Paternal dietary macronutrient balance and energy intake drive metabolic and behavioral differences among offspring.

Paternal diet can influence the phenotype of the next generation, yet, the dietary components inducing specific responses in the offspring are not identified. Here, we use the Nutritional Geometry Framework to determine the effects of pre-conception paternal dietary macronutrient balance on offspring metabolic and behavioral traits in mice. Ten isocaloric diets varying in the relative proportion of protein, fats, and carbohydrates are fed to male mice prior to mating. Dams and offspring are fed standard chow and never exposed to treatment diets. Body fat in female offspring is positively associated with the paternal consumption of fat, while in male offspring, an anxiety-like phenotype is associated to paternal diets low in protein and high in carbohydrates. Our study uncovers that the nature and the magnitude of paternal effects are driven by interactions between macronutrient balance and energy intake and are not solely the result of over- or undernutrition.

The effects of paternal dietary fat versus sugar on offspring body composition and anxiety-related behavior.

Increasing evidence suggests that the pre-conception parental environment has long-term consequences for offspring health and disease susceptibility. Though much of the work in this field concentrates on maternal influences, there is growing understanding that fathers also play a significant role in affecting offspring phenotypes. In this study, we investigate effects of altering the proportion of dietary fats and carbohydrates on paternal and offspring body composition and anxiety-related behavior in C57Bl/6-JArc mice. We show that in an isocaloric context, greater dietary fat increased body fat and reduced anxiety-like behavior of studs, whereas increased dietary sucrose had no significant effect. These dietary effects were not reflected in offspring traits, rather, we found sex-specific effects that differed between offspring body composition and behavioral traits. This finding is consistent with past paternal effect studies, where transgenerational effects have been shown to be more prominent in one sex over the other. Here, male offspring of fathers fed high-fat diets were heavier at 10 weeks of age due to increased lean body mass, whereas paternal diet had no significant effect on female offspring body fat or lean mass. In contrast, paternal dietary sugar appeared to have the strongest effects on male offspring behavior, with male offspring of high-sucrose fathers spending less time in the closed arms of the elevated plus maze. Both high-fat and high-sugar paternal diets were found to reduce anxiety-like behavior of female offspring, although this effect was only evident when offspring were fed a control diet. This study provides new understanding of the ways in which diet can shape the behavior of fathers and their offspring and contribute to the development of dietary guidelines to improve obesity and mental health conditions, such as anxiety.

Dietary macronutrient composition impacts gene regulation in adipose tissue.

Diet is a key lifestyle component that influences metabolic health through several factors, including total energy intake and macronutrient composition. While the impact of caloric intake on gene expression and physiological phenomena in various tissues is well described, the influence of dietary macronutrient composition on these parameters is less well studied. Here, we use the Nutritional Geometry framework to investigate the role of macronutrient composition on metabolic function and gene regulation in adipose tissue. Using ten isocaloric diets that vary systematically in their proportion of energy from fat, protein, and carbohydrates, we find that gene expression and splicing are highly responsive to macronutrient composition, with distinct sets of genes regulated by different macronutrient interactions. Specifically, the expression of many genes associated with Bardet-Biedl syndrome is responsive to dietary fat content. Splicing and expression changes occur in largely separate gene sets, highlighting distinct mechanisms by which dietary composition influences the transcriptome and emphasizing the importance of considering splicing changes to more fully capture the gene regulation response to environmental changes such as diet. Our study provides insight into the gene regulation plasticity of adipose tissue in response to macronutrient composition, beyond the already well-characterized response to caloric intake.

Maternal macronutrient intake effects on offspring macronutrient targets and metabolism.

