Data and code from: The macroecology of immunity: predominant influence of climate on invertebrate immune response

The immune system serves as the first line of defense against attack by
parasites. With the ever-increasing rate of disease, epidemiologic models
that consider geographic variation in the strength of immune responses
among individuals and populations could prove useful. Although
there is increasing interest in the macroecology of parasitism and
infectious diseases, we know very little about the macroecology of immune
responses. Characteristics of the host, exposure to parasites,
and environmental factors can all affect immunity, but how these factors
interact to shape spatial variation in the strength of immune responses
remains unexplored. We captured odonates (dragonflies and damselflies) and
their conspicuous ectoparasitic mites across a geographic area spanning
two biomes in eastern Canada. We then conducted immune response bioassays
on 1,237 individuals from 63 odonate species. We estimated the strength of
a key aspect of odonate immune response against ectoparasites by inserting
a nylon thread into adult individuals and quantifying the encapsulation
response. We then used linear regressions and structural equation models
to relate these measurements to host body size, parasite load, pH,
temperature, and precipitation while accounting for evolutionary
relationships among host species. We found significant differences in the
strength of immune response among host individuals, and this variation was
best explained by climatic conditions, specifically decreasing with
precipitation and, to a lesser degree, temperature. While host species
significantly differed in the strength of their immune response, we found
no effect of host body size, evolutionary relationships among hosts, or
parasitism on immune response. Our study investigating the drivers of
immune response across dozens of species spread in two biomes is the most
comprehensive to date. Climatic conditions have a strong influence on host
immune response, regardless of host characteristics or parasitism rates.
In this specific case, strong immune responses were associated with low
levels of annual precipitation, which could possibly relate to the role of
cuticular melanin content in desiccation resistance, and the melanin-based
encapsulation response being a byproduct of this adaptation. A
spatially-explicit understanding of the biological processes affecting
immunity could improve epidemiological models of disease risk that inform
disease management globally.