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Uploaded:2021-09-10
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Today we're talking about birds — from how they are evolving in response to climate change and how one species is surprisingly healthy, genetically, despite being critically endangered.

Hosted by: Stefan Chin

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Sources:
Ryding S, Klaasen M, Tattersall GJ, Gardner JL, Symonds MRE. Shape-shifting: changing animal morphologies as a response to climatic warming. Trends in Ecology & Evolution. 2021. https://doi.org/10.1016/j.tree.2021.07.006
Press release: https://www.eurekalert.org/news-releases/927171

Dussex et al. Population genomics analyses of the critically endangered kākāpō. Cell Genomics. 2021. https://doi.org/10.1016/j.xgen.2021.100002
Press release: https://www.eurekalert.org/news-releases/927300

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Thank you to Omaze for sponsoring today’s episode.

To support a great cause and  potentially win a Tesla Model S Plaid, go to omaze.com/scishow. [♪ INTRO]. The news is all about birds this week!

Well, our news, at least. And really,  what else do you need to know?   So first up, a review paper out this  week in Trends in Ecology and Evolution suggests that certain bird  species, as well as other animals, may be sort of shape-shifting to  keep up with the climate crisis.   In particular, scientists were  looking at a general pattern naturalists have noticed called Allen’s rule.   Picture a bird, like a  little sparrow or something, sitting on a branch in a snowy  forest, trying to keep warm.   Most of its body is covered in feathers,  which it can poof up for insulation. But not its beak, which is naked.   This makes the beak kind of a weak point,  a little uninsulated spot where the poofy sparrow will lose body heat, putting  it at risk of bird hypothermia.   So you might imagine that, in this  snowy forest, having a tiny beak might be advantageous, because  you’re minimizing heat loss.   On the other hand, take that  little bird and put it in a desert, where the bird is no longer  at risk of hypothermia, but instead birdy heat stroke.

There, maybe a big honking  schnozz would be better, since it can help heat escape. And that’s the logic behind Allen’s rule. In short, warm-blooded  animals tend to evolve to have bigger heat-radiating appendages, like  ears, tails, or beaks, in warmer areas and smaller ones in colder areas.   And, indeed, we do generally see this play  out in a lot of species, including birds.   What’s interesting here today  is that, all around the world, the average temperature of different regions  is rising due to the climate crisis.

Which begs the question of  whether we’ll see a corresponding shift in the size of heat-radiating  appendages, as predicted by Allen’s rule. Like, if the average size of certain birds’ beaks has increased over time in  areas that are getting warmer. To figure this out, the researchers in  this study compiled and sifted through studies of both old museum collections  and living animals in the wild.   And lo and behold, it seems like this is, indeed, happening to many animal  populations around the world.

For example, it turns out that Australian  parrots are getting bigger bills, with changes lining up with the  average summer high temperatures in the five years before collection. And in the North American dark-eyed junco,  which is an extremely cute little bird, bigger bill sizes were associated with  episodes of unusually warm winter weather. And the researchers saw this in mammals too, such as increasingly large  appendages in shrews and bats.

Now, it’s worth pointing  out that this doesn’t mean that individual animals are morphing their bodies. Rather, it reflects an overall  shift in the population over time thanks to natural selection. So it’s the average appendage.

And it’s difficult to actually tie any one  particular change to the climate crisis specifically, since there  are a lot of other factors, like possible changes in food  sources, that could be responsible. Nevertheless, taken as a whole,  there is enough there to argue this is happening on a broad scale. Now, speaking of birds with big schnozzes, let’s zoom in on the southern  hemisphere for our second story.

Aotearoa New Zealand, if you  didn’t know, is home to the kākāpō, a large, flightless parrot that’s  just, well, just look at it. I think we can all just really enjoy  the fact that this bird exists. Unfortunately, like a lot of large  flightless birds that live on islands, while it used to be really common  before people, today it’s pretty rare.

While their historic numbers may have  been in the hundreds of thousands, by 1995 they’d dropped to 51 individuals. 50 on an isolated island and just one,  named Richard Henry, on the mainland. Today their numbers have  improved, up to about 200. But going through such a sudden population drop is rarely good news for a species.

Even if kākāpōs were to swell  back up to previous numbers, they still seem to have lost about 70-80%  of their previous genetic diversity. This kind of population bottleneck  generally results in in-breeding, which typically increases the  number of harmful mutations present in a population’s collective DNA. But, remarkably, these parrots may  actually be doing better than we’d expect.

Scientists publishing this week in Cell  Genomics analyzed the genomes of 36 modern individuals and compared them to DNA from 13 130-year-old specimens from the mainland. That is, before the bottleneck took place  and the mainland population went extinct. They found that the current population  actually seems to have lower overall numbers of potentially harmful  mutations, counter to what we’d expect.

Now, this could be partly due to genetic drift, which is basically just the random  chance of a mutation disappearing. But it could also be the result  of something called purging. See, in a large population, harmful  variants of genes are more likely to get spread around and  paired with healthier versions, so they don’t end up having much impact.

But in a small population, as happens  with inbreeding, the mutations are more likely to get concentrated  in individuals, and then natural selection kind of does its thing. Basically, in smaller populations, the  harmful mutations have a harder time hiding. Unfortunately, kākāpōs still  experience other problems as a result of their small population.

For example, their eggs have a  relatively low chance of hatching, which may be a result of inbreeding. But the good news is that these  findings could be helpful in protecting and growing the kākāpō population. So, they’re still critically endangered,  but it does give us a bit more hope about keeping these birds around for a long time.

Thank you to Omaze for sponsoring this episode. Omaze is a fundraising platform  that gives everyone a chance to win unique prizes while helping to  make the world a better place. Right now, they are partnering with  Reverb.org to offer a chance to win a Tesla Model S Plaid.

REVERB works with musicians, festivals,  and venues to make events greener by eliminating single-use plastic  water bottles at concerts, composting and donating food waste, and using  sustainable biodiesel in tour buses. They hope to inspire both music lovers  and creators to take environmental and social action that collectively  creates large-scale, measurable change. If you’d like to support REVERB and  potentially win a Tesla Model S Plaid, you can go to omaze.com/scishow to get started. [♪ OUTRO].