Bioenergetics Model Research Articles

Heat stress and bleaching in corals: a bioenergetic model

AbstractThe coral-dinoflagellate endosymbiosis is based on nutrient exchanges that impact holobiont energetics. Of particular concern is the breakdown or dysbiosis of this partnership that is seen in response to elevated temperatures, where loss of symbionts through coral bleaching can lead to starvation and mortality. Here we extend a dynamic bioenergetic model of coral symbioses to explore the mechanisms by which temperature impacts various processes in the symbiosis and to enable simulational analysis of thermal bleaching. Our model tests the effects of two distinct mechanisms for how increased temperature impacts the symbiosis: 1) accelerated metabolic rates due to thermodynamics and 2) damage to the photosynthetic machinery of the symbiont caused by heat stress. Model simulations show that the model can capture key biological responses to different levels of increased temperatures. Moderately increased temperatures increase metabolic rates and slightly decrease photosynthesis. The slightly decreased photosynthesis rates cause the host to receive less carbon and share more nitrogen with the symbiont. This results in temporarily increased symbiont growth and a higher symbiont/host ratio. In contrast, higher temperatures cause a breakdown of the symbiosis due to escalating feedback that involves further reduction in photosynthesis and insufficient energy supply for $$\hbox {CO}_2$$ CO 2 concentration by the host. This leads to the accumulation of excess light energy and the generation of reactive oxygen species, eventually triggering symbiont expulsion and coral bleaching. Importantly, bleaching does not result from accelerated metabolic rates alone; it only occurs as a result of the photodamage mechanism due to its effect on nutrient cycling. Both higher light intensities and higher levels of DIN render corals more susceptible to heat stress. Conversely, heterotrophic feeding can increase the maximal temperature that can be tolerated by the coral. Collectively these results show that a bioenergetics model can capture many observed patterns of heat stress in corals, such as higher metabolic rates and higher symbiont/host ratios at moderately increased temperatures and symbiont expulsion at strongly increased temperatures.

Condition states in anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) revealed by energy and proximate composition relationships.

Energy content has long been proposed as a fundamental, integrated, and reliable indicator of the condition of individuals as it reflects past bioenergetics and influences future life-history traits. There is a direct biochemical link between energy density and body composition described by four main compounds in fish (protein, lipid, ash, and water), with proteins and lipids being the sources of energy. If relationships between water content, or lipid content, and energy density have been well described in relative terms, the absolute mass variations in the proximate composition have been overlooked and thus their interpretation is often equivocal. In our study, based on a large and unique dataset on the proximate composition and energy density of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) from sampling in the Bay of Biscay and the English Channel, we aimed to better explain the patterns between water content and other proximate components or energy density, based on the dynamics of proteins, lipids, and water absolute masses. For the first time, we defined good, intermediate, and poor condition states in wild fish, based on water content, corresponding to the different dynamics of lipids and proteins in the metabolism of individuals. Anchovy and sardine exhibited remarkably similar patterns of variation in the compounds and in the limits between the condition states with respect to water content. Those patterns revealed that water mass remained constant for a given fish size whatever its condition state, and that variability in water content only resulted from the variation in lipid and protein masses. Furthermore, the differential dynamics of proteins and lipids, with only lipids mobilized in the good condition state, only proteins in the poor condition state, and both proteins and lipids in the intermediate condition state, elucidates the nonlinear pattern observed in the relationship between energy density and water content. Overall, our results highlight the importance of monitoring the intraspecific variations in water content to predict the proximate composition and energy content in small pelagic fish and better assess individual and population conditions in changing ecosystems as well as to better parameterize bioenergetic models.

