Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout

Effect of long-term confinement on metabolic and physiological parameters in mice

Long-term and mild confinement or isolation in an enclosed environment can occur in situations such as disasters, specific political, economic or social events, nuclear shelters, seabed exploration, polar expeditions, and space travel. To investigate the effects of stress caused by long-term confinement in an enclosed environment in mammals, we divided 8-week-old C57BL/6J mice into four groups that were housed in a closed environment with a narrow metabolic cage (stress group), normal metabolic cage (control group), conventional cage (conventional group) or conventional cage with wire mesh floor (wire mesh group). The phenotypes of the mice were examined for four weeks, followed by behavioral tests. Weight gain suppression was observed in the stress group. Continuous analysis of these mice every two minutes for four weeks using an implanted measuring device showed a significantly decreased amount of spontaneous activity and subcutaneous temperature in the stress group. After housing in each environment for four weeks, the behavioral tests of mice in the stress group also revealed a shorter latency to fall off in the rotarod test and shorter stride length and interstep distance in the footprint test. Interestingly, the lower spontaneous activity of mice in the stress group was rescued by housing in conventional cages. These results suggest a temporary effect of long-term confinement in an enclosed environment as a chronic and mild stress on homeostasis in mammals.

Physiological and behavioral flexibility to an acute CO2 challenge, within and between genotypes in rainbow trout

Adaptive capacities, governing the ability of animals to cope with an environmental stressor, have been demonstrated to be strongly dependent upon genetic factors. Two isogenic lines of rainbow trout, previously described for their sensitivity and resilience to an acute confinement challenge, were used in the present study to investigate whether adaptive capacities remain consistent when fish are exposed to a different type of challenge. For this purpose, the effects of a 4-hour hypercapnia (CO₂ increase) challenge at concentrations relevant in aquaculture conditions are described for the two isogenic lines. Oxygen consumption, cortisol release, group dispersion and group swimming activity were measured before, during and after the challenge. Sensitivity and resilience for each measure were extracted from temporal responses and analyzed using multivariate statistics. The two fish lines displayed significant differences in their cortisol response, translating differences in the stress axis sensitivity to the stressor. On the contrary, both lines showed, for other measures, similar temporal patterns across the study. Notable within line variability in the stress response was observed, despite identical genome between fish. The results are discussed in the context of animal robustness.

On the Use of a Simple Physical System Analogy to Study Robustness Features in Animal Sciences

Environmental perturbations can affect the health, welfare, and fitness of animals. Being able to characterize and phenotype adaptive capacity is therefore of growing scientific concern in animal ecology and in animal production sciences. Terms borrowed from physics are commonly used to describe adaptive responses of animals facing an environmental perturbation, but no quantitative characterization of these responses has been made. Modeling the dynamic responses to an acute challenge was used in this study to facilitate the characterization of adaptive capacity and therefore robustness. A simple model based on a spring and damper was developed to simulate the dynamic responses of animals facing an acute challenge. The parameters characterizing the spring and the damper can be interpreted in terms of stiffness and resistance to the change of the system. The model was tested on physiological and behavioral responses of rainbow trout facing an acute confinement challenge. The model has proven to properly fit the different responses measured in this study and to quantitatively describe the different temporal patterns for each statistical individual in the study. It provides therefore a new way to explicitly describe, analyze and compare responses of individuals facing an acute perturbation. This study suggests that such physical models may be usefully applied to characterize robustness in many other biological systems.

Identification of single-nucleotide polymorphism markers associated with cortisol response to crowding in rainbow trout

Understanding stress responses is essential for improving animal welfare and increasing agriculture production efficiency. Previously, we reported microsatellite markers associated with quantitative trait loci (QTL) affecting plasma cortisol response to crowding in rainbow trout. In this study, our main objectives were to identify single-nucleotide polymorphism (SNP) markers associated with cortisol response to crowding in rainbow trout using both GWAS (genome-wide association studies) and QTL mapping methods and to employ rapidly expanding genomic resources for rainbow trout toward the identification of candidate genes affecting this trait. A three-generation F2 mapping family (2008052) was genotyped using RAD-seq (restriction-site-associated DNA sequencing) to identify 4874 informative SNPs. GWAS identified 26 SNPs associated with cortisol response to crowding whereas QTL mapping revealed two significant QTL on chromosomes Omy8 and Omy12, respectively. Positional candidate genes were identified using marker sequences to search the draft genome assembly of rainbow trout. One of the genes in the QTL interval on Omy12 is a putative serine/threonine protein kinase gene that was differentially expressed in the liver in response to handling and confinement stress in our previous study. A homologue of this gene was differentially expressed in zebrafish embryos exposed to diclofenac, a nonsteroidal anti-inflammatory drug (NSAID) and an environmental toxicant. NSAIDs have been shown to affect the cortisol response in rainbow trout; therefore, this gene is a good candidate based on its physical position and expression. However, the reference genome resources currently available for rainbow trout require continued improvement as demonstrated by the unmapped SNPs and the putative assembly errors detected in this study.

Assessment of genetic variability of fish personality traits using rainbow trout isogenic lines

The study of inter-individual variability of personality in fish is a growing field of interest but the genetic basis of this complex trait is still poorly investigated due to the difficulty in controlling fish genetic origin and life history. When available, isogenic lines that allow performing independent tests on different individuals having identical genotype constitute a very relevant experimental material to disentangle the genetic and environmental components of behavioural individuality. We took advantage of heterozygous isogenic lines to investigate the personality in rainbow trout through the analysis of their reactions to different experimental situations. To this end, seven to ten rainbow trout isogenic lines were screened for their spatial exploratory behaviour, their flight response toward a stressor and their risk taking behaviour. Results showed that some lines seemed less sensitive to new events or environmental changes and could be defined as low responsive, while others were very sensitive and defined as high responsive. The use of isogenic lines highlighted the importance of genetic factors, in combination with life history, in the expression of personality in domesticated fish.