Academic Appointments

  • Basic Life Science Research Associate, Biology

All Publications

  • Quantification of Environmental DNA (eDNA) Shedding and Decay Rates for Three Marine Fish ENVIRONMENTAL SCIENCE & TECHNOLOGY Sassoubre, L. M., Yamahara, K. M., Gardner, L. D., Block, B. A., Boehm, A. B. 2016; 50 (19): 10456-10464


    Analysis of environmental DNA (eDNA) to identify macroorganisms and biodiversity has the potential to significantly augment spatial and temporal biological monitoring in aquatic ecosystems. Current monitoring methods relying on the physical identification of organisms can be time consuming, expensive, and invasive. Measuring eDNA shed from organisms provides detailed information on the presence and abundance of communities of organisms. However, little is known about eDNA shedding and decay in aquatic environments. In the present study, we designed novel Taqman qPCR assays for three ecologically and economically important marine fish-Engraulis mordax (Northern Anchovy), Sardinops sagax (Pacific Sardine), and Scomber japonicas (Pacific Chub Mackerel). We subsequently measured fish eDNA shedding and decay rates in seawater mesocosms. eDNA shedding rates ranged from 165 to 3368 pg of DNA per hour per gram of biomass. First-order decay rate constants ranged from 0.055 to 0.101 per hour. We also examined the size fractionation of eDNA and concluded eDNA is both intra- and extracellular. Finally, we derived a simple mass-balance model to estimate fish abundance from eDNA concentration. The mesocosm-derived shedding and decay rates inform the interpretation of eDNA concentrations measured in environmental samples and future use of eDNA as a monitoring tool.

    View details for DOI 10.1021/acs.est.6b03114

    View details for Web of Science ID 000384841900019

    View details for PubMedID 27580258

  • The effect of temperature on postprandial metabolism of yellowfin tuna (Thunnus albacares) COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY Klinger, D. H., Dale, J. J., Gleiss, A. C., Brandt, T., Estess, E. E., Gardner, L., Machado, B., Norton, A., Rodriguez, L., Stiltner, J., Farwell, C., Block, B. A. 2016; 195: 32-38


    Specific dynamic action (SDA), the increase in metabolic expenditure associated with consumption of a meal, represents a substantial portion of fish energy budgets and is highly influenced by ambient temperature. The effect of temperature on SDA has not been studied in yellowfin tuna (Thunnus albacares, Bonnaterre 1788), an active pelagic predator that occupies temperate and subtropical waters. The energetic cost and duration of SDA were calculated by comparing routine and post-prandial oxygen consumption rates. Mean routine metabolic rates in yellowfin tuna increased with temperature, from 136mgO2kg(-1)h(-1) at 20°C to 211mgO2kg(-1)h at 24°C. The mean duration of SDA decreased from 40.2h at 20°C to 33.1h at 24°C, while mean SDA coefficient, the percentage of energy in a meal that is consumed during digestion, increased from 5.9% at 20°C to 12.7% at 24°C. Digestion in yellowfin tuna is faster at a higher temperature but requires additional oxidative energy. Enhanced characterization of the role of temperature in SDA of yellowfin tuna deepens our understanding of tuna physiology and can help improve management of aquaculture and fisheries.

    View details for DOI 10.1016/j.cbpa.2016.01.005

    View details for Web of Science ID 000373410500005

    View details for PubMedID 26794613

  • Assessing niche width of endothermic fish from genes to ecosystem PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Madigan, D. J., Carlisle, A. B., Gardner, L. D., Jayasundara, N., Micheli, F., Schaefer, K. M., Fuller, D. W., Block, B. A. 2015; 112 (27): 8350-8355


    Endothermy in vertebrates has been postulated to confer physiological and ecological advantages. In endothermic fish, niche expansion into cooler waters is correlated with specific physiological traits and is hypothesized to lead to greater foraging success and increased fitness. Using the seasonal co-occurrence of three tuna species in the eastern Pacific Ocean as a model system, we used cardiac gene expression data (as a proxy for thermal tolerance to low temperatures), archival tag data, and diet analyses to examine the vertical niche expansion hypothesis for endothermy in situ. Yellowfin, albacore, and Pacific bluefin tuna (PBFT) in the California Current system used more surface, mesopelagic, and deep waters, respectively. Expression of cardiac genes for calcium cycling increased in PBFT and coincided with broader vertical and thermal niche utilization. However, the PBFT diet was less diverse and focused on energy-rich forage fishes but did not show the greatest energy gains. Ecosystem-based management strategies for tunas should thus consider species-specific differences in physiology and foraging specialization.

