New reproductive anomalies in fruitless-mutant Drosophila males: extreme lengthening of mating durations and infertility correlated with defective serotonergic innervation of reproductive organs

Several features of male reproductive behavior are under the neural control of fruitless (fru) in Drosophila melanogaster. This gene is known to influence courtship steps prior to mating, due to the absence of attempted copulation in the behavioral repertoire of most types of fru-mutant males. However, certain combinations of fru mutations allow for fertility. By analyzing such matings and their consequences, we uncovered two striking defects: mating times up to four times the normal average duration of copulation; and frequent infertility, regardless of the time of mating by a given transheterozygous fru-mutant male. The lengthened copulation times may be connected with fru-induced defects in the formation of a male-specific abdominal muscle. Production of sperm and certain seminal fluid proteins are normal in these fru mutants. However, analysis of postmating qualities of females that copulated with transheterozygous mutants strongly implied defects in the ability of these males to transfer sperm and seminal fluids. Such abnormalities may be associated with certain serotonergic neurons in the abdominal ganglion in which production of 5HT is regulated by fru. These cells send processes to contractile muscles of the male's internal sex organs; such projection patterns are aberrant in the semifertile fru mutants. Therefore, the reproductive functions regulated by fruitless are expanded in their scope, encompassing not only the earliest stages of courtship behavior along with almost all subsequent steps in the behavioral sequence, but also more than one component of the culminating events.     

Inbreeding depression and male-mating behavior inDrosophila melanogaster

There have been relatively few studies designed to investigate the effects of inbreeding on behavioral traits. To study this phenomenon, five experimental lines ofDrosophila melanogaster made isogenic for chromosome 2 were evaluated for their male-mating ability and, subsequently, male courtship behavior. All lines showed significant reductions in overall mating ability, and males from all of these lines displayed impaired mating behavior, with two lines displaying particularly aberrant courtship patterns. Line 16 displayed an inability to successfully initiate copulation following successful courtship, while line 17 displayed significant reduction in locomotor activity, resulting in virtually no successful courtship or copulatory activity. The implications of these findings for competitive mating ability in wildDrosophila populations are presented. Further, the importance of mating success as a fitness component in the management of potentially highly inbred populations of endangered species is discussed.     

Male reproductive behavior in Drosophila melanogaster strains with different alleles of the flamenco gene

The allelic state of gene flamenco has been determined in a number of Drosophila melanogaster strains using the ovoD test. The presence of an active copy of gypsy in these strains was detected by restriction analysis. Then male reproduction behavior was studied in the strains carrying a mutation in gene flamenco. In these experiments mating success has been experimentally estimated in groups of flies. It has been demonstrated that the presence of mutant allele flamMS decreases male mating activity irrespective of the presence or absence of mutation white. The active copy of gypsy does not affect mating activity in the absence of the mutation in gene flamenco. Individual analysis has demonstrated that that mutation flamMS results in characteristic changes in courtship: flamMS males exhibit a delay in the transition from the orientation stage to the vibration stage (the so-called vibration delay). The role of locus flamenco in the formation of male mating behavior in Drosophila is discussed.     

A putative Drosophila pheromone receptor expressed in male-specific taste neurons is required for efficient courtship

Propagation in higher animals requires the efficient and accurate display of innate mating behaviors. In Drosophila melanogaster, male courtship consists of a stereotypic sequence of behaviors involving multiple sensory modalities, such as vision, audition, and chemosensation. For example, taste bristles located in the male forelegs and the labial palps are thought to recognize nonvolatile pheromones secreted by the female. Here, we report the identification of the putative pheromone receptor GR68a, which is expressed in chemosensory neurons of about 20 male-specific gustatory bristles in the forelegs. Gr68a expression is dependent on the sex determination gene doublesex, which controls many aspects of sexual differentiation and is necessary for normal courtship behavior. Tetanus toxin-mediated inactivation of Gr68a-expressing neurons or transgene-mediated RNA interference of Gr68a RNA leads to a significant reduction in male courtship performance, suggesting that GR68a protein is an essential component of pheromone-driven courtship behavior in Drosophila.     

Mating success and courtship ritual in strains of Drosophila melanogaster carrying mutation flamenco

Mating success was examined in groups of Drosophila melanogaster carrying mutation flamMS (SS, MSn1-2, and MSn1-3) and in wild-type flies. The proportion of normally copulating males was significantly lower in the mutant strains. The reduction in mating efficiency was caused by changes in male behavior rather than in female attractiveness. Individual analyses showed that male mating behavior in strains carrying flamMS was qualitatively and quantitatively different from that in the wild-type strain Canton S. The proportion of males that performed consecutive courtship stages was significantly lower in the mutant strains. The sequence and duration of some courtship stages (in particular, orientation and wing vibration) in mutant flies was shown to be altered. The significance of the flamenco locus in regulation of processes occurring at the organismal level are discussed.     