OBJECTIVE: Exposure in utero to maternal diet can program offspring health and susceptibility to disease. Using C57BL6/JArc mice, we investigated how maternal dietary protein to carbohydrate balance influences male and female offspring appetite and metabolic health. METHODS: Dams were placed on either a low-protein (LP) or high-protein (HP) diet. Male and female offspring were placed on a food choice experiment post weaning and were then constrained to either a standard diet or Western diet. Food intake, body weight, and composition were measured, and various metabolic tests were performed at different timepoints. RESULTS: Offspring from mothers fed HP diets selected a higher protein intake and had increased body weight in early life relative to offspring from LP diet-fed dams. As predicted by protein leverage theory, higher protein intake targets led to increased food intake when offspring were placed on no-choice diets, resulting in greater body weight and fat mass. The combination of an HP maternal diet and a Western diet further exacerbated this obesity phenotype and led to long-term consequences for body composition and metabolism. CONCLUSIONS: This work could help explain the association between elevated protein intake in humans during early life and increased risk of obesity in childhood and later life.

Low-Fat, High-Carbohydrate Diets Reduce Body Weight and Sperm Count but Increase Sperm Motility in Mice.

BACKGROUND: Male reproduction is impacted by both over- and under-nutrition, demonstrated by animal studies using high-fat and low-protein dietary interventions. Little is known about the impacts of low-fat, high-carb diets and types of dietary carbohydrates on sperm traits. OBJECTIVES: Using a nutritional geometry approach, we investigated the effects of partially or completely substituting glucose for fructose in isocaloric diets containing either 10%, 20%, or 30% fat (by energy) on sperm traits in mice. METHODS: Male C57BL/6J mice were fed 1 of 15 experimental diets for 18 wk starting from 8 wk of age. Reproductive organs were then harvested, and sperm concentration, motility, and velocity were measured using Computer-Assisted Sperm Analysis. RESULTS: Increasing dietary fat from 10% to 30% while maintaining energy density at 14.3 kJ/g and protein content at 20% resulted in increased body weight and sperm production but reduced the percentage of motile sperm. Body weight and seminal vesicle weight were maximized on diets containing a 50:50 mix of fructose and glucose, but carbohydrate type had few significant impacts on epididymal sperm traits. CONCLUSIONS: The opposing impacts of dietary fat on mouse sperm quantity and quality observed suggest that male fertility may not be optimized by a single diet; rather, context-specific dietary guidelines targeted to specific concerns in semen quality may prove useful in treating male infertility.

Nutrition, anxiety and hormones. Why sex differences matter in the link between obesity and behavior.

Obesity and mood disorders are two of the most serious health issues of modern times. These health conditions are often linked, with obesity acting both as a cause and consequence of anxiety and depression. Although sex differences in the relationship between obesity and mood disorders are observed in clinical populations, the relative influence of biology versus societal conditioning is unclear. In part, this is because sex effects are rarely examined in the animal models used to derive our understanding of basic biological mechanisms. Due to the perceived confounding nature of hormonal fluctuations in females, rodent studies examining nutritional effects on behavioral responses are typically restricted to males. Yet, hormones play an important role in mediating effects of diet on behavior. In this mini-review, we outline interactions between obesity, hormones and the brain to illustrate the importance of considering sex-specific effects in studies of nutritional effects on behavior. We highlight the need for a more nuanced understanding of how dietary factors influence these relationships, arguing that such knowledge will help improve clinical health outcomes in the management of both obesity and mood disorders.

Obesogenic diets induce anxiety in rodents: A systematic review and meta-analysis.

Obesity and mood disorders have been linked in a positive feedback loop. However, due to the bidirectional relationship between obesity and mental health, it is not clear whether anxiety is correlated with or caused by consumption of obesogenic diets. Here, we present a meta-analysis on the effects of dietary manipulation on rodent behavior in the elevated plus maze and open field test, the most common tests of anxiety-like behavior in animal models. The main dataset examined effects of obesogenic diets on time spent in the open and movement around the mazes. Auxiliary datasets examined effects of caloric restriction and protein restriction. Obesogenic diets had a negative effect on the time spent in the open overall. Effects were stronger in males than females. No effect of diet on locomotion was found, indicating that increases in anxiety-like behavior are not due to altered activity levels. No consistent effect of caloric restriction was observed, whereas protein restriction was associated with an increase in the time spent in the open. We show that obesogenic diets have a causative effect on anxiety-like behaviors in rodents, and not via a change in activity. Further studies are required to determine why obesogenic diets induce these behavioral changes.

