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

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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.