Electrophoretic and Functional Enzymic Evolution in Four Species of Eastern Pacific Barracudas from Different Thermal Environments

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Abstract
Lesser barracudas (genus Sphyraena), with marginally overlapping ranges, occur in the eastern Pacific Ocean. An electrophoretic analysis of these 4 congeners, revealed that the Gulf of California [USA] species, S. lucasana, is a valid species and not a synonym of the California barracuda, S. argentea. These 2 species are closely related to the lesser barracuda from the Peru coast, S. idiastes, and these three barracuda are all about equally distant from the Panama barracuda, S. ensis. The genetic distances separating the 3 closely related temperate and subtropical species suggest an absence of genetic contact among these species during .apprx. the past 3.5 million yr. The electrophoretically different muscle-type (M4) lactate dehydrogenases of the temperate, subtropical and tropical barracudas displayed temperature-compensatory differences in kinetic properties (apparent Km of pyruvate and catalytic rate constant, kcat). These kinetic adaptations are reflected in a strong conservation of enzyme functional characteristics at the mean habitat temperatures of the species, which differ by 5-8.degree. C. Only minor differences in habitat (body) temperature are sufficient to favor the evolution of functional adaptations in enzymes. The use of closely related congeneric species living in different thermal environments for studies of fine-scale molecular adaptation processes is a fruitful approach to the study of molecular evolution.