Reference: Biol. Bull. 167: 647-657. (December, 1984) ENVIRONMENTAL CONTROL OF AMYLASE PHENOTYPE IN AMPHIPODS OF THE GENUS GAMMARUS RICHARD BOROWSKY Department of Biology. New York University. Washington Square, New York 10003 Abstract The amylases of three species of Gammarus amphipods, G. palustris, G. mu-cronatus and G. lawrencianus, were studied using polyacrylamide gel electrophoresis In all three species there are two principal zones of activity {Amy-1 and Amy-2), but occasional individuals exhibit a third band (Amy-X). Amy-X variants are more common in the deeper water species and in collections made during late wmter or early spnng than in the shallower water species or in summer collections. Expenmental work shows that Amv-X can be induced by a diet rich in amylose or glycogen, but not by amylopectin or other foods, and by reducing the temperature at which they are maintained. It is hypothesized that the relative expressions of Amy-X and Amy-1 vary seasonally, and that this variation is an adaptive response to seasonal vanation in diet, or conditions for the hydrolysis of substrate. Introduction One of the least understood phenomena in population biology is how the envi-ronment influences the genetic contents and phenotypic expressions of natural pop-ulations. Amphipods of the genus Gammarus are useful in the study of this question because they are distributed among a variety of aquatic environments, ranging from freshwater, through estuarine, to marine. Gammarus species found in the intertidal zone in marine and estuarine environments can be easily collected in large numbers and tend also to be hardy enough to culture in the laboratory. Thus, data on gene frequencies in natural populations can be obtained easily, and hypotheses relating to the effects of environmental factors on the population can be tested by laboratory experiment. Furthermore, the amphipods are an intrinsically interesting group tor evolutionary studies because they are believed to be currently in the midst of an explosive adaptive radiation (Bousfield, 1973). . ^^ / This paper reports work on amylase variation in populations of Gammarus pal-ustris G. mucronatus, and G. lawrencianus. These three species are estuanne to marine in distribution, co-occur at a number of localities in the New York area, and are zoned ecologically in areas of sympatry, from the high intertidal through the low intertidal-subtidal, in the order listed above. Amylase was chosen for study because the enzyme acts upon a heterogeneous substrate set which is externally denved. Environmental variation is expected to influence isozyme vanation at such loc, more than at loci coding for enzymes which act upon ^ntema^ly denved homogeneous substrate sets (Gillespie and Kojima, 1968; Kojima, .'/^A. 1970; Johnson, 1973^1975) Amylases in these species are coded by at least two distinct loci {Amy-1 and Amy-2) and can easily be resolved by electrophoresis on polyacrylamide gels. In occasional individuals of all three species, a third band {Amy-X\ running close to Amy-L is Received 12 May 1984; accepted 28 August 1984. 647
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