Scientists Solve the Mystery of Why Zebras Have Stripes 190
Hugh Pickens DOT Com (2995471) writes "There have been many explanations for the zebra's impressive stripes including Darwin who thought that the stripes help males and females make sensible choices about whom they mate with. Now Henry Nicholls reports at The Guardian that Tim Caro at the University of California, Davis, has taken a completely original approach, stepping back from one species of zebra and attempting to account for the differences in patterning across different species and subspecies of zebras, horses and asses to see if there is anything about the habitat or ecology of these different equids that hints at the function of stripes. To answer that question, Caro and his colleagues created a detailed map charting the ranges of striped vs. non-striped species and subspecies. Then they worked on a map for the bloodsuckers that targeted those species — specifically, abanid biting flies (horse flies) and tsetse flies.
'I was amazed by our results,' says Caro. 'Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.' Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. Biologists who buy into the bug-repellent hypothesis say that, all other things being equal, striped animals would have an evolutionary advantage because they wouldn't suffer from the loss of blood, reduced weight gain and lowered milk production that's associated with bug bites. Tsetse flies are also associated with the transmission of diseases. 'There are a lot of them, such as sleeping sickness, equine anemia and equine influenza,' Caro says. Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
'I was amazed by our results,' says Caro. 'Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.' Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. Biologists who buy into the bug-repellent hypothesis say that, all other things being equal, striped animals would have an evolutionary advantage because they wouldn't suffer from the loss of blood, reduced weight gain and lowered milk production that's associated with bug bites. Tsetse flies are also associated with the transmission of diseases. 'There are a lot of them, such as sleeping sickness, equine anemia and equine influenza,' Caro says. Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
Terrible summary (Score:5, Insightful)
You know, if you're going to just copy and paste part of the article as your summary, you might as well post the last paragraph, and get to the actual explanation:
Zebras have stripes because biting flies have an aversion to landing on striped surfaces.
Re:Terrible summary (Score:3, Insightful)
biting flies have an aversion to landing on striped surfaces.
Biting flies can't evolve?
I found the whole thing very unconvincing.
Re:Terrible summary (Score:5, Insightful)
They can evolve, but they have evolved to a local maximum where they can't determine whether visual information received indicates a zebra, mud, or water. As they seem to be thriving at this level, there is no pressure for them to evolve the required discriminatory abilities.
Re:Terrible summary (Score:5, Insightful)
That would make the idea of evolving insect repellent coloring even more amazing.
For proof like in the pudding, the biting flies would have to be shown to exert selection pressure on zebras that is not present where equines without stripes flourish.
It could be the striped coat offers an amalgam of advantages. Hindering attacks from predators trying to pick out a single quarry in a sea of seizure-inducing undulating stripes should not be considered mutually exclusive from hindering insect bites.
Re:Terrible summary (Score:5, Insightful)
Biting flies can't evolve?
I found the whole thing very unconvincing.
If it's proven that biting flies have aversion to landing on striped surfaces, it makes no sense to say it can't be true because flies would evolve.
Correlation != causation.
To me it makes much more sense that biting flies have evolved to avoid landing on Zebras (eg. because Zebras have a secret anti-fly weapon we don't know about yet).
How do they know to avoid Zebras? Because of the stripes.
Carts and horses. Make sure you know which is which...
Re:Terrible summary (Score:5, Insightful)
biting flies have an aversion to landing on striped surfaces.
Biting flies can't evolve?
I found the whole thing very unconvincing.
For biting flies to evolve, there would likely have to be a considerable reason to, such as zebras being their only source to lay eggs. Chances are their ecosystem was hardly impacted at all by zebra evolution due to diversity.
As evidenced, zebras did evolve due to considerable reasons, as their short hair made them rather specific targets for the flies above many other animals.
Thankfully, evolution does require considerable justification. Questionable mutations would evolve otherwise, and we should be thankful it's not a knee-jerk reaction in nature, no matter how much we would like to prove it actually exists to those who refuse to acknowledge it on every level.
Re:Terrible summary (Score:4, Insightful)
Don't forget complexity of the change required.
Flies eyes are segmented and see completely different to us. It could be that there's some sort of visual effect of stripes and segmented eyes.
Evolving stripes is much easier than evolving a different kind of eye or vision system.
Re:Terrible summary (Score:5, Insightful)
very unconvincing... wouldnt it be easier to grow your hair a few mm longer?
What's to say that didn't happen? We just don't call the ones with longer hair instead of stripes "zebras".
Evolution doesn't involve a species voting on how it would prefer to evolve. If there are multiple possible adaptations then it's entirely possible that different subgroups will evolve in different directions in response to the same environmental factors. This is one path to speciation, if the change are significant enough.
Re:Terrible summary (Score:5, Insightful)
Or, the flies just move on to the millions of other herd animals around without stripes.