[Taxacom] more selection sillyness
calabar.john at gmail.com
Fri Jun 14 11:48:28 CDT 2019
The fairy tales are endless. Here you can chose between thermoregulation or
biting flies to 'explain' zebra stripes. Failing that, you can invent
something else. As one says below, there has to be a 'reason' for the
stripes. And that reason lies in its function (which cannot exist until
after the morphology anyway). Bring back honest intelligent design (instead
of intelligent design disguised as zebra stripes).
(Inside Science) -- A gangrene-inducing bite in Africa, 40 years of
curiosity, and backyard experiments her daughters still complain about have
all come together to tell Alison Cobb one thing: Stripes help zebras keep
their cool. New research
today in the Journal of Natural History shows stripes may create air flows
that give zebras a kind of natural air conditioning system that helps them
ward off the blazing sun.
“It’s about thermoregulation to avoid the heat and cold,” said Cobb, a
retired amateur naturalist, who conducted the research with her zoologist
husband, Stephen Cobb. Other scientists argue the main reason for stripes
is to deter biting insects.
When she was four years old, Cobb, now 85, first wondered about zebra
stripes after reading Rudyard Kipling’s story “How the Leopard Got His
Spots.” A nature documentary she watched claimed zebra stripes were a type
of camouflage. But camouflage seemed a poor explanation to Cobb in light of
her own observations in Africa of lions prowling up and down herds of
zebras deciding which one to eat. She had also witnessed zebras spending a
great deal of time grazing in the hot midday sun -- more than the antelopes
which lived in the same area -- and believed the stripes might be helping
them deal with the heat.
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respond to you: Study)
Forty years ago she did her first experiment by draping different colored
felt coats on water-filled oil drums out in the sun and taking the
temperature of the water inside. Without direct access to research animals,
she enlisted the help of her three daughters, aged 8, 9 and 10. She made
them wear rugby shirts she sewed with zebra stripes and had her
“experimental animals” crawl around on their hands and knees in the sun in
“They still complain about it. They are now in their early 60s,” Cobb said.
But when she touched the different stripes on their backs, they could tell
her which was black and which was white without seeing. But this still
didn’t give her a full explanation: If the white spots were cooler, why did
they have black bits at all? Plus, she knew from extensive experience with
horses that the animals sweat a lot, and she was still unsure how sweat
would interact with the different colored stripes.
The research didn’t come without casualties -- Stephen Cobb got bit by a
territorial male stallion, and his wound later turned to gangrene. “He
still has a scar,” Alison Cobb said.She didn’t get the chance to get close
to zebras again until her 70th birthday, when she and her husband traveled
back to Africa to test her idea on a couple of captive zebras living on
private ranches in Kenya in December 2003. They measured the temperatures
of adjacent black and white stripes on various parts of the zebras every 15
minutes throughout the day, as well as taking ambient air temperatures near
the animals. They also took similar measurements of a zebra hide wrapped
around clothes in the shape of a horse left in the sun on the ranch.
But their research proved enlightening. They found the temperature of the
black and white stripes differed greatly on the living animals, with
greater differences at the hottest points of the day. The stripes on the
inanimate hide had a similar difference between black and white stripes,
but the highest temperatures of the black stripes were 15 degrees Celsius
hotter than the peak black stripe temperatures of living zebras.
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The research couple believes that these differences in temperature are
enough to cause small air eddies. In the living zebras, these air flows
could help to cool the zebras in the hottest times of the day by speeding
up the evaporation of sweat.
The Cobbs also noted that the living zebras were able to stick their black
hairs straight up in the air, and did so at some of the hottest times of
the day. They hypothesize this behavior may also help in heat regulation,
though the mechanism is still unclear.
Gabor Horvath, a researcher at Eotvos Lorand University in Budapest who has
studied zebra stripes, but was not involved in the Cobbs’ research, does
not believe that thermoregulation is the primary function of zebra stripes.
“Such alleged convective air eddies could be formed exclusively above
horizontal striped surfaces,” he said in an email. “If the main function of
zebra stripes were cooling by these air eddies, then only the nearly
horizontal areas of the back of zebras should be striped.”
“We’re absolutely sure that it’s about thwarting biting flies,” Caro said,
adding that tsetse and horseflies that pester the zebras in Africa can
carry deadly diseases like African horse sickness, equine influenza and a
form of horse sleeping sickness called nagana. “They just cannot afford to
let these biting flies land on their coats.”Tim Caro, a wildlife biologist
at the University of California, Davis who has also studied zebra stripes
but was not involved in the Cobbs’ research, said that “it’s an interesting
descriptive study” about the differences in temperature between black and
white zebra stripes. However, he doesn’t think the article advances our
understanding of the principal evolutionary drivers of these stripe
patterns in the animals. His research
that of Horvath <https://www.nature.com/articles/s41598-018-27637-1> and
others indicates the stripes could deter insects from landing.
At the same time, Caro still believes that the stripes have thermal
consequences for zebras. He, Horvath and the Cobbs all agree that there
likely isn’t one single reason zebras have evolved stripes.
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