Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (42 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2015)
Juvenile Dungeness crabs spend ~1 year in the San Francisco Estuary, where they undergo considerable growth before returning to the coastal ocean. Previous studies suggest that competition, food scarcity and avoidance of conspecifics may cause some juvenile Dungeness crabs in the San Francisco Estuary to become food limited. Food limitation may force these crabs to forage in higher temperature intertidal environments in the estuary, exposing them to stressful conditions in order to sustain growth and, potentially, necessitating physiological trade-offs in energy allocation between growth and stress tolerance. To investigate the effects of food limitation on aerobic metabolism and physiological performance of crabs, we assessed growth, moulting frequency, metabolic rate, citrate synthase and malate dehydrogenase enzyme activity and cardiac performance, as an index of temperature sensitivity and upper temperature tolerance. Summer- and winter-caught crabs were acclimated to either a high- or a low-food ration for 5 weeks. Overall, our results demonstrated that while food limitation had a negative effect on growth of juvenile Dungeness crabs in both the summer and the winter feeding trials, crabs in the low-food group maintained both metabolic rate at ambient San Francisco Estuary temperatures (15°C; summer trial only) and upper temperature tolerance as determined by failure of cardiac function when compared with crabs in the high-food group (summer and winter trials). Therefore, the ability to maintain stress tolerance when food is limited appears to come as a physiological trade-off to growth. Food-limited crabs were unable to increase their metabolic rate to the same level as that achieved by well-fed crabs; therefore, if exposure to elevated temperatures persists and requires more energy than can be met by crabs in their food-limited state, physiological performance may be compromised.
    Cover page: Effect of food availability on the growth and thermal physiology of juvenile Dungeness crabs ( Metacarcinus magister )
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2013)
    Population response to global change will depend on responses to a multivariate set of changes in abiotic habitat characteristics and biotic interactions. Organismal biologists seeking to make ecological inferences about the impacts of global change by studying physiological performance have traditionally performed carefully controlled experimental studies that examine one variable at a time. Those studies, while of high value, may not lead to accurate predictions of organismal responses in the natural habitat, where organisms experience concomitant changes in multiple environmental factors. The symposium "Physiological Responses to Simultaneous Shifts in Multiple Environmental Stressors: Relevance in a Changing World" focused on physiological studies in which multiple environmental variables were simultaneously examined and brought together an international group of early-career and established speakers with unique perspectives on studies of multistressors. In doing so, the objective of the symposium was to frame the necessary next steps for increasing predictive capacity of organismal responses to environmental shifts in the natural habitat, establish novel collaborations among researchers actively investigating physiological responses to a multivariate environment, and broaden the number of researchers conducting such studies.
      Cover page: Physiological Responses to Shifts in Multiple Environmental Stressors: Relevance in a Changing World
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2018)
      For ectotherms, temperature modifies the rate of physiological function across a temperature tolerance window depending on thermal history, ontogeny, and evolutionary history. Some adult Antarctic fishes, with comparatively narrow thermal windows, exhibit thermal plasticity in standard metabolic rate; however, little is known about the shape or breadth of thermal performance curves of earlier life stages of Antarctic fishes. We tested the effects of acute warming (- 1 to 8 °C) and temperature acclimation (2 weeks at - 1, 2, 4 °C) on survival and standard metabolic rate in early embryos of the dragonfish Gymnodraco acuticeps from McMurdo Sound, Ross Island, Antarctica. Contrary to predictions, embryos acclimated to warmer temperatures did not experience greater mortality and nearly all embryos survived acute warming to 8 °C. Metabolic performance curve height and shape were both significantly altered after 2 weeks of development at - 1 °C, with further increase in curve height, but not alteration of shape, with warm temperature acclimation. Overall metabolic rate temperature sensitivity (Q 10) from - 1 to 8 °C varied from 2.6 to 3.6, with the greatest thermal sensitivity exhibited by embryos at earlier developmental stages. Interclutch variation in metabolic rates, mass, and development of simultaneously collected embryos was also documented. Taken together, metabolic performance curves provide insight into the costs of early development under warming temperatures, with the potential for thermal sensitivity to be modified by dragonfish phenology and magnitude of seasonal changes in temperature.
