Behavioural infection tolerance of malaria is negatively correlated with pro-inflammatory cytokine expression in the brain of an invasive songbird

Document Type

Article

Publication Date

4-1-2025

Abstract

Invasive species are often freed from the co-evolved parasites of their native range (“enemy release hypothesis”), leaving little benefit for the host to induce self-harming inflammatory responses against novel pathogens in the invading range. Instead, selection may favour the allocation of energetic resources to traits that facilitate growth and reproduction to increase competitive ability (“evolution of increased competitive ability hypothesis”). In extension of these hypotheses, we tested whether the globally invasive house sparrow (Passer domesticus; n = 21) exhibits sickness behaviours during acute experimental inoculation with Plasmodium relictum. Because sickness behaviours are a consequence of inflammation, we quantified cytokine expression in the liver and brain. Overall, we did not detect any changes in feeding duration, preening duration, or activity in malaria-infected sparrows (n = 10) during acute malaria infection, and infected sparrow behaviour did not differ from malaria-resistant sparrows (n = 5) or sham controls (n = 6). However, pro-inflammatory IFN-γ expression in the brain, but not the liver, was negatively correlated with infected sparrow activity, suggesting individuals that mount strong inflammatory responses are more likely to show sickness behaviours. Disease transmission is often linked with host behaviour; if invasive species behaviourally tolerate infection and maintain normal activity and sociality, they may disproportionately facilitate the spread of disease.

Publication Source (Journal or Book title)

Behavioral Ecology and Sociobiology

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