The Course of Evolution When Selection For A Behavioral Adaption Is Relaxed: Host Defenses Against Parasitic Birds

有些鸟，如牛郎鸟和杜鹃，不照顾自己的孩子，而是寄生在其他鸟类（它们的宿主）的父母的努力上，把蛋产在宿主的巢里。这种社会性或“幼虫寄生”抑制了宿主的繁殖输出，一些宿主进化出了防御措施，例如去除寄生卵。本研究将通过对目前未被寄生的种群进行卵识别实验，并通过评估DNA序列差异水平来估计这些种群摆脱幼虫寄生后经过的时间，来确定鸟类在不再被寄生时保留宿主防御的程度。在没有益处的情况下，适应是否会被保留是进化生物学中的一个基本问题。适应性的保留问题对于理解人性的努力也是至关重要的，因为过去具有适应性但今天不再有益的行为倾向可能仍然表现出来，往往对社会有害。幼虫寄生对保护生物多样性具有重要意义，因为一些濒危寄主物种因寄生而遭受损失。目前，至少有六种濒危物种通过花费大量公共资金的牛仔鸟控制计划免受寄生。了解卵子识别在没有任何好处的情况下保留的程度，将揭示这种特性是否有显著的成本，并将为一些濒危宿主没有发展出这种行为的原因提供见解。

Some birds, such as cowbirds and cuckoos, do not care for their own young but instead parasitize the parental efforts of other birds, their hosts, by laying their eggs in the hosts' nests. This social or "brood parasitism" depresses host reproductive output and some hosts have evolved defenses, such as removal of parasitic eggs. This study will determine the extent to which bird species retain host defenses when they are no longer parasitized by carrying out egg recognition experiments on populations that are not currently parasitized and by assessing levels of DNA sequence divergence to estimate the elapsed time since such populations became free of brood parasitism. Whether an adaptation is retained in the absence of benefits is a fundamental question in evolutionary biology. The issue of the retention of adaptations is also vital to efforts to understand human nature as behavioral tendencies that were adaptive in the past but are no longer beneficial today may still be expressed, often to the detriment of society. Brood parasitism is significant to efforts to preserve biodiversity because some endangered host species are impacted by the losses suffered to parasitism. Currently, at least six endangered species are protected from parasitism by cowbird control programs that expend significant amounts of public funds. Understanding the extent to which egg recognition is retained in the absence of any benefits will reveal whether this trait has significant costs and will provide insights into the reasons some endangered hosts have not developed this behavior.