Systematics and the Study of Organismal Form and Function Advances in Systematics Are Defining New Directions for Functional Morphology and Comparative Physiology

Systematics and the Study of Organismal Form and Function Advances in systematics are defining new directions for functional morphology and comparative physiology George V. Lauder, Ray B. Huey, Russell K. Monson, and Richard J. Jensen he study of form and function Growth and Form (1917) is a clas- in organisms has a long and A broadly comparative, sic earlv attemDt to understand Tdistinguished history, dating physical causes of biological form. at least from the sixth century B.C., historical approach to The second new area, an expan- the time of the first recorddd me: sion of physiological studies of or- thodical investigations of animal the study of "eanismal functidn. was associated structure and function (Russell with interest in mechanistic aspects [I9161 1982). Investigations into the organismal function is of organismal function. The physi- design of plants and animals gained ological tradition of mechanistic increased visibility in the eighteenth just beginning research on organisms, begun in and nineteenth centuries with the nineteenth-century Europe, diverged work of German poet Johann rapidly from morphological and Wolfgang von Goethe, French natu- flourished as the study of the mecha- structural work. Morphologists and ralist Georges L. C. Cuvier, and nistic basis of animal and plant life anatomists were focusing on the use Swiss zoologist Louis Agassiz. Their began in earnest. A British mor- of morphological data for phyloge- investigations of structure captured phologist of that time, Richard netic analysis, and mechanistic bi- the attention not only of profes- Owen, formulated the concepts of ologists eschewed phylogenetic goals sional naturalists and scientists but homology and analogy-the central for experimental and manipulative also much of the general public. theme underlying all of compara- investigation (Allen 1975, Coleman Physiological investigation also tive biology (Hall 1994). 1977). The discipline of physiology, With the start of the twentieth even comparative investigations of George V. Lauder is a functional and century, the comparative analysis of physiological differences among in- evolutionary morphologist in the De- organismal design expanded into dividuals, populations, or species, partment of Ecology and Evolutionary two new areas. while research in remained strangely divorced from Biology, University of California, Irvine, historical biology continued to be systematics and phylogeny for many CA 92717. He works on vertebrate feed- ~erformedlargely by paleontolo- years. ing and locomotor systems. Ray B. Huey gists, systematists, and comparative In the last 30 vears. with the rise is an evolutionary physiologist in the anatomists. The first new area em- of integrative research areas such as Zoology Department, University of biomechanics and experimental ! Washington, Seattle, WA 98195. He is phasized physical principles that interested in the evolution of locomotor govern the structure of plants and functional morphology, compara- performance in lizards and of thermal animals. This focus on physical bi- tive physiology and comparative sensitivity in flies. Russell K. Monson is ology included mechanistic analy- anatomy have begun to overlap a physiological ecologist in the Depart- ses of developmental patterns by broadly in their subject matter and ment of Environmental, Population, and biologists such as T. H. Morgan, E. techniques of analysis. But even more Organismic Biology, University of Colo- G. Conklin, and E. B. Wilson (build- significant has been the explicit move rado, Boulder, CO 80309. He works on ing on the earlier work of German toward the incorporationof system- the evolution of photosynthetic mecha- anatomist and zoologist Wilhelm atic concepts and hypotheses into nisms in plants. Richard J. Jensen is a Roux in the late nineteenth century; both comparative physiological and plant systematist in the Department of morphological research (Burggren Biology, Saint Mary's College, Notre Allen 1975). There were also gen- Dame, IN 46556. He uses morpho- eral investigations into possible and Bemis 1990, Emerson 1988, metrics to address problems in oak tax- physical determinants of morpho- Huev 1987. Lauder 1990). Within onomy. 