Over the past three decades, giraffe populations have experienced a rapid decline, leaving fewer than 100,000 individuals remaining worldwide. Specifically, the Masai giraffes, a species found in Tanzania and southern Kenya, are classified as endangered by the International Union for Conservation of Nature (IUCN) and have witnessed a 50% decrease in numbers during this period. Illegal hunting and human activities encroaching upon their habitat have been the primary causes of this decline, resulting in only approximately 35,000 individuals remaining.
“The habitat of Masai 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,” explain the authors of the study.
A recent study conducted by researchers at Penn State reveals alarming findings, suggesting that giraffes in eastern Africa may be even more endangered than previously estimated. The study focused on Masai giraffes and found that populations separated by the Great Rift Valley have not interbred or exchanged genetic material for over a thousand years, and in some instances, even hundreds of thousands of years.
“The Great Rift Valley cuts down through East Africa, and the steep slopes of its escarpments are formidable barriers to wildlife migration. We 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, which has important implications for conservation,” add the authors.
According to the research conducted, giraffes are known for their poor climbing abilities. High-resolution satellite data was utilized by the researchers to identify two potential locations where giraffes could climb over due to shallow slopes in the rift. However, there have been no documented reports of giraffes actually doing so.
To gain insights into the historical exchange of genetic information, the team employed a combination of whole genome sequencing techniques. This involved analyzing the nuclear genome, which encompasses genetic information inherited from both parents, as well as the mitochondrial genome, which contains information inherited solely from the maternal line.
The findings of study were just published in the journal Ecology and Evolution.
“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,” explains researcher Lan Wu-Cavener. “To understand potential gene flow across the rift, we sequenced the more than 2 billion base pairs that make up entire nuclear genome as well as the more than 16,000 base pairs that make up the entire mitochondrial genome. This complex data presented a variety of computational and data storage challenges for our small team, but using the entire genome instead of a small portion allowed us to definitively investigate the extent of gene flow among these populations.”
By analyzing the mitochondrial genome, they identified specific blocks of genes, known as haplotypes, which are typically inherited together. They conducted a network analysis based on patterns of similarity among these haplotypes. The results revealed that giraffes on the east side of the rift did not share any overlapping haplotypes with those on the west side. This finding suggests that female giraffes have not migrated across the rift to mate for approximately 250,000-300,000 years.
“Female-mediated gene flow between the two populations has not occurred in hundreds of thousands of years, or probably ever,” adds Cavener. “This raised a new question that we hadn’t anticipated about the origin of these populations. We originally thought that one population was founded and then some individuals crossed over to the other side of the rift to establish the second population. But we now think that the two populations were founded independently more than 200,000 years ago.”
Analysis of the nuclear genome indicated the possibility of gene flow through the movement of males, which may have occurred as recently as a thousand years ago. To gain a better understanding of when and why this gene flow ceased, the authors intend to collect samples from additional animals in both populations.
Based on the findings, it can be inferred that the populations of giraffes on each side of the rift possess distinct genetic characteristics, with less genetic diversity compared to what would exist in a single, interconnected population. The authors emphasize the difficulty of giraffes crossing the rift independently, and translocation is deemed impractical. As a result, the Masai giraffes are more endangered than previously believed, and conservation efforts should be independently coordinated for each population. The team calls upon the Tanzanian and Kenyan governments to increase protection measures for Masai giraffes and their habitats, particularly considering the recent surge in giraffe poaching in the region.
The researchers also discovered alarmingly high levels of inbreeding on both sides of the rift. Inbreeding reduces genetic diversity and overall fitness of the population. To better understand the risks associated with inbreeding, scientists plan to further study the populations of Masai giraffes on both sides of the rift, especially those that are particularly isolated. Additionally, they intend to investigate the movement patterns of giraffes on the east side of the rift, where the habitat is fragmented, to determine how to prioritize conservation efforts and maintain connectivity between the groups.
“We would also like to use genetics to clarify parental and sibling relationships in Masai giraffes,” adds Cavener. “There’s a lot we don’t know about how giraffes mate, for example do only a few males successfully breed in a local population over many years or do several males breed in that population? These questions are critically important to estimating the actual breeding population of the populations and will continue to guide our efforts to protect and conserve these majestic and charismatic animals.”
Source: 10.1002/ECE3.10160
Image Credit: Getty