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0 Botanical Museum, Harvard University, Cambridge, Massachusetts 02138 USA
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INTRODUCTION |
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 TOP INTRODUCTION LITERATURE CITED |
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Nearly three decades later, that perspective seems almost charmingly antique. Invigorated by molecular biology and biogeochemistry, phycology now claims center stage in some of the most exciting developments in modern biology. For the first time, molecular sequence comparisons are placing the cyanobacteria and algae in phylogenetic perspective (e.g., Cavalier-Smith, Allsopp, and Chao, 1994
; Sogin, 1997
; Medlin et al., 1997
; Stiller and Hall, 1997
). This, in turn, provides a new framework for thinking about the deep evolutionary history of photoautotrophs.
As their revised name attests, the cyanobacteria (nee blue-green "algae") have long since been recognized as true bacteria whose capacity for "green plant photosynthesis" reflects the assembly through time of several distinct biochemical pathways, at least some brought together by lateral transfer (Blankenship, 1992
). Of course, cyanobacteria do not really conduct green plant photosynthesis—just the opposite: the unique molecular assembly of the photosynthetic apparatus was propagated across the Eukarya by (again) lateral transfer, this time in the form of endosymbiotic associations. It was Lynn Margulis' (1970, 1981) compelling articulation of the venerable (see Khakhina, 1992
) endosymbiotic hypothesis in the language of modern cell biology that inspired me to seek paleontological fortune in Precambrian rocks, and in its most up-to-date telling, this best of all evolutionary stories continues to rivet the attention of biologists. Yes, the plastids of glaucophytes, red algae, and green algae can be traced directly to cyanobacterial ancestors, but those of euglenids, cryptophytes, heterokonts, and prymnesiophytes originated via eukaryotic symbionts (Gibbs, 1981, 1992
; Douglas, Murphy, and Gray, 1991
; McFadden et al., 1994
). Dinoflagellates gained photosynthesis several times, most notably by swallowing a chlorophyll a + c-bearing alga to form a remarkable cellular Matrushka doll that may include contributions from four distinct genomes (Palmer and Delwiche, 1996
).
In fact, we now recognize that the symbiotic acquisition of photosynthesis is not a rare event confined to the establishment of principal algal clades, but rather a widespread feature of biology. Cyanobacterial and algal symbioses are well known among the fungi, ciliates, rhizopods, sponges, and cnidarians, and occur, as well, in some flatworms, bivalves, and ascidians (Reisser, 1992
). (Of course, a few vascular plants also harbor cyanobacterial symbionts, although in this case it is nitrogen metabolism and not photosynthesis that underpins the relationship.) Vertebrates ("us," again) might even be considered unusual in their failure to harness the metabolic benefits of cyanobacteria and microalgae.
The phylogenetic perspective enables us to look afresh at features of algal biology well beyond the acquisition of plastids. Model organisms such as Chlamydomonas offer experimentally tractable routes to a molecular understanding of photosystems and other aspects of plant cell biology (reviewed by Falkowski and Raven, 1997
). And, freed from constraining view that algae are "simple plants," we can more clearly recognize the biological significance of observed variety in algal development and life cycles. Multicellularity evolved several times among the algae, producing a broad array of body plans that challenge us to seek general principles of development and function (e.g., Niklas, in press). Botanists grown complacent about the alternation of plant generations can rekindle their sense of wonder with the genetic and morphological complexities of red algal life cycles (e.g., Haig, 1993
).
In ecology as well as evolution, algae loom large in contemporary research. As the primary producers of the marine realm, as well as dominant players in the marine carbonate and silica cycles, phytoplankton are key to understanding the biogeochemical dynamics of oceans. Improved understanding of algal biology, thus, makes possible new insights into such persistent mysteries as the fate of anthropogenic CO2 and the glacial/interglacial modulation of Earth's climate system (Falkowski and Raven, 1997
). Even the fossil record of algae grows richer by the year (e.g., Lipps, 1992
; Knoll, 1996
; Xiao, Zhang, and Knoll, 1998
).
If we can agree, then, that biologists, oceanographers, and geochemists all need to know something about the algae, where can we go to learn? Two new texts provide excellent starting points.
