Diamant Eleanor S, Falk Jay J, Rubenstein Dustin R
Department of Ecology Evolution and Environmental Biology, Columbia University, 1200 Amsterdam Avenue, New York, NY 10027, USA.
Department of Ecology and Evolutionary Biology, University of California Los Angeles, CA 90095, USA.
Proc Biol Sci. 2021 Feb 24;288(1945):20203004. doi: 10.1098/rspb.2020.3004.
Differences in the way males and females look or behave are common in animals. However, discrete variation within sexes (sex-limited polymorphism) also occurs in several vertebrate and invertebrate lineages. In birds, female-limited polymorphism (FLP) in which some females resemble males in coloration is most prominent in hummingbirds, a group known for its morphological and behavioural sexual dimorphism. Yet, it remains unclear whether this intrasexual colour variation in hummingbirds arises through direct selection on females, or indirectly as a non-adaptive byproduct resulting from selection on males. Here, we analysed specimens from more than 300 hummingbird species to determine the extent, evolutionary history and function of FLP. We found that FLP evolved independently in every major clade and occurs in nearly 25% of hummingbird species. Using phylogenetically informed analyses, we rejected non-adaptive hypotheses that FLP is the result of indirect selection or pleiotropy across species. Instead, FLP is associated with ecology, migratory status, and marginally with social dominance, suggesting a socioecological benefit to females. Ultimately, we show that FLP is not only widespread in hummingbirds and likely adaptive, but may also be useful for understanding the evolution of female ornamentation in systems under strong sexual selection.
雄性和雌性在外观或行为上的差异在动物中很常见。然而，性别内部的离散变异（性别限制多态性）也出现在几个脊椎动物和无脊椎动物谱系中。在鸟类中，雌性限制多态性（FLP），即一些雌性在颜色上与雄性相似，在蜂鸟中最为突出，蜂鸟是一个以形态和行为上的两性异形而闻名的群体。然而，尚不清楚蜂鸟的这种性别内部颜色变异是通过对雌性的直接选择产生的，还是作为对雄性选择的非适应性副产品间接产生的。在这里，我们分析了来自300多种蜂鸟物种的标本，以确定FLP的程度、进化历史和功能。我们发现FLP在每个主要分支中独立进化，并且出现在近25%的蜂鸟物种中。使用系统发育信息分析，我们拒绝了FLP是间接选择或物种间多效性结果的非适应性假设。相反，FLP与生态、迁徙状态以及在一定程度上与社会优势相关，这表明对雌性有社会生态益处。最终，我们表明FLP不仅在蜂鸟中广泛存在且可能具有适应性，而且可能有助于理解在强烈性选择系统中雌性装饰的进化。
