Are Bird Feeders Driving Evolution Of Longer Beaks In British Tits? | @GrrlScientist

How a simple pleasure, feeding birds, has been translated into a mechanism for rapid evolutionary change in beak length in a British backyard bird species

by GrrlScientist for Forbes | @GrrlScientist

Great tit (Parus major) on a garden bird feeder.
(Credit:
Dennis van de Water)

I ran across a sweet little paper in Science recently that documents the rapid evolution of a physical trait in a bird in response to an environmental change. The study bird, the great tit, Parus major, is a small, common garden bird in much of Europe and Asia.

In this study, several international teams of researchers collaborated to compare measurements for beak length in more than 3000 great tits living in three separate populations; one in the United Kingdom and two in the Netherlands. The research teams found that beaks of great tits living in a long-term study site, Wytham Woods in the UK (949 birds total; grey triangle, Figure 1), were 0.3mm longer, on average, than beaks of great tits living in two other long-term study sites, Oosterhout (254 birds; yellow square, Figure 1) and Veluwe (1812 birds; green circle, Figure 1) in the Netherlands (Figure 1).

Fig. 1. Population structure of Western European great tits. (A) Worldwide distribution of P. major and sampling locations in Wytham (gray triangle), Oosterhout (yellow square), and Veluwe (green circle). (B) Principal component analysis of genotype data. © ADMIXTURE plot with K = 3, which is both the most likely number of clusters and the number of geographically distinct sampling sites. Levels of genetic structure are low.
(doi:
10.1126/science.aal3298)

This was a surprise because great tits are thought to be nearly alike throughout their entire huge range (yellow, Figure 1A, lower panel). Even more surprising is that historical data indicated this trend towards longer beaks in British tits was quite recent — and it occurred quickly.

“Between the 1970s and the present day, beak length has got longer among the British birds,” said study co-author, Jon Slate, a professor at the University of Sheffield. He noted that beak length had been increasing over a period of roughly 100 years or so.

“That’s a really short time period in which to see this sort of difference emerging.”

Which genetic differences underlie this trait? This question was a bit more complicated to answer because beak length in birds is a “polygenic trait”, which means that it is influenced by a group of genes, working in concert. So identifying which genes these are is where the real work began.

The research teams screened these birds’ genomes and identified regions that were changing rapidly in the UK tits, indicating the genes in those regions were being affected by natural selection. Further investigations uncovered a handful of likely genes in these genomic regions. A look through an online genetic database was encouraging: several of these candidate genes are known to affect beak shape in Darwin’s finches (ref), which are world famous for rapidly changing their beak size and shape to adapt to environmental challenges (read more). These candidate genes also closely matched some of the genes known to influence face shape in humans (ref).

The researchers’ analyses confirmed that several of these candidate genes were consistently associated with the bill length variation that they had measured. One gene in particular stood out: the collagen gene, COL4A5. The teams found that British tits with the long-beak variant of the COL4A5 collagen gene raised more chicks to fledging, on average, than tits with the short-beak variant. This indicated that there is strong ongoing selective pressure for tits to grow longer bills in the United Kingdom. This contrasted sharply with the Netherlands data, where tits with the long-beak gene variant raised fewer chicks to fledging.

We’ve long known that birds’ beak structures are often specially adapted to the food they eat, which has led to the huge variety of distinctive beak shapes and sizes that we see today. In addition to Darwin’s finches, the Hawaiian honeycreepers are another example of the stunning variation in avian beak shapes and sizes amongst closely related birds (read more). But beak specializations in honeycreepers took thousands of years to evolve — but not so, apparently, for British tits.

Hawaiian honeycreepers. Look at those beaks!
(Credit: H. Douglas Pratt.)

This raises the question: Is beak length in great tits related somehow to food? If so, why do we see opposite effects on beak length between tits in Britain versus those in the Netherlands?

The one big difference between Europe and Britain is the presence of garden bird feeders. Unlike many Europeans, the British became avid bird feeders around Victorian times, and this, in turn, could be driving the evolution for longer beaks in common garden birds throughout the UK.

“In the UK, we spend around twice as much on birdseed and birdfeeders than mainland Europe — and, we’ve been doing this for some time,” said another of the study’s co-authors,” said Lewis Spurgin, a Research Fellow at the University of East Anglia. “In fact, at the start of the 20th century, Punch magazine described bird feeding as a British national pastime.”

People in the UK are estimated to spend £334m per year on seeds for wild birds, whereas people in mainland Europe — a much larger landmass, might I add — spend only half as much; £167m.

When the researchers analyzed data collected by electronic monitoring tags attached to some of the Wytham Woods tits, they could track how much time each tagged individual spent at bird feeders. They found that Wytham Woods tits with the long-beak gene variant visited bird feeders more often than those with the short-beak gene variant.

“Although we can’t say definitively that bird feeders are responsible, it seems reasonable to suggest that the longer beaks amongst British great tits may have evolved as a response to this supplementary feeding,” said Dr. Spurgin.

Preliminary data indicate that the longer beak gene variant may only be found in tits living in the UK, where garden bird feeders are much more common.

“What is it that gives birds with longer beaks an advantage at the feeder sites?” asked the lead author of the study, Mirte Bosse, a postdoctoral fellow at the Netherlands Institute of Ecology and at Wageningen University.

It’s possible that longer beaks allow those birds to get the best seeds buried deeper in bird feeders or, as Dr. Spurgin speculated: “it could be that they don’t drop seeds when they’re carrying them away.”

Nevertheless, eating more or better food can have direct, lasting effects upon a population. So investigating the changes in bird feeder design over the years, and studies into how great tits eat from feeders could clarify this situation.

“It’s certainly true that birds who have adapted to better access food will be in better condition generally, and so better able to reproduce and outperform others without that adaptation,” Dr. Spurgin pointed out. So bird feeding is a powerful way to drive evolution of physical traits, particularly beak structure, in wild birds.

“The way we’ve detected evolutionary differences in the wild is unique,” said lead author of the study, Mirte Bosse, a postdoctoral fellow at the Netherlands Institute of Ecology and at Wageningen University. “It was the genome that led the way. That this is possible for a trait influenced by so many genes, holds many promises for future discoveries.”

“We now know that this increase in beak length, and the difference in beak length between birds in Britain and mainland Europe, is down to genes that have evolved by natural selection,” agreed Professor Slate.

Not only does this paper describe the relationship between a physical trait and the genetics that underlie it, but I think this paper is a lovely reminder that evolution is a dynamic process and, in today’s world, humans are a major player driving evolutionary change.

Source:

Mirte Bosse, Lewis G. Spurgin, Veronika N. Laine, Ella F. Cole, Josh A. Firth, Phillip Gienapp, Andrew G. Gosler, Keith McMahon, Jocelyn Poissant, Irene Verhagen, Martien A. M. Groenen, Kees van Oers, Ben C. Sheldon, Marcel E. Visser, and Jon Slate (2017). Recent natural selection causes adaptive evolution of an avian polygenic trait, Science, 358(6361):365–368 | doi:10.1126/science.aal3298

Also cited:

Sangeet Lamichhaney, Jonas Berglund, Markus Sällman Almén, Khurram Maqbool, Manfred Grabherr, Alvaro Martinez-Barrio, Marta Promerová, Carl-Johan Rubin, Chao Wang, Neda Zamani, B. Rosemary Grant, Peter R. Grant, Matthew T. Webster & Leif Andersson (2015). Evolution of Darwin’s finches and their beaks revealed by genome sequencing, Nature, 518:371–375 | doi:10.1038/nature14181


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Originally published at Forbes on 30 November 2017.

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