Disease outbreaks have decimated reef-building Acroporid corals in the Caribbean. Recent work has shown that certain Acroporid genotypes appear to be resistant to disease and may thus promote the recovery of these critical coral populations. However, resistant genotypes also appear to grow more slowly than susceptible genotypes. Here, we use a series of spatially-implicit and spatial-explicit metacommunity models to understand the consequences of this tradeoff between growth and susceptibility on the genetic structure and persistence of coral populations experiencing disease outbreaks.
We show that under low disease-induced mortality (i.e., virulence), genetic diversity amplifies the size of disease outbreaks when transmission is high but reduces it when transmission is low. Disease amplification occurs when high transmission and low virulence allow the fixation of susceptible but fast-growing genotypes because infected corals occupy patches for a long time and thus make it harder for resistant but slow-growing genotypes to colonize empty patches. Conversely, disease dilution occurs when low transmission and virulence lead to the fixation of resistant but slow-growing genotypes because there are fewer infected corals and thus more empty patches available for colonization. Overall, these results suggest that understanding these reciprocal feedbacks between coral genetic diversity and disease are critical for devising effective management strategies to ensure the persistence of these important ecosystems.