The effect of warming on seagrass wasting disease depends on host genotypic identity and diversity

Abstract

Temperature increases due to climate change have affected the distribution and severity of diseases in natural systems, causing outbreaks that can destroy host populations. Host identity, diversity, and the associated microbiome can affect host responses to both infection and temperature, but little is known about how they could function as important mediators of disease in altered thermal environments. We conducted an 8‐week warming experiment to test the independent and interactive effects of warming, host genotypic identity, and host genotypic diversity on the prevalence and intensity of infections of seagrass (Zostera marina) by the wasting disease parasite (Labyrinthula zosterae). At elevated temperatures, we found that genotypically diverse host assemblages had reduced infection intensity, but not reduced prevalence, relative to less diverse assemblages. This dilution effect on parasite intensity was the result of both host composition effects as well as emergent properties of biodiversity. In contrast with the benefits of genotypic diversity under warming, diversity actually increased parasite intensity slightly in ambient temperatures. We found mixed support for the hypothesis that a growth–defense trade‐off contributed to elevated disease intensity under warming. Changes in the abundance (but not composition) of a few taxa in the host microbiome were correlated with genotype‐specific responses to wasting disease infections under warming, consistent with the emerging evidence linking changes in the host microbiome to the outcome of host–parasite interactions. This work emphasizes the context dependence of biodiversity–disease relationships and highlights the potential importance of interactions among biodiversity loss, climate change, and disease outbreaks in a key foundation species.

Contrasting effects of sheep and cattle grazing on foliar fungal diseases by changing plant community characteristics

“…The negative effects of diversity on infection are consistent with previous meta-analysis (Civitello et al, 2015) and field studies (Halliday et al, 2020;Mipam et al, 2022;Rottstock et al, 2014;Schenck et al, 2023), and supported a dilution effect, where individual host plants enjoy reduced infection when growing in mixtures (Keesing et al, 2010). We found negative effects of biodiversity on disease severity for biotrophic, rather than necrotrophic pathogens, which agrees with a previous meta-analysis (Liu et al, 2020).…”

“…Alongside changes in host community composition, changes in host diversity could be an important driver of pathogen infection, as host species richness can reduce pathogen abundance through dilution effects in grassland ecosystems (Civitello et al., 2015; Halliday et al., 2020). Dilution effects and negative impacts of diversity on disease have been shown in many systems, including tick borne diseases in rodents (Keesing et al., 2010), pathogens of seagrass in marine systems (Schenck et al., 2023) and fungal pathogens in grasslands (Liu et al., 2016). However, the opposite pattern is also possible, where pathogen infection is amplified in diversity communities (Halliday et al., 2017).…”