Mating and Parasitic Behavior of Brown-Headed Cowbirds

摘要对褐头牛鹂（Molothrus ater）的交配与寄生行为进行了野外和室内综合研究。在伊利诺斯州莱尔的莫顿植物园的一个野外地点，从绘制的巢址收集了450-500枚牛鹂蛋和雏鸟，通过对它们的父母身份进行鉴定，研究了雌性牛鹂的交配系统和寄生行为。这将通过DNA微卫星基因分型来完成，它允许通过排除来确定亲子关系。遗传数据将用于确定该研究地点的牛郎鸟是否像之前报道的那样是一夫一妻制，还是滥交。像褐头牛鹂这样的幼虫寄生虫脱离了父母的照顾，这使得一夫一妻制在理论上是不可能的。如果确定牛郎鸟确实是一夫一妻制的，那么流行的鸟类交配系统理论可能需要重新评估。基因分析还将用于验证一种假设，即雌性牛椋鸟将产卵限制在基本不重叠的可定义区域。不重叠的繁殖区域意味着对有限资源——宿主巢穴的竞争。这将通过绘制分配给单个雌性后代的位置并将其与其他雌性后代的分布进行比较来完成。先前在该研究地点的实地工作表明，当有多个宿主可用时，牛椋鸟会不同地寄生在某些宿主物种的巢穴中。生境、巢型、寄主大小和寄主防御等生态因素与寄生蜂的寄生率密切相关。拟议的研究将检查这些模式在多大程度上反映了雌性牛郎鸟的行为适应（例如，宿主选择）。将进行两项相关的实地研究，以确定雌蝇是否优先寄生于质量最高的寄主物种和/或避免质量较低的寄主物种，如那些已知会从巢中排出牛鹂蛋的寄主物种（RrejectorsS）。第一次实地研究将确定不同常见寄主物种成功培育牛鹂雏鸟的相对能力。将不同寄主的相对质量与观察到的寄生模式进行比较，以确定是否有选择性地寄生优质寄主物种。第二项野外研究将确定拒斥昆虫的寄生率。在我们的研究地点，我们观察到三种已知会排出牛鹂卵的寄主的寄生，这表明雌性牛鹂并没有完全避开这些寄主。通过实验寄生在这些物种的巢穴中，将确定卵子排出率。从这一测量和观察到的寄生率，我们可以确定牛鹂是否更喜欢接受的宿主而不是拒绝的宿主，或者相反，不能区分这些低质量的宿主。揭示寄主选择的模式对于理解寄主-寄生虫的共同进化以及制定保护策略以保护受牛郎鸟威胁的寄主物种具有重要意义。

ABSTRACT PI: ASHLEY PROPOSAL NUMBER: 9601201 Mating and Parasitic Behavior of Brown-headed Cowbirds The breeding biology of the brown-headed cowbird, Molothrus ater, will be investigated through a comprehensive field and laboratory study. Both the mating system and the parasitism practices of individual female cowbirds will be studied by assigning parentage to 450-500 cowbird eggs and nestlings collected at a field site at the Morton Arboretum in Lisle Illinois from mapped nest locations. This will be done by DNA microsatellite genotyping, which allows parentage to be determined by exclusion. The genetic data will be used to determine whether cowbirds at this study site mate monogamously, as has been previously reported, or promiscuously. Brood parasites such as the brown-headed cowbird are freed from parental care, which makes monogamy theoretically improbable. If it is determined that cowbirds are indeed monogamous, prevailing theories of avian mating systems may need to be reevaluated. The genetic analysis will also be used to test the hypothesis that female cowbirds restrict egg-laying to definable areas that are largely non-overlapping. Non-overlapping reproductive areas would suggest competition for a limited resource, host nests. This will be done by mapping the locations of offspring assigned to an individual female and comparing these to distributions of other femalesU offspring. Previous field work at this study site demonstrates that cowbirds differentially parasitize the nests of certain host species when multiple hosts are available. Several ecological factors including habitat, nest type, host size, and host defenses are strongly correlated with observed rates of parasitism. The proposed study will examine the extent to which these patterns reflect behavioral adaptations (e.g. host choice) of female cowbirds. Two related field studies will be conducted to determine if fem ales preferentially parasitize the highest quality host species and/or avoid low quality host species such as those known to eject cowbird eggs from their nests (RrejectorsS). The first field study will determine the relative abilities of different commonly parasitized host species to successfully foster cowbird nestlings. The relative qualities of different hosts as cowbird surrogates will be compared to observed patterns of parasitism to determine if high-quality host species are selectively parasitized. The second field study will determine parasitism rates of RrejectorS species. At our study site we have observed parasitism of three species of hosts known to eject cowbird eggs, indicating that female cowbirds are not completely avoiding these host species. By experimentally parasitizing the nests of these species, the rate of egg-ejection will be determined. From this measure and the observed rate of parasitism, we can ascertain whether cowbirds prefer acceptor host species over rejectors, or alternatively, fail to discriminate against these low-quality hosts. Demonstrating patterns of host choice is important both for understanding host-parasite coevolution and for developing conservation strategies to protect host species threatened by cowbirds.