Male-mediated early maturation unlikely to evolve via adaptive evolution.

The Vandenbergh effect, or male-mediated maturation, occurs when females reach sexual maturation upon exposure to a novel male. Male-mediated maturation is found across mammals, including in geladas, Theropithecus gelada, where it may be an adaptive counterstrategy to infanticide that follows the immigration of a new male; maturing after male immigration maximizes a female's chances of weaning her first offspring before the next infanticidal male immigrates (the 'optimal timing hypothesis'). Alternatively, the nonadaptive 'Bruce effect by-product hypothesis' posits that male-mediated maturation in geladas (and possibly other mammals) is triggered by the same physiological changes that, in pregnant females, produce spontaneous abortion (the Bruce effect). We test both hypotheses using theory and observational data. We show that neither male-mediated maturation nor its associated hormonal changes occur in baboons (Papio cynocephalus × P. anubis), a primate without the Bruce effect. An individual-based model suggests that male-mediated maturation should not evolve via adaptive evolution in either geladas or baboons. Finally, we derive the selection coefficient for male-mediated maturation and show it is likely to be very small because male-mediated maturation yields only marginal potential benefits unless the system is extremely fine-tuned. We conclude that male-mediated maturation in geladas is a by-product of the Bruce effect and more broadly that the Vandenbergh effect may be nonadaptive.

Resource availability alters breeding strategies in a small mammal community.

Following a resource pulse, animals may finance reproduction by consuming concurrently available resources (income breeding) or by storing resources for future reproduction (capital breeding). Understanding how these reproductive strategies are used is important for determining the ecological mechanisms that structure timing of reproduction and that drive interannual population fluctuations in animals. We gathered a reproductive dataset for five small mammal species over a 12-year period in Northeastern USA during which six masting events of American beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis) occurred. Masting created alternate years where seeds were either available late (masting year) or early (cached from the previous year) in the breeding season. The small mammal species differed in reliance on seeds and overwintering strategies. We quantified the diet using stable isotopes and recorded reproduction timing, proportion breeding and litter size in females and testes size in males. Timing of seed availability minimally affected litter size but strongly affected proportion breeding and timing of reproduction. During masting years (late seed availability), a higher proportion of females reproduced, with breeding taking place later in the season (lactation timed with peak seed availability), although the delay was restricted in Napaeozapus insignis, an obligate hibernator. After a fall mast, cached seeds were used as capital in the following spring (early seed availability) to support a litter that, depending on the species, occurred 24-79 days sooner than a mast year. No late-season reproduction occurred in years with early seed availability except for Myodes gapperi which produced a second litter, likely financed by fungal consumption. Males also showed strong responses to seed availability, mirroring female reproduction with testes size staying constant in years with late seed availability and sharply decreasing over the breeding season in years with early seed availability. Our results highlight that although photoperiod and temperature broadly set bounds of the breeding season in temperate environments, resource availability influences the reproductive strategies that species use, which in turn alters reproductive timing and can drive large inter-annual population fluctuations. Differences in overwintering strategies and diet may further modulate reproductive timing and output relative to resource pulses.

"You feel like you're fairly disadvantaged with an advert over your head saying 'in final years of reproduction'": social egg freezing, dating and the (unequal) politics of reproductive ageing.

Recent decades have seen an increasing gap occurring between the 'desired' and 'actual' family size of middle-class and professional women. This situation of 'unrealised fertility' and 'incomplete families' carries implications at a population, but also couple and individual level. This paper explores how middle-class professional women make decisions about partnering and parenthood and how these are shaped by a contemporary neoliberal feminist discourse which articulates the possibility of 'having it all' through engagement in careful life planning, appropriate self-investment, and by drawing on new technologies of reproductive biomedicine. Informed by semi-structured interviews with UK and US women conducted at two different points in time, it explores how they approach and experience the process of relationship formation in the face of age-related fertility decline. It also examines how the use of social egg freezing shape their romantic and family building expectations but also their interactions with (potential) partners. In doing so, it explores how gendered cultural dating scripts and unequal gender power relations shape the formation and progression of intimate relationships in a manner which can disempower women as they age. It therefore questions whether egg freezing may be the 'great equaliser' that some have hoped.

Parental age at death is associated with age at first birth in offspring.

