Adult dietary protein has age- and context-dependent effects on male post-copulatory performance.

The highly conserved effect of dietary protein restriction on lifespan and ageing is observed in both sexes and across a vast range of taxa. This extension of lifespan is frequently accompanied by a reduction in female fecundity, and it has been hypothesized that individuals may reallocate resources away from reproduction and into somatic maintenance. However, effects of dietary protein restriction on male reproduction are less consistent, suggesting that these effects may depend on other environmental parameters. Using the neriid fly, Telostylinus angusticollis, we examined age-specific effects of adult dietary protein restriction on male post-copulatory reproductive performance (fecundity and offspring viability). To explore the context dependence of these effects, we simultaneously manipulated male larval diet and adult mating history. We found that protein-restricted males sired less viable offspring at young ages, but offspring viability increased with paternal age and eventually exceeded that of fully fed males. The number of eggs laid by females was not affected by male dietary protein, whereas egg hatching success was subject to a complex interaction of male adult diet, age, larval diet and mating history. These findings suggest that effects of protein restriction on male reproduction are highly context dependent and cannot be explained by a simple reallocation of resources from reproduction to somatic maintenance. Rather, these effects appear to involve changes in the scheduling of male reproductive investment with age.

Male reproductive traits are differentially affected by dietary macronutrient balance but unrelated to adiposity.

Dietary factors influence male reproductive function in both experimental and epidemiological studies. However, there are currently no specific dietary guidelines for male preconception health. Here, we use the Nutritional Geometry framework to examine the effects of dietary macronutrient balance on reproductive traits in C57BL/6 J male mice. Dietary effects are observed in a range of morphological, testicular and spermatozoa traits, although the relative influence of protein, fat, carbohydrate, and their interactions differ depending on the trait being examined. Interestingly, dietary fat has a positive influence on sperm motility and antioxidant capacity, differing to typical high fat diet studies where calorie content is not controlled for. Moreover, body adiposity is not significantly correlated with any of the reproductive traits measured in this study. These results demonstrate the importance of macronutrient balance and calorie intake on reproductive function and support the need to develop specific, targeted, preconception dietary guidelines for males.

Dietary protein and lifespan across the metamorphic boundary: protein-restricted larvae develop into short-lived adults.

Restriction of nutrients in the adult diet extends lifespan across a diverse range of species, but less is known about the long-term effects of developmental dietary restriction. In particular, it is not known whether adult lifespan is influenced by developmental caloric restriction or macronutrient balance. We used the nutritional geometry approach to independently manipulate protein and carbohydrate contents of the larval diet in the neriid fly, Telostylinus angusticollis, and measured adult lifespan. We found that adult male and female lifespan was shortest when larvae were fed a protein restricted diet. Thus, protein restriction in the larval diet has the opposite effect of protein restriction in the adult diet (which prolongs life in this species and across a wide range of taxa). Adult lifespan was unaffected by larval dietary carbohydrate. These patterns persisted after controlling for larval diet effects on adult body size. We propose that larval and adult protein sources are used for distinct metabolic tasks: during development, dietary protein is used to build a durable soma that enhances adult lifespan, although excessive protein consumption partially reverses this effect.