• Phylogeography and population genetics of a Beringian endemic: Dallia (Esociformes: Teleostei)

      Campbell, Matthew A.; López, J. Andrés; Takebayashi, Naoki; Olson, Matthew (2011-08)
      In this thesis I examine the population genetics of an endemic Beringian freshwater fish genus, Dallia (blackfish). The current distribution of blackfish was heavily influenced by paleoclimatic instability during the Pleistocene. Beringian paleoclimatic changes during the Pleistocene included the fluctuating growth and decline of glaciers and an overall decrease in temperature and increased aridity in areas not adjacent to the Bering Sea. Pleistocene glacial advances resulted in the cyclical emergence of the Bering land bridge. The effects of paleoclimatic instability on blackfish distribution and abundance can be inferred through the distribution of genetic variation across the Beringian landscape. I address three basic questions: 1: Are separate populations of blackfish taxonomically distinct entities? I found that while there is clear genetic structuring and isolation, there is insufficient information to make a strong statement in this regard. 2: Did blackfish survive Pleistocene glaciations within multiple Beringian refugia? My results indicate that blackfish persisted in at least four broad geographic areas. 3: How did the Bering land bridge influence intercontinental aquatic interchange? My evidence points to close genetic relationships and potentially high exchange of blackfish across the Bering land bridge, which supports the Bering land bridge as conduit for freshwater aquatic migration.
    • Respiratory anatomy, physiology, and central CO₂ chemosensitivity of the Arctic air-breathing fish Dallia pectoralis

      Hoffman, Megan (2010-05)
      "Aerial respiration using a ancestral lung, central respiratory rhythm generation, and central CO₂ chemosensitivity arose early in vertebrate evolution prior to the divergence of sarcopterygian and actinopterygian fish. All vertebrate air breathing, however, is not homologous as this trait evolved independently several times among teleost fishes. Two long-standing questions in respiratory physiology are whether air breathing in fish is controlled by a central rhythm generator and whether air breathing and central CO₂ chemosensitivity co-evolved. One means to address these questions is to investigate control of breathing in the brainstem; therefore, we established an isolated brainstem preparation from the Alaska blackfish, Dallia pectoralis, a rare example of an arctic air-breathing fish. In blackfish, air breathing consists of gulping and swallowing an air bubble into the esophagus and holding it in place by closing off the esophagus from the buccal cavity with a sphincter. Gulping the air bubble is accomplished by the same opercular and mandibular muscles that draw water into the buccal cavity during gill ventilation. Activation of the opercular and mandibular muscles for ventilation is effected by a central rhythm generator in the brainstem that is spontaneously active in the absence of peripheral input. This central rhythm generator, however, is not modulated by central CO₂ chemosensitivity. Unless central CO₂ chemosensitivity was lost in blackfish, we might conclude that centrally controlled vertebrate air breathing can evolve independent of central CO₂ chemosensitivity"--Leaf iii