Consequences of terrestrial top predator control by Patagonian sheep farmers for coastal marine food webs

Most seabird species avoid predation by locating their breeding colonies in predator-free islands, inaccessible cliffs, capes, or on the mainland in Antarctica, the only continent without terrestrial predators. Departing from this general rule, a significant number of large Magellanic penguin (Spheniscus magellanicus) colonies exist nowadays in South American Atlantic mainland shores spanning a wide latitudinal range. Based on published radiocarbon dating of colonies, along with historical and archaeological records, we postulate that the current distribution of these colonies may be a response to predator eradication by sheep farmers. This would have made breeding habitats near marine food resources accessible and may have also reduced competition with neighboring colonies. We employed stable isotope analysis to estimate the penguin contribution to the diet of four pumas responsible for killing thousands of penguins in a breeding colony located within a coastal national park. Furthermore, we used a bioenergetic model to quantify the consumption of forage fish under different population distribution and abundance scenarios. We briefly discuss the implications of our results in the context of conservation policies aimed at establishing ecosystem baselines along the Patagonian shores.

Juvenile coho salmon growth differences track biennial pink salmon spawning patterns

Abstract Spawning Pacific salmon (Oncorhynchus spp.) provide marine‐derived resources (MDR) to freshwater food webs in the form of eggs, flesh and maggots that consume salmon carcasses, all of which positively impact stream‐dwelling fish growth. Pink salmon (O. gorbuscha) are widely distributed throughout coastal catchments along the North Pacific Ocean and display increased spawning abundances in odd years, owing to a fixed 2‐year life history. While many studies have found that foraging and growth of stream‐dwelling salmonids are improved by increased adult salmon spawning abundance, few studies have investigated the importance of alternating pink salmon spawning abundance between years. Here, we examined how patterns of pink salmon spawning abundance impact the foraging and growth of juvenile coho salmon (O. kisutch). First, we used bioenergetic simulations to generate a hypothesis that coho salmon growth would increase during odd relative to even years. We then collected empirical juvenile coho salmon diet and growth data from a Southeast Alaska catchment in 2021 (pink salmon spawning) and 2022 (no pink salmon spawning). Field data were compared against simulation predictions to understand impacts of biennial pink salmon spawning patterns on juvenile coho salmon growth. Empirical growth data revealed similar patterns to bioenergetic simulations. Age‐1 coho salmon grew 16.6 mm longer and 5.5 g heavier on average in 2021 compared to 2022. Age‐0 coho salmon displayed minor growth differences between years. These results support bioenergetic model predictions and suggest that patterns of pink salmon spawning abundance can impart interannual growth disparities to juvenile coho salmon. Moreover, we show that distinct spawning characteristics of Pacific salmon species are important when understanding patterns of MDR transfer and growth responses in stream fishes.

Assessing between-individual variability in bioenergetics modelling: Opportunities, challenges, and potential applications

Population dynamics is influenced by between-individual variability. Dynamic Energy Budget (DEB) theory is an appealing framework for assessing such a variability, yet DEB parameters have rarely been estimated at the individual level. Bayesian hierarchical models show promise for inferring individual variability in DEB parameters, thought computational challenges have limited their use due to the need to solve differential equations. Timely, Stan has emerged as a general-purpose statistical tool for fitting dynamic models. This paper introduces an analytical strategy using Bayesian parametric inference and hierarchical modelling to estimate individual-specific DEB parameters. Two biologically relevant DEB parameters were successfully estimated for 69 Gilt-head breams (Sparus aurata) with up to 11 measures of length and wet weight each. The estimated between-individual variability in these two DEB parameters explained well the observed patterns in length and weight at between- and within-individual levels. Moreover, data-simulation experiments highlighted the potential and limitations of our approach, suggesting that improved data collection could enable to increase precision and the number of DEB parameters that can be estimated at the individual level. This strategy can better represent between-individual variability in DEB parameters, which ultimately may improve forecasting of population dynamics after integrating DEB into population models.

Calibrating acceleration transmitters to quantify the seasonal energetic costs of activity in lake trout.