        Cover page: Thermal windows and metabolic performance curves in a developing Antarctic fish
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2017)
        There is an accumulating body of evidence suggesting that the sub-zero Antarctic marine environment places physiological constraints on protein homeostasis. Levels of ubiquitin (Ub)-conjugated proteins, 20S proteasome activity and mRNA expression of many proteins involved in both the Ub tagging of damaged proteins as well as the different complexes of the 26S proteasome were measured to examine whether there is thermal compensation of the Ub-proteasome pathway in Antarctic fishes to better understand the efficiency of the protein degradation machinery in polar species. Both Antarctic (Trematomus bernacchii, Pagothenia borchgrevinki) and non-Antarctic (Notothenia angustata, Bovichtus variegatus) notothenioids were included in this study to investigate the mechanisms of cold adaptation of this pathway in polar species. Overall, there were significant differences in the levels of Ub-conjugated proteins between the Antarctic notothenioids and B. variegatus, with N. angustata possessing levels very similar to those of the Antarctic fishes. Proteasome activity in the gills of Antarctic fishes demonstrated a high degree of temperature compensation such that activity levels were similar to activities measured in their temperate relatives at ecologically relevant temperatures. A similar level of thermal compensation of proteasome activity was not present in the liver of two Antarctic fishes. Higher gill proteasome activity is likely due in part to higher cellular levels of proteins involved in the Ub-proteasome pathway, as evidenced by high mRNA expression of relevant genes. Reduced activity of the Ub-proteasome pathway does not appear to be the mechanism responsible for elevated levels of denatured proteins in Antarctic fishes, at least in the gills.
          Cover page: The effect of temperature adaptation on the ubiquitin–proteasome pathway in notothenioid fishes
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2017)
          Much of our understanding of the thermal physiology of intertidal organisms comes from experiments with animals acclimated under constant conditions and exposed to a single heat stress. In nature, however, the thermal environment is more complex. Aerial exposure and the unpredictable nature of thermal stress during low tides may be critical factors in defining the thermal physiology of intertidal organisms. In the fingered limpet, Lottia digitalis, we investigated whether upper temperature tolerance and thermal sensitivity were influenced by the pattern of fluctuation with which thermal stress was applied. Specifically, we examined whether there was a differential response (measured as cardiac performance) to repeated heat stress of a constant and predictable magnitude compared with heat stress applied in a stochastic and unpredictable nature. We also investigated differences in cellular metabolism and damage following immersion for insights into biochemical mechanisms of tolerance. Upper temperature tolerance increased with aerial exposure, but no significant differences were found between predictable treatments of varying magnitudes (13°C versus 24°C versus 32°C). Significant differences in thermal tolerance were found between unpredictable trials with different heating patterns. There were no significant differences among treatments in basal citrate synthase activity, glycogen content, oxidative stress or antioxidants. Our results suggest that aerial exposure and recent thermal history, paired with relief from high low-tide temperatures, are important factors modulating the capacity of limpets to deal with thermal stress.
            Cover page: The role of stochastic thermal environments in modulating the thermal physiology of an intertidal limpet, Lottia digitalis
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2016)
            Reintroduction of endangered fishes to historic habitat has been used as a recovery tool; however, these fish may face competition from other fishes that established in their native habitat since extirpation. This study investigated the physiological response of tidewater goby, Eucyclogobius newberryi, an endangered California fish, when competing for food with threespine stickleback, Gasterosteus aculeatus, a native species, and rainwater killifish, Lucania parva, a non-native species. Survival, growth and physiological indicators of stress (i.e. cortisol, glucose and lactate concentrations) were assessed for juvenile fish held for 28 days in two food-limited conditions. When fed a 75% ration, survival of E. newberryi was significantly lower when held with G. aculeatus. In all fish assemblages, weight and relative condition decreased then stabilized over the 28 day experiment, while length remained unchanged. Whole-body cortisol in E. newberryi was not affected by fish assemblage; however, glucose and lactate concentrations were significantly higher with conspecifics than with other fish assemblages. When fed a 50% ration, survival of E. newberryi decreased during the second half of the experiment, while weight and relative condition decreased and length remained unchanged in all three fish assemblages. Cortisol concentrations were significantly higher for all fish assemblages compared with concentrations at the start of the experiment, whereas glucose and lactate concentrations were depressed relative to concentrations at the start of the experiment, with the magnitude of decrease dependent on the species assemblage. Our findings indicate that E. newberryi exhibited reduced growth and an elevated generalized stress response during low food availability. In response to reduced food availability, competition with G. aculeatus had the greatest physiological effect on E. newberryi, with minimal effects from the non-native L. parva. This study presents the first reported cortisol, glucose and lactate concentrations in response to chronic stress for E. newberryi.
