Leveraging genetics to inform giraffe conservation

Genetic data is increasingly used in conservation strategies. But how do scientists apply the data to conservation management? Giraffes present an exemplary case study to explore this question.

Currently, the International Union for Conservation of Nature (IUCN) recognizes only one species of giraffe with nine known subspecies. A subspecies is a group within a species that is geographically, genetically, and/or physically different from others, and is able to inter-breed with other subspecies.

Intriguingly, a genetic study from 2018 by the Giraffe Conservation Foundation and Senckenberg BiK points to four distinct species of giraffe. A separate study from 2020 by researchers from the University of Paris investigated the totality of DNA data from giraffes. DNA, or deoxyribonucleic acid, is a molecule that contains the genetic instructions that determine the development and traits of all living organisms. The genetic analysis supports at least three distinct species of giraffe.

Despite these claims, the exact number of giraffe species has not yet been settled. Furthermore, the IUCN has not assessed the giraffe species recognition status since 2016. This imposes direct consequences for giraffe conservation. Conservation management relies on species data obtained from the IUCN. If the species data is wrong or not updated, it may impact the effectiveness of conservation measures.

While the species debate continues for giraffes, researchers are using genetics to address other conservation concerns. Monica L. Bond, a researcher with the Wild Nature Institute and University of Zurich—who has studied giraffes for over a decade—states that giraffes are undergoing what has been termed a ‘silent extinction’. This means that people generally aren’t aware that the world’s tallest land mammals are endangered. They are threatened by the same pressures affecting wildlife across the globe, namely overhunting, loss of habitat, and climate change.

Conservation of populations

Such pressures apply widely across giraffes. However, the degree of concern varies among giraffe populations.

Such pressures apply widely across giraffes. However, the degree of concern varies among giraffe populations. For example, Masai giraffes face different threats depending on their location. Masai giraffes, a species or subspecies of giraffe, are located in Kenya and Tanzania. They were declared endangered by the IUCN in 2019. Sadly, their populations have declined over 50 percent since 1985, accelerated by human development. Douglas Cavener— a professor at the Pennsylvania State University, who studies giraffe genetics— says that the habitat of Masai giraffes is highly fragmented, in part due to the rapid expansion of the human settlements in East Africa in the last 30 years, and the subsequent loss of wildlife habitats.

Further exacerbating these issues, Masai giraffes are separated by a large rift in part of their range. Cavaner informs that the Great Rift Valley cuts down through East Africa, and the steep slopes of its escarpments are formidable barriers to wildlife migration. Giraffes on either side of the rift face separate conservation concerns. On the eastern side, giraffes are experiencing heightened habitat fragmentation due to human development, whereas on the western side, they face intensified illegal hunting.

Diving into the genome

To better inform conservation of the Masai giraffe populations around the rift, a study published last month by Cavener, Bond and co-authors takes a closer look at giraffe genetics. The conclusions drawn from a copious amount of giraffe genetic data are striking. The researchers 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. For this purpose, they sequenced more than two billion base pairs that make up the entire nuclear genome as well as the more than 16,000 base pairs that make up the entire mitochondrial genome.

Sequencing is a process used to determine the precise order of the base pairs and provides crucial information for understanding the genome. Base pairs are the genetic code that collectively make up an organism’s DNA. The entirety of DNA in an organism is known as a genome. For giraffes, this totals over two billion base pairs per individual.

Within an individual, there are two types of genomes—one genome in a cell’s nucleus, the cell’s brain so to speak, and one genome in a cell’s mitochondria, the cell’s energy producer. Together, the two genomes encode information about an organism. For a giraffe, they specify information about spot patterning, neck length and energy production, alongside other things.

Importantly, information from the nuclear genome is passed down from both parents, while information from the mitochondrial genome is only passed down through the maternal line. Comparing both genomes across individual giraffes can provide evidence for female versus male movements within the Masai giraffe range.

The researchers found that giraffes on the east of the rift share mitochondrial haplotypes—chunks of the mitochondrial genome that are inherited together. Strikingly, giraffes on the east side do not show overlap of haplotypes with giraffes on the west side. This clued researchers into how genetic material is being shared from mother giraffe to calf, as the mitochondrial genome is maternally inherited. Their results show that female Masai giraffes have not moved across the Great Rift Wall that separates the Serengeti-Ngorongoro (west) and Tarangire-Manyara (east) populations in the past 250,000 to 300,000 years, and it is possible they never did.

Moreover, the results from the nuclear genome demonstrate that male-mediated interbreeding has not occurred in at least 1,000 years—as nuclear genome information identifies patterns passed down from both parents. Cavener says that there are very few prospects of giraffes crossing over the rift on their own. Some male giraffes may have crossed the rift in the past, but certainly not in recent years.

