Ultrastructural identity

David Hibberd's comparison of the ultrastructural identities of a typical chrysophyte and a typical haptophyte

Ultrastructural identity is a concept in biology. It asserts that evolutionary lineages of eukaryotes in general and protists in particular can be distinguished by complements and arrangements of cellular organelles. These ultrastructural components can be visualized by electron microscopy.

The concept emerged following the application of electron microscopy to protists.

Protists

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Early ultrastructural studies revealed that many previously accepted groupings of protists based on optical microscopy included organisms with differing cellular organelles. Those groups included amoebae, flagellates, heliozoa, radiolaria, sporozoa, slime molds, and chromophytic algae. They were deemed likely to be polyphyletic, and their inclusion in efforts to assemble a phylogenetic tree would cause confusion. As an example of this work, German cell biologist Christian Bardele established unexpected diversity with the simply organized heliozoa.[1][2][3][4] His work made it evident that heliozoa were not monophyletic and subsequent studies revealed that the heliozoa was composed of seven types of organisms: actinophryids, centrohelids, ciliophryids, desmothoracids, dimporphids, gymnosphaerids and taxopodids.[5]

A critical advance was made by British phycologist David Hibberd.[6] He demonstrated that two types of chromophytic algae, previously presumed to be closely related, had different organizations that were revealed by electron microscopy. The number and organization of locomotor organelles differed (chrysophyte - two flagella; haptophyte - two flagella and haponema), the surfaces of which differed (chrysophyte - with tripartite flagellar hairs now regarded as apomorphic for stramenopiles; haptophyte - naked), as did the transitional zone between axoneme and basal body (chrysophyte with helix); as did flagellar anchorage systems; presence or absence of embellishments on the cell surface (chrysophyte - naked; haptophyte - with scales), plastids especially eyespot, location and functions of dictyosomes, inter alia. This careful study prompted further examination of algal and flagellate organization. Protozoologists Brugerolle and Patterson were the first to use the term 'ultrastructural identity' in discussing the differences between ciliates and a lookalike protist, Stephanopogon.[7] Patterson later applied the concept to all eukaryotes, classifying their diversity into 71 types, each without clear sister group affinities.[8] A further 200 or so genera that had not yet been studied by electron microscopy were listed.

The catalog of groups with distinctive ultrastructural identities has been used as a base-line for efforts to build a stable tree for all eukaryotes using molecular data.[9]

An indirect benefit of the focus on ultrastructural characters was that it allowed synapomorphies to be identified for emerging lineages. Molecular protistologist Gunderson and colleagues established that dinoflagellates, apicomplexa and ciliates were likely related.[10] They, and some related flagellates, were shown to share a distinctive system of sacs or alveoli under the cell membrane, and because of this were given the name Alveolates. Similarly, tripartite tubular hairs attached to various algae, fungi and protozoa provided the synapomorphy for the 'stramenopiles' (straw-hairs)[11] A distinctive flagellar root system that caused grooving on their cell surface was treated as a synapomorphy of the excavate flagellates.[12]

References

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  1. ^ Bardele, C. F. 1972. Cell cycle, morphogenesis, and ultrastructure in the pseudoheliozoan Clathrulina elegans. Zeitschrift für Zellforschung 130:219–242
  2. ^ Bardele, C. F. 1975 The fine structure of the centrohelidian heliozoan Heterophrys marina. Cell Tiss. Res, 161: 85-102
  3. ^ Bardele, C. F. 1977. Comparative study of axopodial microtubule patterns and possible mechanisms of pattern control in the centrohelidian heliozoa Acanthocystis, Raphidiophrys and Heterophrys. J. Cell Sci. 25, 205-23
  4. ^ Bardele, C. F. 1977. Organization and control of microtubule pattern in centrohelidian heliozoa. J. Protozool. 24, 9-14
  5. ^ Smith, R. McK., and Patterson, D.J. 1986. Analyses of heliozoan interrelationships: an example of the potentials and limitations of ultrastructural approaches to the study of protistan phylogeny. Proceedings of the Royal Society of London. Series B, Biological Sciences, 227: 325-366
  6. ^ Hibberd, D. J. 1976. The ultrastructure and taxonomy of the Chrysophyceae and Prymnesiophyceae (Haptophyceae): a survey with some new observations on the ultra-structure of the Chrysophyceae. Botanical Journal of the Linnean Society 72:55–80
  7. ^ Patterson, D. J. & Brugerolle, G. 1988. The ultrastructural identity of Stephanopogon apogon and the relatedness of the genus to other kinds of protists. Europ. J. Protistol. 23: 279-290.
  8. ^ Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist 154: S96-124
  9. ^ Parfrey, L. W., Grant, J., Tekle, Y. I., Lasek-Nesselquist, E., Morrison, H. G., Sogin, M. L., Patterson, D. J., & Katz, L. A. (2010). Broadly sampled multigene analyses yield a well-resolved eukaryotic tree of life. Systematic biology, 59(5), 518–533. https://doi.org/10.1093/sysbio/syq037
  10. ^ Gajadhar, A. A., W. C. Marquardt, R. Hall, J. Gunderson, E. V. Ariztia-Carmona, and M. L. Sogin. 1991. Ribosomal RNA sequences of Sarcocystis muris, Theileria annulata and Crypthecodinium cohnii reveal evolutionary relationships among apicomplexans, dinoflagellates, and ciliates. Molecular and Biochemical Parasitology 45: 147–154
  11. ^ Patterson, D. J. 1989. Stramenopiles: chromophytes from a protistological perspective. In: Green, J.C., Leadbeater, B.S.C. & Diver, W. L. 1989. The chromophyte algae: problems and perspectives. Clarendon Press, Oxford. 357-379.
  12. ^ Simpson A. G. B. & Patterson, D. J. 1999. The ultrastructure of Carpediemonas membranifera: (Eukaryota), with reference to the 'excavate hypothesis'. European Journal of Protistology 35: 353-370
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