PURPOSE: People age at different rates and the available evidence suggests that the rate of aging is partly inherited from previous generations. This heterogeneity in aging is evident already in midlife, but to what extent aging is associated with the timing of events earlier in life is not fully known. Here we aim to shed light on this topic by investigating the trade-off between reproduction and aging postulated by evolutionary theories of aging. METHODS: Drawing on the inheritance of aging we use parental age at death as a proxy for aging-rates in the offspring, and study how age at first birth depends on this variable. We use data from an almost complete Swedish birth cohort comprising 92,359 individuals. Accelerated failure time models are used to estimate the association between parental age at death and age at first birth while adjusting for parental occupational class, educational attainment, and income. RESULTS: Longer parental lifespans were consistently associated with older age at first births, both in men and women. CONCLUSION: Our findings suggest that aging-related processes may be interrelated with the processes underlying the timing of reproduction and are in general agreement with evolutionary theories of aging.

Childhood adversity and accelerated reproductive events: a systematic review and meta-analysis.

OBJECTIVE: Accelerated female reproductive events represent the early onset of reproductive events involving puberty, menarche, pregnancy loss, first sexual intercourse, first birth, parity, and menopause. This study aimed to explore the association between childhood adversity and accelerated female reproductive events. DATA SOURCES: PubMed, Web of Science, and Embase were systematically searched from September 22, 2022 to September 23, 2022. STUDY ELIGIBILITY CRITERIA: Observational cohort, cross-sectional, and case-control studies in human populations were included if they reported the time of reproductive events for female individuals with experience of childhood adversity and were published in English. METHODS: Two reviewers independently screened studies, obtained data, and assessed study quality, and conflicts were resolved by a third reviewer. Dichotomous outcomes were evaluated using meta-analysis, and pooled odds ratios and 95% confidence intervals were generated using random-effects models. Moderation analysis and meta-regression were used to investigate heterogeneity. RESULTS: In total, 21 cohort studies, 9 cross-sectional studies, and 3 case-control studies were identified. Overall, female individuals with childhood adversity were nearly 2 times more likely to report accelerated reproductive events than those with no adversity exposure (odds ratio, 1.91; 95% confidence interval, 1.33-2.76; I2=99.6%; P<.001). Moderation analysis indicated that effect sizes for the types of childhood adversity ranged from an odds ratio of 1.61 (95% confidence interval, 1.23-2.09) for low socioeconomic status to 2.13 (95% confidence interval, 1.14-3.99) for dysfunctional family dynamics. Among the 7 groups based on different reproductive events, including early onset of puberty, early menarche, early sexual initiation, teenage childbirth, preterm birth, pregnancy loss, and early menopause, early sexual initiation had a nonsignificant correlation with childhood adversity (odds ratio, 2.70; 95% confidence interval, 0.88-8.30; I2=99.9%; P<.001). Considerable heterogeneity (I2>75%) between estimates was observed for over half of the outcomes. Age, study type, and method of data collection could explain 35.9% of the variance. CONCLUSION: The literature tentatively corroborates that female individuals who reported adverse events in childhood are more likely to experience accelerated reproductive events. This association is especially strong for exposure to abuse and dysfunctional family dynamics. However, the heterogeneity among studies was high, requiring caution in interpreting the findings and highlighting the need for further evaluation of the types and timing of childhood events that influence accelerated female reproductive events.

"It was not an accident": Women's experiences of renewing motherhood at 40.

In recent decades, there has been an increase in motherhood at an advanced age that has raised several medical and social concerns. We conducted a qualitative interview study, guided by Interpretative Phenomenological Analysis, to focus on the motivations and experiences of Belgian women who 'renewed' their motherhood later in life, meaning they had one or several children and then (at least 10 years later) had another child at the age of 40 or older. We focused on ten women's experiences of motherhood later in life, as well as on the way they managed social norms and expectations regarding family building and the appropriate life course. We identified two main themes. The first theme describes the participants' encounters with social norms that challenged their decision to reproduce and parent later in life, and how they managed and anticipated criticism, surprise, disbelief and incomprehension about their renewed motherhood in various ways. The second theme shows how these women talked about taking responsibility as a (renewed) mother of advanced age. For them, responsible motherhood involved making thoughtful reproductive choices, attending to the range of needs of their children, and making extra efforts to safeguard the social and emotional wellbeing of their youngest children, thereby seeking to reduce potential harm resulting from these reproductive choices. This study provides insight into these women's self-conception and their interactions with prejudiced social views of motherhood and family building.

Individual Variation in Parturition Timing within and among Years for a Bat Maternity Colony.

