The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species

Resource polymorphism is common across taxa and can result in alternate ecotypes with specific morphologies, feeding modes, and behaviors that increase performance in a specific habitat. This can result in high intraspecific variation in the expression of specific traits and the extent to which these traits are correlated within a single population. Although metabolic rate influences resource acquisition and the overall pace of life of individuals it is not clear how metabolic rate interacts with the larger suite of traits to ultimately determine individual fitness. We examined the relationship between metabolic rates and the major differences (habitat use, morphology, and resource use) between littoral and pelagic ecotypes of European perch (Perca fluviatilis) from a single lake in Central Sweden. Standard metabolic rate (SMR) was significantly higher in pelagic perch but did not correlate with resource use or morphology. Maximum metabolic rate (MMR) was not correlated with any of our explanatory variables or with SMR. Aerobic scope (AS) showed the same pattern as SMR, differing across habitats, but contrary to expectations, was lower in pelagic perch. This study helps to establish a framework for future experiments further exploring the drivers of intraspecific differences in metabolism. In addition, since metabolic rates scale with temperature and determine predator energy requirements, our observed differences in SMR across habitats will help determine ecotype-specific vulnerabilities to climate change and differences in top-down predation pressure across habitats

Comparison of Xpert MTB/RIF with Other Nucleic Acid Technologies for Diagnosing Pulmonary Tuberculosis in a High HIV Prevalence Setting: A Prospective Study

In this prospective, real-world cohort study nested within a national screening program for tuberculosis, Lesley Scott and colleagues compare the performance of Xpert MTB/RIF on a single sputum sample with different TB sputum detection technologies

Fish population responses to climate change : Causes and consequences

Lake environments are heterogeneous, and animals show a variety of adaptations to deal with this heterogeneity. Fish often show intraspecific variation in diet, metabolism, and behavior, corresponding to their habitat use. Studies on climate change often ignore this heterogeneity and its importance in determining population-level responses to climate change.  This thesis can be broken into two interacting pieces. First, my goal was to assess how water color and temperature changes impact the size, number, and distribution of a common predator, Eurasian perch (Perca fluviatilis), in Swedish lakes. Second, I aimed to examine whether metabolism and resource use differed between lake habitats, corresponding with documented patterns of polymorphism and whether diet differences were maintained along a thermal and water color gradient. By combining the information gleaned from these studies, the overarching goal of my thesis is to better understand how climate change will impact fish populations and how intraspecific variance in these responses will impact ecosystem functioning.  I found that warming and browning will likely decrease fish biomass but via different mechanisms. Warming reduces average fish size through its impact on metabolism and energy requirements. Browning decreases fish abundance likely due to its negative effects on resource abundance, increasing mortality, and decreasing reproductive effort. Though warming decreases biomass at the lake level, pelagic perch abundance increases. I found that these pelagic perch have higher metabolic rates and, especially in darker lakes, rely heavily on pelagic resources. As more fish shift into the pelagic habitat, this will increase top-down pressure on pelagic resources and decrease energy transfer from littoral to pelagic habitats altering energy flow within lakes.  Variation in metabolic phenotype across habitats, combined with the positive scaling of metabolic rates with temperature, will likely determine which fish can persist under climate change scenarios. Studies that measure this variation rely heavily on respirometry to measure fish metabolism. I found that current respirometry methods underestimate maximum metabolic rate and suggest an updated method to improve the accuracy of future studies.  Overall, I conclude that habitats should be examined separately to better understand population-level responses to climate change. Perch caught in different habitats have different energy requirements and respond differently to warming and browning. These differences will affect the distribution of top-down pressure and habitat coupling within lake ecosystems, with implications for broader ecosystem functioning in the future.