              Cover page: Survival, growth and stress response of juvenile tidewater goby, Eucyclogobius newberryi, to interspecific competition for food
              • Thesis
              • Peer Reviewed
              UC Davis Electronic Theses and Dissertations (2022)

              In late 2019, at multiple hatcheries in California’s Central Valley (CCV), offspring of recently spawned fall-run Chinook salmon (Oncorhynchus tshawytscha) exhibited abnormalities in swimming, lethargy, and high early life-stage mortality; the combination of these symptoms is commonly referred to as thiamine deficiency complex (TDC). The cause of thiamine deficiency in Pacific salmonids is hypothesized to be due to a lack of diet heterogeneity and reliance on northern anchovies (Engraulis mordax), containing high levels of thiaminase, a thiamine-cleaving enzyme. Of CCV’s four runs, the endangered Sacramento River winter-run Chinook salmon (WRCS) is perhaps the most vulnerable to thiamine deficiency as any additional stressor will exacerbate current threats to survival. The goal of this study was to evaluate the effect of thiamine supplementation in pre-spawn WRCS females on their offspring egg thiamine concentrations, survival, prevalence of TDC-related symptoms, and physiological performance and behavioral traits. Sixty female WRCS at Livingston Stone National Fish Hatchery were randomly administered either a thiamine injection (n=33; 500 mg/ml thiamine hydrochloride) at a dose of 50 mg/kg body weight or a sham injection (n=27; sterile saline solution) at a volume of 0.127 ml/kg body weight. After spawn, a subset of fertilized eggs from each female were analyzed for thiamine concentration. Eyed embryos were transferred to the University of California, Davis and kept for observations of TDC, survival, and to assess the effects of maternal thiamine treatments on offspring physiology and behavior. Upper thermal tolerance, routine metabolic rate, spontaneous swimming activity, boldness, and anti-predator responses were evaluated in swim-up fry. On average, total egg thiamine concentrations were 5.02 and 34.91 nmol/g for untreated (n=27) and thiamine treated (n=33) females, respectively. Mortality rate of offspring from untreated females averaged 32.97 ± 0.33 %, with rates ranging from 0 to 100%, while offspring from thiamine treated females had a mean mortality rate of less than 1%. Using a binomial logistic regression model, we predicted that a mean total egg thiamine concentration of ~5 nmol/g supports 95% survival within a family (EC95). There were no statistically significant effects of maternal treatment on any of the physiological or behavioral metrics assessed in this study. Overall, we recommend the administration of supplemental thiamine to increase thiamine concentrations past the threshold at which TDC symptoms are commonly observed; however, additional research should be conducted to further examine potential latent effects of thiamine deficiency in Pacific salmonids.