BACKGROUND: In monoestrous species, the timing of reproduction can have important impacts on offspring survival. For heterotherms in temperate areas, parturition timing is constrained by cold weather survival strategies, such as hibernation and torpor. Female bats that are year-round residents of temperate regions, such as little brown myotis (Myotis lucifugus), invest significantly in parental care resulting in sharp changes in behavior immediately following parturition. These behavior changes may include increases in nighttime roost revisits, which can be used to identify parturition dates for individual bats that have been passive integrated transponder (PIT) tagged and use monitored roosts. METHODS: Using a system of tagged bats and monitored roosts in Pynn's Brook and Salmonier Nature Park Newfoundland, Canada, we estimated parturition dates for 426 female M. lucifugus in at least one year, based on changes in nighttime roost revisit patterns, and quantified the variation in parturition dates within years among individuals, and within individuals among years. RESULTS: Overall, we report on a wide variation in parturition dates within years among individuals as well as year-to-year variations, both across the population and within individuals. Spring weather conditions appeared to be important influences on parturition timing. CONCLUSIONS: Changes in spring and summer temperature and extreme weather events, as expected due to ongoing climate change, may impact parturition timing, and therefore, offspring survival of temperate bats.

Infertility, reproductive timing and 'cure' in families affected by Turner Syndrome.

This article discusses the influence of a chromosome condition affecting women's reproductive capacity, Turner Syndrome (TS), on affected women's social timing, examining the strategic decisions that are made within families in relation to reproduction, to navigate these disruptions. Based on photo elicitation interviews with 19 women with TS and 11 mothers of girls with TS in the UK, it presents findings from an under-researched topic, TS and reproductive choices. In a social context where motherhood is not only desirable, but expected (Suppes, 2020), the social imaginary of infertility anticipates a future of unhappiness and rejection, an undesirable condition that should be avoided. Accordingly, mothers of girls with TS often expect that their daughter will want to have children. Infertility diagnosed in childhood has a distinctive impact on reproductive timing, as future options may be anticipated for years. This article uses the concept of 'crip time' (Kafer, 2013) to explore how women with TS and mothers of girls with TS experience temporal misfitting based on a childhood diagnosis of infertility, and manage, resist and re-frame this to minimise stigma. The 'curative imaginary' (Kafer, 2013), a social norm where disabled people are expected to desire a cure for their condition, is used as an analogy for infertility, describing how mothers of girls with TS respond to social pressure to plan for their daughter's reproductive future. These findings may be useful both for families navigating childhood infertility and practitioners who support them. This article demonstrates the cross-disciplinary potential of applying disability studies concepts to the context of infertility and chronic illness, where concepts shed new light on the dimensions of timing and anticipation in this context, improving our understanding of the lived experience of women with TS, and how they view and use reproductive technologies.

The ART clock: Temporal limits to assisted reproduction.

Conceptualizations of the 'biological clock' in popular imaginary in the USA centre on the temporal limits of fertility, with assisted reproductive technology (ART) an increasingly proposed answer to these constraints (at least in the public imaginary). In this study, I analyse how surrogates in the USA understand their own bioavailability for others' reproductive needs in the commercial ART market vis-à-vis their own reproductive trajectories. Based on interview data with gestational surrogates, I propose a new concept of the 'ART clock' to capture how time shapes the experiences of reproductive workers in the US fertility clinic. My findings point to four important ART time-related issues: (i) women desiring to extend their own 'biological clocks' via surrogacy; (ii) significant time being needed to achieve and sustain third-party pregnancy; (iii) women extending their total reproductive time via repeat surrogacy 'journeys'; and (iv) temporal constraints to surrogacy reproduction regarding time of year, the day-to-day time effort, the number of surrogacy journeys, the total number of pregnancies, and surrogates' age and the ages of their children. Each of these aspects point to important ways that reproductive desire and time shape the labour of reproductive workers, highlighting temporal constraints to assisted reproduction and limits to ART as a solution to delayed reproduction and the biological clock.

Associations between distinct dimensions of early life adversity and accelerated reproductive strategy among middle-aged women in China.

