Wildebeest suffer genetically from blocked migration routes

The ground shakes and dust fills the air as massive herds of animals stampede across the African savanna, navigating rivers teeming with predators such as lions, hyenas, and crocodiles.

This spectacle, often presented by David Attenborough, Disney, and National Geographic, is the annual migration of 1.3 million wildebeest through Tanzania’s Serengeti and Kenya’s Masai Mara. 

The event not only draws hundreds of thousands of tourists but has also secured the Serengeti a place on UNESCO’s World Heritage List. More than just a stunning display, this migration is crucial for maintaining the balance of the ecosystem.

Disrupted migratory routes and wildebeest genetics

However, migrations on this grand scale are now rare in Africa. Modern developments such as roads, fences, farms, and urban expansion have disrupted traditional migratory routes, limiting the wildebeest’s ability to roam freely in search of fresh pastures and water.

According to a recent study led by the University of Copenhagen, these disruptions have negatively impacted the genetic health of the wildebeest populations.

“No one ever knew that this affected the genetics of wildebeest. But our results clearly show that wildebeest populations which no longer migrate, but have historically done so, are simply less genetically healthy than those that continue to migrate. And this weakens their chances of long-term survival,” said senior author Rasmus Heller, an associate professor of biology at the University of Copenhagen.

Genetic degradation of stationary wildebeest populations 

The study details how the genetic degradation of stationary populations manifests across various metrics used to evaluate genetic health in conservation efforts.

“Wildebeest that can no longer migrate have lower genetic diversity, are more genetically isolated and are more inbred. We expect this to lead to lower survival, reduced fertility and other negative effects on fitness,” explained lead author Xiaodong Liu, a postdoctoral fellow in biology at the same university.

Low genetic diversity threatens wildebeest survival

“The long-term consequence is that populations with low genetic diversity are less equipped to cope with the effects of environmental changes. Their evolutionary potential is reduced. So, if climatic changes continue to occur, there isn’t as much genetic variation for them to work with to adapt – which could ultimately threaten their survival,” Heller added.

This groundbreaking study involved the analysis of whole genomes from 121 wildebeest across their range from South Africa to Kenya, marking the first scientific investigation into the genetic effects of migration in this species.

“Because we studied the genomes of many wildebeest from virtually their entire range, we have been able to make a general genetic comparison of migratory versus non-migratory populations. And because we witness a consistent difference across multiple locations, the conclusion is clear.

Indeed, we can say that the overall negative effect is evident in those wildebeest that have been prevented from migrating – regardless of where they live on the continent,” Liu said.

Last great migrations under threat 

With the last great migrations under threat from planned roads and railways, the future of these animals is uncertain. Previously, large wildebeest migrations were more common, but now only a few remain, including the significant migrations in the Serengeti-Mara and the Kalahari.

“However, in Botswana in particular, fencing to protect cattle from coming into contact with migratory wild animals was put up in recent times. Botswana’s Kalahari population declined from roughly 260,000 in the 1970’s to fewer than 15,000 in the late 1980’s. So today, the only remaining large population is that of the Serengeti-Mara. But the Serengeti-Mara migration is also threatened by plans for roads and rail corridors through the area, which worries many,” said co-author Mikkel Sinding, a biologist at the University of Copenhagen.

Wildebeest as a keystone species 

The implications extend beyond individual species, impacting entire ecosystems and economic interests linked to tourism. “The migrations of wildebeest make them a keystone species in ecosystems, as their grazing keeps vegetation healthy, transports and distributes nutrients, while they themselves serve as prey for predators and carrion for scavengers,” explained co-author Joseph O. Ogutu, a senior statistician at the University of Hohenheim. 

“Therefore, it isn’t just the iconic animal that we threaten when we prevent them from migrating – but many other species as well. And to that, we might add the enormous amount of tourism revenue that benefits governments and local communities.”

Preserving natural migration routes 

The researchers hope their findings will lead to further studies on other species and influence policy decisions. 

“The study shows us that wild animal species, for whom migration is an essential part of their biology, struggle to survive in an increasingly human-dominated world, unless special attention is paid to preserving their old and natural migratory routes,” said Heller.

“As such, we hope that people will be more cautious about continuing to disrupt these routes. This concern is not just with regards to wildebeest, but also for other migratory species in Africa and elsewhere. If we want the species to not just exist for, say, the next 50 years, but to thrive and actually survive in the much longer term, we need to halt the genetic decay caused by curtailing their natural migration routes.”

The study is published in the journal Nature Communications.

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