Graduation Year

2018

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Pamela Hallock Muller, Ph.D.

Committee Member

James Garey, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Committee Member

Mya Breitbart, Ph.D.

Committee Member

Susan Richardson, Ph.D.

Keywords

CellTracker Green, fluorescence, Photic stress, Quiescence, symbiosis

Abstract

Dormancy, a state of severely decreased or suspended metabolism, is a widespread survival strategy in nature. In the Foraminifera, one of the most studied groups of marine organisms, its presence had been suggested by circumstantial evidence, but rarely studied directly until recently. Despite the lack of research, stressor-induced dormancy can significantly alter the way in which foraminiferal ecology is understood, especially in marginal environments. In this dissertation, I reviewed the evidence for dormancy in the foraminiferal literature, concluding that evidence for dormancy is widespread across the Phylum. I then explored the role of dormancy in the survival of the diatom-bearing foraminifer Amphistegina gibbosa d’Orbigny when exposed to toxic chemicals, and when kept in dark conditions for extended periods of time. I developed methods for utilizing CellTracker Green™, a fluorescent probe, to explore metabolic activity in symbiont-bearing foraminifers, finding that it can be used in some situations, such as bioassay experiments or other cases of toxic chemical exposure, to distinguish dead from dormant individuals. The results of the associated experiments demonstrated that reduced metabolism occurred in individuals that survived toxic chemical exposure for over two months in darkness, as well as indicating that metabolic recovery can begin to occur within 30 minutes of removal from darkness. Fluorescence microscopy of symbiont autofluorescence also demonstrated that the diatom symbionts are also capable of surviving aphotic conditions, recovering when returned to lighted conditions.

Further experiments showed that A. gibbosa and its associated symbionts are capable of surviving up to 20 months in darkness. Although survival decreased as the length of time in darkness increased, 80% of the specimens survived a 20-month treatment. In addition, all treatment lengths showed color recovery, indicating survival of the diatom symbionts, which give A. gibbosa its characteristic golden-brown color. However, patterns of color recovery indicated that extended periods in darkness increased the photosensitivity of the A. gibbosa holobiont, despite entering dormancy.

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