Abstract
It is well understood that heat stress causes bleaching in corals. Much work has focused on the way heat stress disrupts corals’ symbiotic relationship with endosymbiotic algal dinoflagellate, Symbiodiniaceae, a process called bleaching. However, the damage to the coral tissue that occurs during the bleaching process and, importantly, the factors that contribute to subsequent recovery, are not well understood. I hypothesize that the host tissue damage created by heat stress initiates cascades of wound healing factors that maintain epithelial integrity. These factors may be found to contribute to the coral’s potential capacity to recover. In this study, I present evidence that heat stress causes damage to the coral host tissue and that collagen is present in the gastrodermis of heat-stressed corals. I found that, during the early stages of bleaching, an important transcription factor for wound healing, Grainyhead, is expressed throughout the gastrodermis, where the cellular and tissue rearrangements occur. Lastly, using phylogenetics, I found that cnidarian Grainyhead proteins evolved three distinct groups and that evolution of this protein family likely happened within each taxonomic group. These findings have important implications for our study of coral resiliency in the face of climate change.
Highlights
Corals are critical ecosystem builders that are important for promoting marine biodiversity, economic development, and human health (Hughes et al, 2003)
In this study I found evidence for heat stress causing a cellular pathology of necrosis and degradation, and the initiation of wound healing factors including collagen production (Figs. 1B, 2 and 3)
In the coral Acropora aspera, cellular aspects of bleaching including apoptosis were observed in corals exposed to heat stress early in the bleaching response, indicating that the coral host was reacting to the heat stress long before the bleaching event occurred (Ainsworth et al, 2008)
Summary
Corals (phylum: Cnidaria) are critical ecosystem builders that are important for promoting marine biodiversity, economic development, and human health (Hughes et al, 2003). Within the endodermal epithelium, called the gastrodermis, many coral cells contain symbiotic dinoflagellates called Symbiodinium (recently renamed Symbiodiniaceae (LaJeunesse et al, 2018)). Through this critical partnership, the Symbiodiniaceae provides nutrients for the coral host, and in turn Symbiodiniaceae uses the wastes of the coral (Gates, Baghdasarian & Muscatine, 1992; Weis, 2008). The Symbiodiniaceae provides nutrients for the coral host, and in turn Symbiodiniaceae uses the wastes of the coral (Gates, Baghdasarian & Muscatine, 1992; Weis, 2008) During disturbance events such as heat stress, corals can ‘‘bleach’’, disassociating from the Symbiodiniaceae partner, and the coral’s normally brown-pigmented tissue appears white as the skeleton shows through the translucent tissue. The phenomena of bleaching is highly variable, and different levels of bleaching can occur in different species of coral, as
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