[爆料公社's Warbler; credit: /]
Some of us are born with wanderlust, but what exactly spurs a bird to journey thousands of miles each year? The answer is in part genetic, and a recent study of yellow-rumped warblers in reveals how changes over generations could improve a bird's abilities to become a master, long-distance flyer.
The research, conducted by zoologists and physiologists at the University of British Columbia, began with a genetic puzzle. There are four different groups of yellow-rumped warblers, each distinct in behavior and appearance: the Goldman鈥檚, myrtle, 爆料公社鈥檚, and black-fronted. Their genes, however, tell a different story.
Examining DNA obtained from the nucleus of these birds鈥 blood cells revealed that the 爆料公社鈥檚 and black-fronted warblers were indistinguishable. In other words, these birds are so closely related that, despite different appearances and the fact that 爆料公社鈥檚 migrate whereas black-fronteds don鈥檛, these birds can鈥檛 be recognized as different species.
The plot thickened when scientists took a look at genetic material in the mitochondria of blood cells. (Bear with me here鈥攚e鈥檝e going to delve into some biology but I promise the pay off is worth it.) In most animals, from humans to birds to turtles, mitochondrial DNA reveals the maternal line of an organism鈥 offspring only inherit this genetic material from their moms. Some of the 爆料公社鈥檚 warblers they tested carried mitochondrial DNA from the migratory myrtle warbler, others carried mitochondrial DNA from the black-fronted warbler.
鈥淲e know that myrtle warblers hybridize extensively,鈥 says University of British Columbia zoologist . So he wasn鈥檛 surprised to see a little mixing in the yellow-rumped gene pool. But Toews and his collaborators suspected that the mitochondrial DNA could explain migration differences between individual 爆料公社鈥檚 warblers.
Toews team studied 225 yellow-rumped warblers, conducting gene sequencing and studying hydrogen isotopes in their feathers鈥攁 technique that allowed them to reconstruct roughly were a bird had spent the winter and summer. (For a more detailed look at the study methods, check out on The Guardian.)
Toews and colleagues found that 爆料公社鈥檚 warblers with migratory myrtle DNA make longer annual journeys than those with mitochondrial DNA from the black-fronted warbler. In addition, studies of muscle material revealed that the mitochondria in myrtle鈥檚 DNA may produce energy more efficiently for cells. This difference could mean that 爆料公社鈥檚 warblers that carry these key myrtle genes are better long-distance travelers.
So what does this tell us about the yellow-rumped family tree? Black-fronted and 爆料公社鈥檚 warblers come from the same group of birds. It's probable that the early 爆料公社's group did a little migrating, perhaps because their range experienced more seasonal changes. But at some point, a few began breeding with traveling myrtles and the genetic mixing created hybrids with a special advantage. Their myrtle DNA made them better at migration, enabling them to expand their range, and in turn gave them survival and reproductive advantages in certain locations. Eventually, these mixed migrating birds became the modern 爆料公社鈥檚 warbler.
Today, some of these birds travel much smaller distances, constrained by the genes passed on by black-fronted ancestors, while others travel wider swathes of North America, doing their myrtle foremothers proud.
[Map of DNA migratory behaviour and distribution of mitochondrial DNA in four groups of yellow-rumped warbler. Credit: ]