Diversity concerns

Collectively, the data implies that giraffes on opposite sides of the rift do not interbreed, and hence do not share genetic material. Males have not crossed the rift in at least 1,000 years, and females have been mating only with giraffes on the same side of the rift for over 250,000 years. Thus, the researchers urge that the populations be considered as separate.

In considering the giraffe populations separately, each population now consists of less individuals than if they were one larger population. Cavaner reveals that the populations of giraffes on each side of the rift are genetically distinct, with each population having less genetic diversity than if they were one, larger interconnected population.

The Masai giraffes’ inability to share genetic material across populations is not good for genetic diversity. Lan Wu-Cavener—an assistant research professor at the Pennsylvania State University and member of the research team—reveals that interbreeding among different populations results in the exchange of genetic information, and is generally considered to be beneficial as it can improve overall genetic diversity. Thus, the Masai giraffes on either side of the rift are more endangered than previously thought, as the amount of genetic diversity thought to be shared among them is less than once assumed. The new study highlights that conservation is of the utmost concern in order to preserve the variation that is left.

Conservation applications

The finding that Masai giraffes are not interbreeding or sharing genetic material across the rift has direct implications for conservation. Researchers have some ideas for how their genetic data can inform conservation efforts in Tanzania and Kenya. In consideration of the decreased genetic diversity within these populations, it is believed by Bond and Cavener that not interfering with the natural course of evolution is the best conservation strategy.

It may seem intuitive to translocate giraffes across the rift to increase their genetic diversity. On the contrary, researchers believe this would not be beneficial. Bond and fellow researchers caution against translocating giraffes across the rift wall for any reason, in order to preserve the genetic distinction between these two populations.

The decline of these populations due to human impact has been occurring since 1985. This timescale does not compare to the 250,000 years of non-interbreeding between these Masai giraffe populations—which ultimately led to genetic distinction between the populations. While translocation across the rift would increase genetic diversity, it would also change the course of evolution of the giraffe populations.

Bond states that the two giraffe populations are on their own evolutionary trajectory and shouldn’t be tampered with. This means that we need to focus on conserving giraffe populations in their present range, through targeted habitat conservation and connectivity within the two geographic regions.

Cavener adds that conservation efforts for each population should be considered in an independent but coordinated fashion. The researchers hope that the Tanzanian and Kenyan governments will increase the protection of Masai giraffes and their habitats, especially given the recent increase in giraffe poaching in the area. Ultimately, the researchers believe that conservation of Masai giraffes needs to shift to mirror the genetic status of these two populations by considering them separately.

Excitingly, the application of Masai giraffe genetic data to conservation management does not end here. The research team plans to use the collected genetic data in future studies.

Knowing the genetics of individual giraffes provides information about relatedness, and can be used to study reproductive behaviours, influence of relatedness on behaviour, and heritability of traits. The researchers maintain that these questions are critically important for estimating the actual breeding population of the entire population, and will continue to guide their efforts to protect and conserve these majestic and charismatic animals.

Looking beyond giraffes

Besides Masai giraffes, genetic data has been employed in several other conservation efforts. For example, researchers at the San Diego Zoo in California have used genetic data to guide breeding and reintroduction of California condors for over three decades. Australian researchers used genetic data to show that critically endangered vaquitas can bounce back if illegal fishing is stopped. Scientists with the Royal Zoological Society of Scotland are training researchers in Cambodia to set up a genetic laboratory. They are working on a genetic test to aid Siamese crocodile reintroduction. The applications of genetic data for conservation are evidently endless across myriad organisms.

Collectively, genetic data has the ability to inform conservation management at multiple levels—from breeding programs to policies that limit human development and activities. In the case of the Masai giraffes, genetic data collection and analysis is not stopping anytime soon. It is clear that genetic data is an asset to their conservation. As Dr. Bond says, “We hope that this research can inform science-based giraffe conservation so we can sustain these wondrous animals into the future.”

Further Reading

San Diego Zoo Wildlife Alliance. 2020. Genotyping the California condor: What we’ve learned. Science Blog. https://science.sandiegozoo.org/science-blog/genotyping-california-condor-what-we%E2%80%99ve-learned. Accessed on July 2, 2023.

Giraffe. The IUCN Red List of Threatened Species. 2018. https://www.iucnredlist.org/species/9194/136266699#taxonomy. Accessed on July 2, 2023.

Lohay, G. G., D. E. Lee, L. Wu-Cavener, D. L. Pearce, X. Hou, M. L. Bond and D. R. Cavener. 2023. Genetic evidence of population subdivision among Masai giraffes separated by the Gregory Rift Valley in Tanzania. Ecology and Evolution 13:e10160. https://doi.org/10.1002/ece3.10160. Accessed on July 2, 2023.

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2024 Mar