Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.07.31.231142v1?rss=1

Authors: Freeman, B., Schluter, D., Tobias, J.

Abstract:

Where is evolution fastest? The biotic interactions hypothesis proposes that greater species richness creates more ecological opportunity, driving faster evolution at low latitudes, whereas the "empty niches" hypothesis proposes that ecological opportunity is greater where diversity is low, spurring faster evolution at high latitudes. Here we test these contrasting predictions by analyzing rates of bird beak evolution for a global dataset of 1141 sister pairs of birds. We find that beak size evolves at similar rates across latitudes, while beak shape evolves faster in the temperate zone, consistent with the empty niches hypothesis. By comparing rates of evolution in sympatric versus allopatric sister lineages, we also find evidence that character displacement is similar between latitudes. Our analyses focusing on recent speciation events finds that drivers of evolutionary diversification are more potent at higher latitudes, thus calling into question multiple hypotheses invoking faster tropical evolution to explain the latitudinal diversity gradient.

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