Ph.D. Dissertation Defense - Hagen Gegner

Nov 08 2018 02:00 PM - Nov 08 2018 03:00 PM

Evn_2018_Hagen.jpg Hagen Gegner

 TITLE: Investigating the Role of Salinity in the Thermotolerance of Corals

 ADVISOR:  Prof. Christian Voolstra

 DATE:  Thursday, 6 November

 TIME:  2 pm

 LOCATION: Auditorium level 0, between buildings 2 and 3

BIO: Hagen is a trained marine scientist who focuses on metabolic responses of marine invertebrates and has a background in molecular cloning and population genetics. Despite his general marine sciences focus, he developed expertise in a broad range of laboratory techniques throughout my academic career, from basic molecular techniques in model organisms, such as Hydra (B.Sc. in Marburg, Germany), to population genetic approaches (M.Sc. in Bremen, Germany/ Belem, Brazil) and most recently, metabolomics in corals (Ph.D. at KAUST). In his recent projects, Hagen used targeted and untargeted metabolomics to better understand the coral holobiont (comprised of the coral host, it's algal endosymbiont and a suite of microbes) when exposed to salinity and temperature stress. Hagen aimed to elucidate the production of metabolites that may link the observed thermotolerance and osmoadaptation in a potentially cumulative effort by each compartment of the coral holobiont. Exactly this complex relation of the compartments, besides a rather simple overall structure, intrigued him when he started his Ph.D.

ABSTRACT: Coral reefs are globally threatened by increasing sea surface temperatures (SST) that trigger coral bleaching, the disruption of the symbiosis of the coral host and its photosynthetic algal endosymbiont. Hence, it is important to identify drivers and mechanisms underlying coral thermotolerance. It is compelling that some of the most thermotolerant corals live also in particularly saline habitats, such as the Red Sea, but possible effects of high salinity on thermotolerance in corals are anecdotal. Emerging from this observation is the intriguing hypothesis that high salinity conditions may assist thermotolerance in corals. In my Ph.D. defense, I will focus on the effects of salinity on thermotolerance and bleaching of corals. To systematically test that I conducted several salinity-heat stress experiments using the coral model Aiptasia. I show that Aiptasia retained more endosymbionts and experienced lower photosynthetic impairment under heat stress in higher salinities. Notably, this effect was dependent on the host-endosymbiont combination. To identify candidate molecules that could confer the observed 'salinity effect,' I characterized metabolites produced in salinity and heat using targeted GC/MS.  One key osmolyte, in particular, stood out in the analyses: the carbohydrate floridoside was strongly upregulated in high salinity as well as high salinity-high heat conditions. Interestingly, floridoside, besides its osmoadaptation function, can act as an antioxidant capable of scavenging reactive oxygen species (ROS). This provides a direct link between decreased bleaching sensitivity and salinity and highlights the putative importance of osmoadaptation in the thermal tolerance of cnidarian-endosymbiont symbioses.