Bioenergetics models are powerful tools used to address a range of questions in fish biology. However, these models are rarely informed by free-swimming activity data, introducing error. To quantify the costs of activity in free-swimming fish, calibrations produced from standardized laboratory trials can be applied to estimate energy expenditure from sensor data for specific tags and species. Using swim tunnel respirometry, we calibrated acceleration sensor-equipped transmitting tags to estimate the aerobic metabolic rates (ṀO2) of lake trout (Salvelinus namaycush) at three environmentally relevant temperatures. Aerobic and swim performance were also assessed. Like other calibrations, we found strong relationships between ṀO2 and acceleration or swimming speed, and jackknife validations and data simulations suggest that our models accurately predict metabolic costs of activity in adult lake trout (~5% algebraic error and ~20% absolute error). Aerobic and swim performance metrics were similar to those reported in other studies, but their critical swimming speed was lower than expected. Additionally, lake trout exhibited a wide aerobic scope, suggesting that the avoidance of waters ≥15°C may be related to selection for optimal growing temperatures. The ability to quantify the free-swimming energetic costs of activity will advance our understanding of lake trout ecology and may yield improvements to bioenergetics model.

Predicting population-level impacts of projected climate heating on a temperate freshwater fish.

Climate heating has the potential to drive changes in ecosystems at multiple levels of biological organization. Temperature directly affects the inherent physiology of plants and animals, resulting in changes in rates of photosynthesis and respiration, and trophic interactions. Predicting temperature-dependent changes in physiological and trophic processes, however, is challenging because environmental conditions and ecosystem structure vary across biogeographical regions of the globe. To realistically predict the effects of projected climate heating on wildlife populations, mechanistic tools are required to incorporate the inherent physiological effects of temperature changes, as well as the associated effects on food availability within and across comparable ecosystems. Here we applied an agent-based bioenergetics model to explore the combined effects of projected temperature increases for 2100 (1.4, 2.7, and 4.4°C), and associated changes in prey availability, on three-spined stickleback (Gasterosteus aculeatus) populations representing latitudes 50, 55, and 60°N. Our results showed a decline in population density after a simulated 1.4°C temperature increase at 50°N. In all other modeled scenarios there was an increase (inflation) in population density and biomass (per unit area) with climate heating, and this inflation increased with increasing latitude. We conclude that agent-based bioenergetics models are valuable tools in discerning the impacts of climate change on wild fish populations, which play important roles in aquatic food webs.

Investigating the ecological and toxicological significance of Cyanox®53 recovered from intertidal sediments and varnish clam

We examined the ecological and toxicological implications of the microplastic, Cyanox®53, found in sediments and varnish clams across seven beaches in Burrard Inlet, British Columbia (BC). Using the simulation models embedded within Estimation Programs Interface (EPI) Suite™, the potential persistence, bioaccumulation, and toxicity of Cyanox®53 was assessed to evaluate the risk to varnish clams foraging on sediment containing this contaminant. Moreover, we used a bioenergetic model, based on the blue-listed surf scoter species, to estimate the risk of daily ingestion of Cyanox®53 per body weight in overwintering seabirds. Our findings indicate that varnish clams collected from Burrard Inlet accumulate on average 0.46 particles of Cyanox®53/clam, and based on bioenergetic modeling, results in surf scoters potentially consuming 78 (for males) to 83 (for females) pieces of Cyanox®53 daily from foraged varnish clams. EPI Suite™ predicted Cyanox®53 to be persistent, however, unlikely to bioaccumulate as a “traditional” chemical. Furthermore, the estimation of potential acute and chronic toxicity of Cyanox®53 to aquatic organism surrogates, such as fish, Daphnia magna, and green algae, was inconclusive due to model variability and limitations within EPI Suite™. To fully understand the potential risks of Cyanox®53 further investigation is warranted.

