Morphological and Allozymic Variation in the Stichaeid Fish Anoplarchus purpurescens

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Abstract
Morphological and allozymic variation in the stichaeid fish, A. purpurescens, was compared among samples collected from open-coast localities from Alaska to California and from inner-coastal localities in Washington [USA]. The possibility that fish from southern California (Monterey Bay southward) are genetically distinct from fish from more northern areas, which has bearing on the relevance of allozymic data from southern California fish in interpreting patterns of allozymic variation in A. purpurescens elsewhere in its geographical range, was evaluated. Examination of 3 morphological characters and 12 enzyme loci indicated the lack of genetic distinctiveness of southern California populations from more northern ones, which is consistent with the suggestion that current-mediated transport of the planktonic larvae promotes genetic dispersal and/or mixing among populations. The lack of genetic distinctiveness argues against the validity of a separate southern California subspecies (A. p. archolepis; Hubbs, 1927), but more importantly allows the use of the geographical pattern of muscle lactate dehydrogenase (LDH-A) variation in California to refute the hypothesis that the A'' allele is directly favored by elevated environmental temperature. Allelic frequencies in Alaska populations provide a 2nd test of, and similarly refute, the hypothesis that elevated temperature per se selectively favors individuals with the A'' allele. Although several alternative hypotheses on the evolutionary significance of LDH-A variation in A. purpurescens can be envisioned, presently a plausible one is that heterozygosity at the LDH-A locus is selectively favored by increased environmental thermal variation. This hypothesis is consistent not only with the geographical pattern of variation within Washington innercoastal waters (Johnson, 1971), but also with observed changes in allelic frequencies along the outer coast both to the south (California) and to the north (Alaska). No significant correlation was found between the amount of allozymic variation (at the LDH-A and phosphoglucomutase loci) and morphological variation present within localities; heterozygous fish were no more variable for meristic traits than were homozyous fish. There was no clear and consistent pattern of association between particular genotypes and morphological characters. The lack of a significant relationship between enzyme and morphological traits probably is due to appreciable environmental (non-genetic) influences on the morphological characters examined, which may obscure whatever enzyme-morphological covariation exists.