    View details for DOI 10.1073/pnas.1500524112

    View details for Web of Science ID 000357527600063

  • Deepwater Horizon crude oil impacts the developing hearts of large predatory pelagic fish PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Incardona, J. P., Gardner, L. D., Linbo, T. L., Brown, T. L., Esbaugh, A. J., Mager, E. M., Stieglitz, J. D., French, B. L., Labenia, J. S., Laetz, C. A., Tagal, M., Sloan, C. A., Elizur, A., Benetti, D. D., Grosell, M., Block, B. A., Scholz, N. L. 2014; 111 (15): E1510-E1518


    The Deepwater Horizon disaster released more than 636 million L of crude oil into the northern Gulf of Mexico. The spill oiled upper surface water spawning habitats for many commercially and ecologically important pelagic fish species. Consequently, the developing spawn (embryos and larvae) of tunas, swordfish, and other large predators were potentially exposed to crude oil-derived polycyclic aromatic hydrocarbons (PAHs). Fish embryos are generally very sensitive to PAH-induced cardiotoxicity, and adverse changes in heart physiology and morphology can cause both acute and delayed mortality. Cardiac function is particularly important for fast-swimming pelagic predators with high aerobic demand. Offspring for these species develop rapidly at relatively high temperatures, and their vulnerability to crude oil toxicity is unknown. We assessed the impacts of field-collected Deepwater Horizon (MC252) oil samples on embryos of three pelagic fish: bluefin tuna, yellowfin tuna, and an amberjack. We show that environmentally realistic exposures (1-15 µg/L total PAH) cause specific dose-dependent defects in cardiac function in all three species, with circulatory disruption culminating in pericardial edema and other secondary malformations. Each species displayed an irregular atrial arrhythmia following oil exposure, indicating a highly conserved response to oil toxicity. A considerable portion of Gulf water samples collected during the spill had PAH concentrations exceeding toxicity thresholds observed here, indicating the potential for losses of pelagic fish larvae. Vulnerability assessments in other ocean habitats, including the Arctic, should focus on the developing heart of resident fish species as an exceptionally sensitive and consistent indicator of crude oil impacts.

    View details for DOI 10.1073/pnas.1320950111

    View details for Web of Science ID 000334288600012

    View details for PubMedID 24706825

  • Effects of temperature acclimation on Pacific bluefin tuna (Thunnus orientalis) cardiac transcriptome AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY Jayasundara, N., Gardner, L. D., Block, B. A. 2013; 305 (9): R1010-R1020


    Little is known about the mechanisms underpinning thermal plasticity of vertebrate hearts. Bluefin tuna hearts offer a unique model to investigate processes underlying thermal acclimation. Their hearts, while supporting an endothermic physiology, operate at ambient temperature, and are presented with a thermal challenge when migrating to different thermal regimes. Here, we examined the molecular responses in atrial and ventricular tissues of Pacific bluefin tuna acclimated to 14°C, 20°C, and 25°C. Quantitative PCR studies showed an increase in sarcoplasmic reticulum Ca(2+) ATPase gene expression with cold acclimation and an induction of Na(+)/Ca(2+)-exchanger gene at both cold and warm temperatures. These data provide evidence for thermal plasticity of excitation-contraction coupling gene expression in bluefin tunas and indicate an increased capacity for internal Ca(2+) storage in cardiac myocytes at 14°C. Transcriptomic analysis showed profound changes in cardiac tissues with acclimation. A principal component analysis revealed that temperature effect was greatest on gene expression in warm-acclimated atrium. Overall data showed an increase in cardiac energy metabolism at 14°C, potentially compensating for cold temperature to optimize bluefin tuna performance in colder oceans. In contrast, metabolic enzyme activity and gene expression data suggest a decrease in ATP production at 25°C. Expression of genes involved in protein turnover and molecular chaperones was also decreased at 25°C. Expression of genes involved in oxidative stress response and programmed cell death suggest an increase in oxidative damage and apoptosis at 25°C, particularly in the atrium. These findings provide insights into molecular processes that may characterize cardiac phenotypes at upper thermal limits of teleosts.

