DOI: 10.5061/dryad.1zcrjdg1b
title: Influence of melatonin on the successful infection of Daphnia dentifera by Metschnikowia bicuspidata

description: Levels of the hormone melatonin fluctuate daily, with higher
 concentrations often found at night. These fluctuations likely influence
 multiple aspects of physiology, including the immune response. We
 demonstrated that the addition of exogenous melatonin increased the
 proportion of the freshwater zooplankton Daphnia dentifera that became
 infected by the fungal pathogen Metschnikowia bicuspidata, during the day
 but not at night. To determine the stage of this host-pathogen interaction
 at which melatonin may increase susceptibility, we conducted a series of
 laboratory experiments in which we raised Daphnia in the presence and
 absence of exogenous melatonin. To complete its life cycle, Metschnikowia
 must encounter a foraging host, overcome the host’s barrier resistance
 (gut wall) and evade the host’s immune response (internal clearance). We
 quantified encounter rate by measuring the gut passage time and the number
 of spores that entered the gut. We also measured the number of spores that
 successfully entered the body cavity (barrier resistance), and the
 hemocyte response to spores entering the body cavity (one metric of
 internal clearance). Finally, we quantified the effect of exogenous
 melatonin on triggering molting. The addition of exogenous melatonin
 lengthened gut passage time and decreased the number of spores present in
 the gut. We found no effect of melatonin on the percentage of gut spores
 successfully entering the host’s body cavity nor in the hemocyte response.
 Melatonin is known to influence the timing of molting and hosts that
 molted during exposure were more likely to become infected, likely due to
 a decrease in barrier resistance. In a fully factorial experiment, there
 was a high death rate, low infection rate, and therefore no discernible
 effect of melatonin on molting, molting or melatonin on infection. Our
 results provide insight into the stages of infection where melatonin does
 and does not have significant effects.
description: # Hughesetal\_2024\_Ecosphere
 [https://doi.org/10.5061/dryad.1zcrjdg1b](https://doi.org/10.5061/dryad.1zcrjdg1b) ## Description of the data and file structure **This paper presents the results from five laboratory experiments that investigate the role of exogenous melatonin on infection of the freshwater zooplankton *Daphnia dentifera* by the fungus *Metschnikowia bicuspidata*. There are 11 tabs in the datasheet.** Expt1 Infection results from *Daphnia* exposure to exogenous melatonin either during the day or at night.  Expt1_metadata Experiment 1 metadata Expt2 Gut passage time of *Daphnia* exposed to exogenous melatonin and / or *Metschnikowia* in a fully-factorial experiment.  Expt2_metadata Experiment 2 metadata Expt3_analysisI Counts of Metschnikowia spores in the gut, gut wall, and body cavity of the *Daphnia* in the presence and absence of exogenous melatonin. The gut penetrability metric is also calculated. Expt3_analysisII Calculation of the average number of hemocytes per *Metschnikowia* spore for those hosts that had penetrating spores.  Expt3_metadata Experiment 3 metadata   Expt4a_analysisI Data for all *Daphnia* individuals for the analysis of if exposure to *Metschnikowia* or exogenous melatonin influences molting.  Expt4a_analysisII Data for those *Daphnia* individuals that were exposed to *Metschnikowia* to determine the effect of exogenous melatonin on infection.  Expt4b An additional experiment to determine the effect of molting on infection.  Expt4a&b_metadata Experiment 4 metadata ## Sharing/Access information N/A ## Code/Software All analyses and data visualization were conducted in R 4.3.3 (R Core Team 2024) using standard models and packages as described in the methods of the manuscript.