Protistiary - Electron Microscopy

<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> Protistiary - Electron Microscopy

ELECTRON MICROSCOPY
History and Significance:The significance of ultrastructural studies in the history of systematic protistology is discussed below. It provides a context for the other elements. Homology: Discusses the significance of establishing homology in respect of ultrastructure and the definition of taxa Orientation / Symmetry and Asymmetry: Discusses how to distinguish anterior and posterior, left and right, and so on. This is required to establish homology among, for example, flagellar roots. Inventories / Catalogs / Ultrastructural Identity: Discusses the concept of ultrastructural identities - that is, the distinctive makeup of which that allows lineages of protists to be distinguished. The vision is to have extensive catalogs of organelles showing the range of form that is expressed within protists and how the different forms are distinguished. To date, only mitochondria have been documented. Terminology for Flagellar Systems: Terms used for flagella and cilia of eukaryotes, and associated components, such as flagellar roots. Three Dimensional Reconstruction, Architecture: The exercises of reconstructing the internal architecture of a protistan cell. History: There have been 3 primary phases in comparative protistology, each characterised by the dominance of a particular technique. The phase of light-microscopy, then a phase of electron microscopy (1960's - 1990's) and now a phase characterised by the study of sequences. Each phase has had an impact and left a legacy. The legacy of the ultrastructural period was a robust catalog of major types of protists. Those types were defined by the distinctive organization shared by all members of each group. These definitions have proven to be robust and have largely not been undermined by subsequent studies. Our efforts to understand evolutionary history are distinguished by a process in which older and less adequate interpretations are replaced with ones which are more consistent with the evidence before us (I exclude from these efforts the politically motivated approaches such as Intelligent Design that make no serious effort to understand observed data). A key element in the process is to compare insights based on independent data, and to explore them for consensus and inconsistencies. That process should lead to a re-assessment of data and/or new hypotheses. Given the prevalence of sequence-based studies, and the sloppiness with which new taxa are formulated, it is useful to call upon ultrastructural evidence to 'test' the emerging hypotheses of relationships. The hypotheses can usually be considered along the lines of 'If these taxa are related, then their parts also ought to be related.' With protists we need to allow for the significance of symbioses and other vehicles of lateral transfer of properties. We establish relatedness through a study of similarities - seeking to discriminate homologies from homoplasious (convergent) characters. Within the homologies may be a subset of characters that will uniquely define groups of protists. Significance: The purpose of reconstructing the architecture of the cell, and most especially of the flagellar apparatus, is two fold. One is that it improves our understanding of how the cell works. Secondly, it is a critical step in establishing the homologies among various components of the cell (some criteria for homology are that components have the same composition or the same positional relationships). Understanding homologies underpins understanding evolutionary history and phylogenetically informed classification. Process: There are two steps in the process: the simpler one is to create an inventory of cell components, and the second is to reconstruct the architecture (positional relationships) within the cell. References: Thousands of studies have contributed to our understanding of the ultrastructural organization of protist cells generally and of particular lineages. A vision is to assemble a bibliography of these items and ideally obtain on-line access to their content. A couple of general reviews are listed below. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist 154: S96-124. pdf Patterson, D. J. 2002. Changing views of protistan systematics: the taxonomy of protozoa – an overview. In Lee, J.J., Leedale, G.F. and Bradbury, P. (eds) An Illustrated Guide to the Protozoa, 2nd edition, Society of Protozoologists, Lawrence, Kansas. pp. 2-9. The last 35 years of protistan evolution, Powerpoint talk (dating from 2001). Image-rich texts include Harrison, F. W. and Corliss, J. O. 1991. Microscopic Anatomy of Invertebrates. Volume 1. Protozoa. Wiley Liss, New York Hausmann, K., Hülsmann, N., Radek, R. 2003. Protistology. 3rd edition. E. Schweizerbart´sche Verlagsbuchhandlung (Nägele u. Obermiller): Stuttgart.
protistiary home page