Robert Edward Lee's Phycology, now in its third edition, is designed to support a systematically oriented survey course for undergraduates. An opening discussion of the major themes of algal biology introduces readers to aspects of physiology and cell biology, life cycles and ecology. That completed, Lee moves on to patterns of algal diversity, with a succession of chapters that sketch detailed portraits of the cyanobacteria and the principal clades of photosynthetic protists. Plastid origins provide an organizing principle for these discussions, with phyla grouped according to the number of plastid-enveloping membranes. The resulting framework is evolutionary without being strictly phylogenetic. Lee's accounts are heavy on cell biology and ecology, and his discussions of these topics are very good, indeed. He is less concerned with phylogeny and evolution, thereby missing an opportunity to bring conceptual order to the myriad variations of form and physiology introduced in each chapter. Systematic coverage is synoptic, but particular affection for heterokonts seems evident. Beautifully executed line drawings enliven the text—I only wish that they were accompanied more consistently by scale bars. A well-chosen bibliography concludes each chapter, enhancing the value of Phycology for reference as well as pedagogy.
Linda Graham and Lee Wilcox' thoroughly admirable Algae aims at the same audience and covers much the same ground, but differs in both organization and emphasis. Like Lee, Graham and Wilcox begin with a general introduction to algal biology, but they follow up with four chapters that discuss the role of algae in biogeochemistry and biotic associations, the practical reasons for studying algae, and the bases of phylogeny reconstruction. In consequence, by the time a student takes up the long march from cyanobacteria to charophytes, she knows why the attendant details matter. Each chapter includes treatments of fossils and phylogeny, providing a firm evolutionary framework for discussions of morphology, development, physiology and ecology. Graham's longstanding fondness for green algae is easily detected—the clade rates five chapters, including a concise but authoritative review of their relationships to land plants. Algae concludes with two chapters on phytoplankton and benthic algal ecology that are illuminatingly different in approach. The plankton discussion is quantitative and model driven, the periphyton and macroalgal chapter autecologically descriptive.
Phycology remains a road less travelled in biology, and most current biology students will choose to study ants and angiosperms over kelps and chrysophytes. But the sense of opportunity and excitement that pervades Phycology and Algae should ignite the intellectual imagination of at least a few forward-looking students. After all, using cyanobacterial and algal models, our understanding of photobiology has expanded to the point where approaches to the deepest questions of photosynthetic function have been revealed. Complete genomic sequences for a growing number of green algae and chloroplasts are illuminating the genetic cross-talk by which organelles are established and maintained (e.g., Turmel, Otis, and Lemieux, 1999
). Algal models for calcium carbonate mineralization are catching the attention of zoologists interested in shell and bone formation, lending credence to the idea that the several biochemical pathways united in skeletal biomineralization have deep evolutionary roots (Westbroek and Marin, 1998
). As the revolution in developmental genetics broadens to embrace the red and brown algae, as well as a wider selection of greens, we will learn which aspects of multicellular development are truly general and which arose within specific clades. As a result, the current "top-down" view of comparative development (which understandably proceeds from pioneering studies of fruit flies and snapdragons) will be supplemented by a "bottom-up" evolutionary perspective driven by accelerating research on algae, fungi, and slime molds.
And for the paleontologist? New fossils, rigorous phylogenies, and emerging geochemical insights into Earth's environmental history are collectively offering new horizons for understanding evolutionary history.
Phycology and Algae introduce a research world of extraordinary opportunity, and do so in thoughtful, literate fashion. Read them and pass them on to your students. And later, when bright undergraduates tell you that they want to study algae, don't frown—smile.
Submitted by Spencer C. H. Barrett, Book Review Editor
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FOOTNOTES |
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2 Phycology (Third Edition). Robert Edward Lee. 1999. Cambridge University Press, Cambridge UK, HB $100.00; PB $44.95. x + 611 pp. ISBN 0-521-63090-8 (hardback) and 0-521-63883-6 (paperback)
Algae. Linda E. Graham and Lee W. Wilcox. 2000. Prentice Hall, Upper Saddle River NJ, PB $69.00. xiii + 640 pp. ISBN 0-13-660333-5.
