Zebra stripes discourage horseflies from biting - The State Column

The mystery of zebra stripes and horseflies has been revealed. A study published Thursday in the Journal of Experimental Biology provides evidence that zebra stripes may discourage horseflies from biting. Prior to the study, researchers thought the zebra stripes were designed to confuse predators. While this may still be the case, the deterring impact of zebra stripes appears to be aimed primarily at horseflies.

“We demonstrate that a zebra-striped horse model attracts far fewer horseflies (tabanids) than either homogeneous black, brown, grey or white equivalents,” the researchers write in the study’s abstract.

Horseflies, which can carry diseases and distract their victim from feeding or drinking, are unwelcome visitors to zebras and other animals that graze. According to Gábor Horváth, one of the study’s authors, horseflies are attracted to horizontally polarized light because sunlight that reflects off of water is horizontally polarized. When horseflies and other aquatic insects discover water they can mate and lay eggs. The female variety of horseflies, however, are also attracted to linearly polarized light that reflects from the hides of their victims.

Zebra embryos, which start out with dark skin and develop white stripes before being born, raised an important question with the researchers. Did the zebra develop stripes over time in order to deter disease-carrying horseflies and other insects?

In order to determine whether a zebra’s stripes really deter horseflies, the team traveled to Budapest and set up camp at a horse farm with plenty of horseflies. The team attempted to attract horseflies using black and white striped patterns that varied in width. Using oil and glue to capture the horseflies, the narrowest black and white striped strips attracted the fewest insects.

The team of researchers also measured the attractiveness of white, dark and striped horses to horseflies. Although the team expected the results to reveal that white horses were the least attractive, they found that the striped version captured the least number of horse flies.

“We created an experimental set-up where we painted the different patterns onto boards,” researcher Susanne Akesson of Lund University posited to BBC Nature. “We put insect glue on the boards and counted the number of flies that each one attracted,” Ms. Akesson added.

While researchers have not eliminated the possibility that zebra stripes might have benefits besides the deterrence of horseflies, they believe that a zebra’s striped coat pattern is a key factor in repelling disease-carrying insects.

“We believe that escaping biting flies, which are annoying to their hosts and transmit lethal diseases, would be a very important selection factor, which may have a much stronger effect than the benefits of striped coat patterns suggested previously,” Ms. Akesson told LiveScience.

Until recently, zebra stripes were thought to be primarily designed for camouflage in the wild. Scientists believe that zebra stripes act as camouflage in two ways. First, the wavy stripes help the zebras blend into the grasses around them. A lion, one of the animal’s natural predators, is colorblind which means that it is unable to tell the difference between the grass and the zebra. Second, scientists believe that a zebra is able to use its stripes to blend in with other zebras in a herd. When a predator spots a herd of zebras, it sees a mass of black and white stripes instead of individual zebras. Although these uses for zebra stripes are still relevant, the study’s authors believe that they are no longer the primary reasons that a zebra has stripes.

“We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies,” the team of researchers posited in the Journal of Experimental Biology, adding that “the selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa].”

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US Sweetens Offer to Take Sudan Off Terrorist State List - New York Times

WASHINGTON — President Obama has told Sudan that if it allows a politically sensitive referendum to go ahead in January, and abides by the results, the United States will move to take the country off its list of state sponsors of terrorism as early as next July, administration officials said Sunday.

The offer, conveyed to the Sudanese authorities over the weekend by Senator John Kerry, the chairman of the Senate Foreign Relations committee, represents a significant sweetening of the package of incentives the administration offered to Sudan in September for its cooperation with the vote.

Under a peace agreement that ended years of civil war in Sudan, the government in Khartoum agreed to a referendum, now scheduled for Jan. 9, in which the people of southern Sudan will decide whether to secede from the north. They are expected to vote overwhelmingly to do so.

But as the date for the vote nears, there are persistent reports of foot-dragging by the Sudanese authorities in preparing for it, as well as fears of a new outbreak of violence if the north does not honor the results. Dividing Sudan is hugely complicated, since most of its oil fields lie in the south.

In September, the administration presented Sudan with incentives ranging from modest steps like the delivery of agricultural equipment to more sweeping measures, including debt relief, normalized diplomatic relations, the lifting of sanctions and the removal of Sudan from the State Department’s list of state sponsors of terrorism, which it has been on since 1993.

Administration officials said then that they did not expect to take that last step until late 2011 or 2012, one official said, because it was also linked to a resolution of the violence in the Darfur region. But now the United States has made it contingent only on the referendum. The Sudanese government, another official said, had pushed in recent weeks for more clarity in the incentives.

“I believe a broad agreement is within reach if they act with the sense of urgency that is necessary to seize this historic opportunity,” Mr. Kerry said in a statement on Sunday as he left Sudan.

Sudan has long petitioned to be removed from the State Department list, which also includes Iran, Cuba and Syria. Under President Bill Clinton, the administration designated its placement there on the grounds that it harbored Osama bin Laden and other terrorists. But in recent years, Sudan has cooperated in counterterrorism efforts.

Over time, Sudan’s designation has been expanded to include its role in mass killings in Darfur. Economic sanctions against Sudan remain linked to the violence in Darfur, officials said, and cannot be lifted without approval from Congress. Earlier this week, Mr. Obama renewed those sanctions. The president can remove Sudan from the terrorism list after notifying Congress.

The United States, an official said, will not relax “our commitment to solving the problems that have dogged Darfur.”

The administration’s offer does not depend on resolving another sticking point: a separate plebiscite by people in the contested border region of Abyei to decide to join northern or southern Sudan. The two sides have not agreed on the terms of that vote, also scheduled for January.

With diplomats still struggling to break the impasse, administration officials said they recognized that the plebiscite on Abyei may have to be deferred until after the broader vote on independence by southern Sudan.

North Korea was the last nation the United States removed from the terrorism list. That was done by the Bush administration in 2008, in an effort to encourage Pyongyang to be more pliant in talks over its nuclear program — a goal that has been largely unmet, given North Korea’s recent intransigence.

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