Symbioses of Ciliates (Ciliophora) and Diatoms (Bacillariophyceae): Taxonomy and Host–Symbiont Interactions

The nature of the plankton symbioses between ciliates and diatoms has been investigated from the tropical South Atlantic Ocean, and Mediterranean and Caribbean Seas. The obligate symbioses of the diatoms Chaetoceros dadayi or C. tetrastichon with the tintinnid Eutintinnus spp., and Chaetoceros coarctatus with the peritrich ciliate Vorticella oceanica are the most widespread, and the consortium of Chaetoceros densus and Vorticella sp. have been rediscovered. Facultative symbioses between Eutintinnus lususundae and Chaetoceros peruvianus, Hemiaulus spp., and Thalassionema sp. are less frequent, often containing three or four partners because Hemiaulus can also harbor the diazotrophic cyanobacteria Richelia intracellularis. Another three-partner consortium is the peritrich ciliate Zoothamnium pelagicum, ectobiont bacteria, and the diatom Licmophora sp. The predominantly oligotrophic conditions of tropical seas do not favor the survival of large diatoms, but large species of Coscinodiscus and Palmerina in facultative symbiosis with Pseudovorticella coscinodisci have a competitive advantage over other diatoms (i.e., reduction of sinking speed and diffusive boundary layer). Symbioses allow sessile peritric ciliates to extend their distribution in the pelagic environment, permit boreal-polar related diatoms such as C. coarctatus or Fragilariopsis doliolus to inhabit tropical seas, and help large diatoms to extend their survival under unfavorable conditions.

Symbiotic interactions between ciliates (Ciliophora) and diatoms (Bacillariophyceae)

Introduction: Diatoms and ciliates are important components of the marine plankton community, and some species are able to develop symbiotic associations in the tropical seas. Objective: To describe the nature of the symbioses, the morphological adaptations of the members, and the possible ecological advantages of the symbiotic life versus the free-living forms. Methods: Plankton samples were collected from Mediterranean and Caribbean Seas, and the South Atlantic Ocean. Consortia were examined during laboratory incubations, including studies of the motility and the feeding currents by high-speed video recordings, and culture tests of the species as symbiotic or free-living forms. Results: The consortia of the diatoms Chaetoceros dadayi and C. tetrastichon with the tintinnid Eutintinnus spp., and C. coarctatus with the peritrich ciliate Vorticella oceanica are examples of an obligate mutualism. The cultures of the host diatoms as free-living organism were unsuccessful. The consortia between Eutintinnus lususundae and the diatoms Chaetoceros peruvianus, Hemiaulus hauckii, H. membranaceus, and Thalassionema sp. are facultative symbioses. These are examples of three or four partner consortia because Hemiaulus spp. is the host of the diazotrophic cyanobacteria Richelia intracellularis. Other example of facultative three partner consortium is the peritrich ciliate Zoothamnium pelagicum with an ectobiont bacteria, and the diatom Licmophora sp. The barrel-shaped chains of the diatom Fragilariopsis dolious encircled the lorica of Salpingella spp., while these chains were almost flat in the free-living stage. The peritrich ciliate Pseudovorticella coscinodisci lives on large pelagic diatoms such as Coscinodiscus and Palmerina. These symbioses are facultative for the diatoms, but they extended their survival under unfavorable conditions. High-speed video recordings of the consortium of Vorticella oceanica and Chaetoceros coarctatus revealed that during the stalk contraction the zooid of reached 5 400 body length s-1, being the fastest organism with respect to its size. The consortia of Chaetoceros densus and an undescribed species of Vorticella is re-discovered. Conclusions: These symbioses have allowed that the sessile peritric ciliates colonize the pelagic environment and the proliferation of diatoms with a polar origin in the tropical sea.

Primer registro de la diatomea epibionte Pseudohimantidium pacificum y de otras asociaciones simbióticas en el Golfo de California

En México existe poca información sobre las asociaciones simbióticas entre diatomeas y ciliados, así como con otras especies de microalgas y particularmente con crustáceos planctónicos marinos. Es por ello que en este trabajo se presenta el primer registro de la diatomea Pseudohimantidium pacificum en epibiosis con el copépodo Farranula gibbula y otras asociaciones entre microalgas y ciliados marinos en la Bahía de La Paz. Las muestras biológicas se recolectaron mediante una red de plancton con una luz de malla de 20 µm, en diversas áreas de la Bahía de La Paz. Se encontraron 62 copépodos machos de F. gibbula, de los cuales 27 presentaban sobre su caparazón un ramillete compuesto por la diatomea epibionte P. pacificum. Los valores promedio de abundancia de P. pacificum por estación de muestreo variaron entre 16 y 82 ejemplares/copépodo. Otras diatomeas penales fueron observadas como epibiontes de copépodos del género Acartia. Asimismo se encontraron asociaciones simbióticas adicionales entre ciliados, microalgas y cianobacterias, destacando las siguientes: Chaetoceros coarctatum-Vorticella oceanica, Leptocylindrus mediterraneus-Solenicola setigera. Se registra por primera vez la agrupación entre la diatomea Fragilariopsis doliolus y el silicoflagelado Dictyocha pentagona con un ciliado de tipo Vorticella.