Biologists love clines. We’ve been mentally masticating on clines for decades.
Clines in body size. Clines in color. Clines in heart size! Clines that go in circles!
Recognizing clinal patterns in phenotypes or genotypes is fun, but discovering the mechanisms behind these clines has proven to be a real challenge. Sure, clines can be produced by forces of natural selection. But these signals can also be produced by neutral processes like isolation by distance or secondary contact between populations.
A recent study by Slyvain Antoniazza and colleagues builds on previous investigations of a widespread color cline in European Barn Owls (Tyto alba). Whereas nailing down the selective forces that may cause variation in plumage color of these owls is difficult, removing other potential explanations can be done through the process of elimination.
Antoniazza and colleagues do just that, tackling a third neutral process that may produce the observed color clines in Barn Owls, allele surfing.
In the allele surfing process, neutral alleles may ‘surf’ the wave of range expansion and increase their frequency along the way eventually forming a genetic cline.
Here, we investigate whether a postglacial colonization model is compatible with today’s observed genetic diversity of the European barn owl, and investigate how likely it is for the colour cline to have arisen by allele surfing (as opposed to natural selection) during colonization.
Using Approximate Bayesian Computation (ABC) simulations with genetic data from owls all over Europe in combination with analyses of color variation, allele surfing is ruled out as a major contributor to the color clines. When combined with previous results, it looks like the color cline in Barn Owls is most likely due to natural selection.
One explanation eliminated, now only the forces of natural selection to go.
Antoniazza S., Luca Fumagalli, Jérôme Goudet & Alexandre Roulin (2010). Local Adaptation Maintains Clinal Variation in Melanin-Based Coloration of European Barn Owls (Tyto alba), Evolution, DOI: http://dx.doi.org/10.1111/j.1558-5646.2010.00969.x
Antoniazza S., Samuel Neuenschwander, Reto Burri, Arnaud Gaigher, Alexandre Roulin & Jérôme Goudet (2014). Natural selection in a postglacial range expansion: the case of the colour cline in the European barn owl, Molecular Ecology, 23 (22) 5508-5523. DOI: http://dx.doi.org/10.1111/mec.12957