No evidence for minority male mating advantage in wild type strains of Drosophila ananassae tested in multiple-choice experiments

Minority male mating advantage was tested in wild type strains of Drosophila ananassae through multiple-choice experiments. Mating success of two types of flies present in five different ratios was scored by direct observation in an Elens-Wattiaux mating chamber. We found no evidence for minority male mating advantage in wild type strains of D. ananassae. The relative mating success of two types of females was also compared in the multiple-choice experiments at different ratios; there was no evidence for a rare female effect. Further, there was similarity in the results of experiments employing different methods. The total number of homogamic and heterogamic matings was obtained by combining the data (all five ratios) from each experiment. Homogamic matings were significantly more frequent than heterogamic ones, which demonstrates preferential mating between males and females of the same strain; this was also supported by a lower isolation estimate. There was also a significant difference in the degree of mating preference between the two strains.     

Genetics of Drosophila simulans male mating discrimination in crosses with D. melanogaster

The genetic bases of sexual isolation between Drosophila melanogaster and D. simulans have been mainly studied in females, and there is little information about the role of the males in interspecific mating discrimination. Using D. simulans synthetic lines with compound chromosomes from a population of the Seychelles Islands (high frequency of interspecific mating) and a multimarker strain (low frequency), we show that D. simulans males play an important role in discriminating D. melanogaster females. The genetics of male discrimination fits well with the inheritance mode of a single locus, dominant for sexual isolation, located in chromosome II near the net mutation (2L-0.0). The heterospecific mating success of the male was not related to his sexual vigor. The specific load of male cuticular hydrocarbons was counted as a possible source of discrimination used by the D. melanogaster female.     

No accelerated rate of protein evolution in male-biased Drosophila pseudoobscura genes

Sexually dimorphic traits are often subject to diversifying selection. Genes with a male-biased gene expression also are probably affected by sexual selection and have a high rate of protein evolution. We used SAGE to measure sex-biased gene expression in Drosophila pseudoobscura. Consistent with previous results from D. melanogaster, a larger number of genes were male biased (402 genes) than female biased (138 genes). About 34% of the genes changed the sex-related expression pattern between D. melanogaster and D. pseudoobscura. Combining gene expression with protein divergence between both species, we observed a striking difference in the rate of evolution for genes with a male-biased gene expression in one species only. Contrary to expectations, D. pseudoobscura genes in this category showed no accelerated rate of protein evolution, while D. melanogaster genes did. If sexual selection is driving molecular evolution of male-biased genes, our data imply a radically different selection regime in D. pseudoobscura.     

Evidence for minority male mating success and minority female mating disadvantage in Drosophila ananassae

Frequency-dependent mating success was tested for three pairs of wild-type and mutant strains of Drosophila ananassae, MY and yellow body color (y), PN and claret eye color (ca), and TIR and cut wing (ct). The two strains of each pair were chosen for their approximately equal mating propensities. Multiple-choice experiments, using different experimental procedures, were employed. The tests were carried out by direct observation in Elens-Wattiaux mating chambers with five different sex ratios (4:16, 8:12, 10:10, 12:8, and 16:4). There was no assortative mating and sexual isolation between the strains, based on 2 x 2 contingency chi2 analysis and isolation estimate values. One-sided rare male mating advantages were found in two experiments, one for ca males and the other for wild-type males (TIR). However, no advantage was found for rare males in the experiment with MY and y flies. Mating disadvantages for rare females were found for sex-linked mutants (y and ct). Two different observational methods (removal or direct observation of mating pairs) imparted no overall significant effects on the outcome of the frequency-dependent mating tests.     

Male size and mating success in Drosophila melanogaster and D. pseudoobscura under field conditions

Wild mating male D. melanogaster and D. pseudoobscura were larger than randomly sampled males. That this was due to size and not a confounding effect of age was confirmed by release experiments with D. melanogaster of standard age; larger males were at a mating advantage with virgin and inseminated females. In both species larger males delivered more courtship and in D. pseudoobscura they won more aggressive encounters. These results on Drosophila in the field confirm and extend those previously obtained in the laboratory.     

