The effects of temperature acclimation on swimming performance in the pelagic Mahi-mahi (Coryphaena hippurus)

Mahi-mahi (Coryphaena hippurus) are a highly migratory pelagic fish, but little is known about what environmental factors drive their broad distribution. This study examined how temperature influences aerobic scope and swimming performance in mahi. Mahi were acclimated to four temperatures spanning their natural range (20, 24, 28, and 32{\deg}C; 5-27 days) and critical swimming speed (Ucrit), metabolic rates, aerobic scope, and optimal swim speed were measured. Aerobic scope and Ucrit were highest in 28{\deg}C-acclimated fish. 20{\deg}C-acclimated mahi experienced significantly decreased aerobic scope and Ucrit relative to 28{\deg}C-acclimated fish (57 and 28% declines, respectively). 32{\deg}C-acclimated mahi experienced increased mortality and a significant 23% decline in Ucrit, and a trend for a 26% decline in factorial aerobic scope relative to 28{\deg}C-acclimated fish. Absolute aerobic scope showed a similar pattern to factorial aerobic scope. Our results are generally in agreement with previously observed distribution patterns for wild fish. Although thermal performance can vary across life stages, the highest tested swim performance and aerobic scope found in the present study (28{\deg}C), aligns with recently observed habitat utilization patterns for wild mahi and could be relevant for climate change predictions.Comment: 24 pages, 3 figures main text, 6 figures supplemental text, published in Frontiers in Marine Science https://www.frontiersin.org/articles/10.3389/fmars.2021.654276/ful

The effects of predator presence on nectarivorous bat foraging behavior

For many species, predator avoidance changes normal foraging behavior, altering optimal foraging strategies. In this study, foraging behavior of bats was examined by observing the number of feeding visits to control feeders in comparison to feeders with an artificial snake or owl in close proximity. Trials were also performed between snake and owl treatments to determine if one predator was more strongly avoided during feeding. Nectarivorous bats were found to exhibit predator avoidance behaviors for both snake and owl predators (P \u3c 0.0001, P \u3c 0.0001). There was no significant difference in trials comparing owl and snake avoidance, suggesting that bats do not fear one more than the other (P = 0.947). This study shows that predator presence must be taken into account along with search time, handling time, and caloric reward when evaluating optimal foraging models with necatarivorous bats. Para muchas especies, evitar al depredador cambia el comportamiento normal para forrajear, alterando las estrategias óptimas para forrajear. En este estudio, se examinó el comportamiento para forrajear de murciélagos observando el número de visitas al alimentarse en los comederos control en comparación con los comederos con una serpiente o un búho artificial cerca en proximidad. Se realizaron ensayos también entre los tratamientos con serpiente y con búho para determinar si un depredador fue evitado más fuertemente durante la alimentación. Se encontró que los murciélagos nectarívoros exhibieron comportamientos para evitar los depredadores tanto para el depredador serpiente y el búho (P \u3c 0.0001, P \u3c 0.0001). No hubo diferencia significativa en los ensayos que comparaban el evitar el búho y la serpiente, sugiriendo que los murciélagos no temen a uno más que al otro (P = 0.947). Este estudio demuestra que la presencia del depredador se debe tomar en cuenta junto con tiempo de búsqueda, manejando el tiempo, y la recompensa calórica cuando se evalúan los modelos óptimos con los murciélagos nectarívoros.https://digitalcommons.usf.edu/tropical_ecology/1395/thumbnail.jp

The effects of predator presence on nectarivorous bat foraging behavior

For many species, predator avoidance changes normal foraging behavior, altering optimal foraging strategies. In this study, foraging behavior of bats was examined by observing the number of feeding visits to control feeders in comparison to feeders with an artificial snake or owl in close proximity. Trials were also performed between snake and owl treatments to determine if one predator was more strongly avoided during feeding. Nectarivorous bats were found to exhibit predator avoidance behaviors for both snake and owl predators (P \u3c 0.0001, P \u3c 0.0001). There was no significant difference in trials comparing owl and snake avoidance, suggesting that bats do not fear one more than the other (P = 0.947). This study shows that predator presence must be taken into account along with search time, handling time, and caloric reward when evaluating optimal foraging models with necatarivorous bats. Para muchas especies, evitar al depredador cambia el comportamiento normal para forrajear, alterando las estrategias óptimas para forrajear. En este estudio, se examinó el comportamiento para forrajear de murciélagos observando el número de visitas al alimentarse en los comederos control en comparación con los comederos con una serpiente o un búho artificial cerca en proximidad. Se realizaron ensayos también entre los tratamientos con serpiente y con búho para determinar si un depredador fue evitado más fuertemente durante la alimentación. Se encontró que los murciélagos nectarívoros exhibieron comportamientos para evitar los depredadores tanto para el depredador serpiente y el búho (P \u3c 0.0001, P \u3c 0.0001). No hubo diferencia significativa en los ensayos que comparaban el evitar el búho y la serpiente, sugiriendo que los murciélagos no temen a uno más que al otro (P = 0.947). Este estudio demuestra que la presencia del depredador se debe tomar en cuenta junto con tiempo de búsqueda, manejando el tiempo, y la recompensa calórica cuando se evalúan los modelos óptimos con los murciélagos nectarívoros.https://digitalcommons.usf.edu/tropical_ecology/1395/thumbnail.jp

