Mating and Parasitic Behavior of Brown-Headed Cowbirds

摘要Pi：Ashley建议编号：9601201褐头牛鸟的交配和寄生行为将通过全面的野外和实验室研究，对褐头牛鸟的繁殖生物学进行调查。将通过对在伊利诺伊州莱尔莫顿植物园野外采集的450-500枚牛鸟蛋和雏鸟进行亲子鉴定，研究单个雌性牛鸟的交配系统和寄生实践。这将通过DNA微卫星基因分型来完成，这使得亲子关系可以通过排除来确定。遗传数据将被用来确定这个研究地点的牛鸟是像之前报道的那样一夫一妻制，还是混杂交配。像褐头牛鸟这样的幼体寄生虫不受父母的照顾，这使得理论上不太可能实现一夫一妻制。如果确定牛鸟确实是一夫一妻制的，那么关于鸟类交配系统的主流理论可能需要重新评估。遗传分析还将被用来检验这样的假设，即雌性牛鸟将产卵限制在基本上不重叠的可定义区域。不重叠的繁殖区域将意味着对有限资源--寄主巢--的竞争。这将通过绘制分配给单个雌性的后代的位置并将这些位置与其他雌性U后代的分布进行比较来完成。以前在这个研究地点的野外工作表明，当有多个宿主可用时，牛鸟会不同地寄生在某些宿主物种的巢中。包括栖息地、巢类型、寄主大小和寄主防御在内的几个生态因素与观察到的寄生率密切相关。拟议的研究将检查这些模式在多大程度上反映了雌性牛鸟的行为适应(如寄主选择)。将进行两项相关的实地研究，以确定Female是否优先寄生最高质量的寄主物种和/或避免质量较低的寄主物种，如已知的将牛鸟卵从巢中弹出的寄主物种(RreectorsS)。第一项实地研究将确定不同常见寄生寄主物种成功培育牛鸟雏鸟的相对能力。不同寄主作为犀鸟替代品的相对质量将与观察到的寄生模式进行比较，以确定是否有选择地寄生高质量的寄主物种。第二个实地研究将确定RrerectorS物种的寄生率。在我们的研究地点，我们观察到了三种已知的排出牛鸟卵的寄主的寄生，这表明雌性牛鸟并没有完全避开这些寄主物种。通过实验寄生这些物种的巢，将确定排卵的速度。根据这一衡量标准和观察到的寄生率，我们可以确定牛鸟是更喜欢接受宿主物种而不是拒绝宿主物种，或者没有歧视这些低质量的宿主。证明宿主选择的模式对于了解宿主-寄生虫的共同进化和制定保护策略以保护受到牛鸟威胁的宿主物种都是重要的。

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.