Massive migrations of wildebeests have fallen in recent years, casualties of human-built fences, roads and cities. Now, analysis of the magnificent animals’ genomes reveals that those barriers are likely to be affecting the genetic diversity of populations blocked from migrating.

Also known as gnus, wildebeests are a type of antelope. There are two species: blue wildebeests, native to southern and eastern Africa, and black wildebeests, found in southern Africa.

Blue wildebeests are abundant and migratory, traveling en masse during huge annual migrations. But black wildebeests are much less abundant; by the early 20th century, just a few hundred remained because of overhunting. They no longer migrate and have a much smaller range than the one they historically occupied, likely a consequence of both hunting and conservation efforts that confined them to game reserves. Nonetheless, conservation has increased their numbers in recent years.

The new study, published in Nature Communications, looked at the genomes of 121 blue and 22 black wildebeests. The analysis revealed that though the two species probably mixed during the late Pleistocene, between about 129,000 and 11,700 years ago, they have distinct genetic structures and do not now interbreed in large numbers.

The analysis also compared the genes of blue wildebeests that migrate and those in regions where migration has been blocked by human-built infrastructure. The migratory blue wildebeests had more genetic diversity, less inbreeding and signs pointing to larger population sizes compared with non-migrating blue wildebeests.

“No one ever knew that [disruptions in migration] affected the genetics of wildebeest,” Rasmus Heller, an associate professor in the University of Copenhagen’s biology department and one of the study’s lead authors, said in a news release. “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.”

To better protect wildebeests, the researchers write, migration routes should be maintained and wildlife managers should consider the potential pitfalls of building infrastructure in important migration areas like the Serengeti-Mara. Other migratory ungulates — hoofed mammals — may be affected in similar ways, they warn.

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