BACKGROUND: Life history theory argues that unpredictable and harsh conditions such as early life adversity tends to produce a fast life history strategy, characterized by early sexual maturation and less parenting of offspring. It remains unclear whether all forms of early life adversity are associated with accelerated reproductive strategy, and most previous studies predominantly focused on single form of reproductive strategy indicators. OBJECTIVE: To examine the associations between 2 distinct dimensions of early life adversity (ie, threat and deprivation) and reproductive strategies across global metrics. STUDY DESIGN: We used data from 9674 middle-aged women of the China Health and Retirement Longitudinal Study. The experiences of threat and deprivation were assessed using the Life History Survey Questionnaire in 2014. Reproductive strategy information was assessed via self-report from the follow-up of 2013, 2015 and 2018, including age at menarche, age at natural menopause, age at first birth, total number of children, and number of abortions. Multivariate linear regression analyses were performed to assess the associations between distinct dimensions of early life adversity and multiple reproductive strategy indicators, adjusting for age, Hukou location, family socioeconomic status in adulthood and body mass index. RESULTS: Of the 9674 women (mean [standard deviation] age at baseline, 55.89 [10.23] years), 4084 (42.20%) reported exposure to threat-related early life adversity and 7332 (75.79%) reported exposure to deprivation-related early life adversity. Early life adversity characterized by threat was associated with accelerated reproductive strategy. Compared with women who have no experiences of threat-related early life adversity, ≥3 threat-related early life adversity was associated with 3.7-month earlier age at menarche (ß=-0.31, 95% confidence interval, -0.53 to -0.08; P=.007), 8.6-month earlier age at natural menopause (ß=-0.72, 95% confidence interval, -1.29 to -0.15; P=.013), >1-year earlier age at first birth (ß=-1.14, 95% confidence interval, -1.58 to -0.71; P<.0001), and an increased total number of children (ß=0.25, 95% confidence interval, 0.10-0.41; P=.002). In contrast, experiences of deprivation were associated with delayed age at natural menopause (ß=.50, 95% confidence interval, 0.06-0.94; P=.025) and increased number of abortions (ß=.17, 95% confidence interval, 0.01-0.34, P=.037), in models adjusting for co-occurring threat exposures. CONCLUSION: This study suggests that early life adversity characterized by threat was associated with accelerated reproductive strategy, whereas deprivation was associated with slower reproduction strategy. Future research should clarify the biological pathways between different dimensions of early life adversity and reproductive strategies and further determine whether accelerated reproduction is an adaptive response to early life adversity in humans.

Does Nubility Indicate More Than High Reproductive Value? Nubile Primiparas' Pregnancy Outcomes in Evolutionary Perspective.

The idea that human males are most strongly attracted to traits that peak in women in the nubile age group raises the question of how well women in that age group contend with the potential hazards of a first pregnancy. Using data for 1.7 million first births from 1990 U.S. natality and mortality records, we compared outcomes for women with first births (primiparas) aged 16-20 years (when first births typically occur in forager and subsistence groups) with those aged 21-25 years. The younger primiparas had a much lower risk of potentially life-threatening complications of labor and delivery and, when evolutionarily novel risk factors were controlled, fetuses which were significantly more likely to survive despite lower birth weights. Thus, nubile primiparas were more likely to have a successful reproductive outcome defined in an evolutionarily relevant way (an infant of normal birth weight and gestation, surviving to one year, and delivered without a medically necessary cesarean delivery). This suggests that prior to the widespread availability of surgical deliveries, men who mated with women in the nubile age group would have reaped the benefit of having a reproductive partner more likely to have a successful first pregnancy.

Natural variation in reproductive timing and X-chromosome nondisjunction in Caenorhabditis elegans.

Caenorhabditis elegans hermaphrodites first produce a limited number of sperm cells, before their germline switches to oogenesis. Production of progeny then ensues until sperm is depleted. Male production in the self-progeny of hermaphrodites occurs following X-chromosome nondisjunction during gametogenesis, and in the reference strain increases with age of the hermaphrodite parent. To enhance our understanding of the reproductive timecourse in C. elegans, we measured and compared progeny production and male proportion during the early and late reproductive periods of hermaphrodites for 96 wild C. elegans strains. We found that the two traits exhibited natural phenotypic variation with few outliers and a similar reproductive timing pattern as previous reports. Progeny number and male proportion were not correlated in the wild strains, implying that wild strains with a large brood size did not produce males at a higher rate. We also identified loci and candidate genetic variants significantly associated with male-production rate in the late and total reproductive periods. Our results provide an insight into life-history traits in wild C. elegans strains.

Rapid changes in DNA methylation associated with the initiation of reproduction in a small songbird.

