WHY DO GIRAFFES have spots? And what governs their shape and pattern—are they inherited?
Perhaps surprisingly, these are riddles that scientists haven’t yet solved. This lack of certainty led researchers Derek Lee and his partner Monica Bond, who have been surveying giraffes in northern Tanzania since 2011, on a quest to find answers.
As described in a study published today in the journal PeerJ, the scientists found that certain aspects of a giraffe’s spot pattern are heritable, and appear to impact a young giraffe’s likelihood of survival. In particular, mothers giraffes appear to pass their spot roundness and smoothness (a measure technically known as “tortuousness”) on to calfs.
Having bigger, rounder spots seems to correlate with a higher survival rate for young giraffes, the paper found. The authors note that it’s unclear exactly why that might be the case–some hypothesise that the spots help camouflage the animals. But the spots may also impact the animal’s ability to regulate its temperature, besides perhaps having other unknown but useful properties.
A reticulated giraffe (Giraffa camelopardalis reticulata) and a Rothschild's giraffe (Giraffa camelopardalis rothschildi), two giraffe subspecies, photographed at Rolling Hills Wildlife Adventure in Salina, Kansas
PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
“We realised that we know very little about mammalian coat patterns in general”, says Lee, an associate research professor at Pennsylvania State University, who co-founded the conservation organisation Wild Nature Institute with Bond.
"We've never looked closely at what they mean”.
Julian Fennessy, a co-founder of the Giraffe Conservation Foundation and one of the world’s leading experts on the animals, who wasn’t involved in the study, says “the findings are scientifically valid and interesting, but of course this is one sample set”. It would be great to compare this work with research done on giraffes in other areas, and on different species, he says.
The most recent relevant work on giraffe spots dates to 1968, Lee says, when a well-known giraffe expert named Anne Innis Dagg found evidence that spot size, shape, colour, and number were likely heritable. But, Lee says, our understanding of genetics has advanced dramatically since then and Dagg’s research was done with a relatively small zoo population. “No one had really tested it in a wild population”.
Researchers analysing giraffe spot patterns found that mothers passed on traits such as roundness and tortuousness (the outline along the edge of a spot) to their offspring.
PHOTOGRAPH BY SERGIO PITAMITZ, NATIONAL GEOGRAPHIC CREATIVE
In 2012, Lee and Bond set off into the Tanzanian bush to learn more. They travelled deep into the Tarangire National Park on single track-roads rarely travelled by tourists. Battling “innumerable” tsetse flies, they photographed as many giraffes as they could over a four-year period. By watching suckling behaviour, they also worked to identify some 31 mother-offspring pairs.
“Wild female giraffes very rarely suckle a calf that is not their own”, Lee explains. Determining Giraffe paternity, on the other hand, takes either constant observation or genetic testing. As a result, “[the mother] is the one parent that we can determine with confidence”.
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Lee, Bond and co-author Douglas Cavener then used pattern recognition software to analyse the mass of photos they had collected. They measured across 11 traits—such as roundness, colour, size, number, and the like—to see whether spot patterns are passed between mother and offspring, as well as whether the pattern had any effect on the survivability of juveniles.
Craig Holdrege, author of “The Giraffe’s Long Neck”, says the paper presents “strong evidence that some aspects of spot shape are heritable”, but adds that the conclusion about spot size and survivability is a bit more suspect. “It's all too easy to assume the correlation has to do with camouflage and protection from prey, but that is a mere conjecture”.
A recent study found that juvenile giraffes with bigger, rounder spots appeared to have higher survival rates.
PHOTOGRAPH BY YVA MOMATIUK AND JOHN EASTCOTT, MINDEN PICTURES/NATIONAL GEOGRAPHIC CREATIVE
Lee takes the criticism in stride. “Anything is possible, that's why replication is so important to science”, he says.
He hopes that this latest work at least provides a solid basis for future research of not only giraffes but potentially other animals as well. “It’s just the beginning….there are so many mammals that have complicated coat patterns”, about which we know very little, he says.