Kervinen Matti, Lebigre Christophe, Soulsbury Carl D
Department of Biological and Environmental Science, University of Jyväskylä, P. O. Box 35, Jyväskylä, FI-40014, Finland.
Earth and Life Institute, Place de la Croix du Sud 4, Carnoy building, B-1348, Louvain-la-Neuve, Belgium.
J Anim Ecol. 2016 May;85(3):715-25. doi: 10.1111/1365-2656.12496. Epub 2016 Mar 6.
Individuals' reproductive success is often strongly associated with their age, with typical patterns of early-life reproductive improvement and late-life senescence. These age-related patterns are due to the inherent trade-offs between life-history traits competing for a limited amount of resources available to the organisms. In males, such trade-offs are exacerbated by the resource requirements associated with the expression of costly sexual traits, leading to dynamic changes in trait expression throughout their life span. Due to the age dependency of male phenotypes, the relationship between the expression of male traits and mating success can also vary with male age. Hence, using longitudinal data in a lekking species with strong sexual selection - the black grouse Lyrurus tetrix - we quantified the effects of age, life span and age of first lek attendance (AFL) on male annual mating success (AMS) to separate the effects of within-individual improvement and senescence on AMS from selective (dis)appearance of certain phenotypes. Then, we used male AMS to quantify univariate and multivariate sexual selection gradients on male morphological and behavioural traits with and without accounting for age and age-related effects of other traits. Male AMS increased with age, and there was no significant reproductive senescence. Most males never copulated, and of the ones that did, the majority had only one successful year. Life span was unrelated to AMS, but early AFL tended to lead to higher AMS at ages 1-3. AMS was related to most morphological and behavioural traits when male age was ignored. Accounting for age and age-specific trait effects (i.e. the interaction between a trait and age) reduced the magnitude of the selection gradients and revealed that behavioural traits are under consistent sexual selection, while sexual selection on morphological traits is stronger in old males. Therefore, sexual selection in black grouse operates primarily on male behaviour and morphological traits may act as additional cues to supplement female choice. These results demonstrate the multifaceted influence of age on both fitness and sexual traits and highlight the importance of accounting for such effects when quantifying sexual selection.
个体的繁殖成功率通常与其年龄密切相关，呈现出早期繁殖能力提升和后期繁殖衰老的典型模式。这些与年龄相关的模式是由于生命史特征之间在争夺生物体可用的有限资源时存在内在权衡。在雄性中，与表达代价高昂的性特征相关的资源需求加剧了这种权衡，导致其性特征在整个生命周期中发生动态变化。由于雄性表型依赖于年龄，雄性特征表达与交配成功率之间的关系也可能随雄性年龄而变化。因此，我们利用具有强烈性选择的求偶场物种——黑琴鸡（Lyrurus tetrix）的纵向数据，量化了年龄、寿命和首次参加求偶场的年龄（AFL）对雄性年度交配成功率（AMS）的影响，以区分个体内部改善和衰老对AMS的影响与某些表型的选择性（不）出现的影响。然后，我们使用雄性AMS来量化在考虑和不考虑年龄以及其他特征的年龄相关影响的情况下，雄性形态和行为特征上的单变量和多变量性选择梯度。雄性AMS随年龄增加，且没有明显的繁殖衰老现象。大多数雄性从未交配过，而交配过的雄性中，大多数只有一年交配成功。寿命与AMS无关，但早期AFL往往会导致1 - 3岁时的AMS更高。当忽略雄性年龄时，AMS与大多数形态和行为特征相关。考虑年龄和特定年龄的特征效应（即一个特征与年龄之间的相互作用）会降低选择梯度的幅度，并表明行为特征受到持续的性选择，而形态特征的性选择在老年雄性中更强。因此，黑琴鸡的性选择主要作用于雄性行为，形态特征可能作为补充雌性选择的额外线索。这些结果证明了年龄对适应性和性特征的多方面影响，并强调了在量化性选择时考虑此类影响的重要性。
