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.

Sperm specificity and potential paternal effects in gynogenesis in the Amazon Molly (Poecilia formosa)

The Amazon Molly (Poecilia formosa) reproduces by gynogenesis, a relatively rare form of asexual reproduction where sperm is required to trigger embryogenesis, but male genes are not incorporated into the genome of the embryo. Studying gynogenesis could isolate paternal non-genetic effects on reproduction. This study explored which of eleven related species can produce sperm to trigger gynogenesis through natural mating in P. formosa, and whether sympatry affects reproductive success in P. formosa. Reproductive outcomes measured were relative reproductive output (number of offspring in the first brood divided by female standard length), relative embryo output (number of embryos in the first brood divided by female standard length) and combined relative reproductive output (sum of relative reproductive output and relative embryo output). For large (>4 cm) P. formosa, combined relative reproductive output was higher with sympatric Atlantic Molly (Poecilia mexicana) males than with allopatric P. mexicana males. P. formosa produced live offspring or late-stage embryos with all species tested in the genera Poecilia and Limia but did not produce offspring or embryos with males from the genera Gambusia, Girardinus, Heterandria, Poeciliopsis, or Xiphophorus. This information, as well as the limitations characterized in this study, will set a foundation for use of P. formosa as a model for paternal effects and the species specificity of sperm on fertilization, embryogenesis, and reproductive success.

Fathers' preconception smoking and offspring DNA methylation

BACKGROUND

Experimental studies suggest that exposures may impact respiratory health across generations via epigenetic changes transmitted specifically through male germ cells. Studies in humans are, however, limited. We aim to identify epigenetic marks in offspring associated with father's preconception smoking.

METHODS

We conducted epigenome-wide association studies (EWAS) in the RHINESSA cohort (7-50 years) on father's any preconception smoking (n = 875 offspring) and father's pubertal onset smoking < 15 years (n = 304), using Infinium MethylationEPIC Beadchip arrays, adjusting for offspring age, own smoking and maternal smoking. EWAS of maternal and offspring personal smoking were performed for comparison. Father's smoking-associated dmCpGs were checked in subpopulations of offspring who reported no personal smoking and no maternal smoking exposure.

RESULTS

Father's smoking commencing preconception was associated with methylation of blood DNA in offspring at two cytosine-phosphate-guanine sites (CpGs) (false discovery rate (FDR) < 0.05) in PRR5 and CENPP. Father's pubertal onset smoking was associated with 19 CpGs (FDR < 0.05) mapped to 14 genes (TLR9, DNTT, FAM53B, NCAPG2, PSTPIP2, MBIP, C2orf39, NTRK2, DNAJC14, CDO1, PRAP1, TPCN1, IRS1 and CSF1R). These differentially methylated sites were hypermethylated and associated with promoter regions capable of gene silencing. Some of these sites were associated with offspring outcomes in this cohort including ever-asthma (NTRK2), ever-wheezing (DNAJC14, TPCN1), weight (FAM53B, NTRK2) and BMI (FAM53B, NTRK2) (p < 0.05). Pathway analysis showed enrichment for gene ontology pathways including regulation of gene expression, inflammation and innate immune responses. Father's smoking-associated sites did not overlap with dmCpGs identified in EWAS of personal and maternal smoking (FDR < 0.05), and all sites remained significant (p < 0.05) in analyses of offspring with no personal smoking and no maternal smoking exposure.

CONCLUSION

Father's preconception smoking, particularly in puberty, is associated with offspring DNA methylation, providing evidence that epigenetic mechanisms may underlie epidemiological observations that pubertal paternal smoking increases risk of offspring asthma, low lung function and obesity.

Sex-specific effects of chronic paternal stress on offspring development are partially mediated via mothers

Paternal stress exposure is known to impact the development of stress-related behaviors in offspring. Previous work has highlighted the importance of sperm mediated factors, such as RNAs, in transmitting the effects of parental stress. However, a key unanswered question is whether mothers behavior could drive or modulate the transmission of paternal stress effects on offspring development. Here we investigate how chronic variable stress in Balb/C mice influences the sex-specific development of anxiety- and depression-like neural and behavioral development in offspring. Moreover, we examined how stressed fathers influenced mate maternal investment towards their offspring and how this may modulate the transmission of paternal stress effects on offspring. We show that paternal stress leads to sex-specific effects on offspring behavior. Males that are chronically stressed sire female offspring that show increased anxiety and depression-like behaviors. However, male offspring of stressed fathers show reductions in anxiety- and depression-behaviors and are generally more exploratory. Moreover, we show that females mated with stressed males gain less weight during pregnancy and provide less care towards their offspring which additionally influenced offspring development. These data indicate that paternal stress can influence offspring development both directly and indirectly via changes in mothers, with implications for sex-specific offspring development.

