De Nardo Alessio N, Biswas Broti, Perdigón Ferreira Jhoniel, Meena Abhishek, Lüpold Stefan
Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland.
Department of Systematic and Evolutionary Botany, University of Zurich, Zollikerstrasse 107, Zurich 8008, Switzerland.
Proc Biol Sci. 2025 Jan;292(2039):20242501. doi: 10.1098/rspb.2024.2501. Epub 2025 Jan 22.
The intensity and direction of sexual selection are intricately linked to the social and ecological context. Both operational sex ratios (OSRs) and population densities can affect the ability of males to monopolize resources and mates, and thus the form and intensity of sexual selection on them. Here, we studied how the mating system of the promiscuous and strongly sexually dimorphic fruit fly responds to changes in the OSR and population density. We recorded groups of flies over five days and quantified territory occupancy, mating success (MS) and competitive fertilization success. Although sexual selection was stronger under male-biased than even OSRs but unrelated to density, realized selection on morphological traits was higher under even OSRs and increased with density. Larger and more territorial males achieved both higher MS and competitive fertilization success, but only under even OSRs. Our combined results also support a shift in the mating system from territorial contest competition to scramble competition under male-biased OSRs and potentially at low density, where there was no clear contribution of the measured traits to reproductive success. Our study emphasizes the limitations of traditional selection metrics and the role of the socio-ecological context in predicting adaptation to a changing environment.
性选择的强度和方向与社会和生态背景有着复杂的联系。操作性别比（OSRs）和种群密度都会影响雄性独占资源和配偶的能力，进而影响对它们的性选择的形式和强度。在此，我们研究了滥交且具有强烈两性异形的果蝇的交配系统如何响应操作性别比和种群密度的变化。我们对果蝇群体进行了为期五天的记录，并对领地占有情况、交配成功率（MS）和竞争性受精成功率进行了量化。尽管在雄性偏多的操作性别比下性选择比在均等的操作性别比下更强，但与密度无关，然而在均等的操作性别比下对形态特征的实际选择更高，且随密度增加而增加。体型更大且更具领地意识的雄性既获得了更高的交配成功率，也获得了更高的竞争性受精成功率，但这仅在均等的操作性别比下才成立。我们综合得出的结果还支持在雄性偏多的操作性别比下以及可能在低密度情况下交配系统从领地竞争向争夺竞争的转变，在这种情况下，所测量的特征对繁殖成功没有明显贡献。我们的研究强调了传统选择指标的局限性以及社会生态背景在预测对不断变化的环境的适应性方面的作用。