Incorporating ecological heterogeneity and intraspecific variation differentiates complex interactions between apex predators and stocked fish

Ecological heterogeneity and intraspecific variation can impact energy flow from the base of the food web to top predators. We evaluated the effect of intraspecific variation on estimates of lake trout ( Salvelinus namaycush) consumption of stocked kokanee (lacustrine sockeye salmon, Oncorhynchus nerka) in a 390 ha oligotrophic lake with two distinct basins. Lake trout stomach content analyses, stable isotope niche space, and catch rates indicated high intraspecific variation in resource use across habitats and basins. Intraspecific variation and ecological heterogeneity were incorporated into two bioenergetics modeling approaches: one lake-wide model, and one partitioned model that accounted for differences in lake trout diet composition and population size across habitats. The ecologically partitioned model highlighted that lake trout consumption was primarily in the epilimnion of one basin, while the lake-wide, unpartitioned model performed similarly but failed to provide ecological context for where that consumption occurred. Incorporating ecological heterogeneity and intraspecific variation into bioenergetic models can more accurately represent top predators foraging patterns across habitats and inform management actions to mitigate impacts to stocked fish.

Wearable heart rate sensing and critical power-based whole-body fatigue monitoring in the field

Whole-body fatigue (WBF) presents a concerning risk to construction workers, which can impact function and ultimately lead to accidents and diminished productivity. This study proposes a new WBF monitoring technique by applying the Critical Power (CP) model, a bioenergetic model, with a wrist-worn heart rate sensor. The authors modified the CP model to calculate WBF from the percentage of heart rate reserve (%HRR) and generated a personalized model via WBF perception surveys. Data were collected for two days from 33 workers at four construction sites. The results showed that the proposed technique can monitor field workers’ perceived WBF with a mean absolute error of 12.8% and Spearman correlation coefficient of 0.83. This study, therefore, demonstrates the viability of wearable WBF monitoring on construction sites to support programs aimed at improving workplace safety and productivity.

Using heart rate and acceleration biologgers to estimate winter activity costs in free-swimming largemouth bass

Winter is a critical period for largemouth bass (Micropterus nigricans) with winter severity and duration limiting their population growth at northern latitudes. Unfortunately, we have an incomplete understanding of their winter behaviour and energy use in the wild. More winter-focused research is needed to better understand their annual energy budget, improve bioenergetics models, and establish baselines to assess the impacts of climate warming; however, winter research is challenging due to ice cover. Implantable tags show promise for winter-focused research as they can be deployed prior to ice formation. Here, using swim tunnel respirometry, we calibrated heart rate and acceleration biologgers to enable estimations of metabolic rate (ṀO2) and swimming speed in free-swimming largemouth bass across a range of winter-relevant temperatures. In addition, we assessed their aerobic and swim performance. Calculated group thermal sensitivities of most performance metrics indicated the passive physicochemical effects of temperature, suggesting little compensation in the cold; however, resting metabolic rate and critical swimming speed showed partial compensation. We found strong relationships between acceleration and swimming speed, as well as between ṀO2 and heart rate, acceleration, or swimming speed. Jackknife validations indicated that these modeled relationships accurately estimate swimming speed and ṀO2 from biologger recordings. However, there were relatively few reliable heart rate recordings to model the ṀO2 relationship. Recordings of heart rate were high-quality during holding but dropped during experimentation, potentially due to interference from aerobic muscles during swimming. The models informed by acceleration or swimming speed appear to be best suited for field applications.

Insights into the diet and feeding behavior of immature polar cod (Boreogadus saida) from the under-ice habitat of the central Arctic Ocean.

Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea-ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under-ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immature B. saida and the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth of B. saida in this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immature B. saida may be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival of B. saida will not depend on prey presence alone, but also on prey catchability, digestibility, and energy content.

Untangling the complex food webs of tropical rainforest streams.

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems. Here, we first characterised a tropical stream meta-food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population-level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka-Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability. The model resulted in a stable meta-food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta-food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non-specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale. Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size-dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human-impacted landscapes.