                Cover page: Assessment of the Effects of Thiamine Deficiency on the Survival, Physiology, and Behavior of Early Life-Stage Winter-Run Chinook Salmon
                • Thesis
                • Peer Reviewed
                UC Davis Electronic Theses and Dissertations (2022)

                The wild abundance of Longfin smelt (Spirinchus thaleichthys, LFS) in the San Francisco Estuary (SFE) has declined to less than 1% of pre-1980’s numbers. As a result, they have been listed as “threatened” under the California Endangered Species Act since 2009. In an effort to avoid localized species extinction, a captive culture program was created for LFS through the Fish Conservation Culture Laboratory at the University of California, Davis. Larviculture methods for LFS are still being optimized to ensure a successful culture program. For my MS thesis, I tested the impacts of rearing temperature on early post-hatch LFS larvae from three different parental clutches to identify which rearing temperatures are best for successful development of these early life stages. I reared newly fertilized embryos and post-hatch, non-feeding yolk-sac larvae in freshwater (0 ppt) at 10, 12, or 15°C until 3 days post-hatch (dph). I measured larval morphometrics (total length, eye diameter, yolk sac area), and mortality for all groups. I was the first to evaluate the incidence and severity of jaw and spinal malformations for cultured LFS. Larvae reared at 15°C were smaller (mean ± SE; 0.52 ± 0.0040 mm), significantly younger at hatch (13.1 ± 0.1 days post-fertilization; dpf), and had slightly higher mortality and increased spinal malformations compared to other rearing temperatures. Embryos reared at 10 and 12°C were of similar size (10℃: 0.59 ± 0.0030 mm, 12℃: 0.56 ± 0.0030 mm), but 10°C larvae were significantly older at hatch (10℃: 18.4 ± 0.05 dpf, 12℃: 15.8 ± 0.1 dpf). Clutch had a much more variable impact on response metrics, markedly in size, suggesting that parentage may mediate developmental responses to unfavorable environmental conditions and change. No incidences of jaw malformation and a very small percentage of spinal malformations were observed amongst all treatment groups. Overall, the novel results described in this study suggest that parentage modifies the impacts of rearing temperature on larval development and survival. As a result, I make recommendations to broaden the impact of future LFS and other sensitive larval fish studies on conservation larviculture techniques. While our understanding of factors impeding LFS culture is limited, this study represents a significant step towards identifying more biologically efficient larviculture and conservation management techniques for this and other critically threatened fish species.

                  Cover page: Rearing temperature and parentage influence development of early post-hatch Longfin smelt (Spirinchus thaleichthys) in captive culture
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2016)
                  The rocky intertidal zone is among one of the most highly variable environments on Earth, with rapid and unpredictable changes in temperature on a daily basis. Numerous studies have investigated the thermal physiology of intertidal animals; however, few have focused on an organism’s capacity to withstand repeated heat stress during the emersion of low-tide periods and how previous exposures to sublethal increases in temperature may modulate the capacity to withstand severe heat stress. Lottia digitalis, a species of limpet ubiquitous along the Pacific coast of North America, were acclimated under ambient ocean conditions in the laboratory during the summer and winter months. Limpets were aerially exposed with or without preliminary heat exposures of varying magnitudes (15–35 °C for 2 h) the day before being challenged to a lethal temperature increase to investigate how sequential low-tide-period conditions affect upper thermal tolerance and temperature sensitivity. Limpets with a preliminary aerial exposure of 25–35 °C (summer) and 20 °C (winter) had greater upper critical thermal limits of cardiac performance as determined by final breakpoint temperature (~1.5–6 °C increase) and flatline temperature (~1–2 °C increase) than limpets with no previous exposure. The magnitude of temperature increase that conferred significant increases in thermal tolerance differed in summer and winter, reflecting seasonal differences in the thermal environment in nature. Fingered limpets’ upper thermal tolerance is plastic and likely modulated by the previous day’s low-tide exposure, demonstrating the importance of incorporating the repeated nature of stress into thermal physiology research in intertidal organisms.
                    Cover page: Role of sequential low-tide-period conditions on the thermal physiology of summer and winter laboratory-acclimated fingered limpets, Lottia digitalis
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2020)
                    Triploid salmonids have been shown to underperform in suboptimal environments. It is thought this might be due to having larger cells to accommodate the increased number of chromosomes and therefore effects on aerobic metabolism from having smaller cellular surface area to volume ratios. The goal of this study was to examine the aerobic metabolism of diploid and triploid white sturgeon (Acipenser transmontanus) in ambient (18 °C) and elevated water temperatures (24 °C). Resting and maximum metabolic rates, recovery time from exhaustive exercise, and surface area to volume ratios of erythrocytes and their nuclei in diploid and triploid sturgeon were evaluated. Triploid sturgeon had a reduced aerobic scope and hematological response (hematocrit and hemoglobin) to exhaustive exercise. A reduced surface area to volume ratio of erythrocytes in triploid sturgeon provides evidence that cellular surface area could be one mechanism limiting aerobic metabolism in triploid fishes. A lower aerobic scope found in triploid sturgeon may impact reproductive and somatic growth, yet more research is needed to determine implications for management decisions on farms and hatcheries.
                      Creative Commons 'BY' version 4.0 license
                      Top