Understanding Coral Immune Response to Diseases: Experimental and Mathematical Modeling Approach
Ruiz Diaz, Claudia Patricia
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In the last decades the sea fan G. ventalina has suffered from several infectious diseases. Sea fans can either recuperate or succumb to these afflictions depending, in part, to the strength of their immune system. However, the effect of environmental stress on the immune response of sea fans is not well understood. Chapter 1 presents a model that analyzes the capacity of G. ventalina to eradicate a micro-pathogen under three immune states: healthy, chronically and terminally diseased. Under the optimal immune condition, the pathogen is rapidly eradicated. Under the sub-optimal immune condition, polyps and pathogen coexist. And when the colony is immunologically compromised, immune cells are unable to stop pathogen growth, and the colony dies. In Chapter 2 the rehabilitation capacity of G. ventalina after diseased-induced lesions were either scraped or extirpated is examined in a field experiment. With the scraping technique over 51% of the colonies recovered between 80-100% of the lost tissue. With extirpation, lesions did not reappeared in any of the colonies. We conclude that lesion scraping is useful for eliminating relatively small lesions, as these are likely to recover in a short period of time, whereas for relatively large lesions it is more appropriate to extirpate the lesion. Chapter 3 compares the recovery capacity of diseased G. ventalina colonies at two different depths (5m and 12m) with significant differences in light intensity, temperature, and water motion while correcting for genetic differences. We found that the rate of tissue regeneration was not influenced by depth-related conditions or by genetic variability. We also found that lesions recovery occurred within similar time spans in shallow and deep stations. Finally, Chapter 4 presents a model that analyzes the capacity of recovery of G. ventalina under contrasting health conditions after a lesion has been induced. The model predicted three solutions: i) a lesion completely and exclusively covered by healthy tissue; ii) a lesion completely covered by healthy and purpled tissues; and iii) a lesion completely covered by purple tissue. The model was accurate in reproducing three of the macroscopic levels of recovery that have been observed in the field.