UK Great Tit: Why the long beak?

24 October 2017

Interview with

Lewis Spurgin, University of East Anglia

We’ve talked about the bees, now it’s time for the birds! Scientists across Europe have been studying the evolution of the Great Tit for decades. Over time, animals evolve to have features that are most suited to their environment which, in turn, make them more likely to survive and reproduce. This process is known as natural selection, and it’s happening in your back garden! Researchers have found that UK Great Tits have evolved to have longer beaks than their European relatives. How? Well, we Brits are rather fond bird feeders and so the Great Tits have evolved to have longer beaks to get their grub. Izzie Clarke spoke to Lewis Spurgin from the University of East Anglia about what these birds look like...

Lewis - The Great Tit’s a small, colourful bird that you’re very likely to see in your garden. It’s found all across Europe and scientists in Oxford, and the Netherlands, and other places have been studying the biology and ecology of the species for decades. We didn’t just want to look at how natural selection works at the DNA level, we wanted to do that and link the genetic differences that we saw to actual physical differences among individuals and populations.

Izzie - What exactly did you find?

Lewis - In a nutshell, we were able to show using DNA that there’s been really recent and rapid selection for longer beaks specifically in British Great Tits. We showed that if you were a British Great Tit, and you’ve got gene variants that code for a longer beak, you’re likely to fledge more offspring. And we found this intriguing correlation between beak length in the UK and how often birds visit bird feeders. So this led us to speculate the widespread use of bird feeders in the UK might have resulted in natural selection for the longer beaks we see in British Great Tits compared to their counterparts in mainland Europe.

Izzie - So the British Great Tits are a little bit more greedy, shall we say?

Lewis - Yeah, that’s possible.

Izzie - How exactly do you go about collecting all of this information from the UK Great Tits compared to these ones in the Netherlands?

Lewis - We start off by catching birds and taking a small sample, either from a feather or a small blood sample which doesn’t harm them, and from that we can extract their DNA. Using that we can use statistics to compare the DNA of the UK and the Dutch populations and we can look for genes that are involved in natural selection.

The most significant one that we found was a gene called COL 405, which is a gene that produces collagen. And then what we can do is look at what these genes do in order to say something about how selection produces differences among individuals and populations. Using that approach, we found that the genes under natural selection between our UK and our Dutch Great Tits were involved in controlling face shape.

We also find evidence of one of the genes that is also associated with beak shape variation in Darwin’s finches. So this was what led us to think that perhaps these genes might be involved in controlling beak variation in birds and, when we looked at that statistically, we showed that that was the case.

Izzie - Over what period are we talking about because we have this idea that natural selection in evolution takes quite a long time, so how long has this process been going on?

Lewis - Natural selection can take quite a long time, but it can also be quite rapid. We actually have a long term study of Great Tits in Wytham Woods, so run by Oxford University, and they’ve been measuring beaks in Great Tits for a really long time in Wytham Woods. If we take Great Tits from the 1970s through to today, over that period of time we can measure an observable increase in beak length, but probably this has been over the last couple of hundred years or so this natural selection. So that’s one of the striking things about the study is that it’s an example of really quite rapid and recent natural selection.

Izzie - What does this tell us to have this longer beak for these UK Great Tits?

Lewis - In the sense that with the birds that have longer beaks, or at least the birds the genetic variation for longer beaks, are able to fledge more offspring. So in that sense, if you are able to fledge more offspring, then more of your genetic descendants can be recruited into the breeding population and you’re going to evolutionarily be more successful. Even small differences in your survival or reproduction can make a big effect overall on variation in a population.

I think what we really need to get at next is what exactly is the cause, and so I think we’d like to follow up on this bird feeder link and think about what, how, and where might bird feeders be driving differences between British and mainland European populations? Does this occur in other species and what are the consequences of removing that selection pressure and mechanistically how does that work? There’s lots of interesting things that we can look into there.


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