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Summary: ORIGINAL ARTICLE
doi:10.1111/j.1558-5646.2010.01062.x
VARIATION IN THE STRENGTH AND SOFTNESS
OF SELECTION ON DELETERIOUS MUTATIONS
Azadeh Laffafian,1
James D. King,1
and Aneil F. Agrawal1,2
1
Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario,
M5S 3B2, Canada
2
E-mail: a.agrawal@utoronoto.ca
Received March 18, 2010
Accepted May 23, 2010
Deleterious alleles constantly enter populations through mutation. Understanding the nature of selection against such alleles is
required to assess their impact on populations. In a subdivided population, two distinct aspects of selection are important: the
strength and softness of selection. Using Drosophila melanogaster, we estimated both aspects of selection for each of eight loci
across two environments. These data allow us to test conflicting predictions about the factors affecting the softness of selection.
First, we show that the softness of selection is not determined by ecological conditions alone. Second, we find that resource
limitation makes selection stronger but does not make it softer. Third, we find that wild-type individuals tend to benefit more than
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