Parental dietary protein effects on offspring viability in insects and other oviparous invertebrates: a meta-analysis.

Dietary protein is a key regulator of reproductive effort in animals, but protein consumption also tends to accelerate senescence and reduce longevity. Given this protein-mediated trade-off between reproduction and survival, how does protein consumption by parents affect the viability of their offspring? In insects, protein consumption by females enhances fecundity, but trade-offs between offspring quantity and quality could result in negative effects of protein consumption on offspring viability. Likewise, protein consumption by males tends to enhance the expression of sexual traits but could have negative effects on offspring viability, mediated by epigenetic factors transmitted via the ejaculate. It remains unclear whether dietary protein has consistent effects on offspring viability across species, and whether these effects are sex-specific. To address this, we conducted a meta-analysis of experimental studies that examined the effects of protein content in the maternal and/or paternal diet in insects and other oviparous invertebrates. We did not find consistent effects of paternal or maternal protein consumption on offspring viability. Rather, effects of dietary protein on offspring vary in both magnitude and sign across taxonomic groups. Further studies are needed to determine how the effects of dietary protein on offspring relate to variation in reproductive biology across species. Our findings also highlight important gaps in the literature and limitations in experiment design.

Evolutionary consequences of environmental effects on gamete performance.

Variation in pre- and post-release gamete environments can influence evolutionary processes by altering fertilization outcomes and offspring traits. It is now widely accepted that offspring inherit epigenetic information from both their mothers and fathers. Genetic and epigenetic alterations to eggs and sperm-acquired post-release may also persist post-fertilization with consequences for offspring developmental success and later-life fitness. In externally fertilizing species, gametes are directly exposed to anthropogenically induced environmental impacts including pollution, ocean acidification and climate change. When fertilization occurs within the female reproductive tract, although gametes are at least partially protected from external environmental variation, the selective environment is likely to vary among females. In both scenarios, gamete traits and selection on gametes can be influenced by environmental conditions such as temperature and pollution as well as intrinsic factors such as male and female reproductive fluids, which may be altered by changes in male and female health and physiology. Here, we highlight some of the pathways through which changes in gamete environments can affect fertilization dynamics, gamete interactions and ultimately offspring fitness. We hope that by drawing attention to this important yet often overlooked source of variation, we will inspire future research into the evolutionary implications of anthropogenic interference of gamete environments including the use of assisted reproductive technologies. This article is part of the theme issue 'How does epigenetics influence the course of evolution?'

Obesity and Male Reproduction; Placing the Western Diet in Context.

There is mounting evidence that obesity has negative repercussions for reproductive physiology in males. Much of this evidence has accumulated from rodent studies employing diets high in fat and sugar ("high fat" or "western" diets). While excessive fats and carbohydrates have long been considered major determinants of diet induced obesity, a growing body of research suggests that the relationships between diet composition and obesity are more complex than originally thought, involving interactions between dietary macronutrients. However, rodent dietary models have yet to evolve to capture this, instead relying heavily on elevated levels of a single macronutrient. While this approach has highlighted important effects of obesity on male reproduction, it does not allow for interpretation of the complex, interacting effects of dietary protein, carbohydrate and fat. Further, the single nutrient approach limits the ability to draw conclusions about which diets best support reproductive function. Nutritional Geometry offers an alternative approach, assessing outcomes of interest over an extended range of dietary macronutrient compositions. This review explores the practical application of Nutritional Geometry to study the effects of dietary macronutrient balance on male reproduction, including experimental considerations specific to studies of diet and reproductive physiology. Finally, this review discusses the promising use of Nutritional Geometry in the development of evidence-based pre-conception nutritional guidance for men.

Identifying Sources of Potential Bias When Using Online Survey Data to Explore Horse Training, Management, and Behaviour: A Systematic Literature Review.

