BRC-BIO: Bird feeders in the city: the effect of urbanization on ecological immunology and microbiology in cardueline finches

Urban bird feeders promote social contact between seed-eating birds, increasing potential exposure to bacteria containing antibiotic resistance genes. This has negative consequences for birds and humans who handle soiled bird feeders, as they may acquire antibiotic-resistant bacteria from these feeders. Birds exhibiting strong immune responses may not be harmed by these microbes, but urban environments can stress birds and thereby impede their immune system.

Also, urban development causes habitat fragmentation, which can decrease the spread of beneficial immune gene variants between rural and urban bird populations in species with limited dispersal. To explore these issues, the researchers will gather data across three sites along an urban-rural gradient for three finch species that routinely occupy bird feeders in California.

The project aims are to (1) measure the presence of antimicrobial resistance genes in birds and at bird feeders, (2) measure the birds' bacteria-killing ability in vitro, and (3) measure the variation between six immune genes in house finches. The researchers will involve the community through a regional birding society and scouting organizations. They will also have students in four courses at their minority-serving institution help collect, process, and analyze their data.

Ultimately, their goal is to increase the participation of historically marginalized people in scientific research and connect with the public on the importance of how humans can impact avian health and how they can help protect local bird populations.

Along an urban-rural gradient near Fresno, California, the researchers will study the effect of urbanization on the innate immunity of three finch species (pine siskins Spinus pinus, lesser goldfinches Spinus psaltria, and house finches Haemorhous mexicanus) by performing bacteria-killing assays and analyzing leukocytes profiles. The researchers will measure immunogenetic diversity and differentiation of the major histocompatibility complex (MHC; the cornerstone of the adaptive immune system) and Toll-like receptors (TLRs; innate immune genes) and at neutral loci in non-migratory house finches, which commonly occupy feeders in rural and urban environments.

The researchers will quantify and characterize the prevalence of bacteria and their antimicrobial resistance genes (ARGs) in these birds and on the bird feeders. To accomplish this, the researchers and their students will catch and sample finches along an urban-rural gradient to (1) measure constitutive innate immunity by running bacteria-killing assays against three bacteria species and analyze leukocyte profiles with light microscopy; (2) measure immunogenetic variation by genetically characterizing the hypervariable peptide-binding region of MHC class I and II using high-throughput sequencing, the pathogen-recognition domains of four TLRs, and measure neutral genetic diversity using 14 microsatellite loci; and (3) perform metagenomic analysis to characterize microbes and ARGs in the three finches and the bird feeders they use.

Ultimately, this research will allow biologists to better understand how urbanization plays a role in the evolutionary ecology of the avian immune system and the spread of microbes containing ARGs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.