Dietary restriction and life-history trade-offs: insights into mTOR pathway regulation and reproductive investment in Japanese quail

Abstract

Resources are needed for growth, reproduction and survival, and organisms must trade-off limited resources among competing processes. Nutritional availability in organisms is sensed and monitored by nutrient-sensing pathways that can trigger physiological changes or alter gene expression. Previous studies have proposed that one such signalling pathway, the mechanistic target of rapamycin (mTOR), underpins a form of adaptive plasticity when individuals encounter constraints in their energy budget. Despite the fundamental importance of this process in evolutionary biology, how nutritional limitation is regulated through the expression of genes governing this pathway and its consequential effects on fitness remains understudied, particularly in birds. We used dietary restriction to simulate resource depletion and examined its effects on body mass, reproduction and gene expression in Japanese quails (Coturnix japonica). Quails were subjected to feeding 20%, 30%, 40% restriction levels or ad libitum for two weeks. All restricted groups exhibited reduced body mass, whereas reductions in the number and mass of eggs were observed only under more severe restrictions. Additionally, dietary restriction led to decreased expression of mTOR and insulin-like growth factor 1 (IGF1), whereas the ribosomal protein S6 kinase 1 (RPS6K1) and autophagy-related genes (ATG9A and ATG5) were upregulated. The pattern in which mTOR respond to restriction was similar to what has been seen in body mass. Regardless of the treatment, proportionally higher reproductive investment was associated with individual variation in mTOR expression. These findings reveal the connection between dietary intake and the expression of mTOR and related genes in this pathway.

Dietary restriction reveals sex-specific expression of the mTOR pathway genes in Japanese quails

“…Dots and vertical bars represent the mean ± SEM from 8 birds per group, and data were analysed using ANOVA of linear mixed-effect model. Female data is obtained from our previous study 32 . ‘ns’, not significant at p < 0.05; ‘*’significantly different at p < 0.05; ‘**’significantly different at p < 0.01; ***significantly different at p < 0.001.…”

“…Birds were maintained in an experimental house until they reached maturity for an additional 4 weeks before being subjected to the acclimation of experimental conditions. At the age of 8 weeks, 32 male birds with similar body mass were selected for acclimation and assigned to individual cages alongside another 32 female birds from the same batch and reared in the same housing condition 32 . We kept them under ad libitum feed and water for 7 days of acclimation for individual living and the experimental room conditions.…”

“…The collected liver tissue samples were placed in a collection tube, rapidly frozen on dry ice, immediately taken to the laboratory, and stored at − 80 °C until further assays. Male and female samples were collected at the same time and were handled in an identical way 32 .…”

“…To compute differences between males and females and compare sex-specific responses to dietary restriction, we included previously reported data from a parallel experiment conducted in females, following the same protocols and conditions 32 . Using the male and female data, we employed linear mixed-effect models to analyse the sex-specific effects of dietary restriction on body mass, where sex, dietary treatment, time points and their interactions considered as fixed factors and individual bird identity as random factor.…”

“…Recently, we have shown that liver genes governing the mTOR signalling pathway expressed differentially across dietary restriction gradients and were related to patterns of changes in body mass and reproductive parameters in female Japanese quails ( Coturnix japonica ) 32 . Specifically, DR downregulated the expression of liver mTOR , IGF1 (insulin-like growth factor 1) and its receptor ( IGF1R ), whereas genes downstream to mTOR, such as ribosomal protein kinase 1 (RPS6K1) and autophagy-related 9A ( ATG9A), showed an increasing trend with the level of restriction.…”