Marine aquaculture spatial planning on market orientation for Pacific oyster in Shandong, China

Accessing the production value is essential to the selection of suitable sites for aquaculture farms. This study employed a Dynamic Energy Budget (DEB) model and used market-oriented indicators, including shell length, flesh weight, condition index and minimum farming duration, to analyze the suitability for Pacific oyster aquaculture in offshore Shandong, China. Chlorophyll a (Chl-a) concentration, Total Suspended Sediment (TSS) concentration, and Sea Surface Temperature (SST) were extracted by remote sensing and used as forcing variables in the bioenergetic model. Four market-oriented indicators and five zones in the study area were chosen to develop a Suitable Market-Aquaculture site-selection model (SMASM) and estimate the oyster farming suitability. The results demonstrated that Sanggou Bay exhibits high potential for Pacific oyster year-round aquaculture. Eastern Laizhou Bay is suitable for the autumn-spring fattening culture of adult oysters. Laoshan Bay and Changshan Islands are suitable for promoting rapid growth in juvenile oysters. The results of our model were consistent with the oyster production value in Shandong, showing an overall increasing trend except for the anomalous value observed in 2019. Sudden drops in water temperature, red tides, and significant increases in turbidity can exert detrimental effects on oyster production, which has been evidenced to be influenced by Super Typhoon Lekima in 2019. Although this study concentrated on a specific geographical region, the model could be applied to other regions to develop market-oriented suitability management for species and environments worldwide.

Effects of the 2014-2016 marine heatwave on Steller sea lions in the Gulf of Alaska and implications for top-down forcing

Marine heatwaves can have rapid and wide-reaching biological and economic impacts. We explored the effects of a recent severe marine heatwave on Steller sea lions in the Gulf of Alaska and Southeast Alaska using biennial counts of pups and non-pups from aerial surveys of terrestrial sites between 2013 and 2019. We combined count data with a bioenergetic model to explore the potential effects of Steller sea lion responses to the heatwave on prey populations. Pup production was anomalously low in the eastern and central Gulf in 2017 following the end of the heatwave in 2016, with a 33.5 and 17.4% reduction from 2015 values respectively. Based on the energetic costs of pregnancy and lactation, these reductions in pup production represent an average difference of 6121 metric tons of prey between 2015 and 2017. Non-pup counts were anomalously low in Southeast Alaska in 2017 and in the central and eastern Gulf in 2019. No effects were detected in the western Gulf, although they could have been masked by the variability in count estimates. Such changes in non-pup abundance had the potential to induce changes in predation pressure on the order of thousands to tens of thousands of metric tons of prey, even when responses were assumed to persist for a relatively short time (1 yr or less). In addition to these short-term effects, declining counts of non-pups from the eastern Gulf and Southeast Alaska occurred following the 2014-2016 heatwave, suggesting more lasting effects on Steller sea lion populations and top-down forcing from these regions.

Killer whale respiration rates.

Measuring breathing rates is a means by which oxygen intake and metabolic rates can be estimated to determine food requirements and energy expenditure of killer whales (Orcinus orca) and other cetaceans. This relatively simple measure also allows the energetic consequences of environmental stressors to cetaceans to be understood but requires knowing respiration rates while they are engaged in different behaviours such as resting, travelling and foraging. We calculated respiration rates for different behavioural states of southern and northern resident killer whales using video from UAV drones and concurrent biologging data from animal-borne tags. Behavioural states of dive tracks were predicted using hierarchical hidden Markov models (HHMM) parameterized with time-depth data and with labeled tracks of drone-identified behavioural states (from drone footage that overlapped with the time-depth data). Dive tracks were sequences of dives and surface intervals lasting ≥ 10 minutes cumulative duration. We calculated respiration rates and estimated oxygen consumption rates for the predicted behavioural states of the tracks. We found that juvenile killer whales breathed at a higher rate when travelling (1.6 breaths min-1) compared to resting (1.2) and foraging (1.5)-and that adult males breathed at a higher rate when travelling (1.8) compared to both foraging (1.7) and resting (1.3). The juveniles in our study were estimated to consume 2.5-18.3 L O2 min-1 compared with 14.3-59.8 L O2 min-1 for adult males across all behaviours based on estimates of mass-specific tidal volume and oxygen extraction. Our findings confirm that killer whales take single breaths between dives and indicate that energy expenditure derived from respirations requires using sex, age, and behavioural-specific respiration rates. These findings can be applied to bioenergetics models on a behavioural-specific basis, and contribute towards obtaining better predictions of dive behaviours, energy expenditure and the food requirements of apex predators.

