New research led by scientists at Penn State suggests that giraffes in eastern Africa are facing a greater risk of extinction than previously believed.
The study reveals that populations of Masai giraffes, separated geographically by the Great Rift Valley, have not interbred or exchanged genetic material for over a thousand years, and in some cases, even hundreds of thousands of years. Based on these findings, the researchers recommend treating the two populations separately for conservation purposes and implementing coordinated efforts to manage each population effectively.
The global population of giraffes has significantly declined over the past three decades, with fewer than 100,000 individuals remaining. Masai giraffes, a species found in Tanzania and southern Kenya, are classified as endangered by the International Union for Conservation of Nature (IUCN), with their numbers having declined by approximately 50% in this period due to factors such as illegal hunting and habitat encroachment. Only about 35,000 Masai giraffes now exist.
Dr. Douglas Cavener, the Dorothy Foehr Huck and J. Lloyd Huck Distinguished Chair in Evolutionary Genetics and professor of biology at Penn State, led the research team. He explains that the highly fragmented habitat of Masai giraffes, resulting from rapid human population expansion in East Africa and the geographical barriers posed by the Great Rift Valley, has contributed to their plight. To investigate the potential impact of these factors on gene flow between giraffe populations, the team studied the genomes of 100 Masai giraffes.
Giraffes are not skilled climbers, so the researchers used high-resolution satellite data to identify only two locations along the rift where the slopes were shallow enough for giraffes to potentially cross. However, there have been no reports of giraffes doing so. To understand historical genetic exchange, the researchers employed whole genome sequencing of the nuclear genome and mitochondrial genome. The results, published in the journal Ecology and Evolution, reveal that there has been no overlapping of genetic traits or migration of females across the rift in the past 250,000-300,000 years.
The team identified blocks of genes within the mitochondrial genome, known as haplotypes, that are commonly inherited together. Network analysis based on these haplotypes showed no overlap between giraffes on the east and west sides of the rift, indicating a lack of genetic exchange. According to Cavener, this raises questions about the origin of these populations. It was previously believed that one population had migrated across the rift to establish the other. However, the researchers now speculate that the two populations evolved independently over 200,000 years ago.
Analysis of the nuclear genome suggests that gene flow through the movement of males may have occurred as recently as a thousand years ago. The researchers plan to gather additional samples from both populations to further investigate when and why gene flow ceased.
These findings suggest that the populations of giraffes on each side of the rift are genetically distinct, with lower genetic diversity compared to what would be expected in one interconnected population. Given the difficulties giraffes face in naturally crossing the rift and the impracticality of translocation, the researchers emphasize the need for independent yet coordinated conservation efforts for each population. They hope that Tanzanian and Kenyan governments will enhance protection for Masai giraffes and their habitats, particularly in response to the recent increase in giraffe poaching.
The research team also discovered concerning indications of inbreeding on both sides of the rift, which decreases genetic diversity and overall population fitness. Further studies will explore the risks associated with inbreeding and investigate the movement patterns of giraffes on the fragmented east side of the rift to guide conservation efforts and maintain connectivity between populations.
In addition to Dr. Cavener and Lan Wu-Cavener, the research team includes George Lohay, a postdoctor
al scholar who collected biological samples from wild giraffes in Tanzania, as the first author. The team also includes Associate Research Professor of Biology Derek Lee and academic affiliate in biology Monica Bond, who contributed crucial work on Masai giraffe populations. The project received support from the Penn State Department of Biology, the Eberly College of Science, the Huck Institutes of the Life Sciences, and the Wild Nature Institute.