Courtship song analysis of Drosophila muscle mutants

As part of the mating ritual, males of Drosophila species produce species-specific courtship songs through wing vibrations generated by the thoracic musculature. While previous studies have shown that indirect flight muscles (IFM) are neurally activated during courtship song production, the precise role of these muscles in song production has not been investigated. Fortunately, IFM mutants abound in Drosophila melanogaster and studies spanning several decades have shed light on the role of muscle proteins in IFM-powered flight. Analysis of courtship songs in these mutants offers the opportunity to uncover the role of the IFM in a behavior distinct than flight and subject to different evolutionary selection regimes. Here, we describe protocols for the recording and analysis of courtship behavior and mating song of D. melanogaster muscle transgenic and mutant strains. To record faint acoustic signal of courtship songs, an insulated mating compartment was used inside a recording device (INSECTAVOX) equipped with a modified electret microphone, a low-noise power supply, and noise filters. Songs recorded in the INSECTAVOX are digitized using Goldwave, whose several features enable extraction of critical song parameters, including carrier frequencies for pulse song and sine song. We demonstrate the utility of this approach by showing that deletion of the N-terminal region of the myosin regulatory light chain, a mutation known to decrease wing beat frequency and flight power, affects courtship song parameters.     

Diversification of takeout, a male-biased gene family in Drosophila

The display of courtship behavior has evolved in response to sexual selection driven by competition to obtain mates. Sexually dimorphic mate selection rituals are likely controlled at least in part by genes with sex-biased patterns of expression. In Drosophila melanogaster, male courtship behavior has been well described and consists of a series of stereotyped behaviors. The takeout gene is predominantly expressed in males and affects male courtship behavior. In this study, we examine the patterns of expression and evolution in takeout and the family of related proteins. We show that a number of genes in the takeout gene family show male-biased expression in D. melanogaster, largely in non-reproductive tissues. Phylogenetic analysis reveals that this gene family is conserved across insects. As expected for genes with male-biased expression, we also find evidence of positive selection in some lineages. Our results suggest that the genes in this family may have evolutionarily conserved sex specific roles in male mating behavior across insects.     

Drosophila female courtship and mating behaviors: sensory signals, genes, neural structures and evolution

Interest in Drosophila courtship behavior has a long-standing tradition, starting with the works by Sturtevant in 1915, and by Bastock and Manning in the 50s. The neural and genetic base of Drosophila melanogaster courtship behavior has made big strides in recent years, but the studies on males far outnumber those on females. Recent technical developments have made it possible to begin to unravel the biological substrates underlying the complexity of Drosophila female sexual behavior and its decisive effect on mating success. The present review focus more on the female side and summarizes the sensory signals that the male sends, using multiple channels, and which neural circuits and genes are mediating sex-specific behavioral responses.     

New reproductive anomalies in fruitless‐mutant Drosophila males: Extreme lengthening of mating durations and infertility correlated with defective serotonergic innervation of reproductive organs

Several features of male reproductive behavior are under the neural control of fruitless (fru) in Drosophila melanogaster. This gene is known to influence courtship steps prior to mating, due to the absence of attempted copulation in the behavioral repertoire of most types of fru‐mutant males. However, certain combinations of fru mutations allow for fertility. By analyzing such matings and their consequences, we uncovered two striking defects: mating times up to four times the normal average duration of copulation; and frequent infertility, regardless of the time of mating by a given transheterozygous fru‐mutant male. The lengthened copulation times may be connected with fru‐induced defects in the formation of a male‐specific abdominal muscle. Production of sperm and certain seminal fluid proteins are normal in these fru mutants. However, analysis of postmating qualities of females that copulated with transheterozygous mutants strongly implied defects in the ability of these males to transfer sperm and seminal fluids. Such abnormalities may be associated with certain serotonergic neurons in the abdominal ganglion in which production of 5HT is regulated by fru. These cells send processes to contractile muscles of the male's internal sex organs; such projection patterns are aberrant in the semifertile fru mutants. Therefore, the reproductive functions regulated by fruitless are expanded in their scope, encompassing not only the earliest stages of courtship behavior along with almost all subsequent steps in the behavioral sequence, but also more than one component of the culminating events. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 121–149, 2001     

Genetics of divergence in male wing pigmentation and courtship behavior between Drosophila elegans and D. gunungcola