Paternal care effects outweigh gamete-mediated and personal environment effects during the transgenerational estimation of risk in fathead minnows

BACKGROUND

Individuals can estimate risk by integrating prenatal with postnatal and personal information, but the relative importance of different information sources during the transgenerational response is unclear. The estimated level of risk can be tested using the cognitive rule of risk allocation, which postulates that under consistent high-risk, antipredator efforts should decrease so that individual metabolic requirements can be satisfied. Here we conduct a comprehensive study on transgenerational risk transmission by testing whether risk allocation occurs across 12 treatments that consist of different maternal, paternal, parental care (including cross-fostering) and offspring risk environment combinations in the fathead minnow Pimephales promelas, a small cyprinid fish with alloparental care. In each risk environment, we manipulated perceived risk by continuously exposing individuals from birth onwards to conspecific alarm cues or a control water treatment. Using 2810 1-month old individuals, we then estimated shoaling behaviour prior to and subsequent to a novel mechanical predator disturbance.

RESULTS

Overall, shoals estimating risk to be high were denser during the prestimulus period, and, following the risk allocation hypothesis, resumed normal shoaling densities faster following the disturbance. Treatments involving parental care consistently induced densest shoals and greatest levels of risk allocation. Although prenatal risk environments did not relate to paternal care intensity, greater care intensity induced more risk allocation when parents provided care for their own offspring as opposed to those that cross-fostered fry. In the absence of care, parental effects on shoaling density were relatively weak and personal environments modulated risk allocation only when parental risk was low.

CONCLUSIONS

Our study highlights the high relative importance of parental care as opposed to other information sources, and its function as a mechanism underlying transgenerational risk transmission.

Plasticity in parental effects confers rapid larval thermal tolerance in the estuarine anemone Nematostella vectensis

Parental effects can prepare offspring for different environments and facilitate survival across generations. We exposed parental populations of the estuarine anemone, Nematostella vectensis, from Massachusetts to elevated temperatures and quantified larval mortality across a temperature gradient. We found that parental exposure to elevated temperatures resulted in a consistent increase in larval thermal tolerance, as measured by the temperature at which 50% of larvae die (LT50), with a mean increase in LT50 of 0.3°C. Larvae from subsequent spawns returned to baseline thermal thresholds when parents were returned to normal temperatures, indicating plasticity in these parental effects. Histological analyses of gametogenesis in females suggested that these dynamic shifts in larval thermal tolerance may be facilitated by maternal effects in non-overlapping gametic cohorts. We also compared larvae from North Carolina (a genetically distinct population with higher baseline thermal tolerance) and Massachusetts parents, and observed that larvae from heat-exposed Massachusetts parents had thermal thresholds comparable to those of larvae from unexposed North Carolina parents. North Carolina parents also increased larval thermal tolerance under the same high-temperature regime, suggesting that plasticity in parental effects is an inherent trait for N. vectensis Overall, we find that larval thermal tolerance in N. vectensis shows a strong genetic basis and can be modulated by parental effects. Further understanding of the mechanisms behind these shifts can elucidate the fate of thermally sensitive ectotherms in a rapidly changing thermal environment.

Experimentally altered male mating behaviour affects offspring exploratory behaviour via nongenetic paternal effects

Evidence is emerging that fathers can have nongenetic effects on the phenotypes of their offspring. Most studies have focused on the role that nongenetic modifications to sperm can have on offspring phenotype; however, fathers can also have nongenetic effects on offspring through their interactions with females, called female-mediated paternal effects. These effects can occur in situations where male phenotype, e.g. behaviour or morphology, affects female stress and/or provisioning of offspring. These effects are potentially widespread, but few studies have explicitly investigated the role of female-mediated paternal effects on offspring phenotype. Here, we asked if male mating interactions can affect offspring via female mediated paternal effects in the Trinidadian guppy, Poecilia reticulata. To do this, we manipulated mating behaviour by: (i) administering a drug known to affect the neurotransmitter dopamine, and (ii) varying the familiarity of potential mates, which affects attractiveness in this species. With these treatments, we successfully manipulated the mating behaviour of male guppies and female preference for those males. Further, we found significant effects of sire mating behaviour, sire drug treatment, and parental familiarity status on behavioural measures of offspring anxiety in response to a novel object. Because Control offspring of 'familiar' and 'unfamiliar' pairs differed in their behaviour, our results cannot be solely attributed to potential nongenetic modifications to sperm caused by the drug. These results emphasize the importance of female-mediated paternal effects, including those caused by altered male mating behaviour, in shaping offspring phenotype.