0 1995 American Institute of logical features by workers such as the iast dec'ade, many studies have Biological Sciences. D'Arcy Thompson. Thompson's On appeared that integrate compara- 696 BioScience Vol. 45 No. 10 tive morphological and physiological analyses of organismal design with phylogenetic methods and concepts (e.g., Garland and Carter 1994, Huey and Bennett 1987). In many ways, the advances in systematics, phylogeny reconstruction, and comparative methodology are now defining new directions for functional morphology and comparative physiology. In the future, an understand- ing of phylogenetic principles and practices is likely to be a prerequi- site for research in comparative physiology and morphology. This new perspective brings increased precision to the selection of species for structural and physiological analysis, to research on the evolutionary transformation of form and function, and to the statistical analysis of comparative data. Figure 1. Diagram of the coiled shell morphospace. The central cube shows the The comparative study of volume defined by the three axes used by Raup (1966) to model the geometry of the coiled shell. Regions of the cube labeled A, B, C, and D denote the portion of organismal form and function the morphospace occupied by gastropods, ammonoids, pelecypods, and brachio- Research in comparative morphol- pods respectively. Representative computer-generated shell shapes from areas of ogy and physiology lies at the heart the cube are shown also; note that much of the theoretically possible morphospace is unoccupied by either extant or extinct forms. From: Principles of Paleontology of many of the most pressing scien- by D. M. Raup and S. M. Stanley (1971). O W. H. Freeman and Company. Used tific questions in comparative biol- with permission. ogy today, and the recent integration of phylogenetics into the conceptual core of these disciplines occur regularly as new geographic resulted in new analyses of taxo- has redefined many fundamental areas are explored and as extinct nomic diversity and has engendered questions. In this article we con- taxa are discovered by paleontolo- a healthy controversy, rooted in sys- sider several examples in which gists applying new techniques for tematics. of the extent to which the analyses of organismal morphology recovering fossils from previously novel ~&ess Shale morphologies and physiology (largely separately) studied areas. represent fundamentally new groups have provided new approaches or The discovery of novel taxa is an of organisms (Wills et al. 1994).For insights into biological diversity. We important (and yet often underval- example, Briggs and colleagues also consider the integration of these ued) component of research in quan- (1992) have argued that the appar- two disciplines and examples of how titative and evolutionary morphol- ent diversity of morphology (often a phylogenetic framework and more ogy. New discoveries not only termed disparity to avoid confusion rigorous systematic underpinnings contribute to the inventory of bio- with taxonomic diversity) in Bur- have shaped current research on both logical diversity (as new species) but gess Shale taxa is in part 'a'n artifact form and function. they also allow current theories of inadequate phylogenetic knowl- about the evolution of form and edge. Taxa are considered to be dif- Comparative morphology. An im- function to be tested using- these ferent when they cannot be placed portant area in which morphologi- fresh data. into extant clades. As structural cal studies contribute to the knowl- Additional discoveries also may knowledge of Burgess Shale taxa edge of biodiversity is in the overturn previous conceptions of the increases, species previously deemed discovery of previously unknown or- diversity of life in the past, forcing a sufficiently disparate as to consti- ganisms. Organisma] structure pro- reevaluation of models of bioloaicalu tute new higher taxa (and hence vides much of the record of the his- diversification through time. An evidence for so-called explosive tory of life and constitutes the most outstanding recent example of novel adaptive radiation early in the Cam- common means by which new spe- structures discovered in fossil taxa brian) are being placed within es- cies are recognized. Such discover- is the Burgess" Shale fauna. in which tablished monophyletic clades. ies often redefine previously ac- a large number of morphologically Although the discovery of taxa cepted limits of organismal design, distinct species have been found with novel structures provides data and they challenge scientists to ex- (Conway Morris 1992, Gould 1989). on organismal diversity, without a plain novel structures and evolu- The extensive morphological diver- general model of how organisms are tionary patterns. These discoveries gence shown by these species has constructed one would have little November 1995 from three of these parameters by considering x-, y-, and z-axes to be defined, respect~vely,by the transla- tion rate of the shell coil down the coiling axis, the rate of expansion along the coiling axis, and the dis- tance of the generating curve from the coiling axis (Figure 1).Each point in this three-dimensional sDace marks a theoretical shape deiived from appropriate parameters for each axis. Raup

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