Drosophila Prolongata Research Articles

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.

Reproductive advantage of the winners of male-male competition in Drosophila prolongata

In the resource-defence mating system, where males compete for limited resources to acquire females, male traits associated with fighting ability are selected, leading to the evolution of sexual dimorphism. However, the evolution of sexual dimorphism is also driven by other mechanisms, such as female selection. Therefore, to elucidate the evolutionary mechanisms of male traits, it is necessary to clarify their contribution to fitness through male-male competition. In this regard, it is surprising that numerous studies on sexually dimorphic species have assumed the resource-defence mating system without directly examining the relationship between resource-defending behaviour and mating success. In a sexually dimorphic fruit fly, Drosophila prolongata, the presence of the resource-defence mating system has been suggested, but technical difficulties had prevented spatial quantification of the resource-defending behaviour. In this study, by using an automated behaviour analysis tool previously developed, we located the occurrence of male-male competition and courtship to investigate their relationship in D. prolongata, considering the position of food resources. We found that the male-male competition led to the exclusive occupation of resources, increasing the courtship opportunities of the resource holders. These results illustrate the importance of resource-defending for reproductive success in D. prolongata.

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.

Contribution of visual stimuli to mating and fighting behaviors of Drosophila prolongata

AbstractThe importance of visual stimuli in a given behavior is often different, even between closely related species. Species of the genus Drosophila have been categorized into three classes according to their reproductive dependency on vision. Class I and II species reproduce in the darkness, whereas class III species never reproduce without vision. Therefore, in class III species, mutants at the white locus that are deprived of normal visual function are not able to be established as homozygous stocks. Drosophila prolongata is a species with a conspicuous body color pattern, suggesting that an increased importance of visual stimuli underlies the evolution of this species. In this study, to examine the behavioral dependency on visual stimuli in D. prolongata, we generated white gene‐knockout (w−) mutants using the CRISPR/Cas9 system and examined their mating and fighting behaviors in light and dark conditions. The courtship and fighting activities of w− males were extremely reduced regardless of the light condition. Furthermore, wildtype males did not perform any courtship or fighting behaviors in dark conditions. Our results showed that D. prolongata is a class III species that strongly relies on visual stimuli in both behaviors.

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.

Condition- and context-dependent alternative reproductive tactic in Drosophila prolongata

Abstract Species with intense male–male competition for access to females often show alternative reproductive tactics (ARTs) where males of lower competitive ability adopt a sneaky behavior to gain access to mates. These ARTs are usually associated with intrasexual dimorphisms, in that males with distinct morphologies show different tactics. In some cases, however, males adopt different tactics without being dimorphic. Male Drosophila prolongata exhibit continuous variation in body size and shape, with enlarged forelegs that they use in male-male contests and in courtship, including stimulation of the female’s abdomen. During this “leg vibration,” however, nearby males can intercept the courted female and mate without their own courtship. Here, we studied the causes and consequences of these different mating tactics in competitive mating trials between males varying in their size and shape. We found that male mating tactics were condition-dependent. Whereas large, high-condition males were more likely to show leg vibration in their courtship, smaller, lower-condition males were more likely to intercept. However, the number of offspring produced was independent of male condition and reproductive tactic. We discuss possible scenarios for the evolution and maintenance of the ARTs and some future directions for the study of ARTs in this species and in general.

Intraspecific variation in longevity of Drosophila prolongata (Diptera: Drosophilidae) under solitary and group conditions

AbstractConsiderable variations in behavior and physiology exist among sexes and strains of species. The amount and allocation of energy resources can affect the health and survival of individuals. If an individual devotes a large amount of energy to interact with other conspecifics, the resources may become too scarce to maintain their physical condition, which could reduce longevity. In this study, I examined the interactive effects of sex, strain, and the presence of conspecifics on adult longevity using four strains of Drosophila prolongata. This species shows a large intraspecific variation in behavior and morphology among isofemale strains. Under solitary conditions, longevity was significantly different among strains for both sexes. The effects of same‐sex conspecifics on adult longevity were also highly variable between the sexes and among strains. When exposed to conspecifics, the longevity of males of a hyper‐aggressive strain was more notably decreased than that of females of the same strain or either sex of other less aggressive strains. These results indicate that differences in the balance of costs and benefits of social interactions lead to differences in adult longevity under group conditions between the sexes and among strains within the same species.

Digest: Male courting prompts female fly remating-The evolution of polyandry.

Does a male courting behavior proximately cause polyandry in a fruit fly species? Minekawa etal. found that in Drosophila prolongata, male flies vibrate their legs to overcome female remating suppression, resulting in multiple matings for females that otherwise may have remained monandrous.

Intra- Versus Inter-Sexual Selection on Sexually Dimorphic Traits in Drosophila prolongata.

