Cappuccino anyone? This week At the Lab, CSHL Professor Adam Siepel introduces the capuchino seedeater鈥攁 South American subspecies known for its ultraviolet plumage. Join us on a voyage across evolution鈥檚 鈥渋slands of differentiation鈥� to find out how these birds got their distinct colors.
Read the related story: Birds of a feather do flock together
Transcript
Sam Diamond: You鈥檙e now At the Lab with 黑料吃瓜资源. My name is Sam Diamond. And this week At the Lab: 鈥淏irds of a feather.鈥�
{Birds chirp.}
SD: Birds come in all shapes and sizes. Just this morning I saw a blue jay in one of the trees outside my office. Right now I see a flock of seagulls floating in the Harbor. And if I鈥檓 really lucky I might even spot one of the bald eagles that calls our campus home.
SD: But what makes these birds so different from one another? To find out, we sat down with CSHL Professor Adam Siepel.
Adam Siepel: Birds often display very pronounced morphological differences from one subspecies to the next. They often exhibit sexual selection for particular prominent coat color or song changes.
SD: Siepel is an expert in population genetics. Recently, his lab took an interest in seedeaters鈥攆inch-like birds from South America. Tens of thousands of generations ago, these birds all had identical genetic codes. That meant similar feathers and birdsongs. But since then, they鈥檝e broken off into many species with different coats and calls. Siepel says the different species鈥� genes reflect these changes.
AS: When we sequence their genomes, their genomes are quite similar to one another. But they have local regions that are highly differentiated. These have been referred to as islands of differentiation.
SD: What causes these islands to emerge? One way they can come about is through physical separation. Birds may develop a new species when one group becomes separated by a large barrier, like a mountain range or an ocean. However, Siepel and his lab found that it wasn鈥檛 geographic boundaries that caused seedeaters to drift apart鈥攊t was something else.
AS: A selective sweep, when a group of organisms that carry some mutation that gives them an advantage over other organisms, rapidly become much more frequent鈥攎aybe because of a change of environment, a new predator, a new food.
VO: The sweep occurs when individual animals with a particular genetic variant begin to reproduce at higher rates. Siepel explains.
AS: In this case, we think the birds of the opposite sex found some aspect of that variant attractive, whether it鈥檚 coloration or song. And that helped push it to high frequency.
SD: From there, the variant individuals stay together, eventually forming a new species. Biologists are still trying to figure out why birds find certain colors, songs, or other variants more attractive. In the meantime, Siepel鈥檚 work suggests that the old saying holds true in evolution. Birds of a feather really do flock together.
SD: Thanks for listening to At the Lab. Please be sure to subscribe wherever you get your podcasts. And visit us at www.cshl.edu for more fascinating stories like this one. For 黑料吃瓜资源, I鈥檓 Sam Diamond. And I鈥檒l see you next time At the Lab.