Meeting Abstract
77.6 Wednesday, Jan. 6 Elevated autophagic activity during hyperthermic stress in the common anemone, Aiptasia pallida: A novel cellular mechanism during bleaching. HANES, S. D.*; KEMPF, S. C.; Auburn University; Auburn University hanessd@auburn.edu
Coral bleaching involves the loss of symbiotic dinoflagellates from host gastrodermal tissues, which occurs as a result of elevated temperature/light stress. Previous studies examined histological snapshots of bleaching tissues that suggested several different methods of symbiont loss, including multiple forms of host and/or symbiont cell death, which may co-occur to facilitate bleaching. Although this phenomenon has gained much attention in recent years, little is known of the cellular events driving these potential mechanisms. In this study, light and transmission electron microscopy (TEM) were utilized to examine anemone tentacle histology/ultrastructure in the common anemone, Aiptasia pallida, while undergoing progressive bleaching. Bleaching was induced by exposing specimens to hyperthermic conditions of ~32.5oC for 12 hours of light followed by 12 hours of darkness at ~21.5oC, which mimicked thermal stress conditions observed in the field. Examination of heat stressed tissues revealed numerous residual bodies (RBs) throughout both the symbiotic gastrodermal layer and the non-symbiotic epidermal layer. The abundance of RBs increased with extended length of thermal treatment, and noticeable cellular degradation in the form of “cleared” areas of less dense cytoplasm and organelle debris was observed. After ~12 hours of thermal treatment, several individual symbionts were observed in membrane bound cytoplasmic protrusions pinching off or detaching from the apical end of degraded host gastrodermal cells in a apocrine-like manner. These findings indicate that significant autophagic lysosomal degradation of host tissues occurs during thermal stress and is an active cellular mechanism during bleaching.
