The Great Rift Valley has divided the Masai giraffe, preventing interbreeding & exchange of genetic materials
East Africa’s Masai giraffes may be even more endangered than previously thought, according to a new study.
The Great Rift Valley, a crucial geological feature, has divided the Masai giraffe population into two groups. As a result, these factions have not interbred or exchanged genetic material in more than a thousand years and, in some cases, hundreds of thousands of years, revealed the findings of the research published in the journal Ecology and Evolution on June 12, 2023.
Fragmentation of habitats threatens the survival of the Masai giraffe in the wild.
Researchers at Penn State University looked at the genomes of 100 Masai giraffes to determine if populations on either side of the Rift have crossed over to breed with each other in the recent past.
“Interbreeding among different populations results in the exchange of genetic information — often called gene flow — and is generally considered to be beneficial because it can improve overall genetic diversity and help buffer small populations against disease and other threats,” Lan Wu-Cavener, assistant research professor of biology and a member of the research team, said in a press release.
The population of Masai giraffes, native to Tanzania and southern Kenya, has plummeted to 35,000 from 70,000 in the past three decades and was declared an endangered subspecies by the International Union for Conservation of Nature in 2019.
Habitat loss and fragmentation due to increasing pressure on land for agricultural, pastoral use; poaching for bushmeat and traditional medicine and prolonged droughts are undoubtedly the most severe threats to Masai giraffe survival in the wild.
The remaining Masai giraffes are geographically separated by the steep cliffs of the Gregory Rift escarpments (GRE) in Tanzania and Kenya, dividing them into two populations, one west and one east of the GRE.
Giraffes are notoriously bad climbers, according to the researchers. Using high-resolution satellite data, the team found only two locations where the angle of the Rift’s slopes was shallow enough for giraffes to potentially climb over. Still, there are no actual reports of the giraffes doing so.
To better understand the exchange of genetic information, the researchers used genetic information from both parents and the mitochondrial genome, including genes coming only from the animal’s mother.
The researchers sequenced the more than two billion base pairs that comprise the entire nuclear genome and more than 16,000 base pairs that comprise the entire mitochondrial genome to understand potential gene flow across the Rift. They identified several blocks of genes within the mitochondrial genome that are typically inherited together, which researchers call haplotypes.
The study found that giraffes on the east side of the Rift had no overlapping genes with giraffes on the west side, suggesting that females have not migrated across the Rift to breed in the past 250,000-300,000 years.
There are few prospects of giraffes crossing over the Rift independently, and translocation is highly impractical with giraffes. This suggests that Masai giraffes are more endangered than previously thought, the study said.
The researchers aim to further study the populations of Masai giraffes on both sides of the rift, with a special focus on the particularly isolated ones, to more comprehensively understand the risks posed by inbreeding.
Masai giraffes are important in pollinating plants, dispersing seeds and controlling vegetation. They are also a source of income and livelihood for many communities that benefit from tourism and conservation activities.
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