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Published November 2022 | public
Journal Article

Coral larvae suppress heat stress response during the onset of symbiosis decreasing their odds of survival

Abstract

The endosymbiosis between most corals and their photosynthetic dinoflagellate partners begins early in the host life history, when corals are larvae or juvenile polyps. The capacity of coral larvae to buffer climate-induced stress while in the process of symbiont acquisition could come with physiological trade-offs that alter behaviour, development, settlement and survivorship. Here we examined the joint effects of thermal stress and symbiosis onset on colonization dynamics, survival, metamorphosis and host gene expression of Acropora digitifera larvae. We found that thermal stress decreased symbiont colonization of hosts by 50% and symbiont density by 98.5% over 2 weeks. Temperature and colonization also influenced larval survival and metamorphosis in an additive manner, where colonized larvae fared worse or prematurely metamorphosed more often than noncolonized larvae under thermal stress. Transcriptomic responses to colonization and thermal stress treatments were largely independent, while the interaction of these treatments revealed contrasting expression profiles of genes that function in the stress response, immunity, inflammation and cell cycle regulation. The combined treatment either cancelled or lowered the magnitude of expression of heat-stress responsive genes in the presence of symbionts, revealing a physiological cost to acquiring symbionts at the larval stage with elevated temperatures. In addition, host immune suppression, a hallmark of symbiosis onset under ambient temperature, turned to immune activation under heat stress. Thus, by integrating the physical environment and biotic pressures that mediate presettlement event in corals, our results suggest that colonization may hinder larval survival and recruitment under projected climate scenarios.

Additional Information

We would like to thank the students and support staff at Tropical Biosphere Research Center of University of Ryukyus and Okinawa Institute of Science and Technology Graduate University for assistance in coral collection and larval rearing. We thank Dr. Eiichi Shoguchi for providing symbiont cultures and Maria Khalturina for assistance with RNAseq library preparation. This study was supported by funding provided by NSF EAPSI OISE-1311087, JSPS-SP-13027, PADI Foundation Grant 11199, Sigma Xi Grants-in-Aid of Research and Integrative Biology Department at Oregon State University to SAK. Corals were sampled under the Okinawa Prefecture permit No. 25-67.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023