Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
Evolution. 2013 Nov;67(11):3243-57. doi: 10.1111/evo.12201. Epub 2013 Jul 26.
Understanding how demographic processes influence mating systems is important to decode ecological influences on sexual selection in nature. We manipulated sex ratio and density in experimental populations of the sex-role reversed pipefish Syngnathus typhle. We quantified sexual selection using the Bateman gradient (βss'), the opportunity for selection (I), and sexual selection (Is), and the maximum standardized sexual selection differential (smax'). We also measured selection on body length using standardized selection differentials (s') and mating differentials (m'), and tested whether the observed I and Is differ from values obtained by simulating random mating. We found that I, Is, and s'max, but not βss', were higher for females under female than male bias and the opposite for males, but density did not affect these measures. However, higher density decreased sexual selection (m' but not s') on female length, but selection on body length was not affected by sex ratio. Finally, Is but not I was higher than expected from random mating, and only for females under female bias. This study demonstrates that both sex ratio and density affect sexual selection and that disentangling interrelated demographic processes is essential to a more complete understanding of mating behavior and the evolution of mating systems.
了解人口过程如何影响交配系统对于解码自然中生态对性选择的影响至关重要。我们在性角色反转的海龙属鱼类 Syngnathus typhle 的实验种群中操纵了性别比例和密度。我们使用 Bateman 梯度 (βss')、选择机会 (I) 和性选择 (Is) 以及最大标准化性选择差异 (smax') 来量化性选择。我们还使用标准化选择差异 (s') 和交配差异 (m') 测量了体长的选择，并测试了观察到的 I 和 Is 是否与模拟随机交配获得的值不同。我们发现，在雌性偏爱的情况下，I、Is 和 smax' 高于雌性，而在雄性偏爱的情况下则相反，但密度不会影响这些指标。然而，更高的密度降低了对雌性体长的性选择 (m'，但不是 s')，但性别比例对体长选择没有影响。最后，Is 高于随机交配的预期，但仅限于雌性偏爱的情况下。这项研究表明，性别比例和密度都会影响性选择，并且必须分解相互关联的人口过程，才能更全面地了解交配行为和交配系统的进化。
