24th Denman Undergraduate Research Forum (2019)

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    The effect of turbidity on the transition from social to sexual behavior in an African cichlid fish
    (2019-02-20) Hrabak, Taylor; Gray, Suzanne
    Increasing turbidity is among the leading environmental stressors threatening aquatic biodiversity worldwide. To cope with elevated turbidity (i.e. suspended particulates in the water) and associated changes to the visual environment, some fish have demonstrated altered behavioral, morphological, and physiological characteristics. The wide-ranging East African cichlid fish, Psuedocrenilabrus multicolor victoriae, relies heavily on visual cues for reproduction: females choose mates based on male color and courtship displays. However, as turbidity has increased over recent decades due to deforestation and sediment run-off, their ability to detect potential mates has decreased. The objective of this study was to determine if exposure to increased turbidity influences the timing of the transition from the juvenile stage to sexual maturity. If elevated turbidity reduces the ability of P. multicolor to detect potential mates, then we expect delays in the shift from growth to reproduction. To determine the timing of this ontogenetic shift, the behavior of 10 independent P. multicolor broods, each divided in two and reared under clear or turbid conditions, was observed weekly for 25 weeks. Turbidity was maintained at ~10 NTU for the duration of the experiment in the turbid treatment, mimicking turbidity levels observed in natural rivers. All aquaria were filmed once a week for 20 minutes using Canon G16 cameras. The first 10 minutes of each video was used as an acclimation period (i.e. to the video set-up) and the last 10 minutes analyzed for social, aggressive, and reproductive behaviors. A clear signal that fish have reached sexual maturity is the presence of broods, therefore, the first incidence of brooding in each aquarium was recorded (i.e. number of days post-hatch; dph). Fish in clear aquaria began brooding earlier (Mean +/- SE = 114.75 +/- 7.58 dph) than fish turbid aquaria (Mean +/- SE= 125.29 +/- 8.10 dph). The 10.5 day difference between first broods in clear and turbid treatments indicates a difference in age of the ontogenetic shift from growth to reproduction in fish reared in turbid compared to clear waters. Delayed reproduction in degraded water quality could have fitness consequences for P. multicolor populations and other species facing elevated turbidity globally.
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    Visual Detection Thresholds of Walleye Under Varying Turbidity
    (2019-02-20) Oppliger, Andrew; Gray, Suzanne
    Anthropogenic alteration of freshwater systems is contributing to the loss of aquatic biodiversity globally and in Ohio. Among the key stressors affecting freshwaters is elevated turbidity in the form of suspended sediments and algae. Increasing turbidity is likely to alter the visual ecology (e.g. prey detection) of Lake Erie Walleye (Sander vitreus) through changes to the visual environment. Knowledge of how individual Walleye respond to decreased water clarity will provide a framework for understanding expected community and population level interactions. The objective of this study was to determine if the visual sensitivity (i.e. ability of an animal to distinguish between an object and its background) of Walleye is altered by sedimentary and algal turbidity, two forms of turbidity that are increasing in Lake Erie. A secondary objective was to determine if varying turbidity types differentially influence visual sensitivity of juvenile and adult Walleye. To determine how visual sensitivity is impacted by turbidity, optomotor response tests were used to establish visual detection thresholds under algal and sedimentary turbidity treatments. Turbidity was increased incrementally in a cylindrical tank until the fish stopped following a rotating black and white screen, indicating an inability to distinguish between the bars of the screen. Visual detection thresholds were significantly higher in sedimentary compared to algal turbidity for both adult (mean sediment +/- SE = 89.36 +/- 2.38, mean algae +/- SE = 38.12 +/- 0.55) and juvenile (mean sediment +/- SE = 99.98 +/- 5.31, mean algae +/- SE = 40.35 +/- 2.44) Walleye. Within treatment (turbidity type), no significant difference between the visual detection thresholds of juvenile and adult Walleye was found. These results indicate that algae may disrupt vision at a much lower level than suspended sediment. Walleye are a vital species in the Lake Erie sport fishing industry, as well as an ecological top predator, thus understanding the potential impacts of changing turbidity levels and types on the visual ecology of Walleye allows us to understand the dynamics of how populations may respond to increasing anthropogenic turbidity.
