Genetics. Published Articles Ahead of Print: June 18, 2008, Copyright © 2008
doi:10.1534/genetics.107.082479


A more recent version of this article appeared on July 1, 2008.

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Both Costs and Benefits of Sex Correlate with Relative Frequency of Asexual Reproduction in Cyclically Parthenogenic Daphnia pulicaria Populations

Desiree E Allen 1* and Michael Lynch 2

1 University of Edinburgh
2 Indiana University

* To whom correspondence should be addressed. E-mail: desiree.allen{at}ed.ac.uk.

Submitted on September 28, 2007
Revised on December 14, 2007
Accepted on 2 May 2008


Abstract

Sexual reproduction is generally believed to yield beneficial effects via the expansion of expressed genetic variation, which increases the efficiency of selection and the adaptive potential of a population. However, when non-additive gene action is involved, sex can actually impede the adaptive progress of a population. If selection promotes coupling disequilibria between genes of similar effect, recombination and segregation can result in a decrease in expressed genetic variance in the offspring population. In addition, when non-additive gene action underlies a quantitative trait, sex can produce a change in trait means in a direction opposite to that favoured by selection. In this study we measured the change in genotypic trait means and genetic variances across a sexual generation in four populations of the cyclical parthenogen Daphnia pulicaria, which vary predictably in their incidence of sexual reproduction. We show that both the costs and benefits of sex, as measured by changes in means and variances in life-history traits, increase substantially with decreasing frequency of sex.

Key Words: Cyclical parthenogen, Daphnia, Linkage disequilibrium, Sexual reproduction