserve the long-term genetic heritage of the species,” said Kretzschmar.