Warbler migration affected by a single gene

Plenty of birds fly vast distances towards the equator for winter and away again for summer, trying to stay ahead of the changing temperatures of the seasons. And now zoologists have found a single gene that seems to help control where they go. How does it work? The same way a gene inside a person might help them run faster, this one might be giving one group of warblers the stamina to fly further south than their neighbours. Phil Sansom heard from David Toews from Pennsylvania State University...

David - We found this gene that we believe is responsible for differences in migration in a Neotropical migratory wood warbler,

Phil - Really? The genes control it migrating? I would have thought that's all stuff it learns when it's a baby or something.

David - Yeah, these small songbirds, nobody really tells them where to go.

Phil - That's amazing. What are these birds then?

David - So these are Neotropical migratory wood warblers. There's about 110 species, but we were actually focused just on two: golden-winged warblers and blue-winged warblers.

Phil - What do they look like, these ones?

David - They're very colourful; but blue-winged warblers, unlike their name, are actually almost totally yellow with a little black face mask; and golden-winged warblers look very different, they're mostly white and they have a really distinct black face mask and throat. They're genetically very similar.

Phil - And when they migrate, where do they go?

David - These birds live primarily in the Eastern U.S. and Canada, but they migrate to Central and South America.

Phil - How do you figure this out, and track a bird to, I don't know, Central America?

David - That's actually one of the trickiest parts; following a tiny 12 gram bird over its entire annual cycle is logistically very difficult. We can't just put a GPS tracker on one of these birds because the battery that would be needed to power that and transmit data weighs about as much as the bird. And so my collaborators at the University of Toledo use these rather ingenious light loggers; these are little backpacks that you put on a bird where it's breeding, and it just captures passive light throughout the day. And long story short, if you know the precise sunrise, sunset, and midday points, you can get an estimate of latitude and longitude. Now you have to catch the bird the next year to download the data off these backpacks, because again, they don't have the capacity to transmit. So you inevitably... because these birds disperse, some of them don't all survive on their migration. If you are lucky enough or have enough money to put out enough of these backpacks, and get enough of them back, you can actually get individual-level movements for these migratory warblers.

Phil - Okay. So you're learning where the birds go. And then, what, comparing that to the genes?

David - Yeah, there was this really dramatic split between those birds that went all the way to South America to those that went to Central America. And so then we used whole genome resequencing. We found this very strong association with a single region of the avian sex chromosome, and within this single region, we found a single gene; and the gene is VPS13A.

Phil - Oh, that's a mouthful.

David - It is. So this basically is involved in the crosstalk between the nucleus and the mitochondria. This is kind of a gatekeeper protein that allows lipids to move back and forth.

Phil - Why would that be a thing for migration? I don't understand.

David - Yeah. So that is the $65 million question, and we don't know. There are some suggestions that it's involved in regulating these molecular products that are associated with stress, called reactive oxygen species. These are harmful byproducts that are produced when even you and I are exercising. And so the hand-wavey explanation for what different variants of this gene are doing is that it's helping regulate how much of the stressful by-product is being produced. But beyond that, we don't actually have an obvious clue of what this gene is doing.

Phil - If you're right: if you have one version of this gene, you're flying, you got a bit stressed from it, you drop down, you're in Central America; but you have the other version, you don't get as stressed, you're fine to keep flying for a bit, all the way down to South America.

David - Yeah, that's the idea.