The adaptive role of a species-specific courtship behaviour in coping with remating suppression of mated females

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.

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.

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

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.

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 et al. 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.

Satyrization in Drosophila fruitflies

The satyr of Greek mythology was half‐man, half‐goat, with an animal persona signifying immoderate sexual appetites. In biology, satyrization is the disruption of reproduction in matings between closely related species. Interestingly, its effects are often reciprocally asymmetric, manifesting more strongly in one direction of heterospecific mating than the other. Heterospecific matings are well known to result in female fitness costs due to the production of sterile or inviable hybrid offspring and can also occur due to reduced female sexual receptivity, lowering the likelihood of any subsequent conspecific matings. Here we investigated the costs and mechanisms of satyrization in the Drosophila melanogaster species subgroup of fruitflies. The results showed that D. simulans females experienced higher fitness costs from a loss of remating opportunities due to significantly reduced post‐mating sexual receptivity than did D. melanogaster females, as a result of reciprocal heterospecific matings. Reciprocal tests of the effects of male reproductive accessory gland protein (Acp) injections on female receptivity in pairwise comparisons between D. melanogaster and five other species within the melanogaster species subgroup revealed significant post‐mating receptivity asymmetries. This was due to variation in the effects of heterospecific Acps within species with which D. melanogaster can mate, and significant but nonasymmetric Acp effects in species with which it cannot. We conclude that asymmetric satyrization due to post‐mating effects of Acps may be common among diverging and hybridising species. The findings are of interest in understanding the evolution of reproductive isolation and species divergence.

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.