Exploring the effects of dietary restriction and macronutrient composition on life-history traits, in a non-model vertebrate system
Moatt, Joshua Philip
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Dietary restriction (DR), is a reduction in food intake, either through overall calorie or specific macronutrient intake, while avoiding malnutrition. DR has been consistently shown to increase longevity and protect against age related diseases. Although originally thought to be the result of a reduction in caloric intake, recent evidence suggests that the ratio of macronutrients, particularly that of protein : non-protein energy, also plays a role. The broad range of species in which DR is known to be effective, suggests an evolutionary conserved mechanism. However, the suggestion of a strong model species bias and a potential sex bias have led some to question the ubiquity of responses to DR. Here, I address the following questions: (i) How consistent is the effect of DR on reproduction? (ii) How does varying macronutrient intake effect both growth and body composition in three-spine sticklebacks (Gasterosteus aculeatus)? (iii) What is the effect of dietary macronutrient intake on lifespan and reproduction in the three-spine stickleback? and (iv) How does changing macronutrient intake impact fitness related traits, such as condition and performance in three-spine sticklebacks? Through use of a systematic review and meta-analysis, I show that the effect of DR on reproduction is evolutionarily conserved, though the effect is stronger in model species. However, when accounting for all significant moderators there is no evidence of the suggested sex differences in the effect of DR. I show that body composition is predicted by dietary lipid intake, with sticklebacks targeting a lower ratio of protein : fat within the body, potentially via metabolism and excretion of protein. These results hint at a link between conversion and excretion of protein and survival costs associated with high protein diets. I show that mortality risk is reduced at balanced protein : lipid intakes in males and generally at low protein : lipid intakes for females. However, the effect in females is not consistent throughout life. I further show that reproduction is maximised on high protein : lipid intakes for both sexes. These results suggest a macronutrient mediated trade-off between lifespan and reproduction in male three-spine sticklebacks. Finally I show a positive effect of lipid intake on male condition (a possible indicator of overall health) hinting at a relationship between lipid intake, adiposity, health and lifespan in male three-spine sticklebacks.