Abstract

We present a mathematical model using ordinary differential equations that describe the interaction among Gorgonia ventalina under different immune conditions (optimal, intermediate, and immune-compromised), and a potential endo-pathogen. The model has the following assumptions: 1) The polyps are the main unit of the coral; 2) the population of polyps is homogenously distributed through the colony, and thus is considered as single and 3) the immune system is activated by a signal. When the endosymbiont exceeds a density threshold, it becomes pathogenic, decreasing the birth rate of new polyps or increasing their death rate. As a consequence, the colony emits a signal to its stem cells (immune cells) to differentiate into humoral and phagocytic cells, both of which combat the pathogen. Under the optimal immune condition the pathogen is rapidly eradicated by the immune cells and the coral polyp population returns to its equilibrium state. Under the sub-optimal immune condition, polyps and pathogen co-exist, and the maximum capacity of new polyp formation is never reached. In contrast, when coral is immunologically compromised, immune cells cannot stop the pathogen growth, and the number of polyps tend to zero.

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