Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, Riverside, CA, 92521.
Evolution. 2020 Mar;74(3):528-543. doi: 10.1111/evo.13881. Epub 2019 Dec 10.
Male hummingbirds have repeatedly evolved sexually dimorphic tails that they use as ornaments during courtship. We examine how male ornament evolution is reflected in female morphology. Lande's two-step model of the evolution of dimorphism predicts that γ (the genetic correlation between the sexes) causes trait elaboration to first evolve quickly in both sexes, then dimorphism evolves more slowly. On the hummingbird phylogeny, tail length does not fit this two-step model; although hummingbirds repeatedly evolved ornamental, elongated tails, dimorphism evolves on the same phylogenetic branch as elongation, implying that γ quickly evolves to be low over phylogenetic timescales. Male "bee" hummingbirds have evolved diverse rectrix shapes that they use to produce sound. Female morphologies exhibit subtle, pervasive correlations with male morphology. No female-adaptive hypotheses explain these correlations, since females do not also make sounds with their tail. Subtle shape similarity has arisen through the genetic correlation with males, and is subject to intralocus sexual conflict. Intralocus sexual conflict may produce increased phenotypic variation of female ornaments. Other evolutionary constraints on tail morphology include a developmental correlation between neighboring tail-feathers, biasing tail elaboration to occur most often at the ends of the feather tract (rectrix 5 or 1) and not the middle.
雄蜂鸟的尾巴存在明显的性别二态性，它们在求偶时会用尾巴作为装饰。我们研究了雄鸟装饰的进化如何反映在雌鸟的形态上。Lande 的二步模型预测，γ（性别间的遗传相关性）会导致特征在两性中快速进化，然后二态性进化得更慢。在蜂鸟的系统发育树上，尾巴的长度不符合这个二步模型；尽管蜂鸟多次进化出了华丽的、长尾巴，但二态性与伸长的分支进化相同，这意味着在系统发育时间尺度上，γ很快进化到低值。雄性“蜜蜂”蜂鸟进化出了各种各样的尾羽形状，它们用这些尾羽来发声。雌鸟的形态与雄鸟的形态存在微妙而普遍的相关性。没有女性适应的假说可以解释这些相关性，因为雌性不会用尾巴发出声音。这种微妙的形状相似性是通过与雄性的遗传相关性产生的，并且受到同基因间的性冲突的影响。同基因间的性冲突可能会增加雌性装饰物的表型变异。尾巴形态的其他进化限制因素包括相邻尾羽之间的发育相关性，这使得尾羽的复杂化最常发生在羽毛区域的末端（第 5 或 1 根尾羽），而不是中间。
