title: Extremely heat tolerant photo-symbiosis in a shallow marine benthic foraminifera.
abstract: Bleaching, the loss of algal symbionts, occurs in marine photosymbiotic organisms at water temperatures minimally exceeding average summer SST (sea surface temperatures). Pre-adaptation allows organisms to persist under warmer conditions, providing the tolerance can be carried to new habitats. Here we provide evidence for the existence of such adaptation in the benthic foraminifera Pararotalia calcariformata. This species occurs at a thermally polluted site in the Mediterranean, where water temperatures reach a maxima daily average of 36 °C during the summer. To test whether this occurrence represents a widespread adaptation, we conducted manipulative experiments exposing this species from an unpolluted site to elevated temperatures (20-42 °C). It was kept in co-culture with the more thermally sensitive foraminifera Amphistegina lobifera in two experiments (20-36 °C). Reduced photosynthetic activity in A. lobifera occurred at 32 °C whereas photochemical stress in P. calcariformata was first observed during exposure to 36 °C. Pararotalia calcariformata survived all treatment conditions and grew under 36 °C. The photosymbiosis in P. calcariformata is unusually thermally tolerant. These observations imply that marine eukaryote-eukaryote photosymbiosis can respond to elevated temperatures by drawing on a pool of naturally occurring pre-adaptations. It also provides a perspective on the massive occurrence of symbiont-bearing foraminifera in the early Cenozoic hothouse climate.
authors: MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Str. Bremen 28359, Germany.
authors: C
authors: C
authors: Schmidt
authors: Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer Sheva, P.O.B 653, Beer Sheva 84105, Israel.
authors: D
authors: D
authors: Titelboim
authors: MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Str. Bremen 28359, Germany.
authors: J
authors: J
authors: Brandt
authors: National Institute of Oceanography, Israel Oceanographic &Limnological Research, Haifa (IORL), Shikmona, P.O.B. 8030, Haifa 31080, Israel.
authors: B
authors: B
authors: Herut
authors: Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer Sheva, P.O.B 653, Beer Sheva 84105, Israel.
authors: S
authors: S
authors: Abramovich
authors: Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501 Israel.
authors: A
authors: A
authors: Almogi-Labin
authors: MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Str. Bremen 28359, Germany.
authors: M
authors: M
authors: Kucera
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D056908:Foraminifera / Q000502:physiology* / Q000528:radiation effects; D006358:Hot Temperature; D019083:Mediterranean Region; D010777:Photochemistry; D012623:Seawater; D013559:Symbiosis / Q000502:physiology* / Q000528:radiation effects