Evolution of Phenotypic Diversity in Gasterosteus aculeatus Superspecies on the Pacific Coast of North America

Abstract

Bell, M. A. (Department of Biology, University of California, Los Angeles, California 90024) 1976. Evolution of phenotypic diversity in Gasterosteus aculeatus superspecies on the Pacific coast of North America. Syst. Zool. 25:211–227.—A conceptual model for the evolution of phenotypic diversity of the threespine stickleback on the Pacific coast of North America is presented. This model takes into account biological characteristics of the three-spine stickleback and climatic changes during Pleistocene times. Biological features considered include: (1) life history patterns in freshwater and anadromous populations; (2) distribution of freshwater and anadromous populations; (3) morphological variation in freshwater populations; (4) genetics of morphological features; (5) the characteristics of highly divergent populations and their distribution in time and space; (6) character displacement. Previous models for the evolution of phenotypic diversity and the interactions of selection and gene flow are considered. Hypotheses concerning protein evolution in Pacific coast sticklebacks are generated from the model. These hypotheses depend on recent evidence that protein evolution does not have a cause and effect relationship with pheno-typic divergence and speciation. A causal relationship between the unusual mode of evolution in western North American Gasterosteus and their low haploid DNA content is tentatively suggested. If the model is correct, freshwater subspecies proposed by Miller and Hubbs (1969) for the nominal species Gasterosteus aculeatus are polyphyletic.