Wildlife & Wild Places

Stripes Are Cool

And not just cool-looking.

Thanks to funding from the National Geographic Committee for Research and Exploration, we have recently published our first paper about how the zebra got its stripes. The paper was published in Royal Society Open Science (details below) in January and has been receiving some great press, National Geographic, NPR, NBC, and USA Today among others.

For those who are looking forward to a simple answer, I have bad news. There isn’t likely to be one.

For those who enjoy puzzles and the amazing complexity of nature, this is your lucky day.

Tarangiri mare and foal Jeannies crop
Photo Credit: Brenda Larison and Jeannie Barber Choi

We found support for a hypothesis that had been posed, but never seriously considered. Our data provide the first evidence that striping may actually function to keep zebras cool! But please note: This doesn’t mean the end of the predation hypothesis or the biting-fly hypothesis. It means we now have three serious contenders for the explanation of how the zebra got its stripes.

We have a lot of work to do before we will really know why zebras are striped.

We expect to find that there is more than one purpose of the stripes. My favorite comment circulating in the media commentary about our paper is that zebra stripes may be “nature’s multitool”.  Striping may indeed help zebra evade predators, deter biting flies AND keep them cool.

I’ll keep you posted as we make progress, and with other interesting tidbits and thoughts along the way.

Details of the study:

Larison B, Harrigan RJ, Thomassen HA, Rubenstein DI, Chan-Golston AM, Li E, Smith TB. 2015. How the zebra got its stripes: A problem with too many solutions. Royal Society Open Science 2:140452

Taking advantage of the extensive variation in the amount of stripiness plains zebra show throughout their range, we photographed zebra and scored their stripiness at 16 sites. We then examined whether temperature, precipitation, biting flies or predators might be associated with the differences in stripiness among the sites.

We found that variation in striping is best explained by temperature. Specifically we found that the classic, storybook black-and-white zebra covered head to toe in bold stripes keeps to regions that are warm year-round. In areas with seasonally cold temperatures, zebras are less stripy. We didn’t find any effect of whether biting flies or predators were likely to be present.

This could support the idea that bold black-and-white stripes act as a cooling system. The idea here is that because black heats up more than white, this would cause different rates of airflow between black and white stripes thus creating cooling convection currents. Some additional data supporting the idea that stripes are cooling will be coming soon from Dan Rubenstein and Damaris Iriondo of Princeton University, so stay tuned as you will certainly here about it here.

Brenda Larison of the University of California at Los Angeles received a grant from the National Geographic Society’s Committee for Research and Exploration to investigate the genetic basis and adaptive significance of stripe pattern variation in plains zebra (Equus burchelli). The study represents a unique opportunity to gain new insights about the evolution of zebra stripes, and because the topic of zebra stripes inspires not only scientists: but artists, designers, children and the merely curious, it provides a natural bridge to engage people in the scientific process.

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