By Will Dunham
April 16 (Reuters) - The largest genomic study of African elephants to date has found that both species - savanna and forest elephants - remain in generally good genetic health despite long-term numerical declines, though some isolated populations are showing worrisome signs of inbreeding and deleterious mutations.
Researchers analyzed the genetic health of African elephants - Earth's largest land animals - by looking at genome data for 181 savanna elephants and 51 forest elephants from
29 locations across 17 countries.
Their genetic health was found to be positive overall because many populations, particularly in a broad swathe of southern Africa, can still roam across large distances and exchange genes. Signs of genetic trouble were detected in elephants cut off from other populations due to factors such as growing human populations, agricultural expansion and infrastructure projects.
"We mostly see the isolation in the populations on the periphery, at the edge of the elephant distribution," said University of Copenhagen evolutionary geneticist Patrícia Pečnerová, lead author of the research published on Thursday in the journal Nature Communications.
"This includes forest and savanna elephants in the northwestern part of Africa like Sierra Leone, Mali and Cameroon, and it includes savanna elephants in Namibia in the southwest and the northeastern-most populations in Eritrea and Ethiopia," Pečnerová said.
About 100 elephants remain in Eritrea, and they live about 250 miles (400 km) from any other elephant population, Pečnerová said. The roughly 300 elephants living at the Babile Elephant Sanctuary in Ethiopia are not completely isolated but inhabit a harsh environment in shrinking pockets of land amid poaching and expanding settlements, Pečnerová said.
"We see the effects of isolation in increasing levels of inbreeding, mating between relatives, which also leads to a loss of genetic variation and can compromise the health of a population. When a population is isolated, it becomes more common to mate with a relative because the options are limited, even if elephants usually avoid mating with relatives," Pečnerová said.
In these populations, the genome data showed an accumulation of moderately deleterious mutations, which can make the elephants less able to adapt to changes in the environment and more vulnerable to diseases.
The story was a bit different for the isolated savanna elephants in West Africa thanks to a small amount of interbreeding with forest elephants that helped bolster genetic diversity. Such "hybridization," however, risks introducing potentially negative genetic traits.
Elephants are found in 37 countries in sub-Saharan Africa, with a majority in the southern part of the continent. They number roughly half a million continent-wide, with savanna elephants representing perhaps 70% of the total.
African elephants have experienced severe population declines due to the ivory trade and habitat loss. A 2024 study documented alarming population declines at numerous sites across Africa from 1964 to 2016, with savanna elephant populations down by about 70% and forest elephant populations down by about 90%.
Savanna elephants, the larger of the two African species, inhabit open grasslands and have outward-curving tusks. Forest elephants, denizens of dense tropical rainforests, have a darker coloration and possess tusks that are straighter and point downward.
"Elephants are among the world's most iconic animals. Both forest and savanna elephants play major ecological roles. They are highly intelligent and socially complex, and they are central to wildlife conservation efforts across Africa," said geneticist and study co-author Alfred Roca of the University of Illinois Urbana-Champaign.
The world's other elephant species, the Asian elephant, is found in fragmented populations across India and Southeast Asia. The current study did not look at that species.
The genetic problems detected among the isolated African elephants are not as dire, the researchers said, as those experienced by the world's heavily inbred last population of woolly mammoths - relatives of today's elephants - that perished about 4,000 years ago on an Arctic Ocean island off Siberia's coast.
The study found that forest elephants showed greater genetic diversity than savanna elephants even though their population is smaller.
"The evolutionary trajectories inferred from the genomes suggest that the forest and savanna elephant lineages split about four million years ago, making them as distinct from one another as lions and tigers are," Roca said.
"For the last million years or more, the forest elephant pattern suggests a higher number of breeding individuals, consistent with their higher genetic diversity," Roca said. "This is also consistent with the high male-male competition that is documented for savanna elephants, which limits the number of reproductively successful males and in turn lowers their genetic diversity."
(Reporting by Will Dunham in Washington, Editing by Rosalba O'Brien)