Fight outcome influences male mating success in Drosophila prolongata

Journal of Ethology - The outcomes of preceding fights can influence the probability of winning a subsequent fight, known as the winner/loser effect. However, we know relatively little about how...     

Genetic architecture of male sterility and segregation distortion in Drosophila pseudoobscura Bogota-USA hybrids

Understanding the genetic basis of reproductive isolation between recently diverged species is a central problem in evolutionary genetics. Here, I present analyses of the genetic architecture underlying hybrid male sterility and segregation distortion between the Bogota and USA subspecies of Drosophila pseudoobscura. Previously, a single gene, Overdrive (Ovd), was shown to be necessary but not sufficient for both male sterility and segregation distortion in F(1) hybrids between these subspecies, requiring several interacting partner loci for full manifestation of hybrid phenomena. I map these partner loci separately on the Bogota X chromosome and USA autosomes using a combination of different mapping strategies. I find that hybrid sterility involves a single hybrid incompatibility of at least seven interacting partner genes that includes three large-effect loci. Segregation distortion involves three loci on the Bogota X chromosome and one locus on the autosomes. The genetic bases of hybrid sterility and segregation distortion are at least partially--but not completely--overlapping. My results lay the foundation for fine-mapping experiments to identify the complete set of genes that interact with Overdrive. While individual genes that cause hybrid sterility or inviability have been identified in a few cases, my analysis provides a comprehensive look at the genetic architecture of all components of a hybrid incompatibility underlying F(1) hybrid sterility. Such an analysis would likely be unfeasible for most species pairs due to their divergence time and emphasizes the importance of young species pairs such as the D. pseudoobscura subspecies studied here.     

Sexual selection and interacting phenotypes in experimental evolution: a study of Drosophila pseudoobscura mating behavior

Sexual selection requires social interactions, particularly between the sexes. When trait expression is influenced by social interactions, such traits are called interacting phenotypes and only recently have the evolutionary consequences of interacting phenotypes been considered. Here we investigated how variation in relative fitness, or the opportunity for sexual selection, affected the evolutionary trajectories of interacting phenotypes. We used experimentally evolved populations of the naturally promiscuous Drosophila pseudoobscura , in which the numbers of potential interactions between the sexes, and therefore relative fitness, were manipulated by altering natural levels of female promiscuity. We considered two different mating interactions between the sexes: mating speed and copulation duration. We investigated the evolutionary trajectories of means and (co)variances ( P ) and also the influence of genetic drift on the evolutionary response of these interactions. Our sexual selection treatments did not affect the means of either mating speed or copulation duration, but they did affect P . We found that the means of both traits differed among replicates within each selection treatment whereas the P s did not. Changes as a consequence of genetic drift were excluded. Our results show that although variable potential strengths of sexual interactions influence the evolution of interacting phenotypes, the influence may be nonlinear.     

No evidence for postcopulatory inbreeding avoidance in Drosophila melanogaster

Selection to avoid inbreeding is predicted to vary across species due to differences in population structure and reproductive biology. Over the past decade, there have been numerous investigations of postcopulatory inbreeding avoidance, a phenomenon that first requires discrimination of mate (or sperm) relatedness and then requires mechanisms of male ejaculate tailoring and/or cryptic female choice to avoid kin. The number of studies that have found a negative association between male-female genetic relatedness and competitive fertilization success is roughly equal to the number of studies that have not found such a relationship. In the former case, the underlying mechanisms are largely unknown. The present study was undertaken to verify and expand upon a previous report of postcopulatory inbreeding avoidance in D. melanogaster, as well as to resolve underlying mechanisms of inbreeding avoidance using transgenic flies that express a sperm head-specific fluorescent tag. However, siblings did not have a lower fertilization success as compared to unrelated males in either the first (P(1) ) or second (P(2) ) mate role in sperm competition with a standard unrelated competitor male in our study population of D. melanogaster. Analyses of mating latency, copulation duration, egg production rate, and remating interval further revealed no evidence for inbreeding avoidance.     