Sexual dimorphism, such as sexual size dimorphism (SSD) and sexually dimorphic exaggerated traits, often evolves via sexual selection. In many species, evolution of sexual dimorphism is thought to be driven by either of the two forms of sexual selection: intra- and inter-sexual selection. In some species, however, intra- and inter-sexual selection act simultaneously on the same sexually dimorphic trait. Therefore, it is important to consider the effects of both forms of sexual selection to fully understand the evolution of sexual dimorphism. Drosophila prolongata is a fruit fly that shows male-biased SSD and has enlarged forelegs only in males. In this study, the relationship between body size parameters and aggression/mating behavior was examined. Our results showed that aggressive behavior was influenced by body weight and foreleg size, whereas mating success was not influenced by any size parameters, suggesting that intra-sexual selection is the primary mechanism that maintains the sexual dimorphism in the current D. prolongata population.

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.

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.

Inheritance Pattern of Female Receptivity in Drosophila prolongata.

Choosiness, or female receptivity to copulation, is a critical component in female preference for a mating partner, as it functions at the final step in the mating process by determining whether she accepts copulation with a given male. In spite of its importance in the evolutionary process of male traits via sexual selection, little is known about the genetic variation and inheritance pattern of female receptivity. Drosophila prolongata shows a unique courtship behavior, leg vibration, which increases female receptivity to copulation. In the present study, we analyzed variation in female receptivity and its inheritance pattern in isofemale strains of D. prolongata using leg vibration as an index. There was a significant difference in female receptivity among the strains examined. A high-receptivity phenotype was semi-dominantly expressed in F1 females of crosses between strains with low and high receptivity. Backcrossing F1 females to low-receptivity strains resulted in a lower level of receptivity, suggesting that the high-receptivity phenotype is controlled by multiple genes with epistatic interactions. These results indicate a genetic basis of female receptivity, shedding light on the evolutionary process of sexual selection in D. prolongata.

Intraspecific variation in heat tolerance of Drosophila prolongata (Diptera: Drosophilidae)

Tolerance to extreme temperatures is one of the most important components of adaptation to environments in insects. However, the genetic mechanisms of tolerance to long-term heat stress are mostly unknown. In this study, we investigated the genetic variation of susceptibility to long-term heat stress among the isofemale strains of Drosophila prolongata Singh & Gupta. High rates of pupal lethality were observed at 25 °C, showing that D. prolongata is more susceptible to heat stress than other Drosophila species. Susceptibility to heat stress was significantly different among the isofemale strains, suggesting that intraspecific genetic variation is involved in the reduced heat tolerance of D. prolongata. Unexpectedly, the tertiary sex ratio was biased to females at temperatures higher than 20 °C, indicating that the males were more susceptible to heat stress. These results demonstrated that D. prolongata is useful for genetic analysis for elucidating the molecular mechanisms of heat tolerance in insects.

Variation in morphological and behavioral traits among isofemale strains of Drosophila prolongata (Diptera: Drosophilidae)

AbstractDrosophila prolongata, a member of the rhopaloa subgroup of the melanogaster species group, occurs in Southeast Asia. Drosophila prolongata is known to have unique and prominent sexual dimorphism, with extraordinarily thick and elongated forelegs only in males. Mating behavior of D. prolongata is also characteristic: males perform “leg vibration” in their courtship toward females, in which the elongated forelegs play an important role. Comparisons with closely related species suggest that these morphological and behavioral traits have evolved rapidly after the divergence of D. prolongata. In the present study, variation in morphological and behavioral traits was examined among D. prolongata strains derived from single females collected in their natural habitats. Significant variations were detected in the size of various body parts, aggressiveness of interactions between males, and mating behavior. However, no obvious relationship was observed between morphological and behavioral traits. These results suggested that genetic factors contribute to the variation in morphological and behavioral traits in D. prolongata. The strains characterized in this study are useful for studies on the genetic mechanisms underlying the evolution of characteristic traits in D. prolongata.

Sexual dimorphism and courtship behavior in Drosophila prolongata

Abstract Sexual dimorphism is often derived from sexual selection. In sexually dimorphic Drosophila species, exaggerated male structures are used for specific behaviors in male-to-male competition or courtship toward females. In Drosophila prolongata, a member of the melanogaster species group, males have enlarged forelegs whereas females do not. However, the adaptive role of the enlarged forelegs is unclear because little is known about the behavior of D. prolongata. In this study, the courtship behavior of D. prolongata was investigated in comparison with closely related species. Males of D. prolongata use their forelegs in a specific behavior, “leg vibration”, in which the male vigorously vibrates the female’s abdomen by extending his forelegs from in front of her. Leg vibration was observed immediately before “attempting copulation”, indicating that it has an adaptive role in the mating process. In contrast, leg vibration was not observed in closely related species. Because the large forelegs are necessary to accomplish leg vibration, it was suggested that the sexual dimorphism of D. prolongata forelegs is currently under the influence of sexual selection in courtship behavior.