Energetic Costs of Stress in Developing Fishes: Quantifying Allostasis and Allostatic Load.

Stress exerts negative effects on fish health through stimulation of the hypothalamic-pituitary-interrenal axis and autonomic nervous system, resulting in heightened neural and neuroendocrine responses. Energetic investment and physiological adaptation are then required to re-establish homeostatic stability or reach a new allostatic state. The cost of the energetic investment is referred to as allostatic load (AL).

The yin and yang of self-regulation in developing vertebrates.

All living organisms are thermodynamic open systems constantly exchanging energy with the environment to maintain organization and structure. In a state of non-equilibrium they undergo a back and forth pattern of self-regulation and dysregulation in energy exchange. This state of dynamic non-equilibrium can be observed during vertebrate development in which high phenotypic variation and plasticity exists, especially in the presence of stressors.

Multiple stressors, allostasis and metabolic scaling in developing zebrafish.

Deoxygenation and warming affect adult fish physiology in all aquatic ecosystems, but how these stressors impact the energetics of sensitive developing stages is largely unknown. Addressing this knowledge gap, we investigated chronic and acute effects of two stressors (high temperature and hypoxia) in yolk-sac larval (48-168 hpf) zebrafish (Danio rerio) energy budgets measuring, oxygen consumption rate, growth rate (absolute and specific), % net conversion efficiency, net cost of growth and scaling relationships. Embryos and larvae were raised under four chronic treatments: (1) control (28°C and PO2 21 kPa, T28O21), (2) high temperature (31°C and PO2 21 kPa, T31O21), (3) hypoxia (28°C and PO2 11 kPa, T28TO11) and (4) high temperature and hypoxia (31°C and PO2 11 kPa, T31O11).

Crucial Development: Criticality Is Important to Cell-to-Cell Communication and Information Transfer in Living Systems.

In the fourth paper of this Special Issue, we bridge the theoretical debate on the role of memory and criticality discussed in the three earlier manuscripts, with a review of key concepts in biology and focus on cell-to-cell communication in organismal development. While all living organisms are dynamic complex networks of organization and disorder, most studies in biology have used energy and biochemical exchange to explain cell differentiation without considering the importance of information (entropy) transfer. While all complex networks are mixtures of patterns of complexity (non-crucial and crucial events), it is the crucial events that determine the efficiency of information transfer, especially during key transitions, such as in embryogenesis.

Metabolic plasticity in development: Synergistic responses to high temperature and hypoxia in zebrafish, Danio rerio.

This study investigated interactions of temperature and hypoxia on metabolic plasticity and regulation in zebrafish, Danio rerio, in the first week of development. Larval morphometry, oxygen consumption, and metabolic responses to acute changes in temperature and oxygen were measured in larvae reared under four conditions, including control (28°C and partial pressures of oxygen [PO] of 21 kPa), high temperature (31°C), hypoxia (11 kPa), and the two stressors combined. Rearing conditions did not result in consistent morphometric changes; substantial metabolic adjustments, however, were evident.

Genetically engineered probiotic for the treatment of phenylketonuria (PKU); assessment of a novel treatment in vitro and in the PAHenu2 mouse model of PKU.

Phenylketonuria (PKU) is a genetic disease characterized by the inability to convert dietary phenylalanine to tyrosine by phenylalanine hydroxylase. Given the importance of gut microbes in digestion, a genetically engineered microbe could potentially degrade some ingested phenylalanine from the diet prior to absorption. To test this, a phenylalanine lyase gene from Anabaena variabilis (AvPAL) was codon-optimized and cloned into a shuttle vector for expression in Lactobacillus reuteri 100-23C (pHENOMMenal).

Ontogeny of feeding and respiration in larval Atlantic cod Gadus morhua (Teleostei, Gadiformes): I. Morphology.

Cranial development in larval Atlantic cod Gadus morhua was studied throughout ontogeny using specimens treated by staining and clearing, scanning electron microscopy and histology. Newly hatched cod larvae have closed mouths, no operculii, five well-developed branchial arches, and transversii ventralis muscles. During the endogenous feeding (yolk-sac) stage, viscerocranial structures remain simple and nonarticulated.

Ontogeny of feeding and respiration in larval Atlantic cod Gadus morhua (Teleostei, Gadiformes): II. Function.

Feeding mechanisms were studied in larval cod from first feeding to metamorphosis. Structural and functional changes that govern jaw movement and control the flow of water through the mouth change in concert with requirements for food energy. Early in development, exogenous food resources supplement the endogenous yolk-sac, viscerocranial structures and functions are simple and nonintegrated, and respiration is cutaneous.