Parental transgenerational epigenetic inheritance related to dietary crude oil exposure in Danio rerio

Transgenerational inheritance from both parental lines can occur by genetic and epigenetic inheritance. Maternal effects substantially influence offspring survival and fitness. However, investigation of the paternal contribution to offspring success has been somewhat neglected. In the present study, adult zebrafish were separated into female and male groups exposed for 21 days to either a control diet or to a diet containing water accommodated fractions of crude oil. Four F1 offspring groups were obtained: (1) control (non-exposed parents), (2) paternally exposed, (3) maternally exposed and (4) dual-parent-exposed. To determine the maternal and paternal influence on their offspring, we evaluated responses from molecular to whole organismal levels in both generations. Growth rate, hypoxia resistance and heart rate did not differ among parental groups. However, global DNA methylation in heart tissue was decreased in oil-exposed fish compared with control parents. This decrease was accompanied by an upregulation of glycine N-methyltransferase. Unexpectedly, maternal, paternal and dual exposure all enhanced survival of F1 offspring raised in oiled conditions. Regardless of parental exposure, however, F1 offspring exposed to oil exhibited bradycardia. Compared with offspring from control parents, global DNA methylation was decreased in the three offspring groups derived from oil-exposed parents. However, no difference between groups was observed in gene regulation involved in methylation transfer, suggesting that the changes observed in the F1 populations may have been inherited from both parental lines. Phenotypic responses during exposure to persistent environmental stressors in F1 offspring appear to be influenced by maternal and paternal exposure, potentially benefitting offspring populations to survive in challenging environments.

Early life lessons: The lasting effects of germline epigenetic information on organismal development

BACKGROUND

An organism's metabolic phenotype is primarily affected by its genotype, its lifestyle, and the nutritional composition of its food supply. In addition, it is now clear from studies in many different species that ancestral environments can also modulate metabolism in at least one to two generations of offspring.

SCOPE OF REVIEW

We limit ourselves here to paternal effects in mammals, primarily focusing on studies performed in inbred rodent models. Although hundreds of studies link paternal diets and offspring metabolism, the mechanistic basis by which epigenetic information in sperm programs nutrient handling in the next generation remains mysterious. Our goal in this review is to provide a brief overview of paternal effect paradigms and the germline epigenome. We then pivot to exploring one key mystery in this literature: how do epigenetic changes in sperm, most of which are likely to act transiently in the early embryo, ultimately direct a long-lasting physiological response in offspring?

MAJOR CONCLUSIONS

Several potential mechanisms exist by which transient epigenetic modifications, such as small RNAs or methylation states erased shortly after fertilization, could be transferred to more durable heritable information. A detailed mechanistic understanding of this process will provide deep insights into early development, and could be of great relevance for human health and disease.

Time-critical influences of gestational diet in a seahorse model of male pregnancy

Sex role reversal is not uncommon in the animal kingdom but is taken to the extreme by the Syngnathidae, in which male pregnancy is one of the most astonishing idiosyncrasies. However, critical and time-dependent environmental effects on developing embryos, such as those extensively studied in mammalian pregnancy, have not been investigated in the male pregnancy context. Here, we tested the hypothesis that seahorse pregnancy is subject to ‘critical windows’ of environmental sensitivity by feeding male long-snouted seahorses (Hippocampus reidi) a diet deficient in polyunsaturated fatty acids during specific periods before and during pregnancy. Despite embryos being nourished principally by maternally supplied yolk, we found that offspring morphology, fatty acid composition and gene expression profiles were influenced by paternal diet in a manner that depended critically on the timing of manipulation. Specifically, reception of a diet deficient in polyunsaturated fatty acids in the days preceding pregnancy resulted in smaller newborn offspring, while the same diet administered towards the end of pregnancy resulted in substantial alterations to newborn gene expression and elongation of the snout at 10 days old. Although paternal diet did not affect 10 day survival, the observed morphological alterations in some cases could have important fitness consequences in the face of natural selective pressures such as predation and food availability. Our results demonstrate that, under male pregnancy, fine-scale temporal variation in parental diet quality and subsequent critical window effects should not be overlooked as determinants of developing offspring fitness.