Many sex-specific traits involved in mating consist of functionally coordinated morphologies and behaviors. How the components of these complex traits evolve and become coordinated during evolution is unknown. In order to understand how such trait complexes evolve and diversify, we must decipher the genetic underpinnings of their components. In this study, we begin to elucidate the genetic architecture underlying differences in functionally related male pigmentation and behavior between two Asian Drosophila melanogaster group species, D. elegans and D. gunungcola. D. elegans possesses a male-specific wing melanin spot and a stereotypical wing display element in male courtship, whereas D. gunungcola lacks both of these traits. Using reciprocal F1 male hybrids, we demonstrate that the X-chromosome contains a major locus or loci required for wing spot formation and that autosomal loci largely determine the male courtship display. Using phenotypic and genetic analysis of backcross progeny, we further demonstrate that both the wing spot and courtship differences between the two species are polygenic and both depend at least in small part on genetic factors on both the X and the autosomes. Finally, we find that male wing spot size and courtship wing display are highly correlated in backcross progeny, suggesting that linkage or pleiotropy may have been involved in their coordinated evolution.     

Mating behavior as an indicator of quality of Drosophila subobscura males?

According to current theoretical predictions, any deleterious mutations that reduce nonsexual fitness may have a negative influence on mating success. This means that sexual selection may remove deleterious mutations from the populations. Males of good genetic quality should be more successful in mating, compared to the males of lower genetic quality. As mating success is a condition dependent trait, large fractions of the genome may be a target of sexual selection and many behavioral traits are likely to be condition dependent. We manipulated the genetic quality of Drosophila subobscura males by inducing mutations with ionizing radiation and observed the effects of the obtained heterozygous mutations on male mating behavior: courtship occurrence, courtship latency, mating occurrence, latency to mating and duration of mating. We found possible effects of mutations. Females mated more frequently with male progeny of nonirradiated males and that these males courted females faster compared to the male progeny of irradiated males. Our findings indicate a possible important role of sexual selection in purging deleterious mutations.     

Effect of Drosophila melanogaster Female Size on Male Mating Success

In this study, we examined the influence of female size on mating success in Drosophila melanogaster. The results that were obtained from experiments performed in mating chambers allowed us to confirm the results of previous studies, demonstrating higher mating success of larger D. melanogaster males, and to conclude that female size also affects mating success, either when considering a single male or two competing males. We observed that the advantage for larger males depends on their size relative to that of the female, demonstrating a previously unknown role for female size in mating behavior studies. This effect of female size on mating success depends on various factors: males take longer to initiate courtship toward larger females, large females receive more wing vibrations from males prior to mating, and large females tend to keep moving for longer periods during male courtship. The importance of this finding is discussed in the context of recent reports on sexual conflict in D. melanogaster, in which males were observed to depress fitness in females as a result of intercourse.     

Enhancer of garnet/deltaAP-3 is a cryptic allele of the white gene and identifies the intracellular transport system for the white protein.

The white gene encodes an ABC-type transmembrane transporter that has a role in normal eye pigment deposition. In addition, overexpression in Drosophila leads to homosexual male courtship. Its human homologue has been implicated in cholesterol transport in macrophages and in mood disorders in human males. The garnet gene is a member of a group of other Drosophila eye colour genes that have been shown, or proposed, to function in intracellular protein transport. Recent molecular analysis indicates that it encodes the delta subunit of the AP-3 adaptin complex involved in vesicle transport from the trans-Golgi network to lysosomes and related organelles, such as pigment granules. This identification revealed a novel role for intracellular vesicular transport in Drosophila pigmentation. To further analyze this intracellular transport system, we examined the genetic interactions between garnet and a second site enhancer mutation, enhancer of garnet (e(g)). We show here that e(g) is a cryptic allele of the white gene. The white-garnet interaction is highly sensitive to the levels of both gene products but also shows some allele specificity for the white gene. The additive effect on pigmentation and the predicted protein products of these genes suggest that the garnet/AP-3 transport system ensures the correct intracellular localization of the white gene product. This model is further supported by the observation of homosexual male courtship behavior in garnet mutants, similar to that seen in flies overexpressing, and presumably mis-sorting, the white gene product. The w(e(g)) allele also enhances mutations in the subset of other eye-color genes with phenotypes similar to garnet. This observation supports a role for these genes in intracellular transport and leads to a model whereby incorrect sorting of the white gene product can explain the pigmentation phenotypes of an entire group of eye-color genes.     

A novel hypothesis on the biochemical role of the Drosophila Yellow protein

In Drosophila melanogaster, the protein product of the yellow gene is necessary for normal pigmentation and male sexual behavior. Although one of the best characterized loci from a genetic standpoint, the function of the Yellow protein in the development of either phenotype is unknown. Here I propose that Yellow acts as a growth factor- or hormone-like molecule in the development of pigmentation and sexual behavior, and discuss the consistency of this theory with experimental observations in flies and humans.