2023-06-12 19:43:03
Maasai giraffes, also known as Kilimanjaro giraffes, separated geographically by the Great Rift Valley, the great geological fracture of more than 4,800 km in a north-south direction located in eastern Africa, have not interbred or exchanged genetic material in over a thousand years and, in some cases, hundreds of thousands of years. Researchers from Pennsylvania State University (USA) warn that the finding implies that these animals are more threatened than previously thought.
Giraffe populations have declined rapidly in the last thirty years, with fewer than 100,000 individuals remaining worldwide. The number of Maasai giraffes, a species found in Tanzania and southern Kenya that is listed as endangered by the International Union for Conservation of Nature (IUCN), has declined by about 50% over this period due to illegal hunting and other human activities that invade their habitat. Only about 35,000 copies remain.
“The habitat of Maasai giraffes is highly fragmented, in part due to the rapid expansion of the human population in East Africa in the last 30 years and the consequent loss of wildlife habitats,” say the researchers, who have published their results in the magazine ‘Ecology and Evolution’. Furthermore, “the Great Rift Valley runs through eastern Africa, and its steep cliff faces are formidable barriers to wildlife migration.”
The team looked at the genomes of 100 Maasai giraffes to determine whether populations on either side of the rift interbred with each other in the recent past, which has important conservation implications.
bad climbers
According to researchers, giraffes are notoriously poor climbers. Using high-resolution satellite data, they found only two places where the angle of the rift slopes was shallow enough for them to climb, but there are no reports that they actually did. To better understand the historical exchange of genetic information, the researchers used the nuclear genome, which includes genetic information passed down by both parents, and the mitochondrial genome, which includes information passed down only through the maternal line.
“Interbreeding between different populations results in the exchange of genetic information, often called gene flow, and is generally considered beneficial because it can enhance overall genetic diversity and help protect small populations against disease and other threats,” he said. Lan Wu-Cavener, a research assistant professor of biology and a member of the research team. “To understand the potential flow of genes through the rift, we sequenced the more than 2 billion base pairs that make up the complete nuclear genome, as well as the more than 16,000 base pairs that make up the complete mitochondrial genome.”
The researchers identified several gene blocks within the mitochondrial genome that are generally inherited together, what researchers call haplotypes, in the two populations and performed network analysis based on patterns of similarity between those haplotypes. They found that giraffes on the east side of the rift did not have overlapping haplotypes with giraffes on the west side of the rift, suggesting that females have not migrated through the rift to breed in the last 250,000-300,000 years.
“Female-mediated gene flow between the two populations hasn’t happened in hundreds of thousands of years, if ever,” Cavener says. “Originally we thought that one population had been founded and then some individuals crossed over to the other side of the rift to establish the second population. But now we think that the two populations were founded independently more than 200,000 years ago.
Analysis of the nuclear genome suggests that gene flow through male movement may have occurred as little as a thousand years ago. The researchers plan to take additional animal samples from both populations to better understand when and why this gene flow might have stopped.
“Taken together, these results suggest that the giraffe populations on each side of the rift are genetically distinct, with each population having less genetic diversity than if they were a larger interconnected population,” Cavener says. “There is very little chance of giraffes crossing the rift on their own, and translocation is very impractical with giraffes. This suggests that Maasai giraffes are more threatened than previously thought, and that conservation efforts for each population need to be considered in an independent but coordinated manner. We hope that the Tanzanian and Kenyan governments will increase protection of these giraffes and their habitats, especially given the recent increase in poaching in the area.”
Consanguinity
The researchers also found alarmingly high indicators of inbreeding, a process that decreases genetic diversity and general population fitness, on both the eastern and western sides of the rift. The researchers plan to continue studying Maasai giraffe populations on both sides of the rift, including those that are particularly isolated, to better understand any dangers they face due to inbreeding. They also plan to investigate how giraffes move between groups on the eastern side of the rift, where habitat is particularly fragmented, to better understand how to prioritize conservation efforts to maintain connectivity between them.
The team also intends to use genetics to clarify how Maasai giraffes reproduce, a question of “vital importance” to “guide our efforts to protect and conserve these majestic and charismatic animals.”
#survival #giraffes #threatened #great #rift #divides #Africa