DOI: 10.5061/dryad.7m0cfxq31
title: Data from: Behavioural infection tolerance of malaria is negatively correlated with pro-inflammatory cytokine expression in the brain of an invasive songbird

description: 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.
description: We used an experimental inoculation with <em>Plasmodium
 relictum</em> (avian malaria parasites) and quantified overall
 activity, feeding, and preening to assess sickness behaviour. Behaviour
 was quantified from two-hour long video recordings but the first 30
 minutes of each video was not scored to avoid behaviour disruptions caused
 by researchers setting up the recording system. Three observers, blind to
 treatement, scored the videos for activity (the number of hops and
 flights), time spent preening (seconds), and time spent feeding
 (seconds).  We assessed cytokine expression of two
 pro-inflammatory cytokines (IFN-γ & TNF-α) and two
 anti-inflammatory cytokines (IL-10 and TGF-β) that are implicated in the
 pathology of malaria in mammals. We extracted RNA from liver and cerebelum
 tissue obtained 13 days post-inoculation when sparrows experience peak
 parasite loads. We converted RNA to cDNA before conducting Taqman qPCR.
 Probes and primers for cytokines and references were validated in both
 tissues, including the selesction of the most stable reference gene (TBP
 in the liver, ACTB in the cerebellum). Data are reported as relative fold
 expression following Livak & Schmittgen (2001, "Analysis of
 relative gene expression data using real-time quantitative PCR and the
 2^-delta delta Ct" in <em>Methods</em>, 25,
 402-408). 
description: # Behavioural infection tolerance of malaria is negatively correlated with
 pro-inflammatory cytokine expression in the brain of an invasive songbird.
 [https://doi.org/10.5061/dryad.7m0cfxq31](https://doi.org/10.5061/dryad.7m0cfxq31) This dataset includes activity, preening, and feeding behaviour quantified from video recordings of house sparrows (*Passer domesticus*) that were inoculated with blood containing avian malaria parasites (*Plasmodium relictum*) or uninfected blood. We quantified liver and brain cytokine expression to test for relationships between sickness behaviour and tissue-specific inflammation. Infected and uninfected sparrows did not differ in behaviour, overall, but pro-inflammatory IFN-γ expression in the brain, but not in the liver or in uninfected sparrows, was negatively correlated with infected sparrow activity, suggesting individuals that mount strong inflammatory responses are more likely to show sickness behaviours. ## Description of the data and file structure The main datafile (`MALARIAEXP1_BEHAVIOR & CYTOKINE_no repeats_2024-03-07_TRK`) contains behaviour and cytokine expression data. The first sheet contains the raw data and the second sheet describes the content for each data column (e.g., dummy variable interpretation). A second datafile (`MALARIAEXP1_BEHAVIOR_OBSERVER BIAS TEST_2024-01-18`) contains a subset of videos that were watched by multiple viewers to test for viewer bias. Variable/column names are the same in both files. ## Code/Software Statistical analysis was conducted in R (v 1.4.2), and the script for behaviour, cytokine, and viewer bias statistical analysis is available. It is annotated with a glossary, assumption testing, and figure creation.