Quantitative trait loci and interaction effects responsible for variation in female postmating mortality in Drosophila simulans and D. sechellia introgression lines

Sexual conflict and seminal fluid proteins: a dynamic landscape of sexual interactions

Sexual reproduction requires coordinated contributions from both sexes to proceed efficiently. However, the reproductive strategies that the sexes adopt often have the potential to give rise to sexual conflict because they can result in divergent, sex-specific costs and benefits. These conflicts can occur at many levels, from molecular to behavioral. Here, we consider sexual conflict mediated through the actions of seminal fluid proteins. These proteins provide many excellent examples in which to trace the operation of sexual conflict from molecules through to behavior. Seminal fluid proteins are made by males and provided to females during mating. As agents that can modulate egg production at several steps, as well as reproductive behavior, sperm "management," and female feeding, activity, and longevity, the actions of seminal proteins are prime targets for sexual conflict. We review these actions in the context of sexual conflict. We discuss genomic signatures in seminal protein (and related) genes that are consistent with current or previous sexual conflict. Finally, we note promising areas for future study and highlight real-world practical situations that will benefit from understanding the nature of sexual conflicts mediated by seminal proteins.

Selection on the Drosophila seminal fluid protein Acp62F

Sperm competition and sexual conflict are thought to underlie the rapid evolution of reproductive proteins in many taxa. While comparative data are generally consistent with these hypotheses, few manipulative tests have been conducted and those that have provided contradictory results in some cases. Here, we use both comparative and experimental techniques to investigate the evolution of the Drosophila melanogaster seminal fluid protein Acp62F, a protease inhibitor for which extensive functional tests have yielded ambiguous results. Using between-species sequence comparisons, we show that Acp62F has been subject to recurrent positive selection. In addition, we experimentally evolved populations polymorphic for an Acp62F null allele over eight generations, manipulating the opportunities for natural and sexual selection. We found that the Acp62F null allele increased in frequency in the presence of natural selection, with no effect of sexual selection.

Drosophilagenomes and the development of affordable molecular markers for species genotyping

The recent completion of genome sequencing of 12 species of Drosophila has provided a powerful resource for hypothesis testing, as well as the development of technical tools. Here we take advantage of genome sequence data from two closely related species of Drosophila, Drosophila simulans and Drosophila sechellia, to quickly identify candidate molecular markers for genotyping based on expected insertion or deletion (indel) differences between species. Out of 64 candidate molecular markers selected along the second and third chromosome of Drosophila, 51 molecular markers were validated using PCR and gel electrophoresis. We found that the 20% error rate was due to sequencing errors in the genome data, although we cannot rule out possible indel polymorphisms. The approach has the advantage of being affordable and quick, as it only requires the use of bioinformatics tools for predictions and a PCR and agarose gel based assay for validation. Moreover, the approach could be easily extended to a wide variety of taxa with the only limitation being the availability of complete or partial genome sequence data.

Targeted gene deletion and phenotypic analysis of the Drosophila melanogaster seminal fluid protease inhibitor Acp62F

Internally fertilizing organisms transfer a complex assortment of seminal fluid proteins, a substantial fraction of which are proteolysis regulators. In mammals, some seminal protease inhibitors have been implicated in male infertility and these same molecular classes of protease inhibitors are also found in Drosophila seminal fluid. Here, we tested the reproductive functions of the Drosophila melanogaster seminal fluid protease inhibitor Acp62F by generating a precise deletion of the Acp62F gene. We did not detect a nonredundant function for Acp62F in modulating the egg laying, fertility, remating frequency, or life span of mated females. However, loss of Acp62F did alter a male's defensive sperm competitive ability, consistent with the localization of Acp62F to sperm storage organs. In addition, the processing of at least one seminal protein, the ovulation hormone ovulin, is slower in the absence of Acp62F.

Seminal influences: Drosophila Acps and the molecular interplay between males and females during reproduction

Successful reproduction requires contributions from both the male and the female. In Drosophila, contributions from the male include accessory gland proteins (Acps) that are components of the seminal fluid. Upon their transfer to the female, Acps affect the female's physiology and behavior. Although primary sequences of Acp genes exhibit variation among species and genera, the conservation of protein biochemical classes in the seminal fluid suggests a conservation of functions. Bioinformatics coupled with molecular and genetic tools available for Drosophila melanogaster has expanded the functional analysis of Acps in recent years to the genomic/proteomic scale. Molecular interplay between Acps and the female enhances her egg production, reduces her receptivity to remating, alters her immune response and feeding behavior, facilitates storage and utilization of sperm in the female and affects her longevity. Here, we provide an overview of the D. melanogaster Acps and integrate the results from several studies that bring the current number of known D. melanogaster Acps to 112. We then discuss several examples of how the female's physiological processes and behaviors are mediated by interactions between Acps and the female. Understanding how Acps elicit particular female responses will provide insights into reproductive biology and chemical communication, tools for analyzing models of sexual cooperation and/or sexual conflict, and information potentially useful for strategies for managing insect pests.

Epistatic regulation of behavioural and morphological traits in the zebrafish (Danio rerio)

There is currently a lack of studies examining epistasis in general, and specifically for behavioural traits of evolutionary significance. The advent of more efficient analytical methods for exploring epistasis in QTL studies removes the computational restraint on this type of analysis and suggests that performing further analyses of existing datasets may reveal a more complete picture of the genetic architecture of the traits. Here we report the results from an epistatic QTL analysis of an F2 cross between a wild population and a standard laboratory strain of zebrafish. This further analysis was performed using a simultaneous search to identify epistatically interacting QTL affecting behavioural and morphological traits and uncovered several novel epistatic interactions that reached either genome-wide or suggestive significance levels as determined by a randomisation testing approach. These results provide novel insight into the genetic architecture of the regulation of behavioural as well as morphological phenotypes and call for more studies of epistasis for this group of traits.

Natural variation in male-induced 'cost-of-mating' and allele-specific association with male reproductive genes in Drosophila melanogaster

One of the most sharply defined sexual conflicts arises when the act of mating is accompanied by an inflated risk of death. Several reports have documented an increased death rate of female Drosophila as a result of recurrent mating. Transgenic and mutation experiments have further identified components of seminal fluid that are at least in part responsible for this toxicity. Variation among males in their tendency for matings to be toxic to their partners has also been documented, but here for the first time we identify polymorphism within particular genes conferring differential post-mating female mortality. Such polymorphism is important, as it raises the challenge of whether sexual conflict models can provide means for maintenance of polymorphism. Using a set of second chromosome extraction lines, we scored differences in post-mating female fecundity and longevity subsequent to mating, and identified significant among-line differences. Seventy polymorphisms in ten male reproductive genes were scored and permutation tests were used to identify significant associations between genotype and phenotype. One polymorphism upstream of PEBII and an amino acid substitution in CG17331 were both associated with male-induced female mortality. The same allele of CG17331 that is toxic to females also induces greater refractoriness to remating in the females, providing an example of an allele-specific sexual conflict. Postcopulatory sexual selection could lead to sexual conflict by favouring males that prevent their mates from mating, even when there is a viability cost to those females.