DOI: 10.5061/dryad.q573n5tg0
title: Ecological factors mediate immunity and parasitic co-infection in sea fan octocorals

description: The interplay among environment, demography, and host-parasite
 interactions is a challenging frontier. In the ocean, fundamental changes
 are occurring due to anthropogenic pressures, including increased disease
 outbreaks on coral reefs. These outbreaks often include multiple
 parasites, calling into question how coral immunity functions in this
 complex milieu. Corals provide an interesting model to study ecological
 immunity during co-infection, being highly sensitive to environmental
 change, susceptible to many diseases, and defended by the innate immune
 system. Our work investigates the interplay of factors influencing coral
 co-infection using metrics of the innate immune response: levels of
 cellular immunity and the expression of candidate immune genes. We used
 existing copepod infections and live pathogen inoculation with Aspergillus
 fungus to test the effect of sequential co-infections in a laboratory
 experiment. We profile significant increases in the expression of the
 immune recognition gene Tachylectin 5A in response to both of these
 naturally occurring parasites of the Caribbean sea fan octocoral, Gorgonia
 ventalina. Cellular immunity increased significantly by 8.16% in copepod
 infections compared to controls and single Aspergillus infections. We
 evaluated immunity in reef populations and again detected activation of
 cellular immunity, with a 13.6% increase in copepod infections and no
 detectable increase in fungal infections. Thus, cellular immunity measured
 in the field and lab were similar, increasing with copepod infections and
 not Aspergillus. We found random co-occurrence of copepods and fungus
 across 15 reefs in Puerto Rico, suggesting other factors prevail in
 structuring parasite infection. Sea fan colony size strongly predicted
 infection by the copepod parasite. Moreover, the effect of parasitic
 infection on immunity was small relative to the explanatory power of site
 differences and coral cover, and roughly equivalent to the effect of
 reproductive status. We suggest that host size, reproductive status, live
 coral cover, and site-specific factors have large effects on parasitic
 infections and host immunity that overwhelm effects of the parasites on
 each other. Thus, host size and site-specific features emerge as critical
 drivers in this multi-parasite system. Parsing the effects of immunity and
 ecological factors in coral co-infection shows how disease depends on more
 than one host and one parasite.
description: These data are from a laboratory experiment and a field survey.
 The laboratory data on amoebocyte density and copepod severity were
 collected using histology slides of the sea fan G. ventalina. Amoebocyte
 density was calculated using percent area of amoebocytes (immune cells) in
 ImageJ. The gene expression data for T5A, MMP, IKB and EF1 were obtained
 using quantitative PCR. We calculated fold change in gene
 expression relative to the reference gene, EF1. Real-time PCR miner was
 used to calculate primer efficiencies and cycle threshold values, which
 were incorporated into the following equation to calculate relative
 expression: 1/(1 + Efficiency)^Cq (Zhao and Fernald, 2005).
description: Notes are included in R code for each set of files (R code and
 related Excel spreadsheet).