Revival of Philozoon Geddes for host-specialized dinoflagellates, ‘zooxanthellae’, in animals from coastal temperate zones of northern and southern hemispheres

Abstract

The dinoflagellate family Symbiodiniaceae comprises numerous genera and species with large differences in diversity, ecology, and geographic distribution. An evolutionarily divergent lineage common in temperate symbiotic cnidarians and designated in the literature by several informal names including "temperate-A", AI, Phylotype A´ (A-prime), and "Mediterranean A", is here assigned to the genus Philozoon. This genus was proposed by Geddes (1882) in one of the earliest papers that recognized "yellow cells" as distinct biological entities separate from their animal and protist hosts. Using phylogenetic data from nuclear (rDNA), chloroplast (cp23S) and mitochondrial genes (cob and cox1), as well as morphology (cell size), ecological traits (host affinity) and geographic distributions, we emend the genus Philozoon Geddes and two of its species, P. medusarum and P. actiniarum, and describe six new species. Each symbiont species exhibits high host fidelity for particular species of sea anemone, soft coral, stony coral, and a rhizostome jellyfish. Philozoon is most closely related to Symbiodinium (formerly Clade A), but, unlike its tropical counterpart, occurs in hosts in shallow temperate marine habitats from Northern and Southern Hemispheres including the Mediterranean Sea, northeastern Atlantic Ocean, eastern Australia, New Zealand and Chile. The existence of a species-diverse lineage adapted to cnidarian hosts living in high latitude habitats with inherently wide fluctuations in temperature calls further attention to the ecological and biogeographic reach of the Symbiodiniaceae.

Intrinsically High Capacity of Animal Cells From a Symbiotic Cnidarian to Deal With Pro-Oxidative Conditions

“…In the present study, H 2 O 2 exposure on whole organism affected mainly the endosymbiont, Philozoon sp. genus ( LaJeunesse et al, 2021 ), rather than the animal host tissues. Although antioxidant defenses were stimulated after 7 days, an increase of protein carbonylation was measured in the symbiont fraction, whereas no increase was observed in the animal compartments ( Figure 2 ).…”

“…The density of the endosymbionts from the genus Philozoon sp. ( LaJeunesse et al, 2021 ) was assessed according to Zamoum and Furla (2012) . Briefly, two tentacles were cut from each animal before and after H 2 O 2 treatment in each condition (0, 200, or 500 μM H 2 O 2 ) and then put in 2 M solution of NaOH and incubated at 37°C for 1 h to dissolve all animal tissue.…”

Living Inside a Jellyfish: The Symbiosis Case Study of Host-Specialized Dinoflagellates, “Zooxanthellae”, and the Scyphozoan Cotylorhiza tuberculata

“…Symbionts have been genetically identified as Symbiodinium A1 (Lajeunesse et al, 2009) and Symbiodinium Temperate A (Visram et al, 2006). However, specimens isolated from the Mar Menor used in this work, seem to host two genetically distinct Symbiodiniaceae genus: Breviolum and Philozoon (Raspor Dall 'Olio, 2016;LaJeunesse et al, 2021).…”

The Impact of Symbiont Diversity on Cellular Integration and Function in the Cnidarian-Dinoflagellate Symbiosis

“…Thus, eleven genera have been officially described to date (Fig. 1.5) (LaJeunesse et al, 2021(LaJeunesse et al, , 2018Nitschke et al, 2020;Pochon and LaJeunesse, 2021).…”

“…The Symbiodiniaceae are physiologically and ecologically diverse, with eleven genera described to date (LaJeunesse et al, 2021(LaJeunesse et al, , 2018Nitschke et al, 2020;Pochon and LaJeunesse, 2021). When in hospite, the symbionts are located in a host-derived late arrested phagosome known as the symbiosome (Fitt and Trench, 1983;Hohman et al, 1982;Neckelmann and Muscatine, 1983;Wakefield et al, 2000;Wakefield and Kempf, 2001).…”