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Effects of hypothetical developmental barriers and abrupt environmental changes on adaptive walks in a computer-generated domain for early vascular land plants

Published online by Cambridge University Press:  08 February 2016

Karl J. Niklas*
Affiliation:
Section of Plant Biology, Cornell University, Ithaca, New York 14853-5908

Abstract

Computer-generated searches through hypothetical fitness landscapes for progressively more fit variants were used to assess the effects of developmental barriers (mimicked by barring specific types of morphological transformations) and abruptly shifting environmental conditions (mimicked by sudden shifts in how fitness was defined) on the number and accessibility of optimal phenotypes. Relative fitness was defined in terms of maximizing light interception, mechanical stability, or reproductive success, or minimizing surface area, or optimizing the performance of various combinations of these tasks. Developmentally obstructed and unobstructed walks located, on average, equivalent numbers of phenotypic optima. The number of optima identified by both kinds of walks increased in proportion to the number of simultaneously performed tasks used to measure fitness. Walks passing from more complex to less complex fitness landscapes located more optima than walks passing through unchanging, stable landscapes. The model thus suggests that there are no a priori reasons to assume that (1) the morphological options available to adaptive evolution become more restrictive as biological complexity increases, (2) “developmental barriers” necessarily restrain a lineage from evolving well-adapted morphologies, and (3) generalist organisms are less successful than specialists. Also, because the number and accessibility of fitness peaks were proportional to the complexity of fitness landscapes, the model predicts that the probability of cladogenesis will increase as landscape complexity increases, while anagenesis will be encouraged when fitness is defined in terms of performing one or a few tasks simultaneously.

Type
Articles
Copyright
Copyright © The Paleontological Society 

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References

Literature Cited

Alberch, P. 1980. Ontogenesis and morphological differentiation. American Zoology 20:653–67.CrossRefGoogle Scholar
Chaloner, W. G., and Sheerin, A. 1979. Devonian macrofloras. The Devonian System, Special Papers in Palaeontology 23:145–61. Palaeontological Society, London.Google Scholar
Edwards, D., Davies, K. L., and Axe, L. 1992. A vascular conducting strand in the early land plant Cooksonia. Nature 357:683685.CrossRefGoogle Scholar
Ellison, A.M., and Niklas, K. J. 1988. Branching patterns of Salicornia europaea (Chenopodiaceae) at different successional stages: a comparison of theoretical and real plants. American Journal of Botany 75:501512.CrossRefGoogle Scholar
Gould, S. J. 1980. The evolutionary biology of constraint. Daedalus 109:3952.Google Scholar
Knoll, A. H., Niklas, K. J., Gensel, P. G., and Tiffney, B. H. 1984. Character diversification and patterns of evolution in early vascular plants. Paleobiology 10:3447.CrossRefGoogle Scholar
Levins, R. 1968. Evolution in Changing Environments. Monographs in Population Biology No. 2. Princeton University Press, Princeton, N.J.Google Scholar
Niklas, K. J. 1992. Plant biomechanics: an engineering approach to plant form and function. University of Chicago Press, Chicago.Google Scholar
Niklas, K. J. 1994a. Morphological evolution through complex domains of fitness. Proceedings of the National Academy of Sciences USA 91:67726779.CrossRefGoogle ScholarPubMed
Niklas, K. J. 1994b. Plant allometry: the scaling of form and process. University of Chicago Press, Chicago.Google Scholar
Niklas, K. J. 1994c. Simulations of organic shape: the roles of phenomenology and mechanism. Journal of Morphology 219:243246.CrossRefGoogle ScholarPubMed
Niklas, K. J. 1997. Adaptive walks through fitness landscapes for early vascular land plants. American Journal of Botany 84:1625.CrossRefGoogle Scholar
Niklas, K. J., and Kerchner, V. 1984. Mechanical photosynthetic constraints on the evolution of plant shape. Paleobiology 10:79101.CrossRefGoogle Scholar
Niklas, K. J., and Owens, T. G. 1989. Physiological and morphological modifications of Plantago major (Plantaginaceae) in response to light conditions. American Journal of Botany 76:370–82.CrossRefGoogle Scholar
Niklas, K. J., Tiffney, B. H., and Knoll, A. H. 1980. Apparent changes in the diversity of fossil plants: a preliminary assessment. In Hecht, M., Steere, W., and Wallace, B., eds. Evolutionary Biology 12:189. Plenum, New York.Google Scholar
Snedecor, G. W., and Cochran, W. G. 1980. Statistical methods, 7th ed.Iowa State University Press, Ames.Google Scholar
Sokal, R. R., and Rohlf, F. J. 1981. Biometry, 2d ed.W. H. Freeman, New York.Google Scholar
Stewart, W. N., and Rothwell, G. W. 1993. Paleobotany and the evolution of plants, 2d ed. Cambridge University Press, Cambridge.Google Scholar
Sultan, S. E. 1987. Evolutionary implications of phenotypic plasticity in plants. Evolutionary Ecology 21:127–78.Google Scholar
Sultan, S. E. 1992. Phenotypic plasticity and neo-Darwinian legacy. Evolutionary Trends in Plants 6:6171.Google Scholar
Taylor, T. N., and Taylor, E. L. 1993. The biology and evolution of fossil plants. Prentice-Hall, Englewood Cliff, N.J.Google Scholar
Thomas, R. D. K., and Reif, W.-E. 1993. The skeleton space: a finite set of organic designs. Evolution 47:341360.CrossRefGoogle ScholarPubMed