Zebras, horses, and donkeys are all closely related, yet zebras are the only one within the species to have stripes; the only African mammal in the region with stripes, too. These species inhabit a wide variety of different niches such as, grasslands, savannas, woodlands, thorny scrublands, mountains, and costal hills. Until recently, limited information was available on the subject, but many hypothesis have been deduced over the years. These theories include, the stripes evolving as a form of camouflage, disrupting predatory attack by visually confusing carnivores, a mechanism of heat management, a social function, and evolving as a defense against ectoparasite attacks, such as biting flies.
Published on April 1st 2014 2014, in the online journal, Nature Communications, by the University of California- Davis, a new study finds that biting flies, like horseflies (tabanid) and tsetse (glossinid) flies, are a significant influence in the evolution of stripes. A team of researchers mapped and compared geographic distributions for seven different species of horses, zebras, donkeys, and other subspecies measuring different variables such as, the thickness, locations, intensity of their stripes on several parts of their bodies, ranges of large predators, temperature, and the geographic distribution of the biting flies. The researchers found that in areas where zebras had greater stripe density, they also suffered from a greater annoyance of bug biting. Lead author Tim Caro, a UC Davis professor of wildlife biology said, "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." Previous experimentation determined that these species of flies avoid black-and-white stripe patterns. Together, both sets of data suggest that overlapping areas with higher bug density influenced zebras to have greater striping patterns, as a defense. Zebras have shorter hair than most mammals in their region, making them more susceptible to the biting bugs. This study provides logical insight into the evolution of stripes on zebra as a defense against biting bugs.
Evolution is influenced by a magnitude of factors and changing even one can result in major phenotypic or genotypic changes. This is a beautiful example of species interacting, showing how a battle between two species can result in an observable pattern we can study. It cannot be taken as definitive proof as to why stripes evolved, but it suggest that in terms of their geographical distribution a coevolutionary arms race between biting flies and zebra striping has a strong correlation. I believe these other theories hold great value and its possible they all played a major role in the evolution of stripes. However, some factors have a greater influence then others, but as to which is the greater force, is still unknown.
Maxwell Liner (B)
The theory that the first zebra evolved stripes to combat flies is an interesting one. However, it seems to me that a striped zebra would be super easy to spot by a predator, if none of the other zebras are striped. Predators would likely chase and kill this zebra, because of its lack of camouflage. It seems unlikely to me that, for the first striped zebras, the advantage of not getting attacked by flies as much was enough of an advantage to outweigh the disadvantage of giving up camouflage.ReplyDelete
Something that perhaps I am missing, or could be a consideration, is how biting flies could present selective pressure under the model of natural selection? Do biting flies kill or interrupt mating somehow? If not, how could it be that zebras would have a better survival rate with stripes than without?ReplyDelete
One key piece of information I could be mistaken about is the nature of biting bugs, if they kill then I am wrong. If they do not kill, it seems like "annoyance" would not be enough as a selective pressure.
Posted by Michael Dailing
The general idea is that zebras with more intense or vibrant striping patterns have better resistant against bug bites. It seems, at least to the researchers, that the bugs serve as more of an annoyance that anything else ..however that is debatable since the article did not specify any other details. They simply studied geographical locations, and saw a huge correlation between the two species. Perhaps these bugs carry lethal pathogens, or cause open wounds that later lead to infection and lower overall fitness..in any case, these species of bugs demonstrate a general avoidance behavior in response to the black and white patterning, in addition their location with the zebras suggests some sort of coevolution.Delete
this is a very interesting post. Are there possibly diseases that are associated with the fly's bug biting that makes it a more influential selective pressure?ReplyDelete
posted by kristen whitehead
I'm not sure. Unfortunately, the article was not very specific on any other details. They basically mentioned their findings on the bugs and said its possible the bugs are a leading force in the evolution of stripes. They did acknowledge the fact that they were not sure why the bugs and zebras have this correlation, but its seems to like more research will be put into the idea...hopefully. Its a reasonable hypothesis and factors like disease might be a huge influence.Delete