Cladocopium infistulum sp. nov. (Dinophyceae), a thermally tolerant dinoflagellate symbiotic with giant clams from the western Pacific Ocean

ABSTRACT

Members of the genus Cladocopium are the most ecologically dominant and geographically widespread group of mutualistic dinoflagellates. The addition of species descriptions to this newly erected genus should stimulate scientific investigations and communication about the biology of these important symbionts. Here we combine morphology and genetic evidence with ecology to formally describe Cladocopium infistulum sp. nov. An emended description for C. goreaui is also provided. Both are among the few species of Cladocopium capable of growing in culture medium. The cells of C. infistulum are significantly smaller in size and differ in amphiesmal plate tabulation (morphology of the motile cell) from C. goreaui. Both appear to lack knob ornamentation typical of the elongate amphiesmal vesicle (EAV) in other Symbiodiniaceae. Phylogenetic analyses of nucleotide sequences from nuclear ribosomal, chloroplast, and mitochondrial genes differentiate C. infistulum from other Cladocopium spp. This new species is ecologically specialised, and known to occur only at high densities in digestive diverticula–a complex system of capillary-like hollow tubes that ramify the siphonal mantles of giant clams (Tridacnidae). Clams living in predominantly warm and shallow inshore reefal environments harbour this symbiont; and its biogeographic range appears restricted to the equatorial western Pacific Ocean. This new species description emphasises the need to formally recognise the high species diversity and corresponding physiological and ecological breadth that encompass Cladocopium.

KEYWORDS:

• Clade C
• Dinoflagellates
• Ecological specialisation
• Specificity
• Symbiodiniaceae
• Tridacnidae

SUPPLEMENTARY MATERIAL

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Acknowledgements

Research activities in Palau were made possible by permission from the Ministry of Natural Resources, Environment and Tourism, Palau and from the Koror State Government, Department of Conservation and Law Enforcement. The authors thank Kira E. Turnham for her help with cell size measurements, and to Dusty Kemp and Drew F. Wham for help with specimen collections.

Additional information

Funding

Research in Korea was supported by the Useful Dinoflagellate program of the Korea Institute of Marine Science and Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (MOF) and the National Research Foundation (NRF) funded by the Ministry of Science and ICT (NRF-2015M1A5A1041806; NRF-2017R1E1A1A01074419) award to HJJ. Research in the United State was supported by the USA National Science Foundation (IOS-1258058 and OCE-1636022 to TCL), Penn State University, and IOC-UNESCO-World Bank targeted working group on coral bleaching.