15) Variation versus stability
Species can remain mostly unchanged for millions of years, long enough for us to pick up their traces in the fossil record. But they change, too, and often very suddenly. This has led some to wonder whether species — usually those developing along specific tracks — store the potential for sudden change under the hood, unleashing a flood of otherwise hidden variation at times of environmental stress — variation on which selection can act.
This idea of such ‘evolutionary capacitance’ was first mooted by Suzanne Rutherford and Susan Lindquist in startling experiments on fruitflies. Their idea was that key proteins involved in the regulation of developmental processes are ‘chaperoned’ by a protein called Hsp90 that is produced more at times of stress. On occasion, Hsp90 is overwhelmed by other processes and the proteins it normally regulates are left to run free, producing a welter of otherwise hidden variation.
Aviv Bergman from the Albert Einstein College of Medicine in New York and Mark Siegal at New York University explored whether evolutionary capacitance is particular to Hsp90 or found more generally; their study was published in 2003. They used numerical simulations of complex gene networks and genomewide expression data from yeast strains in which single genes had been deleted. They showed that most, and perhaps all, genes hold variation in reserve that is released only when they are functionally compromised. In other words, it looks as if evolutionary capacitance might go wider and deeper than Hsp90.
Reference
Bergman, A. & Siegal, M. L. Nature 424, 549–552 (2003).
Additional resources
Stearns, S. C. Nature 424, 501–504 (2003).
Rutherford, S. L. & Lindquist, S. Nature 396, 336–342 (1998).
Author websites
Mark Siegal: http://www.nyu.edu/fas/biology/faculty/siegal/index.html
Aviv Bergman: http://www.bergmanlab.org
Susan Lindquist: http://www.wi.mit.edu/research/faculty/lindquist.html
Suzanne Rutherford: http://depts.washington.edu/mcb/facultyinfo.php?id=142
Stephen Stearns: http://www.yale.edu/eeb/stearns
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