A genetics‐based description of Symbiodinium minutum sp. nov. and S. psygmophilum sp. nov. (Dinophyceae), two dinoflagellates symbiotic with cnidaria

Abstract

Traditional approaches for describing species of morphologically cryptic and often unculturable forms of endosymbiotic dinoflagellates are problematic. Two new species in the genus Symbiodinium Freudenthal 1962 are described using an integrative evolutionary genetics approach: Symbiodinium minutum sp. nov. are harbored by widespread tropical anemones in the genus Aiptasia; and Symbiodinium psygmophilum sp. nov. are harbored by subtropical and temperate stony corals (e.g., Astrangia, Cladocora, and Oculina) from the Atlantic Ocean and Mediterranean Sea. Both new species are readily distinguished from each other by phylogenetic disparity and reciprocal monophyly of several nucleic acid sequences including nuclear ribosomal internal transcribed spacers 1 and 2, single copy microsatellite flanker Sym15, mitochondrial cytochrome b, and the chloroplast 23S rRNA gene. Such molecular evidence, combined with well-defined differences in cell size, physiology (thermal tolerance), and ecology (host compatibility) establishes these organisms as distinct species. Future descriptions of Symbiodinium spp. will need to emphasize genetics-based descriptions because significant morphological overlap in this group obscures large differences in ecology and evolutionary divergence. By using molecular evidence based on conserved and rapidly evolving genes analyzed from a variety of samples, species boundaries are defined under the precepts of Evolutionary and Biological Species Concepts without reliance on an arbitrary genetic distance metric. Because ecological specialization arises through genetic adaptations, the Ecological Species Concept can also serve to delimit many host-specific Symbiodinium spp.

Marine Invertebrate Larvae Associated with Symbiodinium: A Mutualism from the Start?

“…Species-level diversity is still being assessed, mainly through sequencing of the internal transcribed spacer 2 (ITS2, see LaJeunesse and Trench, 2000), either by denaturing gradient gel electrophoresis (DGGE) based separation of ITS2 genomic copies (LaJeunesse and Trench, 2000;LaJeunesse, 2002;Thornhill et al, 2006) or by next-generation sequencing based elucidation of ITS2 diversity (Arif et al, 2014;Batovska et al, 2016;Hume et al, 2016;Ziegler et al, 2017). As a result, many new taxa and/or strains have been described recently (LaJeunesse et al, 2012;Hume et al, 2015;Lee et al, 2015;Ziegler et al, 2017), with probably more than 100 extant species being present in the genus Symbiodinium (LaJeunesse, 2001).…”

“…Thus, by presenting a free-living stage, the mutualistic association is not obligate for Symbiodinium (Stat et al, 2006). Species within this genus are morphologically cryptic and identification is performed through the use of molecular biology techniques (LaJeunesse et al, 2012;Arif et al, 2014). Based on ribosomal, plastid and mitochondrial phylogenies, Symbiodinium are divided in nine clades (A-I, Figure 1) and many subclades (Rowan and Powers, 1991;LaJeunesse, 2001;Pochon et al, 2014).…”

Long-term monitoring of algal symbiont communities in corals reveals stability is taxon dependent and driven by site-specific thermal regime

“…However, the principal question addressed here is the relative frequency and persistence of Symbiodinium D1a (D-1-4) as a symbiotic generalist that imparts thermotolerance. Pooling all clade C types allows this question to be addressed without needing to resolve intragenomic variants or distinguish species boundaries within this complex group , Sampayo et al 2009, Stat et al 2009b, LaJeunesse et al 2012.…”

Symbiodinium necroappetenssp. nov. (Dinophyceae): an opportunist ‘zooxanthella’ found in bleached and diseased tissues of Caribbean reef corals

“…The majority of these genetic 'types' also exhibit restricted geographic distributions that correspond to ocean basins and latitude . Differences in niche and biogeography indicate that most types are independently evolving species lineages (LaJeunesse et al, 2012Thornhill et al, 2014).…”

“…Finally, samples of YBD tissues obtained from the Florida Keys, Puerto Rico, and Barbados were analysed. Our defining of formal Symbiodinium species using independent lines of evidence serves a practical need to enhance research into coral-dinoflagellate symbioses by standardizing scientific communication and improving interpretations of ecological data (LaJeunesse, 2001(LaJeunesse, , 2002Sampayo et al, 2009;LaJeunesse et al, 2012LaJeunesse et al, , 2014Stat et al, 2012).…”