An evolutionary process that assembles phenotypes through space rather than through time
Richard Shine a,1, Gregory P. Brown a, and Benjamin L. Phillips b
-Author Affiliations
aSchool of Biological Sciences A08, University of Sydney, Sydney, NSW 2006, Australia; and
bSchool of Marine and Tropical Biology, James Cook University, Townsville, QLD 4811, Australia
Edited by David B. Wake, University of California, Berkeley, CA, and approved February 22, 2011 (received for review December 16, 2010)
Abstract
In classical evolutionary theory, traits evolve because they facilitate organismal survival and/or reproduction. We discuss a different type of evolutionary mechanism that relies upon differential dispersal. Traits that enhance rates of dispersal inevitably accumulate at expanding range edges, and assortative mating between fast-dispersing individuals at the invasion front results in an evolutionary increase in dispersal rates in successive generations. This cumulative process (which we dub “spatial sorting”) generates novel phenotypes that are adept at rapid dispersal, irrespective of how the underlying genes affect an organism's survival or its reproductive success. Although the concept is not original with us, its revolutionary implications for evolutionary theory have been overlooked. A range of biological phenomena (e.g., acceleration of invasion fronts, insular flightlessness, preadaptation) may have evolved via spatial sorting as well as (or rather than) by natural selection, and this evolutionary mechanism warrants further study.
colonization, evolution, spatial disequilibrium, nonadaptive evolution
Footnotes
↵1To whom correspondence should be addressed.
E-mail:rick.shine@sydney.edu.au.
Author contributions: R.S., G.P.B., and B.L.P. designed research; R.S. performed research; and R.S. and B.L.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at
Freely available online through the PNAS open access option.
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SUPPORTING INFO EXCERPT/EXCERTO DA INFO SUPLEMENTAR:
"The results of this model demonstrate that (at least in theory) spatial sorting alone is sufficient to cause evolution, that is, to cause rates of dispersal to evolve upwards on the expanding range edge.
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Clearly, the process will occur even faster if the same trend is favored by natural selection as well. However, contrary to Darwinian orthodoxy, our model shows that phenotypic traits that confer higher dispersal rates can evolve simply by spatial assortment, with no need for some genes to leave more copies than do others."
