Gefen Eran, Gibbs Allen G
School of Life Sciences, University of Nevada, Las Vegas, Nevada 89154, USA.
Evolution. 2009 Jun;63(6):1653-9. doi: 10.1111/j.1558-5646.2009.00648.x. Epub 2009 Feb 2.
Adaptation of natural and laboratory-selected populations of Drosophila to desiccation stress results in enhanced water conservation abilities, and thus increased stress resistance. In this study, we tested whether laboratory selection for desiccation resistance is also reflected in increased mating success of adapted D. melanogaster males under desiccating conditions. Adapted flies perform better under stressful conditions, and as expected males from desiccation-selected populations exhibited significantly higher relative mating success in comparison with controls after 5-6 h of desiccation. However, we show evidence for a trade-off between survival under stressful conditions and mating success in nonstressful and even mildly stressful environments (2.5-3 h of desiccation), where males from selected populations were involved in only approximately 40% of observed copulations. This suggests that mutations favored by natural selection, associated with survival when resources are limited, may only be favored by sexual selection above a minimal "threshold" stress level. At milder stress levels increased resistance comes at a cost of lower relative mating success, and thus reduced fitness. This interaction between stress and relative male mating success of adapted and nonadapted males could interrupt gene flow, thus facilitating divergence of resistant populations from the ancestral population.
果蝇自然种群和实验室选择种群对干燥胁迫的适应会增强其保水能力，从而提高抗逆性。在本研究中，我们测试了对干燥抗性的实验室选择是否也体现在适应后的黑腹果蝇雄性在干燥条件下交配成功率的提高上。适应后的果蝇在应激条件下表现更好，正如预期的那样，经过干燥选择的种群中的雄性在干燥5 - 6小时后，与对照组相比，其相对交配成功率显著更高。然而，我们发现有证据表明，在应激条件下的生存与在非应激甚至轻度应激环境（干燥2.5 - 3小时）中的交配成功率之间存在权衡，在这些环境中，来自选择种群的雄性仅参与了约40%的观察到的交配。这表明，自然选择青睐的与资源有限时的生存相关的突变，可能只有在高于最小“阈值”应激水平时才会受到性选择的青睐。在较轻的应激水平下，抗性的增加是以相对交配成功率降低为代价的，从而降低了适应性。适应和未适应的雄性在应激与相对交配成功率之间的这种相互作用可能会中断基因流动，从而促进抗性种群与祖先种群的分化。
