Genetic Divergence of Death Valley Pupfish Species: Biochemical Versus Morphological Evidence

Turner, Bruce

The author used starch-gel electrophoresis to investigate genetic divergence patterns of 5 pupfish species of Death Valley National Park and two adjacent parts of the Pleistocene Death Valley System. The author suggests that finding only moderate differences indicates that the tests dealt primarily with the unchanging part of a genome with both a stable and a varying part. Five morphologically distinctive, relict, monophyletic pupfish (Cyprinodon) species from Death Valley, Owens Valley and the Colorado basin have been surveyed for genetic divergence by gel electrophoresis of hemoglobin, muscle proteins, and tissue enzymes; the products of upwards of 31 genetic loci were involved in the survey. Genetic divergence detected in this manner was minimal and of the range associated with conspecific populations of other vertebrates. Divergent loci were almost entirely those encoding certain esterases; other enzymes provided a few species-specific phenotypes. Where sufficient samples existed, detectable polymorphism was minimal and not obviously associated with environmental variability. Genetic divergence associated with pupfish evolution is apparently not reflected by allozymic differences. A hypothesis is developed to account for these observations: The evolving pupfish genome was essentially dichotomous; a portion of it was virtually invariant. That portion encodes a strongly coadapted, homeostatic, metabolic core of enzymes that initially evolved in an extensively fluctuating habitat like that of the modern C. macularius. There was no selection pressure for substituting new alleles when ancestral populations colonized or were confined in more stable habitats in Death Valley. The electrophoretic survey sampled largely the invariant part of the genome. At present it is not possible to decide which set of data, morphological or biochemical, provide a more valid sample of the pupfish genome useful for determining evolutionary rates and relationships.

Genetic Divergence of Death Valley Pupfish Species: Biochemical Versus Morphological Evidence

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