ELECTRON MICROSCOPY

History and Significance:The significance of ultrastructural studies in the history of systematic protistology is discussed below. It provides a context for the other elements.
Homology: Discusses the significance of establishing homology in respect of ultrastructure and the definition of taxa
Orientation / Symmetry and Asymmetry: Discusses how to distinguish anterior and posterior, left and right, and so on. This is required to establish homology among, for example, flagellar roots.
Inventories / Catalogs / Ultrastructural Identity: Discusses the concept of ultrastructural identities - that is, the distinctive makeup of which that allows lineages of protists to be distinguished. The vision is to have extensive catalogs of organelles showing the range of form that is expressed within protists and how the different forms are distinguished. To date, only mitochondria have been documented.
Terminology for Flagellar Systems: Terms used for flagella and cilia of eukaryotes, and associated components, such as flagellar roots.
Three Dimensional Reconstruction, Architecture: The exercises of reconstructing the internal architecture of a protistan cell.

History:

There have been 3 primary phases in comparative protistology, each characterised by the dominance of a particular technique. The phase of light-microscopy, then a phase of electron microscopy (1960's - 1990's) and now a phase characterised by the study of sequences. Each phase has had an impact and left a legacy. The legacy of the ultrastructural period was a robust catalog of major types of protists. Those types were defined by the distinctive organization shared by all members of each group. These definitions have proven to be robust and have largely not been undermined by subsequent studies.

Our efforts to understand evolutionary history are distinguished by a process in which older and less adequate interpretations are replaced with ones which are more consistent with the evidence before us (I exclude from these efforts the politically motivated approaches such as Intelligent Design that make no serious effort to understand observed data). A key element in the process is to compare insights based on independent data, and to explore them for consensus and inconsistencies. That process should lead to a re-assessment of data and/or new hypotheses.

Given the prevalence of sequence-based studies, and the sloppiness with which new taxa are formulated, it is useful to call upon ultrastructural evidence to 'test' the emerging hypotheses of relationships. The hypotheses can usually be considered along the lines of 'If these taxa are related, then their parts also ought to be related.' With protists we need to allow for the significance of symbioses and other vehicles of lateral transfer of properties. We establish relatedness through a study of similarities - seeking to discriminate homologies from homoplasious (convergent) characters. Within the homologies may be a subset of characters that will uniquely define groups of protists.

Significance:

The purpose of reconstructing the architecture of the cell, and most especially of the flagellar apparatus, is two fold. One is that it improves our understanding of how the cell works. Secondly, it is a critical step in establishing the homologies among various components of the cell (some criteria for homology are that components have the same composition or the same positional relationships). Understanding homologies underpins understanding evolutionary history and phylogenetically informed classification.

Process:

There are two steps in the process: the simpler one is to create an inventory of cell components, and the second is to reconstruct the architecture (positional relationships) within the cell.

References:

Thousands of studies have contributed to our understanding of the ultrastructural organization of protist cells generally and of particular lineages. A vision is to assemble a bibliography of these items and ideally obtain on-line access to their content. A couple of general reviews are listed below.

Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist 154: S96-124. pdf

Patterson, D. J. 2002. Changing views of protistan systematics: the taxonomy of protozoa – an overview. In Lee, J.J., Leedale, G.F. and Bradbury, P. (eds) An Illustrated Guide to the Protozoa, 2nd edition, Society of Protozoologists, Lawrence, Kansas. pp. 2-9.

The last 35 years of protistan evolution, Powerpoint talk (dating from 2001).

Image-rich texts include

Harrison, F. W. and Corliss, J. O. 1991. Microscopic Anatomy of Invertebrates. Volume 1. Protozoa. Wiley Liss, New York

Hausmann, K., Hülsmann, N., Radek, R. 2003. Protistology. 3rd edition. E. Schweizerbart´sche Verlagsbuchhandlung (Nägele u. Obermiller): Stuttgart.

protistiary home page