Chasing away accurate results : exhaustive chase protocols underestimate maximum metabolic rate estimates in European perch Perca fluviatilis

Metabolic rates are one of many measures that are used to explain species' response to environmental change. Static respirometry is used to calculate the standard metabolic rate (SMR) of fish, and when combined with exhaustive chase protocols it can be used to measure maximum metabolic rate (MMR) and aerobic scope (AS) as well. While these methods have been tested in comparison to swim tunnels and chambers with circular currents, they have not been tested in comparison with a no‐chase control. We used a repeated‐measures design to compare estimates of SMR, MMR and AS in European perch Perca fluviatilis following three protocols: (a) a no‐chase control; (b) a 3‐min exhaustive chase; and (c) a 3‐min exhaustive chase followed by 1‐min air exposure. We found that, contrary to expectations, exhaustive chase protocols underestimate MMR and AS at 18°C, compared to the no‐chase control. This suggests that metabolic rates of other species with similar locomotorty modes or lifestyles could be similarly underestimated using chase protocols. These underestimates have implications for studies examining metabolic performance and responses to climate change scenarios. To prevent underestimates, future experiments measuring metabolic rates should include a pilot with a no‐chase control or, when appropriate, an adjusted methodology in which trials end with the exhaustive chase instead of beginning with it

The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species

1.      Resource polymorphism is common across taxa and can result in alternate ecotypes with specific morphologies, feeding modes, and behaviours that increase performance in a specific habitat. This can result in high intraspecific variation in the expression of specific traits and the extent to which these traits are correlated within a single population. Although metabolic rate influences resource acquisition and the overall pace of life of individuals it is not clear how metabolic rate interact with the larger suite of traits to ultimately determine individual fitness. 2.      We examined the relationship between metabolic rates and the major differences (habitat use, morphology, and resource use) between littoral and pelagic ecotypes of European perch (Perca fluviatilis) from a single lake in Central Sweden. 3.      Standard metabolic rate (SMR) was significantly higher in pelagic perch but did not correlate with resource use or morphology. Maximum metabolic rate (MMR) was not correlated with any of our explanatory variables or with SMR. Aerobic scope (AS) showed the same pattern as SMR, differing across habitats, but contrary to expectations was lower in pelagic perch. 4.      This study helps to establish a framework for future experiments further exploring the drivers of intraspecific differences in metabolism. In addition, since metabolic rates scale with temperature and determine predator energy requirements, our observed differences in SMR across habitats will help determine ecotype-specific vulnerabilities to climate change and differences in top-down predation pressure across habitats

Intraspecific differences in metabolic rates shape carbon stable isotope trophic discrimination factors of muscle tissue in the common teleost Eurasian perch (Perca fluviatilis)

1. Stable isotopes represent a unique approach to provide insights into the ecology of organisms. delta C-13 and delta N-15 have specifically been used to obtain information on the trophic ecology and food-web interactions. Trophic discrimination factors (TDF, Delta C-13 and Delta N-15) describe the isotopic fractionation occurring from diet to consumer tissue, and these factors are critical for obtaining precise estimates within any application of delta C-13 and delta N-15 values. It is widely acknowledged that metabolism influences TDF, being responsible for different TDF between tissues of variable metabolic activity (e.g., liver vs. muscle tissue) or species body size (small vs. large). However, the connection between the variation of metabolism occurring within a single species during its ontogeny and TDF has rarely been considered. 2. Here, we conducted a 9-month feeding experiment to report Delta C-13 and Delta N-15 of muscle and liver tissues for several weight classes of Eurasian perch (Perca fluviatilis), a widespread teleost often studied using stable isotopes, but without established TDF for feeding on a natural diet. In addition, we assessed the relationship between the standard metabolic rate (SMR) and TDF by measuring the oxygen consumption of the individuals. 3. Our results showed a significant negative relationship of SMR with Delta C-13, and a significant positive relationship of SMR with Delta N-15 of muscle tissue, but not with TDF of liver tissue. SMR varies inversely with size, which translated into a significantly different TDF of muscle tissue between size classes. 4. In summary, our results emphasize the role of metabolism in shaping-specific TDF (i.e., Delta C-13 and Delta N-15 of muscle tissue) and especially highlight the substantial differences between individuals of different ontogenetic stages within a species. Our findings thus have direct implications for the use of stable isotope data and the applications of stable isotopes in food-web studies

