Social context-dependent modification of courtship behaviour in Drosophila prolongata

Fight outcome influences male mating success in Drosophila prolongata

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 the experience of a preceding fight influences subsequent mating success. Here, we investigated the influence of preceding fight outcomes on subsequent mating behavior in a fruit fly Drosophila prolongata. Subordinate males mated less in two-choice mating assays, showing that the fight outcome predicts male mating success in this species. This tendency remained in a no-choice mating assay where direct interaction between the dominant and subordinate males was eliminated, suggesting that the mating disadvantage of the subordinate males was dependent on the experience of the previous fight rather than the direct interference by the dominant male. When a no-choice mating assay was performed before the fight, the prospective subordinate males mated at the same rate as the dominant males, confirming that the intrinsic male qualities in fighting and mating performances were independent of each other in our experiments. These results indicated that the experience-dependent changes in the subordinate males led to the reduced mating success.

Strongly sexually dimorphic forelegs are not more condition-dependent than less dimorphic traits in Drosophila prolongata

Directional sexual selection drives the evolution of traits that are most closely linked to reproductive success, giving rise to trait exaggeration and sexual dimorphism. Exaggerated structures are often costly and, therefore, thought to be expressed in a condition-dependent manner. Sexual selection theory thus predicts a direct link between directional sexual selection, sexual dimorphism, and sex-specific condition dependence. However, only a handful of studies investigate the relationship between sexual dimorphism and condition dependence. Using 21 genetic lines of Drosophila prolongata, we here compared the degree of sexual dimorphism and sex-specific condition dependence, measured as allometric slopes, in sexually selected and non-sexual traits. Our data revealed male-biased sexual dimorphism in all traits examined, most prominently in the sexually selected forelegs. However, there was no relationship between the degree of sex-specific condition dependence and sexual dimorphism across traits and genetic lines. Our results contradict theoretical predictions and highlight the importance of understanding the role of exaggerated traits in the context of both sexual and natural selection.

An Indirect Cost of Male-Male Aggression Arising from Female Response

Animal behavior is often polymorphic between individuals within a population. A cost/benefit balance of a particular behavioral pattern may be influenced by social interaction with other individuals with different behavioral patterns. Males of a fruitfly, Drosophila prolongata, show genetically defined polymorphism in aggressiveness and boldness against rival males. Males of the H strain are highly aggressive, and their fights tend to escalate into boxing, the highest level of aggressive interaction. H males are also bold against sneaker males and do not hesitate to perform leg vibration (LV), a courtship behavior that is vulnerable to interception of the female by surrounding rival males. In contrast, males of the L strain rarely engage in boxing and do not perform LV in the presence of rival males. We examined their mating success in small experimental populations. The mating success of L males was higher in a pure L population than in a mixed population with H males, whereas that of H males was higher in a mixed population than in a pure H population. Notably, this 'cost of aggression' in a pure H population seemed not directly derived from the male-to-male interaction but was imposed by the female's response of escaping from fighting males, compromising the benefit of the resource monopolization as territory.

Behavioral and environmental contributions to drosophilid social networks

Animals interact with each other in species-specific reproducible patterns. These patterns of organization are captured by social network analysis, and social interaction networks (SINs) have been described for a wide variety of species including fish, insects, birds, and mammals. The aim of this study is to understand the evolution of social organization in Drosophila Using a comparative ecological, phylogenetic, and behavioral approach, the different properties of SINs formed by 20 drosophilids were compared. We investigate whether drosophilid network structures arise from common ancestry, a response to the species' past climate, other social behaviors, or a combination of these factors. This study shows that differences in past climate predicted the species' current SIN properties. The drosophilid phylogeny offered no value to predicting species' differences in SINs through phylogenetic signal tests. This suggests that group-level social behaviors in drosophilid species are shaped by divergent climates. However, we find that the social distance at which flies interact correlated with the drosophilid phylogeny, indicating that behavioral elements of SINs have remained largely unchanged in their evolutionary history. We find a significant correlation of leg length to social distance, outlining the interdependence of anatomy and complex social structures. Although SINs display a complex evolutionary relationship across drosophilids, this study suggests that the ecology, and not common ancestry, contributes to diversity in social structure in Drosophila.

Evolution of sexually dimorphic pheromone profiles coincides with increased number of male-specific chemosensory organs in Drosophila prolongata

Binary communication systems that involve sex-specific signaling and sex-specific signal perception play a key role in sexual selection and in the evolution of sexually dimorphic traits. The driving forces and genetic changes underlying such traits can be investigated in systems where sex-specific signaling and perception have emerged recently and show evidence of potential coevolution. A promising model is found in Drosophila prolongata, which exhibits a species-specific increase in the number of male chemosensory bristles. We show that this transition coincides with recent evolutionary changes in cuticular hydrocarbon (CHC) profiles. Long-chain CHCs that are sexually monomorphic in the closest relatives of D. prolongata (D. rhopaloa, D. carrolli, D. kurseongensis, and D. fuyamai) are strongly male-biased in this species. We also identify an intraspecific female-limited polymorphism, where some females have male-like CHC profiles. Both the origin of sexually dimorphic CHC profiles and the female-limited polymorphism in D. prolongata involve changes in the relative amounts of three mono-alkene homologs, 9-tricosene, 9-pentacosene, and 9-heptacosene, all of which share a common biosynthetic origin and point to a potentially simple genetic change underlying these traits. Our results suggest that pheromone synthesis may have coevolved with chemosensory perception and open the way for reconstructing the origin of sexual dimorphism in this communication system.