    View details for DOI 10.1152/ajpregu.00254.2013

    View details for Web of Science ID 000326584200005

    View details for PubMedID 24005253

  • Exxon Valdez to Deepwater Horizon: Comparable toxicity of both crude oils to fish early life stages AQUATIC TOXICOLOGY Incardona, J. P., Swarts, T. L., Edmunds, R. C., Linbo, T. L., Aquilina-Beck, A., Sloan, C. A., Gardner, L. D., Block, B. A., Scholz, N. L. 2013; 142: 303-316
  • Microarray gene expression profiles from mature gonad tissues of Atlantic bluefin tuna, Thunnus thynnus in the Gulf of Mexico BMC GENOMICS Gardner, L. D., Jayasundara, N., Castilho, P. C., Block, B. 2012; 13


    Bluefin tunas are highly prized pelagic fish species representing a significant economic resource to fisheries throughout the world. Atlantic bluefin tuna (Thunnus thynnus) populations have significantly declined due to overexploitation. As a consequence of their value and population decline, T. thynnus has been the focus of considerable research effort concerning many aspects of their life history. However, in-depth understanding of T. thynnus reproductive biology is still lacking. Knowledge of reproductive physiology is a very important tool for determining effective fisheries and aquaculture management. Transcriptome techniques are proving powerful and provide novel insights into physiological processes. Construction of a microarray from T. thynnus ESTs sourced from reproductive tissues has provided an ideal platform to study the reproductive physiology of bluefin tunas. The aim of this investigation was to compare transcription profiles from the ovaries and testes of mature T. thynnus to establish sex specific variations underlying their reproductive physiology.Male and females T. thynnus gonad tissues were collected from the wild and histologically staged. Sub-samples of sexually mature tissues were also measured for their mRNA differential expression among the sexes using the custom microarray design BFT 4X44K. A total of 7068 ESTs were assessed for differential expression of which 1273 ESTs were significantly different (p<0.05) with >2 fold change in expression according to sex. Differential expression for 13 of these ESTs was validated with quantitative PCR. These include genes involved in egg envelope formation, hydration, and lipid transport/accumulation more highly expressed in ovaries compared with testis, while genes involved in meiosis, sperm motility and lipid metabolism were more highly expressed in testis compared with ovaries.This investigation has furthered our knowledge of bluefin tunas reproductive biology by using a contemporary transcriptome approach. Gene expression profiles in T. thynnus sexually mature testes and ovaries were characterized with reference to gametogenesis and potential alternative functions. This report is the first application of microarray technology for bluefin tunas and demonstrates the efficacy by which this technique may be used for further characterization of specific biological aspects for this valuable teleost fish.

    View details for DOI 10.1186/1471-2164-13-530

    View details for Web of Science ID 000310085500001

    View details for PubMedID 23036107

  • Spatial analysis of biomineralization associated gene expression from the mantle organ of the pearl oyster Pinctada maxima BMC GENOMICS Gardner, L. D., Mills, D., Wiegand, A., Leavesley, D., Elizur, A. 2011; 12


    Biomineralization is a process encompassing all mineral containing tissues produced within an organism. One of the most dynamic examples of this process is the formation of the mollusk shell, comprising a variety of crystal phases and microstructures. The organic component incorporated within the shell is said to dictate this architecture. However general understanding of how this process is achieved remains ambiguous. The mantle is a conserved organ involved in shell formation throughout molluscs. Specifically the mantle is thought to be responsible for secreting the protein component of the shell. This study employs molecular approaches to determine the spatial expression of genes within the mantle tissue to further the elucidation of the shell biomineralization.A microarray platform was custom generated (PmaxArray 1.0) from the pearl oyster Pinctada maxima. PmaxArray 1.0 consists of 4992 expressed sequence tags (ESTs) originating from mantle tissue. This microarray was used to analyze the spatial expression of ESTs throughout the mantle organ. The mantle was dissected into five discrete regions and analyzed for differential gene expression with PmaxArray 1.0. Over 2000 ESTs were determined to be differentially expressed among the tissue sections, identifying five major expression regions. In situ hybridization validated and further localized the expression for a subset of these ESTs. Comparative sequence similarity analysis of these ESTs revealed a number of the transcripts were novel while others showed significant sequence similarities to previously characterized shell related genes.This investigation has mapped the spatial distribution for over 2000 ESTs present on PmaxArray 1.0 with reference to specific locations of the mantle. Expression profile clusters have indicated at least five unique functioning zones in the mantle. Three of these zones are likely involved in shell related activities including formation of nacre, periostracum and calcitic prismatic microstructure. A number of novel and known transcripts have been identified from these clusters. The development of PmaxArray 1.0, and the spatial map of its ESTs expression in the mantle has begun characterizing the molecular mechanisms linking the organics and inorganics of the molluscan shell.

    View details for DOI 10.1186/1471-2164-12-455

    View details for Web of Science ID 000295880600001

    View details for PubMedID 21936921