Why Do Corals Bleach? Conflict and Conflict Mediation in a Host/Symbiont Community. (26th June 2018)

• Record Type: Journal Article
• Authors: Blackstone, Neil W.; Golladay, Jeff M.
• Is Part Of: BioEssays. Volume 40:Number 8(2018:Aug.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-06-26
• Subjects: coral bleaching -- evolutionary conflicts -- levels‐of‐selection -- symbiodinium -- photosynthesis -- symbiosis; Molecular biology -- Periodicals; Cytology -- Periodicals; Developmental biology -- Periodicals; 572.8
• DOI: 10.1002/bies.201800021
• Languages: English
• ISSNs: 0265-9247

Abstract

Abstract : Coral bleaching has attracted considerable study, yet one central question remains unanswered: given that corals and their Symbiodinium symbionts have co‐evolved for millions of years, why does this clearly maladaptive process occur? Bleaching may result from evolutionary conflict between the host corals and their symbionts. Selection at the level of the individual symbiont favors using the products of photosynthesis for selfish replication, while selection at the higher level favors using these products for growth of the entire host/symbiont community. To hold the selfish lower‐level units in check, mechanisms of conflict mediation must evolve. Fundamental features of photosynthesis have been co‐opted into conflict mediation so that symbionts that fail to export these products produce high levels of reactive oxygen species and undergo programmed cell death. These mechanisms function very well under most environmental conditions, but under conditions particularly detrimental to photosynthesis, it is these mechanisms of conflict mediation that trigger bleaching. Abstract : A stable symbiosis requires mediation of evolutionary conflict. Coral photosymbiosis with dinoflagellates co‐opt mechanisms of photosynthesis into conflict mediation. These mechanisms – carbon concentration (CCM) and end‐product inhibition – function well under most environmental conditions. Under conditions unfavorable to photosynthesis, however, these mechanisms collapse, triggering programmed cell death of symbionts and bleaching.