PS 42-145 - Skin microbiome disruption linked to drought-induced disease in Brazilian pumpkin toadlets

Abstract: Abnormal rainfall patterns are predicted to become increasingly common as global climate change continues to worsen. These changes have the potential to impact hosts and their symbionts differently, leading to mismatches between them that may have population-level consequences. We investigated the effects of a short-term drought on the skin bacterial communities (i.e., the microbiome) of a direct-developing pumpkin toadlet species in the Atlantic Rainforest of Brazil. Some skin bacteria have been shown to produce anti-fungal compounds that inhibit the fungal pathogen Batrachochytrium dendrobatidis (Bd), and the community composition of the skin microbiome is correlated with disease outcomes in many amphibian species. Therefore, we focused on the link between changes in the microbiome and pathogen susceptibility and host mortality.

Using 16S rRNA gene amplicon sequencing, we tested for differences in the skin microbiomes of individual frogs before, during, and after a previously documented die-off event. We predicted that the rainfall anomaly led to microbiome dispersion (i.e., more variable communities between conspecifics) that coincided with the observed spike in Bd infection loads and mortality. Structural equation models revealed that the strongest link between the rainfall deficit and infection loads was mediated by increased microbiome dispersion, while the direct link between drought and Bd loads was weak. The skin microbiome became more variable and less diverse a month following the drought, indicating that there may be a lagged effect of drying on the microbiome that could have increased the toadlets’ susceptibility to Bd. Frogs have long been considered important indicators of environmental health, and this case should serve as a warning that illustrates how disturbances like drought and disease can interact synergistically through complex host-symbiont interactions to affect animal populations.