Multiple mating by females establishes the opportunity for postcopulatory sexual selection favoring males whose sperm is preferentially employed in fertilizations. Here we use natural variation in a wild population of Drosophila melanogaster to investigate the genetic basis of sperm competitive ability. Approximately 101 chromosome 2 substitution lines were scored for components of sperm competitive ability (P1Ј, P2Ј, fecundity, remating rate, and refractoriness), genotyped at 70 polymorphic markers in 10 male reproductive genes, and measured for transcript abundance of those genes. Permutation tests were applied to quantify the statistical significance of associations between genotype and phenotype. Nine significant associations were identified between polymorphisms in the male reproductive genes and sperm competitive ability and 13 were identified between genotype and transcript abundance, but no significant associations were found between transcript abundance and sperm competitive ability. Pleiotropy was evident in two genes: a polymorphism in Acp33A associated with both P1Ј and P2Ј and a polymorphism in CG17331 associated with both elevated P2Ј and reduced refractoriness. The latter case is consistent with antagonistic pleiotropy and may serve as a mechanism maintaining genetic variation.

We applied association analysis to elucidate the genetic basis for variation in phenotypes affecting postcopulatory sexual selection in a natural population of Drosophila melanogaster. We scored 96 third chromosome substitution lines for nine phenotypes affecting sperm competitive ability and genotyped them at 72 polymorphisms in 13 male reproductive genes. Significant heterogeneity among lines (P , 0.01) was detected for all phenotypes except male-induced refractoriness (P ¼ 0.053). We identified 24 associations (8 single-marker associations, 12 three-marker haplotype associations, and 4 cases of epistasis revealed by single-marker interactions). Fewer than 9 of these associations are likely to be false positives. Several associations were consistent with previous findings ½Acp70A with the male's influence on the female's refractoriness to remating (refractory), Esterase-6 with a male's remating probability (remating) and a measure of female offspring production ( fecundity), but many are novel associations with uncharacterized seminal fluid proteins. Four genes showed evidence for pleiotropic effects ½CG6168 with a measure of sperm competition (P29) and refractory, CG14560 with a defensive measure of sperm competition (P19) and a measure of female fecundity, Acp62F with P29 and a measure of female fecundity, and Esterase-6 with remating and a measure of female fecundity. Our findings provide evidence that pleiotropy and epistasis are important factors in the genetic architecture of male reproductive success and show that haplotype analyses can identify associations missed in the single-marker approach.

In Drosophila melanogaster, accessory gland proteins (Acps) that a male transfers during mating affect his reproductive success by altering the female's behaviour and physiology. To test the role of male condition in the expression of Acps, we manipulated the pre-adult environment and examined adult males for relative transcript abundance of nine Acps, and for post-copulatory traits that Acps influence. Larval culture density had no effect on any measured trait. Larval nutrient availability impacted the number of sperm transferred and stored, the male's ability to induce refractoriness in his mate, but relative transcript abundance of only a single Acp (Acp36DE). Reduced male body size due to low yeast levels affected sperm competition. Our data indicate that some female-mediated post-copulatory traits (induced refractoriness and sperm transfer and storage) might be influenced by the male's developmental environment, but relative expression of most Acps and some traits they influence (P1') are not.

Mitochondria are essential multifunctional organelles whose metabolic functions, biogenesis, and maintenance are controlled through genetic interactions between mitochondrial and nuclear genomes. In natural populations, mitochondrial efficiencies may be impacted by epistatic interactions between naturally segregating genome variants. The extent that mitochondrial-nuclear epistasis contributes to the phenotypic variation present in nature is unknown. We have systematically replaced mitochondrial DNAs in a collection of divergent Saccharomyces cerevisiae yeast isolates and quantified the effects on growth rates in a variety of environments. We found that mitochondrial-nuclear interactions significantly affected growth rates and explained a substantial proportion of the phenotypic variances under some environmental conditions. Naturally occurring mitochondrial-nuclear genome combinations were more likely to provide growth advantages, but genetic distance could not predict the effects of epistasis. Interruption of naturally occurring mitochondrial-nuclear genome combinations increased endogenous reactive oxygen species in several strains to levels that were not always proportional to growth rate differences. Our results demonstrate that interactions between mitochondrial and nuclear genomes generate phenotypic diversity in natural populations of yeasts and that coadaptation of intergenomic interactions likely occurs quickly within the specific niches that yeast occupy. This study reveals the importance of considering allelic interactions between mitochondrial and nuclear genomes when investigating evolutionary relationships and mapping the genetic basis underlying complex traits. M ITOCHONDRIAL energy production, which affects virtually every aspect of cellular fitness, requires the participation of two genomes. The mitochondrial genome encodes for essential components of the oxidative phosphorylation machinery and mitochondrial ribosomal RNAs and transfer RNAs. The nuclear genome encodes nearly 1000 proteins that are imported to the organelle where they compose the majority of the mitochondrial proteome. Specific interactions between components of both genomes are required at many levels, including mitochondrial DNA (mtDNA) replication, repair, and inheritance and transcription, translation, and assembly of the electron transport chain components. The respiratory complexes themselves are heterogeneous, composed of both nuclear and mitochondrially encoded proteins. Over evolutionary time, these interactions have been optimized, in part, to regulate production of the reactive oxygen species (ROS) that are the by-products of mitochondrial respiration.Allelic variation in both genomes can affect mt-n interactions and alter mitochondrial fitness. These interactions have been shown to have direct consequences on healthrelated and life-history phenotypes in several taxa. In insects such as Drosophila and Callosobruchus (seed beetle), exchanging mtDNA variants between distinct populations has led to lowered metabo...

In many species, seminal fluid proteins (SFPs) affect female post-mating behavioral patterns, including sperm storage, egg laying, feeding, and remating. Yet, few studies have investigated the patterns of allocation, depletion, and replenishment of SFPs in male animals, despite the importance of these proteins to male and female reproductive success. To investigate such SFP dynamics, it is necessary to have a sensitive method for quantifying SFP levels in males and mated females. We developed such a method by adapting the enzyme-linked immunosorbent assay (ELISA) using anti-SFP antibodies. Here, we first use two Drosophila melanogaster SFPs (ovulin and sex peptide) to demonstrate that ELISAs provide accurate measures of SFP levels. We find that, consistent with previous data from Western blotting or immunofluorescence studies, levels of both ovulin and sex peptide decline in the mated female with time since mating, but they do so at different rates. We then use ELISAs to show that males become depleted of SFPs with repeated matings, but that previously mated males are able to transfer “virgin” levels of SFPs after 3 days of sexual inactivity. Finally, we demonstrate that ELISAs can detect SFPs from wild-caught D. melanogaster males and, thus, potentially can be used to track mating patterns in the wild. This method of measuring SFP dynamics can be used in a wide range of species to address questions related to male reproductive investment, female mating history, and variation in female post-mating behavioral changes.