Phylogeny is a description of the evolutionary relatedness amongst different groups of organisms as identified by ancestor-descendant relations.

Evolutionary Tree of Dinoflagellates: Visual Morphologies

image courtesy:Senckenberg Research, SENCKENBERG World of Biodiversity (10)

Dinoflagellates and the Chromalveolate Hypothesis:
Molecular phylogenetic analyses have categorized dinoflagellates in the Alveolata kingdom (7,3); included in the same kingdom are the apicomplexans and ciliates, the two closest relatives of dinoflagellates. The alveolates are united with another group of protists called Chromista (which includes cryptophytes, haptophytes and stramenopiles) (8,3), into a super-group known as Chromalveolates. According to the chromalveolate phylogenetic hypothesis, the ancestor of all dinoflagellates was photosynthetic and contained the same kind of plastids as the ancestor of all apicomplexans (6). This proposition is based on the similarities among chromalveolate photosynthetic organelles (plastids), and plastid gene analyses. The hypothesis is that this organelle originated through secondary endosymbiosis of red alga, their common ancestor (3).

Eukaryote Phylogenetic Tree:

image courtesy: Tree of Life Web Project, Eukaryotes (7)

Uncertainties in Internal Dinoflagellate Phylogenetic Relationships
Determining internal relationships between dinoflagellates has had some difficulties (3). One reason dinoflagellate phylogenies have a rather complicated history is because of the wide range of fields that have studied and individually classified dinoflagellates under their own schemes in the past. Molecular data and analyses have allowed for enhanced insight into some of the gaps and questions surrounding the dinoflagellate evolutionary history. However most of this information hasn’t been transferred into taxonomic data because of the unresolved backbones in the dinoflagellate phylogenetic tree (6). These uncertainties make it difficult to make determinations of relatedness.

Molecular Methods Provide Insights
In the study on “Plankton Diversity in the Bay of Fundy as Measured by Morphological and Molecular Methods” (1) the research illustrated how molecular techniques can elucidate new information about the community diversity of microscopic organisms, including dinoflagellates.  By comparing the traditional morphological techniques with the molecular methods, the study was able show the gap between the data acquired by each method, and the different results and information each method provided on the community diversity of minute organisms in aquatic environments.

Recent research on the structural organization of the luciferase gene in luminous species of dinoflagellates has led to new insights into the evolutionary relatedness among dinoflagellates. The luminous species Noctiluca scintillans (Ns) has been previously determined the most primitive dinoflagellate species studied, based on 18S ribsosomal DNA analysis (2).

Consequently, the amino acid sequence present in a single polypeptide in Noctiluca is present in two separate proteins in the L. polyedrum bioluminescent system (2). This information has shed light on the evolution of dinoflagellate luciferases. It has been postulated in the study by Lui and Hastings that, based on the basal status of Nociluca, its luciferase structure can be seen as the ancestral gene system of dinoflagellates, “which then split in giving rise to the photosynthetic species” (2). This new information should lead to a more accurate dinoflagellate phylogeny and shed light on the evolutionary history of dinoflagellates.


Noctiluca , left image courtesy: Ronald Shimek (17)


Phylogeny of Bioluminescence:
The fascinating phenomenon of bioluminescence in living creatures is much more widespread within the living world than many people realize. A wide variety of organisms, ranging from unicellular bacteria to vertebrates, are capable of harnessing chemical energy to produce light.

The majority of bioluminescent organisms are marine-dwellers. The reason for this ecological distribution of bioluminescent organisms is not well understood. The variety of light-producing organisms, and the broad evolutionary distribution of bioluminescence as a behavior in various organisms, is thought to be connected to the diverse purposes or functions that the behavior provides for a given organism.

Therefore, the apparent wide variety of "function" or adaptive value of light-production as a behavior within different biological systems can potentially elucidate the nature of the evolution of bioluminescence as a property in various organisms.

Some examples of the possible the adaptive functions of bioluminescence as a behavior due to selective pressures include:
• Dinoflagellates: use bioluminescence as a defense mechanism
• Angler fish: uses a specific bioluminescent organ appendage as bait to capture prey
• Dragonfish: uses bioluminescence for different signals and functions by producing different wavelengths of light
• Fireflies: use light production to attract and signal potential mates
• Shrimp species (Systellaspis debilis): uses bioluminescence as a defense against predators by squirting a concealing cloud of symbiotic bioluminescent bacteria
• Some marine organisms use bioluminescence as camouflage in light-penetrated waters – masks ability to be seen
• Millipedes, centipedes, worms: use bioluminescence as warning sign to potential predators
• Bacterial bioluminescence has been postulated to have been developed as a result of the chemical process of producing light facilitating DNA repairs

Bioluminescence is created by chemical energy in which the enzyme luciferase catalyzes the oxidation of an organic molecule called luciferin, which then takes on a high-energy form that then "relaxes" and subsequently releases enough energy to produce a visible photon (light). This same chemical processes has been invented in biological lineages at least 30 times. Although the overall chemical process is the same in each case, the occurrence of these behaviors, from an evolutionary standpoint, are unrelated.

The organic substrate luciferin is found in different forms that are chemically unrelated in different bioluminescent organisms. Likewise, the luciferases come in an array of 3D conformational varieties; between these different luciferases, the primary structures (amino acid sequences) are highly diverse.

As a result, the occurrence of bioluminescence as a behavior appears to be a clear example of convergent evolution, in which the variety of organisms mentioned and many others have developed the ability to produce light through separate evolutionary paths.