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Abstract
Domesticated species have an attenuated behavioral and physiological stress response compared to their wild counterparts, but the genetic mechanisms underlying this change are not fully understood. We investigated gene expression of a panel of stress response-related genes in five tissues known for their involvement in the stress response: hippocampus, hypothalamus, pituitary, adrenal glands and liver of domesticated White Leghorn chickens and compared it with the wild ancestor of all domesticated breeds, the Red Junglefowl. Gene expression was measured both at baseline and after 45 min of restraint stress. Most of the changes in gene expression related to stress were similar to mammals, with an upregulation of genes such as FKBP5, C-FOS and EGR1 in hippocampus and hypothalamus and StAR, MC2R and TH in adrenal glands. We also found a decrease in the expression of CRHR1 in the pituitary of chickens after stress, which could be involved in negative feedback regulation of the stress response. Furthermore, we observed a downregulation of EGR1 and C-FOS in the pituitary following stress, which could be a potential link between stress and its effects on reproduction and growth in chickens.We also found changes in the expression of important genes between breeds such as GR in the hypothalamus, POMC and PC1 in the pituitary and CYP11A1 and HSD3B2 in the adrenal glands. These results suggest that the domesticated White Leghorn may have a higher capacity for negative feedback of the HPA axis, a lower capacity for synthesis of ACTH in the pituitary and a reduced synthesis rate of corticosterone in the adrenal glands compared to Red Junglefowl. All of these findings could explain the attenuated stress response in the domesticated birds.
Highlights
A number of animal species have adapted to living in the captive environments provided by humans during domestication, allowing the individuals to tolerate proximity to humans, and to live in crowded and confined conditions (Price, 1999)
The expression levels of glucocorticoid receptor (GR), corticosterone-releasing hormone receptor 1 (CRHR1) and arginine vasopressin (AVP) were significantly higher in White Leghorns (WL) compared with the Red Junglefowl (RJF) (Fig. 2 and Table S1)
We found that the combination of a higher expression of GR in hypothalamus following stress in domesticated WL, a lowered POMC gene expression in pituitary and a decreased expression of steroidogenic genes in the adrenal glands could explain the hampered HPA axis reactivity in WL compared to ancestral RJF
Summary
A number of animal species have adapted to living in the captive environments provided by humans during domestication, allowing the individuals to tolerate proximity to humans, and to live in crowded and confined conditions (Price, 1999). Natural selection in the new environment and genetic drift have led to a suite of traits that are commonly associated with domestication, the domesticated phenotype This includes changes in morphology, physiology and behavior (Price, 1999, 2002) and modifications in the response to stressful stimuli. Glucocorticoids have a wide variety of effects depending on the target tissue, including glycogen breakdown and gluconeogenesis (Exton, 1978; Munk et al, 1984; Coderre et al, 1991; Myers et al, 2014) Their overall function is to shift resource allocation to promote immediate survival, for instance counteracting blood loss and mobilizing energy, while suppressing body functions that are not crucial for immediate survival, such as reproduction, immune system and digestion (Herman et al, 2016). The HPA axis is dependent on a negative feedback system, in which binding of glucocorticoids to glucocorticoid receptors at several levels within the axis can inhibit its activity (De Kloet et al, 2005; Vandenborne et al, 2005; Chrousos, 2009; Keller-Wood, 2011)
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