Summary: Food quality has a time-dependent impact on the offspring of male seahorses, revealing new insights into male pregnancy and its potential adaptive importance for syngnathid offspring.

Paternal impact on the life course development of obesity and type 2 diabetes in the offspring

The aetiologies of obesity and type 2 diabetes are incredibly complex, but the potential role of paternal influences remains relatively understudied. A better understanding of paternal influences on offspring risk of obesity and type 2 diabetes could have profound implications for public health, clinical practice and society. In this review, we outline potential biological and social mechanisms through which fathers might exert an impact on the health of their offspring. We also present a systematically compiled overview of the current evidence linking paternal factors to offspring development of obesity and type 2 diabetes throughout the life course. Although evidence is accumulating to support paternal associations with offspring outcomes, more high-quality research is needed to overcome specific methodological challenges and provide stronger causal evidence.

Comparative effects of the parasiticide ivermectin on survival and reproduction of adult sepsid flies

Ivermectin is a veterinary pharmaceutical widely applied against parasites of livestock. Being effective against pests, it is also known to have lethal and sublethal effects on non-target organisms. While considerable research demonstrates the impact of ivermectin residues in livestock dung on the development and survival of dung feeding insect larvae, surprisingly little is known about its fitness effects on adults. We tested the impact of ivermectin on the survival of adult sepsid dung fly species (Diptera: Sepsidae) in the laboratory, using an ecologically relevant and realistic range of 69-1978 µg ivermectin/kg wet dung, and compared the sensitivities of larvae and adults in a phylogenetic framework. For one representative, relatively insensitive species, Sepsis punctum, we further investigated effects of ivermectin on female fecundity and male fertility. Moreover, we tested whether females can differentiate between ivermectin-spiked and non-contaminated dung in the wild. Adult sepsid flies exposed to ivermectin suffered increased mortality, whereby closely related species varied strongly in their sensitivity. Adult susceptibility to the drug correlated with larval susceptibility, showing a phylogenetic signal and demonstrating systemic variation in ivermectin sensitivity. Exposure of S. punctum females to even low concentrations of ivermectin lowered the number of eggs laid, while treatment of males reduced egg-to-adult offspring survival, presumably via impairment of sperm quality or quantity. The fitness impact was amplified when both parents were exposed. Lastly, sepsid flies did not discriminate against ivermectin-spiked dung in the field. Treatment of livestock with avermectins may thus have even more far-reaching sublethal ecological consequences than currently assumed via effects on adult dung-feeding insects.

It's the mother!: How assumptions about the causal primacy of maternal effects influence research on the developmental origins of health and disease

Research on the developmental origins of health and disease (DOHaD) has traditionally focused on how maternal exposures around the time of pregnancy might influence offspring health and risk of disease. We acknowledge that for some exposures this is likely to be correct, but argue that the focus on maternal pregnancy effects also reflects implicit and deeply-held assumptions that 1) causal early life exposures are primarily transmitted via maternal traits or exposures, 2) maternal exposures around the time of pregnancy and early infancy are particularly important, and 3) other factors, such as paternal factors and postnatal exposures in later life, have relatively little impact in comparison. These implicit assumptions about the "causal primacy" of maternal pregnancy effects set the agenda for DOHaD research and, through a looping effect, are reinforced rather than tested. We propose practical strategies to redress this imbalance through maintaining a critical perspective about these assumptions.

Effects of paternal high-fat diet and rearing environment on maternal investment and development of defensive responses in the offspring

Paternal preconception risk factors (e.g. stress, diet, drug use) correlate with metabolic dysfunction in offspring, which is often comorbid with depressive and anxiety-like phenotypes. Detection of these risk factors or deleterious phenotypes informs a female about prevailing ecological demands, in addition to potential adverse environment-induced phenotypes that may be disseminated to her offspring. We examined whether a F₀ male rat's prior exposure to an obesogenic high-fat diet (HFD) influences a female's attraction towards a male, subsequent mother-infant interactions and the development of defensive (emotional) responses in the F₁ offspring. Females displayed less interest in the HFD exposed F₀ males relative to control diet-exposed F₀ males. Dams that reared F₁ offspring in larger, semi-naturalistic housing provided more licking and grooming and active arched-back-nursing behavior. However, some of these effects interacted with paternal experience. F₀ HFD and maternal rearing environment revealed sex-dependent, between group differences in F₁ offspring wean weight, juvenile social interactions and anxiety-like behavior in adolescence. Our results show for the first time in mammals that male exposure to HFD may contribute to stable behavioral variation among females in courtship, maternal care, even when the females are not directly exposed to a HFD, and anxiety-like behavior in F₁ offspring. Furthermore, when offspring were exposed to a predatory threat, hypothalamic Crf gene regulation was influenced by early housing. These results, together with our previous findings, suggest that paternal experience and maternal rearing conditions can influence maternal behavior and development of defensive responses of offspring.