A rapid monitoring protocol to estimate unharvested corn biomass in waterfowl impoundments

AbstractConservation planners use bioenergetic models to develop habitat objectives that satisfy energetic demands of waterfowl during nonbreeding periods. In turn, natural resource managers should estimate yield and availability of natural and cultivated waterfowl forage to monitor contributions to objectives and support adaptive resource management. Because bioenergetic models are particularly sensitive to unharvested flooded croplands, we developed a rapid methodology to estimate biomass of unharvested flooded corn (Zea mays) and tested our methodology in impounded corn fields planted and flooded in western Tennessee during autumn and winter of 2019–2021. We evaluated accuracy of our rapid assessment method and conducted simulations to assess variance‐bias trade‐offs relative to sample size. Rapid assessments lasted 20 min ± 10 minutes per field. Our rapid assessment method underestimated number of kernels per ear by 2.6% ± 0.5%. After adjusting for underestimation bias, corn biomass across all surveys was 5,500 kg/ha ± 250 kg/ha, which is similar yield to previous literature from waterfowl impoundment fields. Sampling 15 ears per field allowed field biomass to be estimated within acceptable accuracy (i.e., variance [SE] of mean percent error <1.8%). We recommend our rapid yield assessment method be incorporated into habitat monitoring protocols to efficiently and precisely estimate corn biomass for improved conservation planning initiatives. Additionally, our rapid assessment method allows managers to monitor field yield rapidly, enabling estimates of corn depletion and availability throughout the nonbreeding season for waterfowl to support management decisions.

Accelerometer-based swimming metabolism of smallmouth bass (Micropterus dolomieu).

Bioenergetics is informative for a range of fundamental and applied resource management questions, but findings are often constrained by a lack of ecological realism due to the challenges of remotely estimating key parameters such as metabolic rate. To enable field applications, we conducted a calibration study with smallmouth bass (Micropterus dolomieu, 0.7-2 kg) surgically implanted with accelerometer transmitters and exposed to a ramp-Ucrit swimming protocol in a swim tunnel respirometer across a range of water temperatures (6, 12, 18, and 24°C). There was an exponential increase in fish acceleration with swimming speed, and acceleration per speed was higher in smaller fish and female fish, and at colder temperatures. Mass-specific fish metabolic rate (MO2; mg O2 kg-1 h-1) increased with swimming speed, acceleration, and temperature, and decreased with fish mass, which when combined were strong predictors of MO2. Maximum metabolic rate (MMR) was estimated to peak at 22°C, but maximum sustained swimming speed (Ucrit) remained high at c. 90-100 m s-1 above 20°C, based on second-order polynomial functions. Aerobic scope (AS) estimates peaked at 20°C (>90% AS at 17-24°C; >50% AS at 11-28°C). Males exhibited marginally higher MMR, AS, and Ucrit than females at higher temperatures. Larger fish generally exhibited higher Ucrit, but smaller fish had a marginally broader performance range (AS, Ucrit) among temperatures, benefiting from higher MMR despite a steeper increase in resting metabolic rate with temperature. These findings enable field studies to estimate metabolic metrics of smallmouth bass in situ to characterize their ecological energetics and inform bioenergetics models.

