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Geographic variation in Novumbra hubbsi Schultz 1929 (Pisches, Umbridale) : External meristic characters, chromosomal state and nuclear DNA content Rosenfeld, Mark Jay


Variation in external meristic characters, chromosomal state and nuclear DNA content was examined across the range of a relict fish, Novumbra hubbsi Schultz, occurring within the general area of the Chehalis periglacial refuge near the terminal moraine of the late Pleistocene Vashon Glacier in western Washington, U.S.A. N. hubbsi shows considerable geographic variation in several external meristic characters. The geographic distributions of mean counts for lateral bars and anal fin rays in males as well as those for the lateral scale row and scales above the lateral scale row for males and females combined indicate that the Montesano Hills, foothills of the Olympic Mountains, are a barrier to gene flow. This barrier may have been present since at least the Pleistocene. Lateral bar counts are lower and dorsal fin ray counts higher in males from predator-free habitats. These character trends are considered important for mate attraction and territorial defense. Reductions in the numbers of pectoral and pelvic fin rays are also associated with predator-free habitats. Lower numbers of pectoral and pelvic fin rays as well as lateral bars and greater numbers of dorsal fin rays may cause fish to be more prone to predation. Character frequencies may change over time, as interpreted from comparisons of fish from the present study with those caught in 1947 and 1968. The elevated counts for lateral row scales and scale rows before the dorsal fin origin in fish from the Wishkah River drainage may be due to abiotic developmental factors. As to chromosome number and morphology, hubbsi appears in-variate intersexually and geographically. Forty-eight chromosomes comprise the diploid number. The fundamental number in chromosome complements is 80 chromosome arms, contrasting with a published value of 74 arms. The revised fundamental number is based on an extensive series of measurements on 186 elongate chromosome sets. Nuclear DNA contents are reported for male and female N. hubbsi from four populations. No intersexual or geographical differences appear present. The Feulgen-DNA determination for erythrocyte nuclei is 1.68 pg/nucleus ± 0.02(S.E.), about 80% of a published value. The difference between determinations may be due to the use of different control cells or too high a reference DNA value by earlier workers. Since the Feulgen-DNA determination is not very different from the fluorometric ones in this study, as well as near a value determined for a close relative, the present DNA estimate for N. hubbsi is considered accurate. The observed conservatism in chromosomal state and DNA content may be a consequence of N. hubbsi persisting in the same environment for several million years, possibly since the Oligocene.

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