Owner-reported behavioural observations form an essential part of the veterinarians' diagnosis and treatment plan. The way we train and manage horses affects their behaviour and, in turn, their health and welfare. Current horse training and management practices are largely driven by traditional techniques and longstanding methodologies. These approaches generally lack an evidence base for evaluation purposes. The absence of evidence and evaluation contributes to the persistent use of risky practices and this, in turn, increases risk of potential harms for both horse and rider, and fuels questioning of the equine industry's current social license to operate. Objective evidence is required to make training and management decisions based on demonstrable best practice. Large-scale experimental or intervention studies using horses are generally not practical because of the associated costs and logistics of gaining ethical approval. Small studies generally lack statistical power and are subject to the effects of many forms of bias that demand caution in the interpretation of any observed effects. An alternative to collecting large amounts of empirical data is the use of owner-reported observations via online survey. Horse owners are ideally placed to report on the domestic equine triad of training, management, and behaviour. The current article highlights three sources of potential bias in a systematic review of literature on large-scale online studies of horse owners' observational reports that met the following selection criteria: English-language, published, peer-reviewed articles reporting on studies with over 1000 respondents and open access to the survey instrument. The online surveys were evaluated for three common forms of bias: recall, confirmation, and sampling bias. This review reveals that online surveys are useful for gathering data on the triad of horse training, management, and behaviour. However, current use of online surveys to collect data on equitation science (including horse training, management, and behaviour) could be improved by using a standardised and validated tool. Such a tool would facilitate comparisons among equine and equitation science studies, thus advancing our understanding of the impacts of training and management on horse behaviour. The authors of the current review suggest the use of a standardised behavioural and management assessment tool for horses. Such a tool would help define what constitutes normal behaviour within geographically disparate populations of horses, leading to improvements in rider safety and horse welfare.

From One Ejaculate to Another: Transference of Sperm Traits via Seminal Plasma Supplementation in the Ram.

Males can adjust sperm motility instantaneously in response to the perceived risk of sperm competition. The speed of this response suggests that sperm motility is regulated by changes in seminal plasma rather than changes in the sperm cells themselves. Hence, here we test whether inter-ejaculate variation in seminal plasma can be used to alter sperm quality prior to use in assisted reproductive technologies. We supplemented fresh ejaculates of Merino rams with seminal plasma collected from previous 'donor' ejaculates to test whether changes in sperm kinetics were related to the relative quality of donor to focal ejaculates. We found a positive relationship between the change in sperm traits before and after supplementation, and the difference in sperm traits between the donor and focal ejaculate. Hence, sperm motility can be either increased or decreased through the addition of seminal plasma from a superior or inferior ejaculate, respectively. This positive relationship held true even when seminal plasma was added from a previous ejaculate of the same ram, although the slope of the relationship depended on the identity of both the donor and receiver ram. These findings indicate that seminal plasma plays a key role in the control and regulation of sperm kinetics, and that sperm kinetic traits can be transferred from one ejaculate to another through seminal plasma supplementation.

Musical Dogs: A Review of the Influence of Auditory Enrichment on Canine Health and Behavior.

Music therapy yields many positive health outcomes in humans, but the effects of music on the health and welfare of nonhuman animals vary greatly with the type of music played, the ethology of the species, and the personality and learning history of individual animals. One context in which music therapy may be used to enhance animal welfare is to alleviate stress in domestic environments. Here, we review studies of the effects of music exposure on dogs as a case study for the implementation of music therapy in veterinary medicine. Nine reports of experimental testing for the therapeutic effects of music on dogs were found, with most of these studies focusing on changes in behavior. Overall, exposure to classical music appears to have a calming influence on dogs in stressful environments, with no additional benefit observed from any music purposely designed for dogs (specifically "Through a dog's ear"). Given the cost effectiveness and ease of implementation, music therapy holds promise in veterinary medicine and animal welfare. However, to address precise research questions, further studies must use clearly defined characteristics of stimulus music in the experimental design, and consider the variability of each individual animal's physical characteristics and past experience in the selection of candidates.

Effects of nutrient limitation on sperm and seminal fluid: a systematic review and meta-analysis.

