Among-individual diet variation within a lake trout ecotype: lack of stability of niche use

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes

A big-data approach to understanding metabolic rate and response to obesity in laboratory mice

Maintaining a healthy body weight requires an exquisite balance between energy intake and energy expenditure. To understand the genetic and environmental factors that contribute to the regulation of body weight, an important first step is to establish the normal range of metabolic values and primary sources contributing to variability. Energy metabolism is measured by powerful and sensitive indirect calorimetry devices. Analysis of nearly 10,000 wild-type mice from two large-scale experiments revealed that the largest variation in energy expenditure is due to body composition, ambient temperature, and institutional site of experimentation. We also analyze variation in 2329 knockout strains and establish a reference for the magnitude of metabolic changes. Based on these findings, we provide suggestions for how best to design and conduct energy balance experiments in rodents. These recommendations will move us closer to the goal of a centralized physiological repository to foster transparency, rigor and reproducibility in metabolic physiology experimentation

Absorption efficiencies and basal turnover of C, N and fatty acids in a marine Calanoid copepod

1. Marine copepods of the genus Calanus can reproduce prior to the spring bloom in the absence of sufficient food. Their starvation physiology, and hence the factors limiting their pre-bloom population growth (egg production), remain poorly understood.2. Stoichiometric theory can provide insights into the factors controlling an organism’s growth and the fate of elements in an ecosystem. It is underpinned by substrate utilization efficiencies that relate to key physiological processes such as absorption efficiencies (AEs) and biomass turnover. These parameters are seldom investigated, particularly in the case of essential ‘micronutrients’ such as the polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).3. Calanus spp. were fed briefly and subsequently starved for 5 days to determine basal turnover rates of biomass carbon, nitrogen and essential PUFAs. The effect of short-term fasting on nitrogen isotope signatures was also examined. The elemental, fatty acid and isotopic composition of their faecal pellets were compared to that of their food, providing insights into AEs and digestive isotopic discrimination.4. Gut AEs typically followed the sequence: PUFA > nitrogen > carbon, although low AE for DHA was a notable exception. Starvation-induced losses of carbon, nitrogen, EPA and DHA demonstrate that homeostatic organisms must ingest all of these substrates in substantial quantity to achieve positive net growth.5. Egested material was significantly depleted in 13C and 15N relative to the ingested food. We attribute this to isotopic discrimination at the macromolecular level, indicating that food quality contributes to the isotopic signature of a consumer organism. Values of d15N in the copepods’ tissues did not increase during starvation, despite significant losses of bulk nitrogen. This supports the suggestion that dissimilatory protein pathways in marine crustaceans are non-discriminating.6. The significant basal turnover rates and variable AEs for essential PUFAs and nitrogen presented herein demonstrate that organisms cannot be assumed to utilize all nutritious substrates with the same, high efficiency, even when scarce in the diet. Our data highlight the need for a more detailed understanding of organismal physiology before isotopic and stoichiometric models can be meaningfully constructed and parameterized