Sex ratio distorter reduces sperm competitive ability in an insect.
Selfish genetic elements (SGEs) are ubiquitous in animals and often associated with low male fertility due to reduced sperm number in male carriers. In the fruit fly Drosophila pseudoobscura, the meiotic driving X chromosome "sex ratio" kills Y-bearing sperm in carrier males (SR males), resulting in female only broods. We competed SR males against the ejaculates of noncarrying standard males (ST males), and quantified the number of sperm transferred by SR and ST males to females. We show that SR males are very poor sperm competitors, which is partly related to transfer of fewer sperm during mating. However, sperm numbers alone cannot explain the observed paternity reduction, indicating SR males' sperm may be of reduced quality, possibly due to damage during the killing of the noncarrying Y-sperm. The reduction in sperm competitive ability due to SR is large enough to potentially stabilize the spread of sex ratio drive through populations. The poor sperm competitive ability of SR males coupled with their low fitness as mates could favor increased remating by females to reduce paternity by SR males. Given the generally poor performance of SGE-carrying males in sperm competition, this may generate strong selective pressure favoring polyandry in many species.
Price
Tom A R
TAR
School of Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, United Kingdom.|E-mail: Tom.Price@exeter.ac.uk.
Bretman
Amanda J
AJ
School of Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, United Kingdom.|School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.|E-mail: A.Bretman@uea.ac.uk.
Avent
Tomos D
TD
School of Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, United Kingdom.|E-mail: tomavent@hotmail.com.
Snook
Rhonda R
RR
Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom.| E-mail: r.snook@sheffield.ac.uk.
Hurst
Gregory D D
GDD
School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, United Kingdom.|E-mail: G.Hurst@liverpool.ac.uk.
Wedell
Nina
N
School of Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, United Kingdom.|E-mail: N.Wedell@Exeter.ac.uk.
D000818:Animals; D003307:Copulation / Q000502:physiology*; D004330:Drosophila / Q000502:physiology*; D005260:Female; D008297:Male; D012091:Repetitive Sequences, Nucleic Acid; D012744:Sex Ratio; D013076:Sperm Count; D013094:Spermatozoa / Q000502:physiology*