During his notable trip to the Galapagos Islands, Charles Darwin collected several mockingbird specimens on different islands in the region. He later discovered that each island only contained a single species of mockingbird and no two species of mockingbird co-existed on an individual island. Due to their geographical separation, over time these birds had evolved different characteristics in coloration, behavior, and beak shape. These observations raise the question: how does a geographical region influence the evolution of a species?
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| Close-up of the ornamental white feathers on a pair of Crescent Honeyeaters, Phylidonyris pyrrhopterus, one of the species of birds examined in this study [Credit: Nicholas Friedman] |
As part of his research in collaboration with Vladimir Remes at Palacky University in the Czech Republic, Friedman headed to Australia to examine the feathers of different birds across the country and its neighboring tropical islands to see if there was a correlation between geographical climate zone and color pattern. Australia is home to a rich mixture of species, many of which are found nowhere else. The fact that Australian species were geographically isolated from the rest of the world for so long makes it an excellent place to study evolution. A trip to Australia as a young man contributed to Charles Darwin's pivotal work on evolution, On the Origin of Species.
Friedman began his study at the Australian National Wildlife Collection, where he examined bird specimens from different regions of Australia. A total of 137 different species from two major songbird families were examined. Songbirds originated in Australia nearly 30 million years ago. Research suggests that these birds began diversifying there before colonizing other parts of the world. The familial relationships of the birds that Friedman examined were compared using an evolutionary tree based on the birds' DNA.
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| Two different habitats seen in Australia: The Australian outback near Eulo, Queensland can be seen on the top and a eucalypt forest in the Brindabella Range seen on the bottom. Birds are evolving different feathers depending on the area they live in [Credit: Gordon Smith (top) and Nicholas Friedman (bottom)] |
The results of this study, published in Global Ecology and Biogeography, show that bird species do not evolve more colorful feathers in the tropics compared to their cousins in temperate climates. "If you look at birds in the tropics, there are a lot of colorful birds that stand out. But there are really more species in general there, and there are just as many more of the little brown ones" describes Friedman. "Instead, birds living in the harsh arid climates of inland Australia tended to have fancier colors than those in the lush tropical islands. Since desert birds have to scramble for mates during the wet season, we think they may be evolving colors that can attract mates quickly".
Meanwhile, birds thriving in climates with more precipitation and vegetation are darker in color overall, while desert birds tend to be lighter. "The pattern is really clear" Friedman reports, "birds living in the desert tend to be more grey on their backs, while birds living in the forest have evolved to be more of a dark green - we think they are evolving these colors to match their background." This would be an example of natural selection, in this case more camouflaged organisms can survive and pass on their genes.
"These results help to explain the origins of the diversity of life, how species end up evolving different characteristics over time", explains Friedman.
Source: Okinawa Institute of Science and Technology [November 04, 2016]