Alveolata - the Alveolates

Dinophyta - the dinoflagellates

1. Introduction
   1. Also called Dinozoa, Pyrrhophyta
   2. The only members of the Alveolata traditionally classified with algae
   3. About half are photosynthetic. The other half are typically either predatory or parasitic.
   4. Can form nuisance blooms, and are sometimes toxic.
   5. The algal symbionts of tropical corals (which are primarily photosynthetic) are coccoid dinoflagellates refered to as zooxanthellae.
2. Structure and Metabolism
1. Typically unicellular flagellates, sometimes coccoid, palmelloid, amoeboid, or with several different forms in the life cycle.
2. Two flagella, both with very fine hairs (not mastigonemes)
   1. Transverse flagellum circles cell latitudinally, typically in a groove called the cingulum
   2. Longitudinal flagellum extends backwards, generally in a groove called the sulcus
3. Cells may be armored (thecate)
4. Nuclei are unusual
   1. Permanently condensed chromosomes
   2. Histones are atypical or absent
   3. Mitosis is closed, with a "spindle" composed of massive bundles of microtubules that puncture the otherwise intact nuclear envelope.
   4. The distinctive dinoflagellate nucleus was once thought to represent the ancestral condition for eukaryotes, and the special term "dinokaryotic" is somtimes used to refer to the nuclear organization. It is now clear that this nuclear organization is a derived condition, but it is so unusual that the term dinokaryotic is still sometimes used.
3. Plastid Diversity in Dinoflagellates
1. A great diversity of plastid types are found in the dinoflagellates
2. They are probably all secondary (or tertiary) plastids.
3. The most important dinoflagellate plastid is the peridinin-type plastid
   1. Bounded by three membranes
   2. Thylakoids in groups of three
   3. Lacks girdle lamellae
   4. Chlorophylls a, and c with fucoxanthin as the major accessory pigment
   5. Most strangely, dinoflagellates with this plastid type have a nuclear-encoded form II rubisco, and apparently do not have rubisco in their chloroplast genomes.
4. Several important species (Gymnodinium breve, Gyrodinium aureolum, and Gymnodinium galatheanum) have fucoxanthin as accessory pigments.
   1. These taxa can be shown to have acquired their plastids from haptophytes.
   2. Plastid ultrastructure resembles that of haptophyte plastids
   3. Rubisco is a typical, form I rubisco encoded in the chloroplast genome.
   4. Molecular phylogenetic analysis places these plastids with haptophytes
   5. Apparently a fully established tertiary endosymbiosis
5. Peridinium foliaceum has a diatom endosymbiont that still retains its eukaryotic nucleus.
   1. It is not clear whether the Peridinium foliaceum endosymbiont is reduced to the point that it would be considered to be an organelle (i.e., it is not known whether the Peridinium foliaceum nuclear genome encodes any essential endosymbiont genes), but it does seem to be a completely obligate and permanent endosymbiont.
6. Lepidodinium has green pigmented plastids that resemble those from prasinophyte green algae
   1. It also has complex external scales which are atypical for dinoflagellates, but closely resemble those of prasinophytes
   2. One hypothesis is that Lepidodinium expresses genes for scale formation acquired from its prasinophyte endosymbiont
7. Gymnodinium acidotum has a cryptomonad endosymbiont, but this may or may not be a permanent endosymbiosis. There is some good reason to think that the endosymbiont may be acquired as prey and retained for long periods of time, but not kept as a permanent endosymbiont.
8. A species of Noctiluca in SE Asia has a prasinophyte that swims around in its vaculole.
4. Reproduction
1. Most are haplontic, with the only diploid stage being the zygote
   1. Gametes are not obviously different from vegetative cells
   2. may be isogamous or anisogamous
2. The exception is Noctiluca, in which the vegetative cells are diploid
   1. Noctiluca gametes have permanently condensed chromosomes, but the vegetative cells do not
5. Classification
1. Traditional classification is based largely on the organization of the cell covering in vegetative cells
   1. This is fine for sorting out closely related species, but seems to have produced some artificial groups
2. Noctiluca sp.
   1. Responsible for phosphorescence in marine waters
   2. The Noctilucales are apparently the outgroup to the rest of the dinoflagellates. This is supported by a variety of evidence, including ultrastructural and molecular phylogenetic data.
3. Peridinium cinctum
4. Gonyaulax polyedra
5. Gymnodinium sanguineum
6. Prorocentrum minimum
7. Pfiesteria piscicida
8. Ceratium sp.
6. Ecology
1. Important primary producers in both marine (particularly on-shore) and freshwater environments
   1. Can also be important predators
1. Wayne Coats (SERC) has written on the dual role of dinoflagellates in the phytoplankton
2. Predation and parasitism
3. Amoebophrya
4. As zooxanthellae, dinoflagellates are extremely important primary producers in tropical reef environments
5. Giant clams also depend upon zooxanthellae for photosynthate
7. Economic Significance
1. Important as primary producers
2. Toxin production is also a major issue
   1. Pfiesteria piscicida seems to produce a water-soluable neurotoxin
      1. Watermen and others working on water suffer memory loss
      2. In acute form may produce sores on skin
      3. No evidence that toxin is transmitted in sea food
      4. Not a major health problem, but disturbing and close to home
   2. Ciguatera poisoning is a much more serious issue in warm marine waters
      1. A stable dinoflagellate toxin moves up food chain, is concentrated in predatory fish.
      2. Humans eat predatory fish, get serious neurological disorder
   3. Some red tides are toxic
      1. Gymnodinium breve forms predictable blooms off the gulf coast of Florida
      2. Bad for manatees, people, etc.
      3. Reports of irritation from wind-blown spray

Apicomplexa

1. Approximately equivalent to the old group "sporozoa"
2. Do have plastids, but these plastids have only recently been recognized for what they are
3. None are photosynthetic, and most are obligate parasites of animals
4. The phylogenetic origin of the apicomplexan plastid is not known, and there is conflicting evidence concerning its origin

Ciliata - the Ciliates

Required Reading: VdH Chapter 16

Supplementary Reading:

Palmer, J.D. and C.F. Delwiche. 1998. The origin and evolution of plastids and their genomes. In D.E. Soltis, P.S. Soltis, and J.J. Doyle (eds.) Molecular Systematics of Plants II: DNA sequencing. Kluwer, Boston.

Tomas, R.N., and E.R. Cox. 1973. Observations on the symbiosis of Peridinium balticum and its intracellular alga I. Ultrastructure. J. Phycol. 9:304-323.

Kite, G.C., and J.D. Dodge. 1985. Structural organization of plastid DNA in to anomalously pigmented dinoflagellates. J. Phycol. 21:50-56.

Chesnick, J.M., C.W. Morden, and A.M. Schmeig. 1996. Identity of the endosymbiont of Peridinium foliaceum (Pyrrophyta): analysis of the rbcLS operon. J. Phycol. 32:850-857.