One thing birds can do to protect their young from the threat of bacteria in the environment is to transfer protective immune compounds, such as antibodies, directly into their eggs. Although these antibodies are associated with improved offspring growth and immunity, it is not known how levels of egg antibodies are influenced by disease risk. The purpose of this project is to test the hypothesis that tree swallows (Tachycineta bicolor) encountering more bacteria in their nests will have higher levels of antibodies in their eggs. To tackle this question, bacterial communities in swallow nests will be characterized using DNA-sequencing and compared with antibody levels in eggs collected from the same nests. This data set, from across North America, will be the most comprehensive ever collected on bacterial communities associated with any bird species, and the investigators predict that, as in plants and animals, bacterial diversity will be highest at the most southerly sites (e.g., Virginia) and lowest at the most northerly sites (e.g., Alaska). As a consequence, southern birds should have more antibodies in their eggs than northern birds. In addition to exploring new ground in bacterial biogeography, this study will bring new perspective to the variety of ways in which female birds can protect their offspring. Results from this study will also contribute to a large collaborative study of investigators working to quantify pathogens inhabiting the nests, feathers, feces, blood, and tissues of swallows through the NSF-funded Golondrinas de las Americas network. And sequence data will add to a growing wealth of 16S rRNA gene sequences publically available through GenBank. This project will also contribute to the training of undergraduates working in the field and laboratory. Through this research, students will have the opportunity to share data, ideas, and personal interactions with investigators throughout the hemisphere.
One thing that wild birds can do to protect their young from the threat of bacteria in the environment is to transfer protective immune compounds, such as antibodies, directly into their eggs. These antibodies help to protect hatchlings from disease, leading biologists to predict that mother birds should transfer more antibodies to their eggs when the threat of infection is high. The purpose of this project was to test this prediction by determining whether the diversity of bacteria that breeding tree swallows (Tachycineta bicolor) encounter within the nesting environment correlates with the amount of antibodies that mothers deposit into their eggs. This was accomplished by measuring antibody content of tree swallow eggs at 15 breeding sites across the United States and Canada and then comparing these data to measures of species diversity for bacteria inhabiting the nests where these particular eggs were laid. Upon completion of this project we have discovered that females breeding at sites with higher bacterial diversity do in fact deposit more protective antibodies into their eggs than females breeding at sites with lower bacterial diversity. We also discovered that unlike for animals and plants, bacterial species diversity does not appear to increase with distance from the equator in this particular system. Results from this project also reveal that female tree swallows respond quickly to changes in the populations of bacteria inhabiting their nests, which may have implications for how wild birds are affected by environmental disturbances that influence naturally occurring bacteria. This project currently represents the largest and most comprehensive survey of bacterial communities associated with any bird species. The results from this project contribute to our understanding of the types of bacteria that birds encounter during the reproductive period and how this exposure influences maternal immune function and protection of offspring. This knowledge may also inform similar studies in mammals where mothers transfer protective immune compounds to their offspring through the placenta and milk. Our in-depth investigation of nest-dwelling bacteria has also contributed to a large collaborative study of investigators working to quantify pathogens inhabiting the nests, feathers, feces, blood, and tissues of swallows through the NSF-funded Golondrinas de las Americas network. Bacterial DNA sequence data from this work are publicly available through the Earth Microbiome Project. This project has also contributed to the training of undergraduate students, graduate students, and postdoctoral fellows working in the field and laboratory. Through this research, students have had and will continue to have the opportunity to share data, ideas, and personal interactions with investigators throughout the hemisphere.