Anthropogenic food provisioning of wildlife can alter the frequency of contacts among hosts and between hosts and environmental sources of pathogens. Despite the popularity of garden bird feeding, few studies have addressed how feeders influence host contact rates and disease dynamics. We experimentally manipulated feeder density in replicate aviaries containing captive, pathogen-naive, groups of house finches () and continuously tracked behaviours at feeders using radio-frequency identification devices. We then inoculated one bird per group with (Mg), a common bacterial pathogen for which feeders are fomites of transmission, and assessed effects of feeder density on house finch behaviour and pathogen transmission. We found that pathogen transmission was significantly higher in groups with the highest density of bird feeders, despite a significantly lower rate of intraspecific aggressive interactions relative to the low feeder density groups. Conversely, among naive group members that never showed signs of disease, we saw significantly higher concentrations of Mg-specific antibodies in low feeder density groups, suggesting that birds in low feeder density treatments had exposure to subclinical doses of Mg. We discuss ways in which the density of garden bird feeders could play an important role in mediating the intensity of Mg epidemics.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

There is growing evidence that symbiotic microbes play key roles in host defense, but less is known about how symbiotic microbes mediate pathogen-induced damage to hosts. Here, we use a natural wildlife disease system, house finches and the conjunctival bacterial pathogen Mycoplasma gallisepticum (MG), to experimentally examine the impact of the ocular microbiome on host damage and pathogen virulence factors during infection. We disrupted the ocular bacterial community of healthy finches using an antibiotic that MG is intrinsically resistant to, then inoculated antibiotic- and sham-treated birds with MG. House finches with antibiotic-disrupted ocular microbiomes had more severe MG-induced conjunctival inflammation than birds with unaltered microbiomes, even after accounting for differences in conjunctival MG load. Furthermore, MG cultures from finches with disrupted microbiomes had increased sialidase enzyme and cytadherence activity, traits associated with enhanced virulence in Mycoplasmas, relative to isolates from sham-treated birds. Variation in sialidase activity and cytadherence among isolates was tightly linked with degree of tissue inflammation in hosts, supporting the consideration of these traits as virulence factors in this system. Overall, our results suggest that microbial dysbiosis can result in enhanced virulence of colonizing pathogens, with critical implications for the health of wildlife, domestic animals, and humans.

Summary Vertebrate ocular microbiomes are poorly characterized and virtually unexplored in wildlife species. Pathogen defense is considered a key function of microbiomes, but determining microbiome stability during disease is critical for understanding the role of resident microbial communities in infectious disease dynamics. Here, we characterize the ocular bacterial microbiome of house finches (Haemorhous mexicanus), prior to and during experimental infection with an inflammatory ocular disease, Mycoplasmal conjunctivitis, caused by Mycoplasma gallisepticum. In ocular tissues of healthy house finches, we identified 526 total bacterial operational taxonomic units (OTUs, 97% similarity), primarily from Firmicutes (92.6%) and Proteobacteria (6.9%), via 16S rRNA gene amplicon sequencing. Resident ocular communities of healthy female finches were characterized by greater evenness and phylogenetic diversity compared to healthy male finches. Regardless of sex, ocular microbiome community structure significantly shifted 11 days after experimental inoculation with M. gallisepticum. A suite of OTUs, including taxa from the genera Methylobacterium, Acinetobacter, and Mycoplasma, appear to drive these changes, indicating that the whole finch ocular microbiome responds to infection. Further study is needed to quantify changes in absolute abundance of resident taxa and to elucidate potential functional roles of the resident ocular microbiome in mediating individual responses to this common songbird bacterial pathogen.

The commensal microbes inhabiting a host tissue can interact with invading pathogens and host physiology in ways that alter pathogen growth and disease manifestation. Prior work in house finches (Haemorhous mexicanus) found that resident ocular microbiomes were protective against conjunctival infection and disease caused by a relatively high dose of Mycoplasma gallisepticum (MG). Here, we used wild-caught house finches to experimentally examine whether protective effects of the resident ocular microbiome vary with the dose of invading pathogen. We hypothesized that commensal protection would be strongest at low MG inoculation doses because the resident microbiome would be less disrupted by invading pathogen. Our five MG dose treatments were fully factorial with an antibiotic treatment to perturb resident microbes just prior to MG inoculation. Unexpectedly, we found no indication of protective effects of the resident microbiome at any pathogen inoculation dose, which was inconsistent with prior work. The ocular bacterial communities at the beginning of our experiment differed significantly from those previously reported in local wild-caught house finches, likely causing this discrepancy. These variable results underscore that microbiome-based protection in natural systems can be context dependent, and natural variation in community composition may alter the function of resident microbiomes in free-living animals.

Experimental logging of Appalachian forests reduced the overall abundance of ovipositing mosquitoes captured by gravid traps. Two container‐breeding Aedes species responded strongly to logging, while Culex pipiens/restuans was largely unaffected. The richness and diversity of the sampled mosquito community were not significantly affected by logging treatment, but gravid traps are unlikely to have robustly sampled all mosquito species present. Logging resulted in significant shifts in community composition of ovipositing mosquitoes. This was probably driven by the differential responses to logging of the container‐breeding Aedes species versus Culex pipiens/restuans.