Theory predicts that costly sexual traits should be reduced when individuals are in poor condition (i.e. traits should exhibit condition-dependent expression). It is therefore widely expected that male ejaculate traits, such as sperm and seminal fluid, will exhibit reduced quantity and quality when dietary nutrients are limited. However, reported patterns of ejaculate condition dependence are highly variable, and there has been no comprehensive synthesis of underlying sources of such variation in condition-dependent responses. In particular, it remains unclear whether all ejaculate traits are equally sensitive to nutrient intake, and whether such traits are particularly sensitive to certain dietary nutrients, respond more strongly to nutrients during specific life stages, or respond more strongly in some taxonomic groups. We systematically reviewed these potential sources of variation through a meta-analysis across 50 species of arthropods and vertebrates (from 71 papers and 348 effect sizes). We found that overall, ejaculate traits are moderately reduced when dietary nutrients are limited, but we also detected substantial variation in responses. Seminal fluid quantity was strongly and consistently condition dependent, while sperm quantity was moderately condition dependent. By contrast, aspects of sperm quality (particularly sperm viability and morphology) were less consistently reduced under nutrient limitation. Ejaculate traits tended to respond in a condition-dependent manner to a wide range of dietary manipulations, especially to caloric and protein restriction. Finally, while all major taxa for which sufficient data exist (i.e. arthropods, mammals, fish) showed condition dependence of ejaculate traits, we detected some taxonomic differences in the life stage that is most sensitive to nutrient limitation, and in the degree of condition dependence of specific ejaculate traits. Together, these biologically relevant factors accounted for nearly 20% of the total variance in ejaculate responses to nutrient limitation. Interestingly, body size showed considerably stronger condition-dependent responses compared to ejaculate traits, suggesting that ejaculate trait expression may be strongly canalised to protect important reproductive functions, or that the cost of producing an ejaculate is relatively low. Taken together, our findings show that condition-dependence of ejaculate traits is taxonomically widespread, but there are also many interesting, biologically relevant sources of variation that require further investigation. In particular, further research is needed to understand the differences in selective pressures that result in differential patterns of ejaculate condition dependence across taxa and ejaculate traits.

High-fat diets reduce male reproductive success in animal models: A systematic review and meta-analysis.

Sperm counts have shown a progressive decline across the world since the mid-1900s. Global rates of obesity have been climbing at a similarly alarming rate, suggesting that these two factors may be linked. However, studies examining the relationship between body mass index (BMI) and male fertility have produced conflicting results. These discrepancies among studies are commonly attributed to limitations that are inherent in human studies such as correlational data and confounding factors-limitations that are absent from animal studies. Hence, we conducted a systematic review and meta-analysis of animal studies that experimentally induced obesity with a high-fat diet and measured impacts on sperm traits and/or male fertility. Overall, we found strong, consistent evidence in animal studies that high-fat diets are detrimental for male fertility. Compared with controls, males fed a high-fat diet had smaller testes and sex accessory glands relative to body size, reduced semen quality, reduced mating success, and reduced fertilization success. This is the first time that experimental data of high-fat diet effects on male reproduction have been synthesized in a meta-analysis, and thus, our results provide novel insight to the complex question of how dietary-induced obesity affects male fertility. The strong negative effects detected in animal models suggest that the inconsistent results plaguing human studies are an artefact of limitations inherent in correlational studies rather than a true effect.

Developmental diet irreversibly shapes male post-copulatory traits in the neriid fly Telostylinus angusticollis.

Nutrient availability has been shown to influence investment in many fitness-related traits, including male reproductive success. Many studies have demonstrated that a reduction in nutrient availability alters male post-copulatory trait expression, with some studies demonstrating an effect of developmental nutrients and others, an effect of adult nutrients. However, few studies have manipulated both developmental and adult nutrients in the same experiment. Therefore, it is not clear what life-stage has the greatest effect on post-copulatory trait expression, and if the effects of developmental and adult nutrients can interact. Here, we investigate effects of developmental and adult nutrition on male testes and accessory gland size, sperm movement within the female reproductive tract and sperm length in the neriid fly, Telostylinus angusticollis. We found that males fed a nutrient-poor developmental diet produced sperm with a reduced tail beat frequency and had smaller testes and accessory glands compared to males fed a nutrient-rich developmental diet. In contrast, we found no effects of adult nutrition on any traits measured, although sperm length was correlated with body size and male age but unaffected by nutrition at any stage. Therefore, investment in adult post-copulatory traits is determined early on by developmental nutrients in male neriid flies, and this effect is not altered by adult nutrient availability.