Physiological Downstream Consequences and Tradeoffs Associated with CO2 Compensation in Marine Fish

Fish are renowned for their ability to defend blood pH following exposure to elevated ambient CO2, a trait that has undoubtedly led to their ability to thrive successfully in a wide variety of habitats. While the defense of internal pH is critical for survival, the sustained elevation of HCO3- and PCO2 that occurs as a part of this compensatory response could potentially lead to sub-lethal impacts. This point is underscored by a growing number of studies demonstrating negative effects of CO2, even at relatively low CO2 tensions. The goal of this dissertation was to assess potential downstream consequences and/or tradeoffs associated with compensation for CO2 exposure in marine fish. This was achieved by examining the intestinal response of the Gulf toadfish (Opsanus beta) and the neurological response of the Spiny damselfish (Acanthochromis polyacanthus). Results from this dissertation indicate that ocean acidification relevant CO2 exposure levels predicted for year 2300 stimulates HCO3- loss through the intestine that is seemingly counterproductive to whole-animal acid-base balance. This base loss incurred an increased energetic demand on isolated intestinal tissue, providing evidence that low level CO2 exposure could lead to increases in baseline metabolism. Increasing the range of tested CO2 levels in the toadfish (up to 20,000 microatm CO2; ~2 kPa) led to the first broad characterization of intestinal transport physiology during elevated CO2. Despite a consistent increase in intestinal HCO3- secretion with CO2 exposure, the quantity and composition of intestinally produced carbonates did not change. Finally, the last portion of this dissertation involved a shift in focus to downstream impacts of CO2 compensation in the brain. To my knowledge, this dissertation provides the first direct measurements of extracellular and intracellular HCO3- in a coral reef species exposed to an ocean acidification relevant CO2 level (1900 microatm CO2; 0.19 kPa) that also induces a behavioral disturbance. These measurements support the hypothesis that CO2 compensation leads to changes in gradients across neuronal membranes that alter behavior. Overall, results from this dissertation indicate that CO2 compensation may lead to an unexpected sensitivity for certain tested endpoints. The potential for sub-lethal impacts on fish is particularly topical, since it is unclear how fast fish will adapt in response to oceans that are currently undergoing acidification at a rapid rate.</p

Physiological Downstream Consequences and Tradeoffs Associated with CO2 Compensation in Marine Fish

Fish are renowned for their ability to defend blood pH following exposure to elevated ambient CO2, a trait that has undoubtedly led to their ability to thrive successfully in a wide variety of habitats. While the defense of internal pH is critical for survival, the sustained elevation of HCO3- and PCO2 that occurs as a part of this compensatory response could potentially lead to sub-lethal impacts. This point is underscored by a growing number of studies demonstrating negative effects of CO2, even at relatively low CO2 tensions. The goal of this dissertation was to assess potential downstream consequences and/or tradeoffs associated with compensation for CO2 exposure in marine fish. This was achieved by examining the intestinal response of the Gulf toadfish (Opsanus beta) and the neurological response of the Spiny damselfish (Acanthochromis polyacanthus). Results from this dissertation indicate that ocean acidification relevant CO2 exposure levels predicted for year 2300 stimulates HCO3- loss through the intestine that is seemingly counterproductive to whole-animal acid-base balance. This base loss incurred an increased energetic demand on isolated intestinal tissue, providing evidence that low level CO2 exposure could lead to increases in baseline metabolism. Increasing the range of tested CO2 levels in the toadfish (up to 20,000 microatm CO2; ~2 kPa) led to the first broad characterization of intestinal transport physiology during elevated CO2. Despite a consistent increase in intestinal HCO3- secretion with CO2 exposure, the quantity and composition of intestinally produced carbonates did not change. Finally, the last portion of this dissertation involved a shift in focus to downstream impacts of CO2 compensation in the brain. To my knowledge, this dissertation provides the first direct measurements of extracellular and intracellular HCO3- in a coral reef species exposed to an ocean acidification relevant CO2 level (1900 microatm CO2; 0.19 kPa) that also induces a behavioral disturbance. These measurements support the hypothesis that CO2 compensation leads to changes in gradients across neuronal membranes that alter behavior. Overall, results from this dissertation indicate that CO2 compensation may lead to an unexpected sensitivity for certain tested endpoints. The potential for sub-lethal impacts on fish is particularly topical, since it is unclear how fast fish will adapt in response to oceans that are currently undergoing acidification at a rapid rate