Brain size affects responsiveness in mating behaviour to variation in predation pressure and sex ratio

Despite ongoing advances in sexual selection theory, the evolution of mating decisions remains enigmatic. Cognitive processes often require simultaneous processing of multiple sources of information from environmental and social cues. However, little experimental data exist on how cognitive ability affects such fitness-associated aspects of behaviour. Using advanced tracking techniques, we studied mating behaviours of guppies artificially selected for divergence in relative brain size, with known differences in cognitive ability, when predation threat and sex ratio was varied. In females, we found a general increase in copulation behaviour in when the sex ratio was female biased, but only large-brained females responded with greater willingness to copulate under a low predation threat. In males, we found that small-brained individuals courted more intensively and displayed more aggressive behaviours than large-brained individuals. However, there were no differences in female response to males with different brain size. These results provide further evidence of a role for female brain size in optimal decision-making in a mating context. In addition, our results indicate that brain size may affect mating display skill in male guppies. We suggest that it is important to consider the association between brain size, cognitive ability and sexual behaviour when studying how morphological and behavioural traits evolve in wild populations.

Evolution and diversity of the courtship repertoire in the Drosophila montium species group (Diptera: Drosophilidae)

Changes in elements of courtship behaviour can influence sexual isolation between species. Large-scale analyses of changes, including loss and gain of courtship elements, across a relatively complete phylogenetic group are rare but needed to understand the significance of such changes, for example whether the gain and loss of courtship elements are essentially arbitrary or equally reversible. In most species of Drosophila, courtship, including singing, mainly occurs before mounting as premounting courtship. The Drosophila montium species group is unusual because loss of premounting courtship and gain of post-mounting one has been detected in this group. Here, we provide an extensive analysis on the courtship repertoire and songs of 42 species in this group. Synchronously captured video and audio recordings were analysed to describe courtship patterns and male courtship songs, and changes were analysed in a phylogenetic context. Ancestral state reconstruction suggests that a gain of post-mounting courtship singing at the ancestor of this species group has been accompanied by a concurrent decrease in the incidence of premounting courtship singing and has led to subsequent further decrease and eventually complete loss of premounting courtship song in several lineages. Alongside this evolutionary trend towards post-mounting courtship, sine song and a special type of "high pulse repetition song" have become more widely used for courtship during species diversification in the montium group. It is likely that the elaboration of post-mounting courtship behaviours is associated with changes in the relative importance of pre- and post-mounting components of mating systems, such as sperm competition or cryptic female choice.

piggyBac- and phiC31 integrase-mediated transgenesis in Drosophila prolongata

The development of transgenesis systems in non-model organisms provides a powerful tool for molecular analysis and contributes to the understanding of phenomena that are not observed in model organisms. Drosophila prolongata is a fruit fly that has unique morphology and behavior not found in other Drosophila species including D. melanogaster. In this study, we developed a phiC31 integrase-mediated transgenesis system for D. prolongata. First, using piggyBac-mediated transgenesis, 37 homozygous attP strains were established. These strains were further transformed with the nosP-Cas9 vector, which was originally designed for phiC31-mediated transgenesis in D. melanogaster. The transformation rate varied from 0% to 3.4%. Nine strains with a high transformation rate of above 2.0% were established, which will serve as host strains in future transformation experiments in D. prolongata. Our results demonstrate that genetic tools developed for D. melanogaster are applicable to D. prolongata with minimal modifications.

Effect of social condition on behavioral development during early adult phase in Drosophila prolongata

Behavioral changes during early development provide useful insights into the internal mechanisms that generate complex behavior expressed by mature individuals. At the same time, social conditions during early adult phase can influence behavior in later stages of development even in holometabolous insects. In this study, age-dependent changes in courtship behavior and the effect of social conditions were examined in a fruit fly, Drosophila prolongata. Younger males showed lower mating activity and simpler courtship behavior. Mating activity reached a maximum level by 5 days after eclosion, whereas expression of complex courtship behavior was not yet fully developed at that time, suggesting that they are controlled by different mechanisms. When two males were maintained in the same vial, not only mating activity but also courtship complexity was reduced, demonstrating for the first time that preceding social experience, not current social conditions, influenced the complexity of male courtship. The effect of social experience was completely erased by 1 day of isolation, however, showing that social experience did not suppress or promote behavioral development itself. Rather, these results suggest that the observed effect of social experience was a plastic response of males that reduced investment in courtship effort by anticipating increased male–male competition.

Comparative analysis of the brain transcriptome in a hyper-aggressive fruit fly, Drosophila prolongata

Aggressive behavior is observed in many animals, but its intensity differs between species. In a model animal of genetics, Drosophila melanogaster, genetic basis of aggressive behavior has been studied intensively, including transcriptome analyses to identify genes whose expression level was associated with intra-species variation in aggressiveness. However, whether these genes are also involved in the evolution of aggressiveness among different species has not been examined. In this study, we performed de novo transcriptome analysis in the brain of Drosophila prolongata to identify genes associated with the evolution of aggressiveness. Males of D. prolongata were hyper-aggressive compared with closely related species. Comparison of the brain transcriptomes identified 21 differentially expressed genes in males of D. prolongata. They did not overlap with the list of aggression-related genes identified in D. melanogaster, suggesting that genes involved in the evolution of aggressiveness were independent of those associated with the intra-species variation in aggressiveness in Drosophila. Although females of D. prolongata were not aggressive as the males, expression levels of the 21 genes identified in this study were more similar between sexes than between species.