Maternal allocation of carotenoids to eggs in an Anolis lizard

The maternal allocation of carotenoids to eggs has been widely documented and manipulated. However, it is often assumed that the sole adaptive value of this allocation is to increase offspring fitness. Because carotenoids can be pro-oxidants or antioxidants depending on their concentrations and their chemical environment (i.e. presence of other antioxidants), dams may need to dispose of excess carotenoids upon depletion of other antioxidants to prevent oxidative damage. Additionally, the amount of carotenoids deposited in eggs may be dependent on male traits such as quality and coloration. We evaluated these two non-mutually exclusive hypotheses for carotenoid allocation to eggs and assessed paternal effects by supplementing male and female brown anole lizards, Anolis sagrei, with dietary carotenoids or with a combination of carotenoids and vitamin C. We found significant differences in the antioxidant capacities of fertilized and unfertilized eggs produced by female lizards, but the treatment did not affect the antioxidant capacity or carotenoid content of eggs. However, the carotenoid concentration of unfertilized eggs from carotenoid-supplemented females was significantly higher than eggs from the control group. Male coloration and body size did not affect the antioxidant capacity or carotenoid content of the eggs. Carotenoids may be allocated to unfertilized eggs to offset oxidative damage to the dam, with a neutral effect on offspring, rather than to solely provide antioxidant benefits to offspring as has been widely assumed.

Paternal identity impacts embryonic development for two species of freshwater fish

Paternal, compared to maternal, contributions were believed to have only a limited influence on embryonic development and larval fitness traits in fishes. Therefore, the perspective of male influence on early life history traits has come under scrutiny. This study was conducted to determine parental effects on the rate of eyed embryos of Ide Leuciscus idus and Northern pike Esox lucius. Five sires and five dams from each species were crossed using a quantitative genetic breeding design and the resulting 25 sib groups of each species were reared to the embryonic eyed stage. We then partition variation in embryonic phenotypic performance to maternal, paternal, and parental interactions using the Restricted Maximum Likelihood (REML) model. Results showed that paternal, maternal, and the paternal×maternal interaction terms were highly significant for both species; clearly demonstrating that certain family combinations were more compatible than others. Paternal effects explained 20.24% of the total variance, which was 2-fold higher than the maternal effects (10.73%) in Ide, while paternal effects explained 18.9% of the total variance, which was 15-fold higher than the maternal effects (1.3%) in Northern pike. Together, these results indicate that male effects are of major importance during embryonic development for these species. Furthermore, this study demonstrates that genetic compatibility between sires and dams plays an important role and needs to be taken into consideration for reproduction of these and likely other economically important fish species.

Male-lineage transmission of an acquired metabolic phenotype induced by grand-paternal obesity

Objective

Parental obesity can induce metabolic phenotypes in offspring independent of the inherited DNA sequence. Here we asked whether such non-genetic acquired metabolic traits can be passed on to a second generation that has never been exposed to obesity, even as germ cells.

Methods

We examined the F1, F2, and F3 a/a offspring derived from F0 matings of obese prediabetic A^vy/a sires and lean a/a dams. After F0, only lean a/a mice were used for breeding.

Results

We found that F1 sons of obese founder males exhibited defects in glucose and lipid metabolism, but only upon a post-weaning dietary challenge. F1 males transmitted these defects to their own male progeny (F2) in the absence of the dietary challenge, but the phenotype was largely attenuated by F3. The sperm of F1 males exhibited changes in the abundance of several small RNA species, including the recently reported diet-responsive tRNA-derived fragments.

Conclusions

These data indicate that induced metabolic phenotypes may be propagated for a generation beyond any direct exposure to an inducing factor. This non-genetic inheritance likely occurs via the actions of sperm noncoding RNA.

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Paternal obesity induces latent defects in metabolism in F1 sons.

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Metabolic disease in F1 sons is exposed by short challenge with a Western diet.

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F1 sons transmit their phenotype to F2 grandsons in the absence of dietary challenge.