Differences in Brain Region Mitochondrial Bioenergetics Detected Using CK Clamp

The brain is a non-uniform organ comprised of discrete structures of varying function and cell composition. The differing function of brain regions ostensibly would necessitate disparate energetic demands, thereby suggesting brain bioenergetics would be different among brain regions. This study aimed to address whether brain regions indeed have different bioenergetics by evaluating substrate preference, fuel-specific mitochondrial function at physiologically relevant energy demands as well as associated membrane potential and electron conductance using high-resolution respirometry (Oroboros O2k) in the frontal cortex, hypothalamus, and hippocampus. We hypothesize there will be different bioenergetics among brain regions. Substrate preference was established using a substrate-uncoupler-inhibitor-titration (SUIT) with additions, in order: ADP, Pyruvate/Malate, UK5099, Octanoylcarnitine, Rotenone, Succinate, and Antimycin A. There was no statistically significant interaction between region and substrate (p=0.15) nor a main effect of region (p=0.91), however, there was a main effect of substrate in which pyruvate/malate (+275%) and succinate/rotenone (+170%) had significantly greater respiration than octanoylcarnitine, independent of region (p<0.001). Given the results of the SUIT test, pyruvate/malate was used for subsequent tests. The SUIT method relies upon saturating ADP levels and non-physiological ATP:ADP concentration ratios, the extent to which this test obscures the interpretation of brain region respiration is unclear. Instead, an alternative approach that leverages the enzymatic reaction of creatine kinase and phosphocreatine to assess mitochondrial respiration and membrane potential at clamped physiological ATP:ADP ratios, “CK Clamp,” was used. Function of mitochondria with a pyruvate fuel was then evaluated in all three brain regions in which energetic demand was clamped at ΔGATP = -12.87 (high demand), -14.08, -14.5, and -14.85 (low demand). There was a statistically significant interaction between brain region and clamped ΔGATP values (p = 0.02). Frontal cortex displayed higher respiration than hippocampus at -12.87 ΔGATP (33%). There was no statistically significant interaction between region and clamp for mitochondrial membrane potential assessed during the CK clamp (p=0.16), however there was a significant main effect of clamped ΔGATP (p<0.001) in which membrane potential increased (i.e., hyperpolarized) as energetic demand decreased. This agrees with the bioenergetic model that a decrease in energetic demand increases the proton motive force (aka, hyperpolarization), thereby applying a backpressure on the electron transport chain, slowing respiration. Electron conductance was then assessed by calculating the slope of respiration versus clamped ΔGATP. Electron conductance was greater in the frontal cortex than hypothalamus (+70%, p = 0.015). The conclusion of this study is there are differences in mitochondrial bioenergetics among brain regions and the CK clamp was more sensitive at detecting these differences than the SUIT method. None. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of joint invasion: How co-invaders affect each other's success in model food webs?

While there has been considerable research on the interactions between invasive and native species, and on the impact of invasive species on the resident community, there has been less focus on exploring the relationship and interactions among invasive species themselves. Nevertheless, it is widely recognised that invasive species can have either positive or negative effects on each other, as well as neutral outcomes. In the present theoretical study, we compared the success of two invasive non-native species in two scenarios: when they invaded the resident food web separately and simultaneously. We examined the correlations between their direct and indirect ecological relationships and their topological positions in the food web, with the varying outcomes of joint invasion. Using the Allometric Bioenergetic Model (ABM) for dynamic simulations, we determined the success of invasion (presence or absence of invaders) and, in the case of successful co-invasion, the direction of their biomass change, comparing separate and simultaneous invasion scenarios. We studied the relationships between these variables after detailed numerical simulations with variable key parameters of the model.We found that direct and indirect ecological relationships between the two invaders can significantly modifiy the outcomes of the invasion scenarios. For example, their predator-prey relationship increases the probability of invasion success for both invaders, but at the same time the equilibrium biomass of at least one of them is likely to be reduced compared to its separate invasion. Trophic cascade or competitive relationship between them during simultaneous invasion also affects their success rate, with the former having a positive effect and the latter a negative one, as they can hinder each other's spread. Further, we found that higher trophic level and lower betweenness centralities of the invaders reduces the likelihood of invasion success regardless of the presence or absence of another invasive species. The results of the study can be tested experimentally in micro- and mesocosms.