Friday, 20 October 2017

Evolving Great Tits - In Our Back Gardens

Great tit (Parus major) on a garden feeder.

Photo credit: Dennis van de Water, dvdwphotography.com
Evolution in your back garden—great tits may be adapting their beaks to birdfeeders.

Great tits are evolving, just up the road from where I live!

Not five minutes drive from where I sit writing this blog-post is probably the most intensely studied piece of woodland in the world, and probably nowhere is studied by people more qualified to study it. Wytham Woods is a mixed woodland owned by Oxford University and widely used for field studies by biologists from the Zoology Department.

It was by comparing the great tits from here and from Oosterhout and Veluwe, in the Netherlands, that an international research team discovered that the UK great tits have been actively evolving over the last few decades and now have longer beaks than their Dutch counterparts.

The conclusion was that it was probably the British tradition of feeding birds with peanuts in feeders designed to be inaccessible to all but the smaller birds such as tits. This may have provided the selection pressure for longer beaks to become the fitter beaks in the environment of British gardens. The British spend about twice as much on bird feeders and the food to put in them as other Europeans. Early in the 20th Century the satirical magazine Punch described bird-feeding as a British national pastime.

Abstract
We used extensive data from a long-term study of great tits (Parus major) in the United Kingdom and Netherlands to better understand how genetic signatures of selection translate into variation in fitness and phenotypes. We found that genomic regions under differential selection contained candidate genes for bill morphology and used genetic architecture analyses to confirm that these genes, especially the collagen gene COL4A5, explained variation in bill length. COL4A5 variation was associated with reproductive success, which, combined with spatiotemporal patterns of bill length, suggested ongoing selection for longer bills in the United Kingdom. Last, bill length and COL4A5 variation were associated with usage of feeders, suggesting that longer bills may have evolved in the United Kingdom as a response to supplementary feeding.

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, Jon Slate
Recent natural selection causes adaptive evolution of an avian polygenic trait
Science
(2017): Vol. 358, Issue 6361, pp. 365-368; DOI: 10.1126/science.aal3298

Copyright © 2017 The Authors
Reprinted with kind permission under licence #4213190603787

Between the 1970s and the present day, beak length has got longer among the British birds. That's a really short time period in which to see this sort of difference emerging. 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.

Professor Jon Slate.
University of Sheffield Department of Animal and Plant Sciences
One advantage the research team had was that the great tits of Wytham Woods have been studied for 70 years giving them extensive historic data to draw on. This clearly showed that the beaks of British great tits have been lengthening over time. Additionally, they were able to use data from electronically tagged birds showing how much time they spent feeding at feeders.

They found that the difference between the British great tits and the Dutch ones was due to genes strongly associated with face shape in humans and with those associated with beak shape in Darwin's finches. It was clear that this was an adaptive evolution involving change in allele frequency.

This is a stunning example of how an environmental difference will lead to a genetic difference which produces and adaptive phenotypic change. It's the sort of thing that has creationists intently examining their shoes whilst muttering, 'Yeah! But they're still great tits!", and quickly changing the subject hoping no-one has noticed that they've pretended to have forgotten what evolution really is again.

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