Abstract
Endosymbiotic dinoflagellates in the genus Symbiodinium are fundamentally important to the biology of scleractinian corals, as well as to a variety of other marine organisms. The genus Symbiodinium is genetically and functionally diverse and the taxonomic nature of the union between Symbiodinium and corals is implicated as a key trait determining the environmental tolerance of the symbiosis. Surprisingly, the question of how Symbiodinium diversity partitions within a species across spatial scales of meters to kilometers has received little attention, but is important to understanding the intrinsic biological scope of a given coral population and adaptations to the local environment. Here we address this gap by describing the Symbiodinium ITS2 sequence assemblages recovered from colonies of the reef building coral Montipora capitata sampled across Kāne'ohe Bay, Hawai'i. A total of 52 corals were sampled in a nested design of Coral Colony(Site(Region)) reflecting spatial scales of meters to kilometers. A diversity of Symbiodinium ITS2 sequences was recovered with the majority of variance partitioning at the level of the Coral Colony. To confirm this result, the Symbiodinium ITS2 sequence diversity in six M. capitata colonies were analyzed in much greater depth with 35 to 55 clones per colony. The ITS2 sequences and quantitative composition recovered from these colonies varied significantly, indicating that each coral hosted a different assemblage of Symbiodinium. The diversity of Symbiodinium ITS2 sequence assemblages retrieved from individual colonies of M. capitata here highlights the problems inherent in interpreting multi-copy and intra-genomically variable molecular markers, and serves as a context for discussing the utility and biological relevance of assigning species names based on Symbiodinium ITS2 genotyping.
Highlights
Coral reefs are biologically diverse ecosystems providing habitat for a wide range of marine organisms
Host symbiont acquisition strategy affects Symbiodinium assemblages with hosts that acquire their symbionts from the environment primarily associating with a similar pool of symbionts, and those that acquire their symbionts from the parent colony harboring their own unique suite of symbionts specific to a host genus [9,10]
A total of 275 Symbiodinium internal transcribed spacer region 2 (ITS2) sequences belonging to clades C and D were recovered from the colonies of M. capitata
Summary
Coral reefs are biologically diverse ecosystems providing habitat for a wide range of marine organisms. Symbiodinium diversity is partitioned by a variety of factors including biogeographical barriers, host species, colony depth, irradiance, and host symbiont transmission strategy [7,8,9,10]. The same coral species from inshore and offshore reefs within the same reef complex (e.g. in the central Great Barrier Reef or in Panama) can associate with different Symbiodinium [12,14], as can colonies of the same species from the same reef environment [5,10,14,15]. Attributed to levels of irradiation, Symbiodinium in corals such as Montastraea spp. and Madracis pharensis in Panama [8,17] and Pocillopora damicornis in the Great Barrier Reef [18] partition as a function of depth and/or location on individual colonies [8]. Host symbiont acquisition strategy affects Symbiodinium assemblages with hosts that acquire their symbionts from the environment (horizontal symbiont acquisition strategy) primarily associating with a similar pool of symbionts, and those that acquire their symbionts from the parent colony (vertical symbiont acquisition strategy) harboring their own unique suite of symbionts specific to a host genus [9,10]
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