Systematics and ecology of chubs (Gila : Cyprinidae) of the Alvord Basin, Oregon and Nevada Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0z708z46f

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  • Seventeen populations of Gila Baird and Girard are identified from the Alvord Basin of southeastern Oregon and northwestern Nevada. Gila in the Alvord Basin occupy a wide range of habitats, including warm springs, cool springs, creeks, reservoirs, and a thermal lake. These populations became isolated in remnant habitats when waters of pluvial Lake Alvord receded 7,000 to 10,000 years ago. Taxonomic analyses; based on morphological, meristic, and osteological characters; indicated local adaptation and subsequent differentiation among populations. Gila inhabiting the Borax Lake area are considered specifically distinct from other populations. The Borax Lake chub is a dwarf species differentiated from other Alvord Basin populations of Gila by their small size at maturity, notably large head and orbit, long snout, long predorsal length, and narrow caudal peduncle. This species also exhibits reduced pectoral fin ray numbers and reduced cephalic and body lateral-line systems. All other Alvord Basin populations of Gila are referred to Gila alvordensis Hubbs and Miller. Both G. alvordensis and the Borax Lake species are placed in the subgenus Siphateles. Alvord Basin fishes of the genus Gila are opportunistic omnivores. Many intestines contained one food in predominance, indicating highly exploitive feeding. Alvord Basin Gila typically consume benthic and midwater foods; however, the Gila inhabiting Borax Lake consumed large amounts of foods of terrestrial origin during the summer and autumn. Reproductive characteristics of the Gila from Borax Lake parallel those of many Southwestern cyprinodontids inhabiting warm springs. Females are asynchronous, with a high degree of individual periodicity, and typically spawn twice. Borax Lake chubs usually have a one year lifespan, with few age I, II, and III fish present. The Borax Lake species is endangered by geothermal development and surface disturbance in the Borax Lake area. The ability of the habitat and the unique species to survive these threats is uncertain.
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