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F1 sperm exhibit changes to prominent small RNA species.

Biparental immune priming in the pipefish Syngnathus typhle

The transfer of immunity from parents to offspring (trans-generational immune priming (TGIP)) boosts offspring immune defence and parasite resistance. TGIP is usually a maternal trait. However, if fathers have a physical connection to their offspring, and if offspring are born in the paternal parasitic environment, evolution of paternal TGIP can become adaptive. In Syngnathus typhle, a sex-role reversed pipefish with male pregnancy, both parents invest into offspring immune defence. To connect TGIP with parental investment, we need to know how parents share the task of TGIP, whether TGIP is asymmetrically distributed between the parents, and how the maternal and paternal effects interact in case of biparental TGIP. We experimentally investigated the strength and differences but also the costs of maternal and paternal contribution, and their interactive biparental influence on offspring immune defence throughout offspring maturation. To disentangle maternal and paternal influences, two different bacteria were used in a fully reciprocal design for parental and offspring exposure. In offspring, we measured gene expression of 29 immune genes, 15 genes associated with epigenetic regulation, immune cell activity and life-history traits. We identified asymmetric maternal and paternal immune priming with a dominating, long-lasting paternal effect. We could not detect an additive adaptive biparental TGIP impact. However, biparental TGIP harbours additive costs as shown in delayed sexual maturity. Epigenetic regulation may play a role both in maternal and paternal TGIP.

Paternal heat exposure causes DNA methylation and gene expression changes of Stat3 in Wild guinea pig sons

Epigenetic mechanisms convey environmental information through generations and can regulate gene expression. Epigenetic studies in wild mammals are rare, but enable understanding adaptation processes as they may occur in nature. In most wild mammal species, males are the dispersing sex and thus often have to cope with differing habitats and thermal changes more rapidly than the often philopatric females. As temperature is a major environmental selection factor, we investigated whether genetically heterogeneous Wild guinea pig (Cavia aperea) males adapt epigenetically to an increase in temperature, whether that response will be transmitted to the next generation(s), and whether it regulates mRNA expression. Five (F0) adult male guinea pigs were exposed to an increased ambient temperature for 2 months, corresponding to the duration of the species' spermatogenesis. To study the effect of heat, we focused on the main thermoregulatory organ, the liver. We analyzed CpG‐methylation changes of male offspring (F1) sired before and after the fathers' heat treatment (as has recently been described in Weyrich et al. [Mol. Ecol., 2015]). Transcription analysis was performed for the three genes with the highest number of differentially methylated changes detected: the thermoregulation gene Signal Transducer and Activator of Transcription 3 (Stat3), the proteolytic peptidase gene Cathepsin Z (Ctsz), and Sirtuin 6 (Sirt6) with function in epigenetic regulation. Stat3 gene expression was significantly reduced (P < 0.05), which indicated a close link between CpG‐methylation and expression levels for this gene. The two other genes did not show gene expression changes. Our results indicate the presence of a paternal transgenerational epigenetic effect. Quick adaptation to climatic changes may become increasingly relevant for the survival of wildlife species as global temperatures are rising.

Environmentally induced (co)variance in sperm and offspring phenotypes as a source of epigenetic effects

Traditionally, it has been assumed that sperm are a vehicle for genes and nothing more. As such, the only source of variance in offspring phenotype via the paternal line has been genetic effects. More recently, however, it has been shown that the phenotype or environment of fathers can affect the phenotype of offspring, challenging traditional theory with implications for evolution, ecology and human in vitro fertilisation. Here, I review sources of non-genetic variation in the sperm phenotype and evidence for co-variation between sperm and offspring phenotypes. I distinguish between two environmental sources of variation in sperm phenotype: the pre-release environment and the post-release environment. Pre-release, sperm phenotypes can vary within species according to male phenotype (e.g. body size) and according to local conditions such as the threat of sperm competition. Post-release, the physicochemical conditions that sperm experience, either when freely spawned or when released into the female reproductive tract, can further filter or modify sperm phenotypes. I find evidence that both pre- and post-release sperm environments can affect offspring phenotype; fertilisation is not a new beginning – rather, the experiences of sperm with the father and upon release can drive variation in the phenotype of the offspring. Interestingly, there was some evidence for co-variation between the stress resistance of sperm and the stress resistance of offspring, though more studies are needed to determine whether such effects are widespread. Overall, it appears that environmentally induced covariation between sperm and offspring phenotypes is non-negligible and further work is needed to determine their prevalence and strength.