Publication Date

2019

Document Type

Dissertation/Thesis

First Advisor

Blackstone, Neil W.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences

Abstract

Climate change is an increasing problem for species all around the globe, including coral reef communities, which are among the most diverse and productive in the world. The mutualistic symbiosis between corals and photosynthetic dinoflagellates (symbionts) is central to these ecosystems. The rising temperatures are causing corals to lose their symbionts in a process known as bleaching, thus endangering the entire community. In this context, it is imperative to discover mechanisms that might mitigate the effects of stress on corals. Previous work has established that stress increases the formation of reactive oxygen species (ROS), that is, partially reduced forms of oxygen. Stress also triggers the migration of symbionts out of their usual intracellular location and into the gastrovascular lumen of the coral. While some of these migrating symbionts exit the coral colony, the vast majority accumulate in the recesses of the colony, as if seeking shelter. Potentially, these migrating symbionts could return to the coral tissue once the stress ceases, thus greatly mitigating the ill-effects of bleaching. Illuminating the migration process is thus a critical priority. As a first step, the relationship between ROS formation and migration was assessed.

While not reef-building corals, octocorals provide useful laboratory models. Experiments were conducted on colonies of Sympodium sp. and Sarcothelia sp. to try to determine if ROS is associated with symbiont migration in octocorals. After conducting a detailed time course, an experimental protocol was developed in which corals were either stressed for 4 h or kept in the culture tank before being imaged for ROS formation and symbiont migration. Using fluorescent microscopy and digital image analysis, the outcomes were measured for three areas per colony and 33 total colonies of each treatment and each species. Statistical analysis indicates that both ROS and the number of migrating symbionts tend to increase in response to stress.

Clearly, an association does not indicate a causal connection. Nevertheless, these results are consistent with the hypothesis that ROS serve as a signal that triggers symbiont migration, at least under some conditions. If further work supports these findings, valuable insight can be provided into the bleaching process. For instance, while bleaching is likely a by-produce of evolutionary conflict, mitigating the process with antioxidant treatment is unlikely to be a successful therapeutic. Antioxidants would diminish the ROS signal and the resulting migration, leaving more symbionts in the tissue subject to programmed cell death. Further experiments are likely to be insightful in this regard.

Extent

28 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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Text

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