Linking behavioural type with cannibalism in Eurasian perch

The propensity to kill and consume conspecifics (cannibalism) varies greatly between and within species, but the underlying mechanisms behind this variation remain poorly understood. A rich literature has documented that consistent behavioural variation is ubiquitous across the animal kingdom. Such inter-individual behavioural differences, sometimes referred to as personality traits, may have far-reaching ecological consequences. However, the link between predator personality traits and the propensity to engage in cannibalistic interactions remains understudied. Here, we first quantified personality in Eurasian perch (Perca fluviatilis), measured as activity (time spent moving) and sociability (time spent near conspecifics). We then gave perch of contrasting behavioural types the option to consume either conspecific or heterospecific (roach, Rutilus rutilus) prey. Individual perch characterized by a social-active behavioural phenotype (n = 5) selected roach before being cannibalistic, while asocial-inactive perch (n = 17) consumed conspecific and heterospecific prey evenly. Thus, asocial-inactive perch expressed significantly higher rates of cannibalism as compared to social-active individuals. Individual variation in cannibalism, linked to behavioural type, adds important mechanistic understanding to complex population and community dynamics, and also provides insight into the diversity and maintenance of animal personality

Conspecific boldness and predator species determine predation-risk consequences of prey personality

Abstract: Individual variation in the behavior of prey can influence predation risk in complex ways. We ran individual roach (Rutilus rutilus), a common freshwater fish, through a standard refuge emergence protocol to characterize their boldness, a key animal personality trait. We then paired a bold and a shy roach and exposed the pair to one of two predator species that have contrasting hunting modes to ascertain how personality traits shaped their survival during predator encounters. When a paired bold and shy prey fish interacted with a perch predator (active foraging mode), bold and shy prey were consumed in almost equal numbers. However, pike predators (ambush foraging mode) selectively consumed more shy prey, and prey body size and boldness score both contributed significantly to which prey fish was eaten. Our findings support the idea that multiple predators with different foraging modes, and hence differential selection on prey personality, could contribute to maintaining variation in personality in prey populations. Furthermore, for social species, including shoaling fish, the ultimate consequences of an individual’s personality may depend upon the personality of its nearby conspecifics. Significance statement: Animals of the same species often look similar, but individuals show differences in their behavior that can have important consequences, for instance when these individuals interact with predators. The common roach is a freshwater fish that shows inter-individual variation in its propensity to take risks, a key personality trait often termed boldness. Variation in boldness may affect the outcome when roach interact with predators, i.e., if they get eaten or survive. However, we found the impact of roachs’ personality type depends on what species of predatory fish they face. When we put a shy and a bold roach together with predatory perch, the roachs’ personality did not significantly affect which individual was eaten. But when the predator was a pike, the predators selectively ate more shy roach, and the likelihood an individual would be eaten depended on their body size

A pan-Baltic assessment of temporal trends in coastal pike populations

The northern pike (Esox lucius) is an iconic predatory fish species of significant recreational value and ecological role in the Baltic Sea. Some earlier studies indicate local declines of pike in the region, but a thorough spatial evaluation of regional population trends of pike in the Baltic Sea is lacking. In this study, we collate data from 59 unique time-series from fisheries landings and fishery-independent monitoring programs to address temporal trends in pike populations since the mid-2000′s in eight countries surrounding the Baltic Sea. In a common analysis considering all time-series in concert, we found indications of an overall regional temporal decline of pike in the Baltic Sea, but trends differed among countries. Individual negative trends in time-series were moreover found in several regions of the Baltic Sea, but predominantly so in the central and southern parts, while positive trends were only found in Estonia and northern Finland. The mix of data used in this study is inherently noisy and to some extent of uncertain quality, but as a result of the overall negative trends, together with the socioeconomic and ecological importance of pike in coastal areas of the Baltic Sea, we suggest that actions should be taken to protect and restore pike populations. Management measures should be performed in combination with improved fishery-independent monitoring programs to provide data of better quality and development of citizen-science approaches as a data source for population estimates. Possible measures that could strengthen pike populations include harvest regulations (including size limits, no-take areas and spawning closures), habitat protection and restoration, and an ecosystem-based approach to management considering also the impact of natural predators