Microbial Infection, Egg Viability, and the Onset of Incubation in Birds

鸟类的微生物感染、卵活力和孵化开始。加州大学伯克利分校的贝辛格鸟类每天只能下一个蛋，并通过决定何时开始孵化来影响孵化的同步性。 然而，父母经常选择异步孵化的模式，导致最后孵化的幼崽因与兄弟姐妹争夺食物而死亡。 大多数以前的研究都假设胚胎被保护在它们的壳内，等待鸟类父母以创造最佳孵化模式的方式开始开始孵化。 另一种想法是，异步孵化可能是在父母产下大量窝卵的好处和延迟孵化以使早期产下的蛋存活的代价之间进行权衡的结果。 最近在热带森林中的研究首次证明，微生物可以感染未孵化的鸡蛋，而感染会大大降低孵化成功率。 在温和环境中进行的初步研究也发现，未孵化的鸡蛋中微生物的渗透率很高。该项目将从三个互补的角度研究微生物如何塑造鸟类孵化的开始。1)研究人员将研究在完全孵化之前微生物感染的后果，通过测量暴露于温带环境的野生鸟蛋的微生物渗透率，以及通过检查微生物的渗透是否会降低孵化成功率。2)蛋壳上的微生物过程影响感染的机会将通过确定蛋壳上的微生物群落在孵化过程中如何变化来研究，以及变化是否是由于孵化雌性的微气候差异或由于鸟类羽毛或皮肤上的化学防御。3)父母对微生物感染的防御将通过研究父母是否通过部分孵化来消毒蛋内容物，并确定这是否会增加孵化成功率来检查。研究人员将测试父母是否通过产蛋顺序赋予鸡蛋不同的抗生素特性，以及这是否提供了更大的保护。 确定微生物对蛋活力的影响可能为理解孵化开始、部分孵化和其他鸟类生殖行为提供新的范例。 实验将在加利福尼亚州门多西诺县的霍普兰研究和推广中心进行，实验对象是西部蓝鸟、树燕、紫罗兰色绿色燕子和橡树山雀。 将在这些物种和绿腰鹦鹉（在委内瑞拉），珍珠眼画眉（在波多黎各），蓝翅水鸭（在北达科他州），和美国黑鸭（在北达科他州）的蛋内和物种之间的抗菌防御的差异进行测试。 该项目包括一个重要的培训组成部分，涉及一名亚裔美国女博士候选人，一名博士后学生，以及大量的研究生和本科生，所有这些人都将接受行为生态学，微生物学和实验设计领域和实验室技能的培训。 少数族裔的招聘工作将利用伯克利的少数族裔教育计划来吸引其他候选人。将该项目的成果应用于鸟类的圈养可能会产生重要影响。 圈养繁殖的濒危鸟类的孵化成功率几乎总是比自然孵化低得多，也许是因为很少采用部分孵化。 家禽业必须管理微生物，以防止储存用于繁殖的鸡蛋感染。 如果该项目确定了野生鸟类的关键微生物过程和抗菌防御，这两个群体都将受益。

Microbial Infection, Egg Viability, and the Onset of Incubation in birdsSteven R. Beissinger University of California at BerkeleyBirds can lay no more than one egg a day and influence the synchrony of hatching by determining when to initiate incubation. Yet parents often opt for a pattern of asynchronous hatching that leads to death of last-hatched young due to competition with siblings for food. Most previous studies have assumed embryos are protected within their shells and waiting for bird parents to begin incubation in a manner that creates optimal hatching patterns. An alternative idea is that asynchronous hatching may be the result of a trade-off between the benefits of laying a large clutch to the parent and the costs of delaying incubation to the survival of early-laid eggs. Recent work in tropical forests provides the first evidence that microbes can infect unincubated eggs and that infection greatly reduces hatching success. Preliminary studies in a temperate environment also found high rates of microbial penetration in unincubated eggs. This project will examine how microbes may shape the onset of incubation in birds from three complementary perspectives. 1) The researchers will study the consequences of microbial infection prior to full incubation, approached by measuring the rate of microbial penetration of wild bird eggs exposed to temperate environments, and by examining whether penetration by microbes reduces hatching success. 2) Microbial processes on the eggshell that affect the chance of infection will be studied by determining how microbial communities on eggshells change during incubation, and if change is due to microclimate differences from the incubating female or due to chemical defenses on the feathers or skins of birds. 3) Parental defenses against microbial infection will be examined by studying whether parents disinfect egg contents by partially incubating them, and determining if this increases hatching success. The investigators will test whether parents differentially endow eggs in antibiotic properties by laying order, and whether this provides greater protection. Identifying the impact of microbes on egg viability may provide a new paradigm for understanding the onset of incubation, partial incubation, and other avian reproductive behaviors. Experiments will be conducted at the Hopland Research and Extension Center in Mendocino County, CA, with Western Bluebirds, Tree Swallows, Violet Green Swallows and Oak Titmice. Differences in antimicrobial defenses of eggs within and among species will be tested on these species and on Green-rumped Parrotlets (in Venezuela), Pearly-eyed Thrashers (in Puerto Rico), Blue-winged Teal (in North Dakota), and American Coots (in North Dakota). This project includes a significant training component involving an Asian American female doctoral candidate, a postdoctoral student, and significant numbers of postgraduate and undergraduate students, all of whom will be trained in field and lab skills in behavioral ecology, microbiology and experimental design. Minority recruitment efforts will use Berkeley's program in minority education to attract other candidates. Applying the results of the project to captive rearing of birds may have important impacts. Hatching success of captive-bred endangered birds is almost always much lower than natural incubation, perhaps because partial incubation is rarely employed. The poultry industry must manage microbes to prevent infection of eggs being stored for breeding stock. Both groups will benefit if this project identifies key microbial processes and antimicrobial defenses of wild birds.