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Individual fish infection data from metapopulation epidemics used to calculate resistance, tolerance and competence

Citation

Tadiri, Christina; Fussmann, Gregor; Scott, Marilyn (2021), Individual fish infection data from metapopulation epidemics used to calculate resistance, tolerance and competence, Dryad, Dataset, https://doi.org/10.5061/dryad.wh70rxwnm

Abstract

Host competence, defined as the likelihood that a host will transmit infection, may be affected by an individual’s resistance to infection and its ability to withstand damage caused by infection (tolerance). Host competence may therefore be one of the most important factors to impact host-parasite dynamics, yet the relationships among resistance, tolerance, and competence are poorly understood.  The objective of the present study was to determine whether individual host resistance (ability to resist or minimize infection) and/or tolerance (ability to withstand or minimize reduction in fitness due to infection) contributed to the competence (ability to spread infection) of hosts using guppies infected with the ectoparasite, Gyrodactylus turnbulli. This individual-fish level analysis used data collected from a previous metapopulation experiment that had tracked host-parasite dynamics at the metapopulation scale using individually marked guppies that were moved among experimental tanks within replicate metapopulations. Fish tolerance was measured as the residual from a fish’s expected survival post-infection for a given parasite burden. Fish resistance was measured as the peak parasite load ( - log-transformed). Host competence was measured as the incidence (number of new infections over two days after the arrival of a fish to a tank) weighted by the density of available uninfected fish in the tank. In contrast to the assumption of a trade-off between resistance and tolerance, individual fish tolerance and resistance were both negatively associated with competence. Connectivity (the number of fish with which an individual came into contact) was not associated with competence.  Our results indicate that resistance and tolerance are both important to disease spread. These findings highlight the importance of understanding how individual defence against parasites may contribute to its competence as a host, and therefore impact metapopulation-level dynamics.

Methods

Fish were weight, measured, marked and assembled into metapopulations consisting of 4 tanks each of 8 fish. Parasites were then introduced to the metapopulations either by infecting one fish in each tank with 2 parasites, or by infection four fish in one tank with two parasites. Infections on each individual were then monitored every two days either for 120 days or until no parasites were found in the whole metapopualtion for two consecutive counting days. Additionally, every 10 days one fish from each tank was haphazardly selected and moved to the next tank in the metapopulation in a unidirectional looped manner (A->B->C->D->A). The raw data recorded for each fish (uploaded here) were initial weight and length, location within the metapopulation for each 10-day interval and parasite load every two days.

These raw data were then used to calculate our variables of interest. Resistance to parasites was calculated as the fish's maximum parasite burden (-log-transformed). Tolerance to parasites was calculated as the residual from a fitted exponential decay curve of survival post-infection and maximum parasite load. Competence of an individual fish was measured as the number of uninfected fish in a tank that became infected two days after that fish was introduced to that tank, multiplied by the density of uninfected fish in the tank and excluding cases where all fish in the tank were already infected or the migrating fish was uninfected to account for opportunity. For infected fish that moved to tanks with uninfected fish more than once, an average of this competence was used.

Funding

Fonds Québécois de la Recherche sur la Nature et les Technologies

Natural Sciences and Engineering Research Council of Canada