title: The Role of Oxygen in Determining Upper Thermal Limits in Lottia digitalis under Air Exposure and Submersion.
abstract: Oxygen limitation of aerobic metabolism is hypothesized to drive organismal thermal tolerance limits. Differences in oxygen availability in air and water may underlie observed differences in upper thermal tolerance of intertidal limpets if oxygen is limiting in submerged environments. We explored how cardiac performance (heart rate, breakpoint temperature [BPT], flat-line temperature [FLT], and temperature sensitivity) was affected by hyperoxia and hypoxia in the finger limpet, Lottia digitalis, under air exposure and submersion. Upper thermal tolerance limits were unchanged by increasing availability of oxygen, although air-exposed limpets were able to maintain cardiac function to higher temperatures than submerged limpets. Maximum heart rate did not increase with greater partial pressure of oxygen (Po2), suggesting that tissue Po2 levels are likely maximized during normoxia. Hypoxia reduced breakpoint BPTs and FLTs in air-exposed and submerged limpets and accentuated the difference in BPTs between the two groups through greater reductions in BPT in submerged limpets. Differences in respiratory structures and the degree to which thermal limits are already maximized may play significant roles in determining how oxygen availability influences upper temperature tolerance.
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, California 94132; 2Department of Animal Science, University of California, Davis, California 95616; 3Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, California 94920; 4Department of Integrative Biology, University of California, Berkeley, California 94720.
authors.forename: Brittany E
authors.initials: BE
authors.lastname: Bjelde
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Miller
authors.forename: Jonathon H
authors.initials: JH
authors.lastname: Stillman
authors.forename: Anne E
authors.initials: AE
authors.lastname: Todgham
mesh_terms: D000818:Animals; D001272:Atmosphere; D049851:Gastropoda / Q000502:physiology*; D006321:Heart / Q000502:physiology; D006339:Heart Rate; D006358:Hot Temperature; D010100:Oxygen / Q000502:physiology*; D012623:Seawater; D055871:Tidal Waves
chemical_list: D010100:Oxygen