3 Phone (671-495-9306), FAX (617-495-5667), e-mail (aknoll{at}oeb.harvard.edu
).
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LITERATURE CITED |
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TOPINTRODUCTIONLITERATURE CITED |
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Cavalier-Smith, T., M. T. E. Allsopp, and E. E. Chao. 1996 Chimeric conundra: are nucleomorphs and chromists monophyletic or polyphyletic? Proceedings of the National Academy of Sciences, USA 91: 11 368–11 372.
Douglas, S. E., C. A. Murphy, and M. W. Gray. 1991 Cryptomonad algae are evolutionary chimeras of two phylogenetically distinct unicellular eukaryotes. Nature 350: 148–151.[CrossRef][Medline]
Falkowski, P. G., and J. A. Raven. 1997 Aquatic photosynthesis. Blackwell Science, Oxford, UK.
Gibbs, S. P. 1981 The chloroplasts of some algal groups may have evolved from endosymbiotic eukaryotic algae. Annals of the New York Academy of Sciences 361: 193–208.[ISI][Medline]
———. 1992 The evolution of algal chloroplasts. In R. A. Lewin [ed.], Origins of plastids, 107–121. Chapman and Hall, New York, New York, USA.
Haig, D. 1993 Alternatives to meiosis: the unusual genetics of red algae, microsporidia, and others. Journal of Theoretical Biology 163: 15–31.[CrossRef][ISI][Medline]
Khakhina, L. N. 1992 Concepts of symbiogenesis: a historical and critical study of the research of Russian botanists. Yale University Press, New Haven, Connecticut, USA.
Knoll, A. H. 1996 Archean and Proterozoic paleontology. In J. Jansonius and D. C. McGregor [eds.], Palynology: principles and applications, vol. I, 51–80. American Association of Stratigraphic Palynologists Foundation, Tulsa, Oklahoma, USA.
Lipps, J. [ed.] Fossil prokaryotes and protists. Blackwell Scientific, Oxford, UK.
Margulis, L. 1970 Origin of eukaryotic cells. Yale University Press, New Haven, Connecticut, USA.
———. 1981 Symbiosis in cell evolution. W. H. Freeman, San Francisco, California, USA.
McFadden, G. I., P. R. Gilson, C. J. B. Hofmann, G. J. Adcock, and U.-G. Maier. 1994 Evidence that an amoeba acquired a chloroplast by retaining part of an engulfed eukaryotic alga. Proceedings of the National Academy of Sciences, USA 91: 3690–3694.
Medlin, L. K., W. H. C. F. Kooistra, D. Potter, G. W. Saunders, and R. A. Anderson. 1997 Phylogenetic relationships of the "golden algae" (haptophytes, heterokont chromophytes) and their plastids. Plant Systematics and Evolution (Supplement) 11: 187–219.
Niklas, K. J. In press. The evolution of plant body plans: a biomechanical perspective. Annals of Botany.
Palmer, J. D., and C. F. Delwiche. 1996 Second-hand chloroplasts and the case of the disappearing nucleus. Proceedings of the National Academy of Sciences, USA 93: 7432–7435.
Reisser, W. [ed.]. 1992 Algae and symbiosis. Bio-Press, Bristol UK.
Sogin, M. 1997 History assignment: when was the mitochondrion founded? Current Opinion in Genetics and Development 7: 792–799.[CrossRef][ISI][Medline]
Stiller, J., and B. D. Hall. 1997 The origin of red algae: implications for plastid evolution. Proceedings of the National Academy of Sciences, USA 94: 4520–4525.
Turmel, M., C. Otis, and C. Lemieux. 1999 The complete chloroplast DNA sequence of the green alga Nephroselmis olivacea: insights into the architecture of ancestral chloroplast genomes. Proceedings, of the National Academy of Sciences, USA 96: 10 248–10 253.
Westbroek, P., and F. Marin. 1998 A marriage of bone and nacre. Nature 392: 861–862.[CrossRef][Medline]
Xiao, S., Y. Zhang, and A. H. Knoll. 1998 Three-dimensional preservation of algae and animal embryos in a Neoproterozoic phosphorite. Nature 391: 553–558.[CrossRef]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
