© 2001 by The Society for Integrative and Comparative Biology
The Role of Phylogenies in Comparative Biology: An Introduction to the Symposium1
1 Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109
Reconstruction of phylogenetic relationships can be an arduous and prolonged task. Large numbers of specimens must be examined to produce even larger numbers of potentially informative traits. These descriptive data are scored and fed into phylogenetic analysis routines to determine which of the myriad possible phylogenies are supported by the data. Often, these analyses are repeated several times, exploring various options, in the hope that one of them will produce a reasonably well resolved and strongly supported tree.
Why do systematists go through so much effort to produce a single picture with a few dozen branching lines? One answer to this question is that the answers to many of the other questions in comparative biology depend on the arrangement of those branching lines. Several biologists have pointed out the tremendous potential for comparative analyses to reach erroneous conclusions when they fail to account for the phylogenetic relationships of the taxa (Lauder, 1981
; Felsenstein, 1985; Coddington, 1988; Donoghue, 1989; Harvey and Pagel, 1991; Garland and Adolph, 1994). With so many people making this argument, often starting from quite different approaches to inferring phylogenetic relationships, it is no surprise that several distinct methods of incorporating phylogenetic information in comparative studies have been proposed (Cheverud et al., 1985; Huey and Bennett, 1987; Coddington, 1988; Felsenstein, 1988; Gittleman and Kot, 1990; Maddison, 1990). Some of these methods have become quite popular: for example, numerous studies have employed the independent contrasts technique. But despite the warnings and the examples, there are still many comparative studies that fail to consider the implications of phylogeny for explaining the observed similarities and differences among taxa.
There are several possible explanations for failure to include phylogenetic information in a comparative study. One explanation may be uncertainty about which "comparative method" to use. This uncertainty is understandable in light of the large number of methods and the continuing debate over their validity (Martins and Garland, 1991; Björklund, 1994; Garland and Adolph, 1994; Wenzel and Carpenter, 1994; Martins, 1996). Another explanation may be uncertainty about which phylogeny to use. It is rare for a phylogenetic analysis to produce a single, fully resolved and strongly supported tree; and it is not unusual for independent analyses of different data sets to produce conflicting trees. Furthermore, the uncertainty about which tree to use may be compounded by uncertainty about which method of phylogenetic inference should be employed to construct a tree in the first place.
Uncertainty about how to proceed should not dissuade anyone from making the attempt to include phylogenetic information in a comparative study. As the papers in this symposium demonstrate, this approach can produce information and insights about evolutionary patterns and processes that can be gained in no other way. However the most important insight derived from this approach is the realization that the observed similarities and differences among observed taxa are the net results of the historical transformations of their respective ancestors. Consequently, biologists who wish to explain those similarities and differences must shift their attention away from the endpoints and focus instead on the historical paths that led to those endpoints and the processes that propelled the lineages along those paths. Only then will it truly be possible to explain the endpoints.
The goal of this symposium is to call attention to the tremendous potential of comparative studies that incorporate phylogenetic information by presenting a variety of studies using this approach. These papers include several analyses of the evolution of morphology and function, in living and extinct organisms. Also included are analyses of subjects less often viewed from a phylogenetic perspective: transformations of ontogeny and behavior. It is our hope that these examples will inspire others to also adopt this perspective.
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ACKNOWLEDGMENTS |
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This symposium was supported by the Society for Integrative and Comparative Biology, the Division of Systematic and Evolutionary Biology, the Division of Vertebrate Morphology, and the Society for Vertebrate Paleontology.
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FOOTNOTES |
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1 From the Symposium Beyond Reconstruction: Using Phylogenies to Test Hypotheses About Vertebrate Evolution presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 4–8 January 2000, at Atlanta, Georgia.
2 E-mail: dlswider{at}umich.edu
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 References |
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Björklund, M. 1994. The independent contrast method in comparative biology. Cladistics, 10:425-433.
Cheverud, J. M., M. M. Dow, and W. Leutenegger. 1985. The quantitative assessment of phylogenetic constraints in comparative analyses: Sexual dimorphism of body weight among primates. Evolution, 39:1335-1351.[CrossRef][Web of Science]
Coddington, J. A. 1988. Cladistic tests of adaptational hypotheses. Cladistics, 4:3-22.
Donoghue, M. J. 1989. Phylogenies and the analysis of evolutionary sequences, with examples from seed plants. Evolution, 43:1137-1156.[CrossRef][Web of Science]
Felsenstein, J. 1985. Phylogenies and the comparative method. Am. Natur, 125:1-15.
Felsenstein, J. 1988. Phylogenies and quantitative characters. Ann. Rev. Ecol. System, 19:445-471.[CrossRef][Web of Science]
Garland, T., Jr. , and S. C. Adolph. 1994. Why not to do two species comparative studies: Limitations on inferring adaptation. Physiol. Zool, 67:797-828.
Gittleman, J. L., and M. Kot. 1990. Adaptation: Statistics and a null model for estimating phylogenetic effects. Syst. Zool, 39:227-241.[CrossRef]
Harvey, P. H., and M. D. Pagel. 1991. The comparative method in evolutionary biology. Oxford University Press, Oxford.
Huey, R. B., and A. F. Bennett. 1987. Phylogenetic studies of coadaptation: Preferred temperatures versus optimal performance temperatures of lizards. Evolution, 41:1098-1115.[CrossRef][Web of Science]
Lauder, G. V. 1981. Form and function: Structural analysis in evolutionary morphology. Paleobiology, 7:430-442.[Abstract]
Maddison, W. P. 1990. A method for testing the correlated evolution of two binary characters: Are gains or losses concentrated on certain branches of a phylogenetic tree? Evolution, 44:539-557.[CrossRef][Web of Science]
Martins, E. P. 1996. Phylogenies, spatial autoregression, and the comparative method: A computer simulation test. Evolution, 50:1750-1765.[CrossRef]
Martins, E. P., and T. Garland Jr. 1991. Phylogenetic analyses of the correlated evolution of continuous characters: A simulation study. Evolution, 45:534-557.[CrossRef][Web of Science]
Wenzel, J. W., and J. M. Carpenter. 1994. Comparing methods: Adaptive traits and tests of adaptation. In P. Eggleton and R. I. Vane-Wright (eds.), Phylogenetics and ecology, pp. 79–101. Academic Press, London.
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