Condition dependence varies with mating success in male Drosophila bunnanda

Although key to sexual selection theories, condition dependence has proven a challenging area of empirical research. It is expected that availability of resources will affect both mean and variation of sexual trait expression, with lower mean and greater variation in harsher environments. Here, I manipulated the environment in a laboratory population of Drosophila bunnanda to test for condition dependence of sexually selected traits. Sexually successful and unsuccessful males differed in how the environment affected sexual trait expression. Specifically, sexual trait attractiveness declined more rapidly with declining resources in sexually unsuccessful males, consistent with the expectation that low quality males were less able to meet the greater signalling costs associated with harsher environments. This study illustrates the potential insights into condition dependence that might be gained through considering sexual trait expression and mating success within the same manipulative experimental design.     

No evidence that within‐group male relatedness reduces harm to females in Drosophila

Conflict between males and females over whether, when, and how often to mate often leads to the evolution of sexually antagonistic interactions that reduce female reproductive success. Because the offspring of relatives contribute to inclusive fitness, high relatedness between rival males might be expected to reduce competition and result in the evolution of reduced harm to females. A recent study investigated this possibility in Drosophila melanogaster and concluded that groups of brothers cause less harm to females than groups of unrelated males, attributing the effect to kin selection. That study did not control for the rearing environment of males, rendering the results impossible to interpret in the context of kin selection. Here, we conducted a similar experiment while manipulating whether males developed with kin prior to being placed with females. We found no difference between related and unrelated males in the harm caused to females when males were reared separately. In contrast, when related males developed and emerged together before the experiment, female reproductive output was higher. Our results show that relatedness among males is insufficient to reduce harm to females, while a shared rearing environment – resulting in males similar to or familiar with one another – is necessary to generate this pattern.     

High frequency of microsatellites in Drosophila pseudoobscura

Using 30,000 bp of anonymous sequence data, we note that dinucleotide repeat arrays appear to be much more common in Drosophila pseudoobscura than in D. melanogaster or D. simulans. Repeat arrays bearing five or more units are situated on average once every 3000 bp in D. pseudoobscura, and repeat arrays bearing ten or more units are situated on average once every 7500 bp. We did not detect an association between microsatellite presence and GC-content of flanking regions.     

Genetics of hybrid male sterility among strains and species in the Drosophila pseudoobscura species group

Taxa in the early stages of speciation may bear intraspecific allelic variation at loci conferring barrier traits in hybrids such as hybrid sterility. Additionally, hybridization may spread alleles that confer barrier traits to other taxa. Historically, few studies examine within- and between-species variation at loci conferring reproductive isolation. Here, we test for allelic variation within Drosophila persimilis and within the Bogota subspecies of D. pseudoobscura at regions previously shown to contribute to hybrid male sterility. We also test whether D. persimilis and the USA subspecies of D. pseudoobscura share an allele conferring hybrid sterility in a D. pseudoobscura bogotana genetic background. All loci conferred similar hybrid sterility effects across all strains studied, although we detected some statistically significant quantitative effect variation among D. persimilis alleles of some hybrid incompatibility QTLs. We also detected allelism between D. persimilis and D. pseudoobscura USA at a second chromosome hybrid sterility QTL. We hypothesize that either the QTL is ancestral in D. persimilis and D. pseudoobscura USA and lost in D. pseudoobscura bogotana, or gene flow transferred the QTL from D. persimilis to D. pseudoobscura USA. We discuss our findings in the context of population features that may contribute to variation in hybrid incompatibilities.     

Increased male mating rate in Drosophila is associated with Wolbachia infection

The maternally inherited bacterium Wolbachia pipientis infects 25-75% of arthropods and manipulates host reproduction to improve its transmission. One way Wolbachia achieves this is by inducing cytoplasmic incompatibility (CI), where crosses between infected males and uninfected females are inviable. Infected males suffer reduced fertility through CI and reduced sperm production. However, Wolbachia induce lower levels of CI in nonvirgin males. We examined the impact of Wolbachia on mating behaviour in male Drosophila melanogaster and D. simulans, which display varying levels of CI, and show that infected males mate at a higher rate than uninfected males in both species. This may serve to increase the spread of Wolbachia, or alternatively, may be a behavioural adaptation employed by males to reduce the level of CI. Mating at high rate restores reproductive compatibility with uninfected females resulting in higher male reproductive success thus promoting male promiscuity. Increased male mating rates also have implications for the transmission of Wolbachia.