Epigenetic paternal effects as costly, condition-dependent traits.

It is now recognized that post-copulatory traits, such as sperm and ejaculate production can impose metabolic costs, and such traits are therefore expected to exhibit condition-dependent expression, whereby, low condition individuals experience a greater marginal cost of investment compared to high condition individuals. Ejaculates are especially costly in species where males invest in offspring quality through nutrient-rich spermatophores or other seminal nuptial gifts. However, recent evidence shows that, in species where males do not provision females or offspring, males can still influence offspring development through paternal effects mediated by epigenetic factors, such as non-coding RNAs, DNA methylation and chromatin structure. Because such epigenetic paternal effects do not involve the transfer of substantial quantities of resources, such as nutrients, the costs of conferring such effects have not been considered. Here we argue that if selection favours paternal investment in offspring quality through epigenetic factors, then the epigenetic machinery required to bring about such effects may also be expected to evolve strongly condition-dependent expression. We outline indirect evidence suggesting that epigenetic paternal effects could impose substantial metabolic costs, consider the conditions under which selection may act on such effects, and suggest ways to test for differential costs and condition-dependence of these effects. Incorporating epigenetic paternal effects into condition-dependent life history theory will further our understanding of the heritability of fitness and the evolution of paternal investment strategies.

Shifting paradigms in restoration of the world's coral reefs.

Many ecosystems around the world are rapidly deteriorating due to both local and global pressures, and perhaps none so precipitously as coral reefs. Management of coral reefs through maintenance (e.g., marine-protected areas, catchment management to improve water quality), restoration, as well as global and national governmental agreements to reduce greenhouse gas emissions (e.g., the 2015 Paris Agreement) is critical for the persistence of coral reefs. Despite these initiatives, the health and abundance of corals reefs are rapidly declining and other solutions will soon be required. We have recently discussed options for using assisted evolution (i.e., selective breeding, assisted gene flow, conditioning or epigenetic programming, and the manipulation of the coral microbiome) as a means to enhance environmental stress tolerance of corals and the success of coral reef restoration efforts. The 2014-2016 global coral bleaching event has sharpened the focus on such interventionist approaches. We highlight the necessity for consideration of alternative (e.g., hybrid) ecosystem states, discuss traits of resilient corals and coral reef ecosystems, and propose a decision tree for incorporating assisted evolution into restoration initiatives to enhance climate resilience of coral reefs.

Seminal Fluid and Mate Choice: New Predictions.

Recent evidence shows that seminal fluid can affect females and offspring independently of fertilisation in species lacking conventional 'nuptial gifts'. We argue that a hypothesis from paternal investment systems - that selection can favour changing female preferences that maximise both sperm-borne and seminal fluid-borne benefits - could therefore apply much more broadly.

Measuring sperm movement within the female reproductive tract using Fourier analysis.

The adaptive significance of variation in sperm phenotype is still largely unknown, in part due to the difficulties of observing and measuring sperm movement in its natural, selective environment (i.e., within the female reproductive tract). Computer-assisted sperm analysis systems allow objective and accurate measurement of sperm velocity, but rely on being able to track individual sperm, and are therefore unable to measure sperm movement in species where sperm move in trains or bundles. Here we describe a newly developed computational method for measuring sperm movement using Fourier analysis to estimate sperm tail beat frequency. High-speed time-lapse videos of sperm movement within the female tract of the neriid fly Telostylinus angusticollis were recorded, and a map of beat frequencies generated by converting the periodic signal of an intensity versus time trace at each pixel to the frequency domain using the Fourier transform. We were able to detect small decreases in sperm tail beat frequency over time, indicating the method is sensitive enough to identify consistent differences in sperm movement. Fourier analysis can be applied to a wide range of species and contexts, and should therefore facilitate novel exploration of the causes and consequences of variation in sperm movement.