Urban living can rescue Darwin's finches from the lethal effects of invasive vampire flies

• Published in: Global change biology Vol. 30; no. 1; pp. e17145 - n/a
• Main Authors: Knutie, Sarah A., Webster, Cynthia N., Vaziri, Grace J., Albert, Lauren, Harvey, Johanna A., LaRue, Michelle, Verrett, Taylor B., Soldo, Alexandria, Koop, Jennifer A. H., Chaves, Jaime A., Wegrzyn, Jill L.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-01-2024
• Subjects: Abundance; Adaptive immunity; Anthropogenic factors; Blood; Blood cells; Darwin's finch; Defence mechanisms; Diet; ecoimmunology; Erythrocytes; Flies; Gene expression; Genes; host defenses; Human influences; Immune response; Immune system; Immunity; Immunological tolerance; Immunology; Inflammation; Inflammatory response; Introduced species; invasive parasites; Invasive species; Juveniles; Lethal effects; Nests; Parasites; resistance; stable isotopes; Survival; Synergistic effect; tolerance; transcriptomics; Urban areas; Urbanization; invasive parasites; stable isotopes; host defenses; Darwin's finch; transcriptomics; ecoimmunology; gene expression; resistance; tolerance
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.17145

Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (Philornis downsi) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non‐urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non‐parasitized nestlings from urban (79%) and non‐urban (75%) nests did not differ significantly. However, parasitized, non‐urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ15N) from urban nestling feces were higher than those from non‐urban nestlings, suggesting that urban nestlings are consuming more protein. δ15N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized, urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro‐inflammatory response (innate immunological resistance), compared to parasitized, non‐urban nestlings. In contrast, parasitized non‐urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro‐inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non‐urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived.
Human activity changes multiple factors in the environment, which can affect the health and survival of birds. Our study shows that urban nestling Darwin’s finches in the Galápagos Islands are less affected by invasive avian vampire flies compared to non‐urban nestlings. Urban nestlings are more tolerant of parasites (via red blood cell production) and resistant to parasites (via innate immune responses), compared to non‐urban nestlings. Although non‐urban nestlings differentially express genes related to adaptive immune pathways, this response is not an effective defense. Artwork by Alexandria Soldo.