Giraffes exhibit a variety of spot patterns, prompting questions about their genetic diversity and potential classification as different species. Recent research explores giraffe ancestry, revealing a complicated family tree with notable genetic distinctions among populations. This variation indicates separate lineages but also poses conservation challenges. Acknowledging multiple species could enhance genetic diversity but may also increase the risk of inbreeding in smaller groups. This study emphasises the importance of re-evaluating the classification of giraffes and the implications for conservation efforts.
A children’s story tells how the leopard got its spots. But what about the giraffe?
Since 2016, scientists have debated whether the variation in giraffes’ spots is a clue to something deeper – profound genetic differences between populations that may rise to the level of different species.
New research published in Current Biology examines the ancestry of giraffes – and explains how some populations got their distinctive spots. The branches of the giraffe family tree are somewhat tangled, with the divisions between the proposed species not being as sharp as previously thought, says co-author Rasmus Heller, a population geneticist at the University of Copenhagen in Denmark.
“The idea that we may – or may not – be talking about four species has a lot of conservation implications,” Heller says.
Spot the difference
Giraffes from different regions of Africa clearly have minor cosmetic differences. Giraffes in Tanzania have dark spots with jagged edges like the inlets of a lake, whereas giraffes from southern Africa have paler, more blocky patterns. Meanwhile, herds in Kenya have sharp, geometric patches that fit together like the pieces of a quilt. “That one really stands out,” Heller says. Ossicones, a giraffe’s horn-like headgear, also differ subtly, he adds.
Until very recently, zoos were not very picky about the region of origin of a giraffe’s ancestors. “There was never any notion that they could be different species, so there has been no impetus to actually separate them very strictly,” Heller explains.
But based on genetic evidence, in the past decade some scientists have asserted that there are between four and nine distinct groups of giraffes – and whether these groups should be considered lineages, subspecies or even separate species depends on whom you ask.
Building a (very tall) family tree
To see how closely – or distantly – related giraffes across Africa are, Heller and colleagues analysed full genomes from 78 giraffes representing 27 locations in 13 countries.
Heller and his team were looking for single-letter mutations, genetic typos that crop up randomly and are passed on from parent to offspring. Tracing which typos different populations have in common enables researchers to build a family tree, ultimately establishing how long ago two giraffes from different locations shared an ancestor.
The data indicate that the root of the giraffe family tree is quite young, Heller says – all the giraffes had a common ancestor between about 200,000 and 280,000 years ago.
Nevertheless, the groups’ genetics differ profoundly. Heller explains that there is significant discretion in where to set the boundaries, but he and his colleagues identified four major lineages that correspond with the four proposed species: the northern giraffe; the reticulated giraffe; the Masai giraffe; and the southern giraffe.
Accumulating these genetic differences required separating the populations in some way – and since experience from zoos shows that the various lineages can produce offspring, the barrier to breeding is not their biology. The barriers must be in the landscape.
Shifting barriers shape giraffe lineages
Heller and his team found physical barriers that might have separated the lineages – for example, the Gregory Rift Valley divides the northern giraffes on one side and Masai giraffes on the other, and river systems divide sublineages. But in some cases, no obvious landscape-level features would have isolated the groups.
“Eastern Africa is a good example – in a very small geographical area, you have all the major lineages very close to each other,” Heller says. “Of course, this invites the thought: what is keeping them from actually mixing with each other?”
In fact, the genetic data indicate that, although the populations are quite different genetically, they have not been as isolated as previously thought. The researchers found evidence of gene flow, meaning breeding between the lineages.
But what kinds of barriers could sometimes keep the lineages apart and sometimes enable them to intermingle?
Heller says the most likely culprits are climate change and shifting vegetation patterns. As rainfall increases, an arid desert that divided two lineages could become lush grasslands perfect for an interlineage meet-cute.
The findings are also the first to demonstrate that the reticulated giraffe, with its distinctive quilt-like spots, is a hybrid of the northern and Masai lineages – although whether that occurred through a single pulse or through multiple events spanning a longer period of time remains unclear.
What does this mean for conservation?
Heller says that he and his team deliberately did not take a position on whether the lineages should be considered different species – they were happy to “kick that can a little bit down the road,” he explains.
That is because “a species designation, for better or for worse, is still an integral part of the currency of biodiversity today,” he says. “Once something gets its own species name, a whole apparatus is set into motion – we are obligated to monitor and conserve each of these species as one more piece of the natural heritage.”
At first blush, a new species designation seems like an unmitigated good. But for conservationists, deciding whether to divide a species is a challenging “balancing act,” he says. Splitting Africa’s giraffes into several species could help to preserve genetic diversity – each lineage could be uniquely adapted to thrive in its home region in ways not yet identified. But drawing bright lines between the lineages would also radically shrink the breeding pool for each one, meaning a risk of inbreeding for smaller lineages such as the West African giraffe, numbering an estimated 600 in the wild. “They are in trouble if you consider them their own species,” Heller says.
“No matter how you dice it, the giraffe lineages have not had independent evolutionary trajectories for more than a few hundred thousand years,” Heller says – the blink of an eye in the evolutionary timescale.
“That does not really resolve whether we can or should call them different species or not,” he says. “But it should be part of the discussion.”