Abstract
Over half of all extant stony corals (Cnidaria: Anthozoa: Scleractinia) harbour endosymbiotic dinoflagellates of the family Symbiodiniaceae, forming the foundational species of modern shallow reefs. However, whether these associations are conserved on the coral phylogeny remains unknown. Here we aim to characterise Symbiodiniaceae communities in eight closely-related species in the genera Merulina, Goniastrea and Scapophyllia, and determine if the variation in endosymbiont community structure can be explained by the phylogenetic relatedness among hosts. We perform DNA metabarcoding of the nuclear internal transcribed spacer 2 using Symbiodiniaceae-specific primers on 30 coral colonies to recover three major endosymbiont clades represented by 23 distinct types. In agreement with previous studies on Southeast Asian corals, we find an abundance of Cladocopium and Durusdinium, but also detect Symbiodinium types in three of the eight coral host species. Interestingly, differences in endosymbiont community structure are dominated by host variation at the intraspecific level, rather than interspecific, intergeneric or among-clade levels, indicating a lack of phylogenetic constraint in the coral-endosymbiont association among host species. Furthermore, the limited geographic sampling of four localities spanning the Western and Central Indo-Pacific preliminarily hints at large-scale spatial structuring of Symbiodiniaceae communities. More extensive collections of corals from various regions and environments will help us better understand the specificity of the coral-endosymbiont relationship.
Highlights
The modern coral reef is one of the most diverse marine ecosystems on Earth (Reaka-Kudla, 1997; Fisher et al, 2015), build mainly by the habitat-forming stony corals (Cnidaria: Anthozoa: Scleractinia) with a calcification process driven largely by their intricate symbiosis with photosynthetic dinoflagellates of the family Symbiodiniaceae (Muscatine & Cernichiari, 1969; Stat, Carter & Hoegh-Guldberg, 2006)
Cladocopium is present in all host species, while Durusdinium and Symbiodinium are present in six and three host species, respectively
Our results mirror previous community-level studies of Symbiodiniaceae showing that Cladocopium is more abundant in tropical latitudes compared to other clades such as Symbiodinium which is mostly found at higher latitudes (Rodriguez-Lanetty et al, 2001; Savage et al, 2002; Baker, 2003)
Summary
The modern coral reef is one of the most diverse marine ecosystems on Earth (Reaka-Kudla, 1997; Fisher et al, 2015), build mainly by the habitat-forming stony corals (Cnidaria: Anthozoa: Scleractinia) with a calcification process driven largely by their intricate symbiosis with photosynthetic dinoflagellates of the family Symbiodiniaceae (Muscatine & Cernichiari, 1969; Stat, Carter & Hoegh-Guldberg, 2006). Symbiodiniaceae is extremely diverse, with at least nine genus-level clades which contain hundreds of species (Arif et al, 2014; Thornhill et al, 2014), fewer than 30 species have been formally named (LaJeunesse et al, 2018) The recognition of this remarkable diversity owes in large part to the use of molecular genetic tools that have helped biologists discover and characterise the major clades and subclades (or types) of Symbiodiniaceae (Rowan & Powers, 1991a; Rowan & Powers, 1991b; Rowan, 1998; LaJeunesse, 2002). Coral hosts dominated by Durusdinium can generally better withstand thermal stress compared to corals with a greater abundance of Cladocopium (Rowan, 2004; Berkelmans & Van Oppen, 2006; LaJeunesse et al, 2014)
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