Data and code for: Transgenerational pathogen effects: Maternal pathogen exposure reduces offspring fitness

Pathogens can alter the phenotype not only of exposed hosts, but also of
future generations. Transgenerational immune priming, where parental
infection drives reduced susceptibility of her offspring, has been
particularly well explored, but pathogens can also alter life history
traits of offspring. Here, we examined the potential for transgenerational
impacts of a microsporidian pathogen, Ordospora pajunii, by experimentally
measuring the impact of maternal exposure on offspring fitness in the
presence and absence of parasites, and then developing mathematical models
that explored the population-level impacts of these transgenerational
effects. We did not find evidence of transgenerational immune priming:
offspring of exposed mothers became infected at high rates, similar to
offspring of unexposed mothers, and the infection burden did not differ
between these two groups. We also did not find any evidence of
transgenerational tolerance, where daughters of exposed mothers have
higher fitness after infection. Instead, we found evidence for negative
transgenerational impacts of infection: uninfected offspring of exposed
mothers had substantially greater early life mortality than uninfected
offspring of unexposed mothers. Offspring of exposed mothers also had
reduced growth rate, fewer clutches, and fewer offspring. We propose that
these observations should be considered transgenerational virulence, where
a pathogen reduces the fitness of the offspring of infected hosts. Our
parameterized mathematical model allowed us to explore the impacts of
transgenerational virulence at the population level. If transgenerational
virulence manifests as decreased reproduction or increased mortality in
offspring, as we saw in the empirical portion of our study, this reduces
total host density, infection prevalence, and infected host density, which
could have implications for both host conservation and spillover risk. We
propose that transgenerational virulence might be common and is a concept
worthy of further empirical and theoretical exploration.