Paper: Group-beneficial traits, frequency-dependent selection and genotypic diversity

From: Robert Karl Stonjek (rstonjek_at_bigpond.net.au)
Date: 01/20/05 

Date: Thu, 20 Jan 2005 13:02:00 -0500 (EST)

Proceedings: Biological Sciences
ISSN: 0962-8452 (Paper) 1471-2954 (Online)
Issue: Volume 272, Number 1558 / January 07, 2005

Pages: 79 - 83
DOI: 10.1098/rspb.2004.2916

Group-beneficial traits, frequency-dependent selection and genotypic
diversity: an antibiotic resistance paradigm

Lee Alan Dugatkin A1, Michael Perlin A1, J. Scott Lucas A1, Ronald Atlas A1
A1 Department of Biology, University of Louisville, Louisville, KY 40208,
USA

Abstract:
The evolution of group-beneficial traits potentially allows the survival of
'cheaters' that would otherwise be unfit. Here we describe experimental work
on group-beneficial traits and the consequences of frequency-dependent
selection in the context of bacterial antibiotic resistance. We constructed
a 'self-limited antibiotic resistant' (SLAR) strain of Escherichia coli in
which a TEM-1 ?-lactamase was anchored to the inner membrane. In pairwise
competition experiments between the SLAR strain and ampicillin-sensitive
strains, only the SLAR strain survived in the presence of ampicillin. We
also constructed a 'shared antibiotic resistant' (SAR) strain in which TEM-1
?-lactamase protected both the SAR strain and nearby sensitive cells, thus
acting as a model for a genetically defined group-beneficial trait. In
pairwise competition experiments of the SAR strain against two different
sensitive strains of E. coli, we found that the sensitive strains maintained
themselves at frequencies of 5-12% in the presence of ampicillin. When the
relative cost of the SAR strain was lowered, its equilibrial frequency rose.
Sensitive strains also arose from pure cultures of the SAR strain. In these
cases, too, the sensitive 'cheaters' were maintained in ampicillin at
frequencies comparable to those observed in the previous competitions. These
results suggest that traits which benefit other group members can permit
survival of genotypes that otherwise would be eliminated by natural
selection, and allow the maintenance of greater genetic variation upon which
evolution can operate.

Keywords:
frequency dependence, group-beneficial traits, antibiotic resistance

Abstract from The Royal Society
http://www.journals.royalsoc.ac.uk/link.asp?id=Q91DXJLL8T0THLTD

Posted by
Robert Karl Stonjek