Bioluminescence in Dinoflagellates
Biology 342 Fall 2010
Caitlin Miller and Madeline Dansky
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:
Eukaryote Phylogenetic Tree:
image courtesy: Tree of Life Web Project, Eukaryotes (7)
Uncertainties in Internal Dinoflagellate Phylogenetic Relationships
Molecular Methods Provide Insights
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 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:
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.