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    Antibiotic Treatment of Persistent Pseudomonas aeruginosa Infections
    (2019-02-20) Li, Anthony; Stoodley, Paul
    Pseudomonas aeruginosa is an opportunistic pathogen associated with infections due to severe burns and in cystic fibrosis patients. Treatment against these bacteria can be difficult because of the increase in antimicrobial resistance and formation of biofilms. P. aeruginosa lawn biofilms when treated with tobramycin showed generation of antibiotic tolerant cells. These persisters are protected within the biofilm, as a result these cells are often tolerant toward antibiotics. The persister cells under favorable growth conditions grow and can re-establish infection. The objective of this study was to test different class of antibiotics for generation of persister cells. To test for the efficacy of antibiotics, a bioluminescent strain of P. aeruginosa, XEN41, was tested against various class of antibiotics including aminoglycosides, fluoroquinolones, carbapenems, and polymyxins. Preformed biofilms (24 h) of XEN41 were formed on tryptic soy agar (TSA). Antibiotic containing beads (4.8mm diameter) made from calcium sulfate were used to deliver the antibiotic. In vivo imaging system (IVIS) was used to test the response of the antibiotic towards Xen41. The benefit of using the bioluminescent strain is that clear differentiation of zone of clearance and the zone of growth is evident using IVIS. The results showed that Xen41 is susceptible to ciprofloxacin, colistin, gentamicin, and tobramycin and resistant to rifampicin and meropenem. Of the susceptible antibiotics, gentamicin and tobramycin (aminoglycosides) produced persister colonies. These colonies appeared even with high concentrations of antibiotics up to 50ug/mL; the MIC of P. aeruginosa is around 4ug/mL. In conclusion, aminoglycosides facilitate generation of persister cells and combination of antibiotic may be used to treat P. aeruginosa infections, given that the bacteria are not resistant to the antibiotic.
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    Effect of Insecticides, Fungicides, and Adjuvant Combinations on Honey Bee Brood Development
    (2019-02-20) Kordecki, Hilary; Kruse, Nick; Lin, Chia-Hua; Johnson, Reed; Johnson, Reed
    Honey bees are highly valued in the booming almond industry because they serve as vital pollinators needed to cross-pollinate almond flowers. California’s almond industry produces approximately 80% of the world’s almonds. Therefore, a significant portion of America’s commercial honey bee colonies are transported to pollinate California’s almonds every year. Various fungicides and insecticides, along with adjuvants are used to minimize crop damage from various diseases and pests. Recent research has demonstrated that these preventative treatments negatively impact honey bee colony health. This is problematic for beekeepers and the almond industry who rely on strong, healthy colonies. In this study we investigate the effects of almond pesticides and an adjuvant on larval mortality. Honey bee larvae were artificially reared to adulthood while being fed a treated diet simulating exposure to commonly used products. First, various concentrations of an organosilicone-based nonionic surfactant with methylated seed oil known as Dyne-Amic were added to the diet of young larvae. The results of the brood mortality were used to plot a dose-response curve for Dyne-Amic to determine lethal and sublethal concentrations. To investigate whether Dyne-Amic increases the toxicity of pesticides to honey bee larvae, a sublethal dose of Dyne-Amic was added with various combinations of insecticides and fungicides to observe any compounding effects. Preliminary results suggest that the label recommended application concentration of Dyne-Amic is 1.9X times higher than the maximum sublethal concentration. However, we did not observe an increase in mortality when Dyne-Amic was added to insecticides and fungicides at sublethal concentrations, alone or in combinations. Further trials will expand to evaluate effects of exposure at field-relevant concentrations. The results of this research are incredibly important and helpful for the almond growers in California, as well as any agricultural practice that utilizes combinations of insecticides, fungicides, and adjuvants. Particularly for almond growers, understanding these chemical interactions can help improve the efficiency of bee pollination services and reduce costs. Product label application instructions may be refined for common insecticides, fungicides, and the surfactant Dyne-Amic as a result of these findings.