Host–symbiont plasticity in the upside-down jellyfish Cassiopea xamachana: strobilation across symbiont genera

IntroductionIn the upside-down jellyfish, Cassiopea xamachana (Cnidaria: Scyphozoa), the establishment of photosymbiosis with dinoflagellates (family Symbiodiniaceae) is necessary for the sessile polyp to undergo metamorphosis (strobilation) into a free-swimming adult. C. xamachana has the capacity to associate with a wide variety of dinoflagellate species and representatives of divergent genera. While some studies have looked at the successful induction of symbiosis, none to date have examined the lasting effect of diverse symbiont taxa on host survivorship and development, which is needed to assess the fitness costs of such symbioses.MethodsOur study exposes C. xamachana polyps to 22 different cultured Symbiodinaceae strains representing 13 species from 5 genera. We analyzed the time to strobilation, the number of ephyra (juvenile medusa) produced, and the proportion of ephyra that died prematurely.ResultsHere we show that C. xamachana strobilation can be induced by nearly each symbiodinacean strain we tested, with the exception of free-living species (i.e., unknown to establish symbiosis with any other marine host). Additionally, ephyrae did not display morphological variation or survivorship differences with varying symbionts. However, we observed intraspecific variation in time to induce strobilation with different cultured dinoflagellate strains.DiscussionThis work expands the known symbiont species that can form stable mutualisms with C. xamachana, primarily in the genera Symbiodinium and Breviolum. Additionally, we provide evidence of differences in ability of cultured symbiodiniaceans to establish symbiosis with a host, which suggests population-level differences in dinoflagellate cultures impact their symbiosis success. By utilizing an animal like C. xamachana with flexible symbiont uptake, we are able to explore how symbiont diversity can influence the timing and success of symbiosis-driven development

Image_1_Host–symbiont plasticity in the upside-down jellyfish Cassiopea xamachana: strobilation across symbiont genera.tif

IntroductionIn the upside-down jellyfish, Cassiopea xamachana (Cnidaria: Scyphozoa), the establishment of photosymbiosis with dinoflagellates (family Symbiodiniaceae) is necessary for the sessile polyp to undergo metamorphosis (strobilation) into a free-swimming adult. C. xamachana has the capacity to associate with a wide variety of dinoflagellate species and representatives of divergent genera. While some studies have looked at the successful induction of symbiosis, none to date have examined the lasting effect of diverse symbiont taxa on host survivorship and development, which is needed to assess the fitness costs of such symbioses.MethodsOur study exposes C. xamachana polyps to 22 different cultured Symbiodinaceae strains representing 13 species from 5 genera. We analyzed the time to strobilation, the number of ephyra (juvenile medusa) produced, and the proportion of ephyra that died prematurely.ResultsHere we show that C. xamachana strobilation can be induced by nearly each symbiodinacean strain we tested, with the exception of free-living species (i.e., unknown to establish symbiosis with any other marine host). Additionally, ephyrae did not display morphological variation or survivorship differences with varying symbionts. However, we observed intraspecific variation in time to induce strobilation with different cultured dinoflagellate strains.DiscussionThis work expands the known symbiont species that can form stable mutualisms with C. xamachana, primarily in the genera Symbiodinium and Breviolum. Additionally, we provide evidence of differences in ability of cultured symbiodiniaceans to establish symbiosis with a host, which suggests population-level differences in dinoflagellate cultures impact their symbiosis success. By utilizing an animal like C. xamachana with flexible symbiont uptake, we are able to explore how symbiont diversity can influence the timing and success of symbiosis-driven development.</p

Image_2_Host–symbiont plasticity in the upside-down jellyfish Cassiopea xamachana: strobilation across symbiont genera.tif

