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Trididemnum sp.

Georgina Walker (2013)

 

 

Fact Sheet

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Summary


Physical Description


Ecology


Life History & Behaviour


Anatomy & Physiology


Evolution & Systematics


Biogeographic Distribution


Conservation & Threats


References & Links

Ecology

Microhabitat

Ascidians inhabit a wide variety of habitats such as soft sediments, coral reefs and rocky substrates(Shenkar & Swalla, 2011). There are a few species of deep-sea ascidians that have been collected from depths greater than 200m. Colonies on Heron were found in shallow waters on the Northern reef crest on the underside of coral boulders and on coral fragments (Figure one). 

Figure one: Colony of Trididemnum sp. attached to a coral fragment on Heron Island. 

Experiment 

The relationship and interactions between didemnid ascidians and the photosynthetic bacterium Prochloron is a growing area of research and understanding. The experiment below was designed to establish the location and chlorophyll content of Prochloron cells in ascidian Trididemnum sp. colonies. 

Methodology 

Ten colonies of Trididemnum sp. were collected from the northern reef crest of Heron Island and brought back to Heron Island Research Station where they were kept in aquaria for the duration of the experiment.


Location of Prochloron cells

One colony was placed in a petrie dish with minimal seawater and photographed. Its tunic was then pierced with a scalpel to allow prochloron cells to flow onto the dish. Three drops of seawater that contained Prochloron were placed on a slide which was viewed under a compound microscope. Photos of individual Prochloron cells were taken. 

Two colonies were sacrificed for sectioning. Saltwater was removed from the specimens tube and replaced with the fixative Paraformaldehyde (4% PFA). Specimens were left for at least two hours before they were transferred into methanol. The transfer of specimens into methanol was done progressively, 25% of solution was removed and replaced with methanol, after 5 minutes 50% of solution was removed and replaced with ethanol. This was continued until almost 100% of solution had been taken out and replaced with methanol. Colonies were then sent to the University of Queensland where lab technicians sectioned one colony without staining while the other was sectioned after staining with H&E (hematoxylin and eosin stain). 

H&E sections were examined and photographed under compound microscopes.

The unstained sections of the second colony were stained with DAPI. Two drops of DAPI and glue solution and a cover slip were placed on each slide before being refrigerated to set the glue. Slides stained with DAPI were viewed under the fluorescence microscope and pictures were taken. 

Chlorophyll Content

The chlorophyll content of three colonies was examined. The volume of each colony was determined before it was placed in a mortar and pestle. It was then ground up with less than 10ml of cold methanol. The solution was added to a tube and centrifuged at 2650g for five minutes then the solution was decanted into a flask. The pellet was extracted with 5ml of methanol and centrifuged for 5 minutes at 1250g. This was repeated until the solution was no longer green. The solution was warmed to room temperature and topped up to 25ml with methanol. 

The solution was placed in 1cm light path cuvettes for measurement (the chlorophyll concentration can only be calculated with the formula used in this experiment when these cuvettes are used). The absorption of the extracts (solution) was measured with a spectrophotometer by taking the spectrum between the wavelengths 750nm and 640nm. The peak wavelength and corresponding absorption of chlorophyll a was found and recorded. 13.2nm was subtracted from the chlorophyll a wavelength to obtain the wavelength of chlorophyll b. Chlorophyll b peak wavelength and corresponding absorption was found and recorded.

The following formula was used to calculate the chlorophyll content of each colony

Concentration in extract (mg l-1)

Chla = 16.29 * Apeak Chla s- 8.54 * Apeak Chla - 13.2nm
Chlb = 30.66 * Apeak Chla - 13.2 nm - 13.58 * Apeak Chla

This protocol was repeated to determine the chlorophyll content of each colony. All specimens that were not used in experimentation were returned to the reef crest off Heron Island.

Results

The photographs taken of live colonies suggested that the Prochloron cells were located in or on the surface of the tunic of Trididemnum sp. and were not associated with individual zooids (Figure one). The sections that were stained with H&E were very faint and difficult to photograph, they were therefore not included in this experiment. Sections stained with DAPI and viewed under the fluorescence microscope also suggest that Prochloron cells are not integrated with zooids and that Prochloron cells may be embedded in the tunic. Fluorescent photographs did show the location and well defined arrangement of Prochloron cells in the colony (Figure two). 


