Life cycles Dinoflagellates Flashcards
(32 cards)
How do Dinoflagellata cells reproduce?
- Asexually (vegetatively: cell division and binary fission)
- Sexually for some species.
What type of life cycle do species of Dinoflagellata that reproduce sexually have?
Haplontic life cycle with zygotic meiosis.
How does cell division occur?
Through cleavage
What type of division occurs in Dinoflagellata?
Oblique binary fission, where the plane of fission is oblique to the longitudinal axis of the cell.
How is division carried out in species of the genus Ceratium?
The theca of the parent cell is partitioned between the daughter cells, each receiving half of the thecal plates, and the daughter cells then construct the missing parts of the theca.
What happens in genera like Protoperidinium during cell division?
The whole of the theca is discarded before or after cell division, so each daughter cell must form a complete new set of thecal elements.
Sexual reproduction in dinoflagellates
What happens to the zygote in Ceratium horridum?
It remains motile, and meiosis takes place in this planozygote (motile zygote)
How is Ceratium horridum classified in terms of gamete production?
It is considered an anisogamous haplont, producing two different gametes:
- a microgamete (male)
- a macrogamete (female).
Very complex life cycle of Pfiesteria piscicida
Life cycle stages in Pfiesteria piscicida
In what forms is P. piscicida is able to exist on the sea bottom for years, without food, in highly variable environmental conditions and a high rate of pollution?
In the forms of:
- a protective cyst
- amorphous amoeba
- palmelloid mass
How is the reproductive capacity of P. piscicida increased?
By the feces of fish that settles on the bottom
What happens when the reproductive capacity is increasing?
Pfiesteria piscicida changes its appearance from a cyst to a flagellate alga or an amoeboid organism.
Thanks to the flagella it reaches its victims and adheres to them.
How does P. piscicida feed after it has changed it appearance?
It releases a neurotoxin into the seawater that has a dual function: to paralyze the central nervous system of fish and to cause tissue breakdown.
A form of peduncle is injected into wounds caused by the toxin; Pfiesteria piscicida feeds red blood cells and becomes red in colour.
What happens when fish are present and the water is brackish, calm and cold (about 12-15°C)?
The fish feces awaken P. piscicida.
Large amoebas present on the bottom can attack the fish, killing and eating it
What happens when fish are present and the water is brackish, calm and warm (usually 26°C)?
With the arrival of fish, Pfiesteria piscicida turns into a kind of ″Doctor Jekill & Mr Hyde″:
- Non-toxic zoospores become toxic;
- Toxic zoospores reproduce;
- There is the fusion between gametes to form a planozygote
When the fish dies, many cells transform into amoebas
What happens when fish are absent and the water is calm and rich in dissolved nutrients?
Toxic zoospores and gametes can transform into the non-toxic form, amoeba or hypnozygote.
Life cycle of Pfiesteria piscicida
What is the main function of the hypnozygote?
The survival during periods of adverse conditions (e.g. low or high temperatures), because it has an obligate period of dormancy (state of being temporarily inactive), which lasts several weeks to six months.
Where can hypnozygotes be found?
Hypnozygotes are capable of surviving the anoxic conditions found in the muddy sediments.
Important stocks of viable hypnozygotes are present in the sediments of inshore parts of the oceans (bays and lagoons).
They can serve as inocula (initiate growth) for planktonic dinoflagellate blooms.
What are dinoflagellate cysts?
The term cyst is generally adopted for a non-motile cell lacking flagella and ability of movement.
Two types of cysts:
- Temporary cysts
- Resting cysts
Temporary cysts
- The loss of flagella is one of external appearance changes induced by sudden and vigorous shock to physiological condition of cell.
- Loss of mobility also occurs by long exposure of stressed condition. These non-motile cells can re-establish motile population within a short time after recovery of environmental condition. This quick recovery ability is one of the important features of temporary cysts.
- A temporary cyst is produced in the process of vegetative cell division.
Resting cysts
- A resting cyst is a resting zygote formed in the process of sexual reproduction.
- Planktonic zygotes may swim for several days and then transform into resting cysts.
- They may float in waters and eventually sink on the sea bottom after encystment.
- Cysts seem to require a mandatory resting period (2 weeks to 5 months depending on species) before they re-establish motile populations under favourable conditions.