IntroductionIn the upside-down jellyfish, Cassiopea xamachana (Cnidaria: Scyphozoa), the establishment of photosymbiosis with dinoflagellates (family Symbiodiniaceae) is necessary for the sessile polyp to undergo metamorphosis (strobilation) into a free-swimming adult. C. xamachana has the capacity to associate with a wide variety of dinoflagellate species and representatives of divergent genera. While some studies have looked at the successful induction of symbiosis, none to date have examined the lasting effect of diverse symbiont taxa on host survivorship and development, which is needed to assess the fitness costs of such symbioses.MethodsOur study exposes C. xamachana polyps to 22 different cultured Symbiodinaceae strains representing 13 species from 5 genera. We analyzed the time to strobilation, the number of ephyra (juvenile medusa) produced, and the proportion of ephyra that died prematurely.ResultsHere we show that C. xamachana strobilation can be induced by nearly each symbiodinacean strain we tested, with the exception of free-living species (i.e., unknown to establish symbiosis with any other marine host). Additionally, ephyrae did not display morphological variation or survivorship differences with varying symbionts. However, we observed intraspecific variation in time to induce strobilation with different cultured dinoflagellate strains.DiscussionThis work expands the known symbiont species that can form stable mutualisms with C. xamachana, primarily in the genera Symbiodinium and Breviolum. Additionally, we provide evidence of differences in ability of cultured symbiodiniaceans to establish symbiosis with a host, which suggests population-level differences in dinoflagellate cultures impact their symbiosis success. By utilizing an animal like C. xamachana with flexible symbiont uptake, we are able to explore how symbiont diversity can influence the timing and success of symbiosis-driven development.</p

Table_1_Host–symbiont plasticity in the upside-down jellyfish Cassiopea xamachana: strobilation across symbiont genera.xlsx

IntroductionIn the upside-down jellyfish, Cassiopea xamachana (Cnidaria: Scyphozoa), the establishment of photosymbiosis with dinoflagellates (family Symbiodiniaceae) is necessary for the sessile polyp to undergo metamorphosis (strobilation) into a free-swimming adult. C. xamachana has the capacity to associate with a wide variety of dinoflagellate species and representatives of divergent genera. While some studies have looked at the successful induction of symbiosis, none to date have examined the lasting effect of diverse symbiont taxa on host survivorship and development, which is needed to assess the fitness costs of such symbioses.MethodsOur study exposes C. xamachana polyps to 22 different cultured Symbiodinaceae strains representing 13 species from 5 genera. We analyzed the time to strobilation, the number of ephyra (juvenile medusa) produced, and the proportion of ephyra that died prematurely.ResultsHere we show that C. xamachana strobilation can be induced by nearly each symbiodinacean strain we tested, with the exception of free-living species (i.e., unknown to establish symbiosis with any other marine host). Additionally, ephyrae did not display morphological variation or survivorship differences with varying symbionts. However, we observed intraspecific variation in time to induce strobilation with different cultured dinoflagellate strains.DiscussionThis work expands the known symbiont species that can form stable mutualisms with C. xamachana, primarily in the genera Symbiodinium and Breviolum. Additionally, we provide evidence of differences in ability of cultured symbiodiniaceans to establish symbiosis with a host, which suggests population-level differences in dinoflagellate cultures impact their symbiosis success. By utilizing an animal like C. xamachana with flexible symbiont uptake, we are able to explore how symbiont diversity can influence the timing and success of symbiosis-driven development.</p

Revival of Philozoon Geddes for host-specialized dinoflagellates, ‘zooxanthellae’, in animals from coastal temperate zones of northern and southern hemispheres

The dinoflagellate family Symbiodiniaceae comprises numerous genera and species with large differences in diversity, ecology and geographic distribution. An evolutionarily divergent lineage common in temperate symbiotic cnidarians and designated in the literature by several informal names including ‘temperate–A’, AI, Phylotype A´ (A-prime) and ‘Mediterranean A’, is here assigned to the genus Philozoon. This genus was proposed by Geddes (1882) in one of the earliest papers that recognized ‘yellow cells’ as distinct biological entities separate from their animal and protist hosts. Using phylogenetic data from nuclear (rDNA), chloroplast (cp23S) and mitochondrial genes (cob and cox1), as well as morphology (cell size), ecological traits (host affinity) and geographic distributions, we emend the genus Philozoon Geddes and two of its species, P. medusarum and P. actiniarum, and describe six new species. Each symbiont species exhibits high host fidelity for particular species of sea anemone, soft coral, stony coral and a rhizostome jellyfish. Philozoon is most closely related to Symbiodinium (formerly Clade A), but, unlike its tropical counterpart, occurs in hosts in shallow temperate marine habitats in northern and southern hemispheres including the Mediterranean Sea, north-eastern Atlantic Ocean, eastern Australia, New Zealand and Chile. The existence of a species-diverse lineage adapted to cnidarian hosts living in high latitude habitats with inherently wide fluctuations in temperature calls further attention to the ecological and biogeographic reach of the Symbiodiniaceae