Figure one: a) and b) the location of Prochloron cells on tunic surface. c) individual algal cells.



Figure two: Trididemnum sp. section a) red shows location of Prochloron cells and purple is the presence of both Trididemnum sp. DNA and Prochloron, b)Trididemnum sp. DNA, c) Prochloron 


Figure three: Prochloron cells (yellow) on either side of the branchial basket (blue) of an individual zooid.

Colony 3 contained the most chlorophyll a and b. Colony’s 1 and 2 had similar amounts of chlorophyll a and very similar amounts of chlorophyll b. Colony size was 0.5cm3, 0.5cm3 and 1.2cm3 and their chlorophyll content can be seen in Table one. 




Discussion 

The location of Prochloron within Ascidian colonies has implications for their mechanism of transmission to daughter colonies. Examining the location of Prochloron will contribute to the evidence for the evolution of the symbiotic relationship they have with ascidians. Kojima & Hirose (2012) state that the evolution of vertical transmission is key to proving why photosymbiosis was established in a very limited number of taxa within phylum Chordata. 

The results obtained for the location of Prochloron cells are supported by the literature. Hirose et al (2006) discovered that Prochloron cells are distributed exclusively in the tunic of Trididemnum miniatum and have no direct contact with ascidian cells. Cox (1986) established that Prochloron can inhabit the external surface of the tunic, the common cloacal cavity or be embedded in the tunic of host ascidians. Photos taken of Trididemnum sp. during this experiment show Prochloron cells are associated with the tunic although do not show precisely whether they are located superficially or embedded. 

Prochloron is a prokaryotic alga that is characterised by its possession of chlorophyll a and b. Before the discovery of Prochloron, chlorophyll b had been found only in eukaryotes. Prochloron is therefore of interest to researchers as the presence of chlorophyll b in a prokaryote means that it may be considered as a precursor to the chloroplasts of land plants. The benefits gained by the ascidian from the relationship with Prochloron is not understood although it has been proposed that excess photosynthate may provide a secondary food source (Cox, 1983). Previous studies involving Prochloron chlorophyll content found higher levels of chlorophyll per colony than this experiment.  Michaels (1983) found that as the host ascidian dies, algae showed signs of distress including lower colony levels of chlorophyll. The lower chlorophyll contents recorded on Heron Island may be partly explained by stress placed on the animal after its removal from the reef.

Although the scope of this experiment was limited, the findings are generally consistent with what is already understood about this symbiotic relationship. Identification of the species would have allowed these results to be more specifically applied for future research. 


Classification

Minimize
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnum areolatum (Herdman, 1906)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Trididemnum africanum (Michaelsen, 1915)
Trididemnum luderitzi (Michaelsen, 1919)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnum cereum (Giard, 1872)
Didemnum niveum (Giard, 1872)
Didemnum sargassicola (Giard, 1872)
Trididemnum fallax ((Lahille, 1890))
Trididemnum graphicum (Lahille, 1890)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Trididemnum symbioticum (Peres, 1962)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnopsis jolense (Van Name, 1918)
Leptoclinum discrepans (Sluiter, 1909)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnum dispersum (Sluiter, 1909)
Trididemnum tegulum (Kott, 1984)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnum farrago (Kott, 2004)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnoides inarmata ((Drasche, 1883))
Didemnopsis inarmata ((Drasche, 1883))
Didemnum inarmatum (Drasche, 1883)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Leptoclinum marmoratum (Sluiter, 1909)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnopsis microzoa (Redikorzev, 1913)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Trididemnum nube (Monniot F., 1991)
Kingdom
Animalia
Phylum
Chordata
Class
Ascidiacea
Order
Aplousobranchia
Family
Didemnidae
Genus
Trididemnum

Synonyms

Didemnum opacum (Ritter, 1907)
Trididemnum dellavallei (Ritter & Forsyth, 1917)
Trididemnum dellavalley (Ritter & Forsyth, 1917)

Images

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(2 objects, created 5/6/2011)

Album: This is a private album that is not visible to anonymous users Great Barrier Reef Invertebrates

Summary:

Date:

Album: 2012

Album: 2011