Flies on the dance floor: social group shapes mating success and rivalry in Drosophila suzukii

The social environment, characterised by interactions between individuals and their surrounding group, has a significant influence on behavioural and life-history traits in many animal species. This study investigates the impact of the social environment on the mating behaviour of the invasive pest Drosophila suzukii. We conducted experiments to examine how variations in density of individuals and sex ratio - two main characteristics of the social environment - affect mating behaviours. First, we observed that both male and female flies were attracted by fruits and aggregate around them, suggesting that fruits may serve as social hubs. We then tested the influence of male density and ratio of males to females on mating behaviour. Results showed a clear mate-finding Allee effect at low densities, with a lower mating probability and an increase of the latency before mating, when male density decreases. The general pattern of results highlights male density as the key determinant of reproductive success, while female density and sex ratio had no significant influence on mating outcomes. Conversely, high density environments facilitated mating probability and increased male-male competition. Thus, physical interactions among males, primarily in the form of aggressive attempts to dislodge copulating pairs, were prevalent at high males’ densities. These results demonstrate that D. suzukii uses social cues to modulate reproductive strategies, a flexibility likely contributing to its invasion success.以个体与周围群体间的互动为核心特征的社会环境，对诸多动物物种的行为与生活史性状具有显著影响。本研究聚焦于社会环境对入侵性害虫斑翅果蝇（Drosophila suzukii）交配行为的影响。我们通过实验探究了作为社会环境两大核心特征的个体密度与性比的变化，如何作用于交配行为。首先，我们观察到雌雄果蝇均会被果实吸引并在果实周围聚集，这表明果实可充当社交枢纽。随后我们测试了雄性密度与雌雄比对交配行为的影响。研究结果显示，在低密度条件下存在显著的觅偶阿利效应（Allee effect）：当雄性密度降低时，交配概率下降且交配前潜伏期延长。整体结果表明，雄性密度是繁殖成功率的关键决定因素，而雌性密度与性比并未对交配结果产生显著影响。与之相反，高密度环境可提升交配概率，并加剧雄性间竞争。因此，在高雄性密度环境中，雄性间以驱逐正在交配的配对个体为主要形式的攻击性行为互动极为普遍。本研究结果证实，斑翅果蝇可通过社会线索调控繁殖策略，这种策略灵活性或为其成功入侵的重要助力。