Conover Michael R, Reese Jan G, Brown Anne D
Am Nat. 2000 Aug;156(2):193-200. doi: 10.1086/303377.
In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype). The AP phenotype results from a recessive allele on the X chromosome; both phenotypes occur in the same population and even in the same brood. We compared costs and benefits of both phenotypes in mute swans on the Chesapeake Bay in 1972-1980 and on Long Island Sound in 1982-1989. Swans with the SAP phenotype had higher survival rates from hatching to fledging than AP swans. In the fall, when AP cygnets began to molt into their white plumage, their parents often attacked and drove them off while allowing SAP cygnets from the same brood to remain on their territories for several more months. SAP males had higher survival rates during their first 2 yr of life than AP males, but AP swans bred at a younger age than SAP swans. The only proposed hypothesis for the evolution of delayed plumage maturation that can explain its occurrence in mute swans is the status-signaling hypothesis. This hypothesis argues that males with subadult plumage honestly advertise their age and subordinate status while AP swans are cheaters and engaging in dishonest communication. SAP males acquire a longer period of parental care, suffer less aggression from older birds, and increase their survival but forgo the opportunity to breed at an early age. This is a unique example of how a single gene resulted in either honest or dishonest communication, changed a bird's relationship with its parents and potential mates, and altered the bird's chances to survive and to reproduce.
在一些鸟类物种中，具备繁殖能力的幼鸟会通过换羽变成亚成体羽毛，而这种羽毛能准确表明它们的亚成体状态，从而降低繁殖的可能性。人们提出了几种假说以解释延迟羽毛成熟的进化，但对其进行检验通常涉及种间比较，而这种比较难以解释。疣鼻天鹅（Cygnus olor）表现出两种表型，区别在于鸟类是否拥有灰色亚成体羽毛（SAP表型），或者是否直接换羽为全白色的成年羽毛（AP表型）。AP表型由X染色体上的一个隐性等位基因导致；两种表型出现在同一群体中，甚至同一窝幼鸟中。我们比较了1972 - 1980年切萨皮克湾以及1982 - 1989年长岛海峡的疣鼻天鹅两种表型的成本和收益。具有SAP表型的天鹅从孵化到羽翼丰满的存活率高于AP天鹅。在秋季，当AP幼天鹅开始换羽为白色羽毛时，它们的父母常常攻击并驱赶它们，而同一窝的SAP幼天鹅却能在其领地多停留几个月。SAP雄性在出生后的头两年存活率高于AP雄性，但AP天鹅比SAP天鹅繁殖年龄更小。关于延迟羽毛成熟进化的唯一被提出的假说，即状态信号假说，能够解释其在疣鼻天鹅中的出现。该假说认为，具有亚成体羽毛的雄性诚实地表明了它们的年龄和从属地位，而AP天鹅是欺骗者，进行不诚实的交流。SAP雄性获得了更长时间的亲代抚育，遭受年长鸟类的攻击较少，提高了存活率，但却放弃了早期繁殖的机会。这是一个独特的例子，展示了单个基因如何导致诚实或不诚实的交流，改变鸟类与其父母及潜在配偶的关系，并改变鸟类生存和繁殖的机会。
