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

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.

Automated summary

Temperature increases due to climate change have impacted disease distribution and severity, leading to outbreaks that can harm host populations. The identity, diversity, and microbiome of hosts can influence their response to infection and temperature, but little is known about their role as important mediators of disease in altered thermal environments. In this study, an 8-week warming experiment was conducted to examine the effects of warming, host genotypic identity, and host genotypic diversity on infection prevalence and intensity in seagrass. The results showed that genotypically diverse host assemblages had lower infection intensity, but not prevalence, at elevated temperatures. Additionally, changes in the host microbiome were correlated with genotype-specific responses to infection under warming. This research highlights the context dependence of biodiversity-disease relationships and emphasizes the potential significance of interactions between biodiversity loss, climate change, and disease outbreaks.