Abstract
Endosymbiosis is widespread among cnidarians and is of high ecological relevance. The tropical sea anemone Aiptasia sp. is a laboratory model system for endosymbiosis between reef-building corals and photosynthetic dinoflagellate algae of the genus Symbiodinium. Here we identify the key environmental cues to induce reproducible spawning in Aiptasia under controlled laboratory conditions. We find that simulating a lunar cycle with blue-wavelength light is necessary to promote abundant gamete production and synchronous release in well-fed animals. Sexual reproduction rates are genetically determined and differ among clonal lines under similar conditions. We also find the inverse difference in rates of asexual reproduction. This study provides the requisite basis for further development of the Aiptasia model system, allowing analysis of basic cellular and molecular mechanisms in the laboratory as well as investigations of broad questions of ecological and evolutionary relevance.
Highlights
Cnidarians exhibit enormous plasticity in their morphologies and life cycles, and have emerged as key models in a broad range of research fields from evolution to ecology
Clonal anemone lines can be generated through asexual reproduction via pedal laceration[25] (Fig. 1b), and the majority of Aiptasia resources have been developed from clonal line CC7, including transcriptomes[26,27] and the genome[28]
We consistently found three distinct chloroplast ribosomal 23S subunit (cp23S) sequences in relatively constant proportions: ~57% of sequences were a single variant of S. minutum; ~35% were identical to SSA01 (GenBank #KT186239); ~8% were identical to S. minutum strain SSB01
Summary
Cnidarians exhibit enormous plasticity in their morphologies and life cycles, and have emerged as key models in a broad range of research fields from evolution to ecology. The breakdown of this symbiosis, termed “coral bleaching”, has become a major threat to coral reefs worldwide[17] Despite this importance, much remains unknown about the cellular and molecular basis of the coral-Symbiodinium symbiosis, including its establishment, www.nature.com/scientificreports/. Most reef-building corals spawn only once per year[20], greatly restricting the experimental availability of larvae and thereby severely limiting the systematic study of endosymbiosis establishment To address this limitation, a practicable symbiotic laboratory model has been developed with the small sea anemone Aiptasia sp. The process of endosymbiosis establishment is similar to that of many reef-building corals: Aiptasia planula larvae are initially non-symbiotic and establish endosymbiosis anew each generation[23] (Fig. 1b). Transcriptomic and genomic resources for many Symbiodinium strains are likewise available[29,30,31]
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