Experimental mutation-accumulation on the X chromosome of Drosophila melanogaster reveals stronger selection on males than females

Martin A Mallet,Jessica M Bouchard,Adam K Chippindale,Christopher M Kimber

doi:10.1186/1471-2148-11-156

Abstract

BackgroundSex differences in the magnitude or direction of mutational effect may be important to a variety of population processes, shaping the mutation load and affecting the cost of sex itself. These differences are expected to be greatest after sexual maturity. Mutation-accumulation (MA) experiments provide the most direct way to examine the consequences of new mutations, but most studies have focused on juvenile viability without regard to sex, and on autosomes rather than sex chromosomes; both adult fitness and X-linkage have been little studied. We therefore investigated the effects of 50 generations of X-chromosome mutation accumulation on the fitness of males and females derived from an outbred population of Drosophila melanogaster.ResultsFitness declined rapidly in both sexes as a result of MA, but adult males showed markedly greater fitness loss relative to their controls compared to females expressing identical genotypes, even when females were made homozygous for the X. We estimate that these mutations are partially additive (h ~ 0.3) in females. In addition, the majority of new mutations appear to harm both males and females.ConclusionsOur data helps fill a gap in our understanding of the consequences of sexual selection for genetic load, and suggests that stronger selection on males may indeed purge deleterious mutations affecting female fitness.

Highlights

Sex differences in the magnitude or direction of mutational effect may be important to a variety of population processes, shaping the mutation load and affecting the cost of sex itself
Understanding the properties of new mutations is critical to a broad range of evolutionary theory, including models relating to the maintenance of genetic variation in the face of selection [1,2,3], the persistence of small populations [4], and the advantages of sexual reproduction [5,6,7]
Mutation-accumulation (MA) experiments, in which new mutations are allowed to fix by removing selection, have typically measured changes in juvenile viability as an indicator of total fitness

Summary

Introduction

Sex differences in the magnitude or direction of mutational effect may be important to a variety of population processes, shaping the mutation load and affecting the cost of sex itself. These differences are expected to be greatest after sexual maturity. Mutation-accumulation (MA) experiments, in which new mutations are allowed to fix by removing selection, have typically measured changes in juvenile viability (egg-to-adult survival) as an indicator of total fitness. Variation in juvenile growth, rather than survival, can have carryover effects to adult size, condition and the realization of adult fitness This would imply that mutation pressure on total fitness could be much greater than studies examining juvenile fitness alone would imply. Sexual selection on males could yield a correlated response in female fitness

Methods

Results

Discussion

Conclusion