ADAPTATION AT SPECIFIC LOCI. II. DEMOGRAPHIC AND BIOCHEMICAL ELEMENTS IN THE MAINTENANCE OF THE COLIAS PGI POLYMORPHISM

Ward B. Watt ¹

¹ Department of Biological Sciences, Stanford University, Stanford, California 94305, and Rocky Mountain Biological Laboratory, Crested Butte, Colorado 81224

Demographically oriented sampling in the wild and biochemical study of allozymes in the laboratory have been used to probe maintenance of the phosphoglucose isomerase polymorphism of Colias butterflies.—The several alleles at this locus show negative or no covariation among their frequencies in the wild. This rules out Wahlund effects as a cause of observations of heterozygote excess at this locus in broods that fly as single cohorts. Unusually heavy mortality among adults, due to drought stress or other causes, can preclude manifestation of differential survivorship among phosphoglucose isomerase genotypes. In broods composed of overlapping cohorts, heterozygote deficiency, apparently due to Wahlund effects in time as cohorts of different survivorship experience mix, can be found. Heterozygotes at this locus fly under a broader range of weather conditions than other genotypes.—Previously detected kinetic differentiation among the genotypes extends in greater magnitude to the glycolytic reaction direction, as well as to a broader range of test conditions than examined before. The heterozygote 3/4 is strikingly heterotic for several measures of kinetic functional effectiveness. Other heterozygotes are sometimes heterotic, more often intermediate (but not exactly so, nor additive in any sense) in properties between homozygotes.—Predictions are made from the biochemical analysis and from the insects' thermal ecology concerning distributions of the genotypes in the wild. Some agree with facts already established. Others are tested and confirmed from data already on hand. Still others are to be tested as reported in an accompanying paper.—All available evidence points to a combination of heterozygote advantage and fluctuating-environment selection as responsible for maintaining this polymorphism. There is considerable evidence for the operation of protein-structural constraint on the range of adaptations possible at this locus.

This article has been cited by other articles:

				A. Wagner Rapid Detection of Positive Selection in Genes and Genomes Through Variation Clusters Genetics, August 1, 2007; 176(4): 2451 - 2463. [Abstract] [Full Text] [PDF]

				N. E. Rank, D. A. Bruce, D. M. McMillan, C. Barclay, and E. P. Dahlhoff Phosphoglucose isomerase genotype affects running speed and heat shock protein expression after exposure to extreme temperatures in a montane willow beetle J. Exp. Biol., March 1, 2007; 210(5): 750 - 764. [Abstract] [Full Text] [PDF]

				C. W. Wheat, W. B. Watt, D. D. Pollock, and P. M. Schulte From DNA to Fitness Differences: Sequences and Structures of Adaptive Variants of Colias Phosphoglucose Isomerase (PGI) Mol. Biol. Evol., March 1, 2006; 23(3): 499 - 512. [Abstract] [Full Text] [PDF]

				B. Wang and A. H. Porter An AFLP-Based Interspecific Linkage Map of Sympatric, Hybridizing Colias Butterflies Genetics, September 1, 2004; 168(1): 215 - 225. [Abstract] [Full Text] [PDF]

				B. C. Verrelli and W. F. Eanes The Functional Impact of Pgm Amino Acid Polymorphism on Glycogen Content in Drosophila melanogaster Genetics, September 1, 2001; 159(1): 201 - 210. [Abstract] [Full Text] [PDF]

				S. E. Travers and T. P. Holtsford Differential siring success of Pgi genotypes in Clarkia Unguiculata (Onagraceae) Am. J. Botany, August 1, 2000; 87(8): 1091 - 1098. [Abstract] [Full Text]

				M. Kohane and W. Watt Flight-muscle adenylate pool responses to flight demands and thermal constraints in individual Colias eurytheme (Lepidoptera, pieridae) J. Exp. Biol., January 11, 1999; 202(22): 3145 - 3154. [Abstract] [PDF]

				W. Watt, P. Carter, and K Donohue Females' choice of "good genotypes" as mates is promoted by an insect mating system Science, September 12, 1986; 233(4769): 1187 - 1190. [Abstract] [PDF]

				E. P. Dahlhoff and N. E. Rank Functional and physiological consequences of genetic variation at phosphoglucose isomerase: Heat shock protein expression is related to enzyme genotype in a montane beetle PNAS, August 29, 2000; 97(18): 10056 - 10061. [Abstract] [Full Text] [PDF]