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

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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.