Effects of urbanization on the foraging ecology and microbiota of the generalist seabird Larus argentatus

Larus gull species have proven adaptable to urbanization and due to their generalist feeding behaviors, they provide useful opportunities to study how urban environments impact foraging behavior and host-associated microbiota. We evaluated how urbanization influenced the foraging behavior and microbiome characteristics of breeding herring gulls (Larus argentatus) at three different colonies on the east coast of the United States. Study colonies represented high, medium and low degrees of urbanization, respectively. At all colonies, gulls frequently foraged at landfills and in other urban environments, but both the use of urban environments and gull foraging metrics differed with the degree of urbanization. Gulls at the more urban colonies used urban environments more frequently, showed higher rates of site fidelity and took shorter trips. Gulls at less urban colonies used a greater diversity of habitat types and foraged offshore. We observed high microbial diversity at all colonies, though microbial diversity was highest at the least urban colony where gulls used a wider variety of foraging habitats. This suggests that gulls may acquire a wider range of bacteria when visiting a higher variety of foraging sites. Our findings highlight the influence of urban habitats on gull movements and microbiome composition and diversity during the breeding season and represent the first application of amplicon sequence variants, an objective and repeatable method of bacterial classification, to study the microbiota of a seabird species.

鸥属（Larus）鸟类已被证实可适应城市化进程，加之其广食性的觅食习性，为探究城市环境如何影响觅食行为以及宿主相关微生物组提供了极佳的研究契机。本研究针对美国东海岸3处不同的银鸥（Larus argentatus）繁殖群，分析了城市化程度对繁殖期银鸥觅食行为与微生物组特征的影响，这3处繁殖群分别代表高、中、低三种城市化梯度。所有繁殖群的银鸥均频繁在垃圾填埋场及其他城市生境中觅食，但城市生境的利用强度与银鸥的觅食指标均随城市化程度呈现差异：城市化程度更高的繁殖群中的银鸥，对城市生境的利用频率更高、栖息地质忠诚度更强且觅食往返行程更短；而城市化程度较低的繁殖群中的银鸥，则利用了更多样化的生境类型，并会前往近海区域觅食。本研究在所有繁殖群中均检测到较高的微生物多样性，但城市化程度最低的繁殖群微生物多样性最高，该群体的银鸥利用了更多样化的觅食生境。这表明银鸥在造访更多样化的觅食生境时，可能会获得更丰富的细菌类群。本研究结果阐明了繁殖期城市生境对银鸥活动与微生物组组成及多样性的影响，同时首次将扩增子序列变体（amplicon sequence variants，ASV）——一种客观且可重复的细菌分类方法——应用于海鸟物种的微生物组研究中。