Species with a circannual life cycle need to match the timing of their life history events to the environment to maximize fitness. However, our understanding of how circannual traits such as timing of reproduction are regulated on a molecular level remains limited. Recent studies have implicated that epigenetic mechanisms can be an important part in the processes that regulate circannual traits. Here, we explore the role of DNA methylation in mediating reproductive timing in a seasonally breeding bird species, the great tit (Parus major), using genome-wide DNA methylation data from individual females that were blood sampled repeatedly throughout the breeding season. We demonstrate rapid and directional changes in DNA methylation within the promoter region of several genes, including a key transcription factor (NR5A1) known from earlier studies to be involved in the initiation of timing of reproduction. Interestingly, the observed changes in DNA methylation at NR5A1 identified here are in line with earlier gene expression studies of reproduction in chicken, indicating that the observed shifts in DNA methylation at this gene can have a regulatory role. Our findings provide an important step towards elucidating the genomic mechanism that mediates seasonal timing of a key life history traits and provide support for the idea that epigenetic mechanisms may play an important role in circannual traits.

Effects of Individual Mortality Experience on Out-of-Wedlock Fertility in Eighteenth- and Nineteenth-Century Krummhörn, Germany.

Life history theory predicts that exposure to high mortality in early childhood leads to faster and riskier reproductive strategies. Individuals who grew up in a high mortality regime will not overly wait until they find a suitable partner and form a stable union because premature death would prevent them from reproducing. Cox proportional hazard models were used to determine whether women who experienced sibling death during early childhood (0-5 years) reproduced earlier and were at an increased risk of giving birth to an illegitimate child, with illegitimacy serving as a proxy for risky sexual behavior. Furthermore, we investigate whether giving birth out of wedlock is influenced by individual mortality experience or by more promiscuous sexual behavior that is clustered in certain families. Models are fitted on pedigree data from the eighteenth- and nineteenth-century Krummhörn population in Germany. The results show a relationship between sibling death in early childhood and the risk of reproducing out of wedlock, and reproductive timing. The risk of giving birth out of wedlock is linked to individual mortality experience rather than to family-level effects. In contrast, adjustments in connubial reproductive timing are influenced more by family-level effects than by individual mortality experience.

The greater the economic inequality, the later people have children: The association between economic inequality and reproductive timing.

Economic inequality is associated with a series of social outcomes, including health, social trust, and crime rates. However, little is known about the role of economic inequality as a characteristic of the socioecological environment in individuals' reproductive behavior. According to embodied capital theory, this research explored how individuals calibrate their reproductive timing to maximize payoffs to investment in embodied capital in an environment of high economic inequality. Five studies were conducted to test the hypothesis that higher economic inequality leads people to delay reproduction. Across nations (Study 1), we found that the average reproductive age is higher in nations with greater economic inequality. Study 2 found that people living in more economically unequal U.S. states tend to marry later. In Study 3, individuals who perceived higher levels of inequality in a given society planned to have their children later. Finally, in Study 4, the priming of high inequality led to a greater preference for delaying reproduction, which represented a desire to pursue one's development rather than to build a family (Study 4a and 4b). These results expand the literature regarding the effect of economic inequality on human behavior.

Financial opportunity costs and deaths among close kin are independently associated with reproductive timing in a contemporary high-income society.

Evolutionary demography predicts that variation in reproductive timing stems from socio-ecologically contingent trade-offs between current and future reproduction. In contemporary high-income societies, the costs and benefits of current reproduction are likely to vary by socioeconomic status (SES). Two influential hypotheses, focusing on the parenthood 'wage penalty', and responses to local mortality have separately been proposed to influence the timing of parenthood. Economic costs of reproduction (i.e. income loss) are hypothesized to delay fertility, especially among high childhood SES individuals who experience greater opportunities to build capital through advantageous education and career opportunities. On the other hand, relatively low childhood SES individuals experience higher mortality risk, which may favour earlier reproduction. Here, we examine both hypotheses with a representative register-based, multigenerational dataset from contemporary Finland (N = 47 678). Consistent with each hypothesis, the predicted financial cost of early parenthood was smaller, and mortality among close kin was higher for individuals with lower childhood SES. Within the same dataset, lower predicted adulthood income and more kin deaths were also independently associated with earlier parenthood. Our results provide a robust demonstration of how economic costs and mortality relate to reproductive timing. We discuss the implications of our findings for demographic theory and public policy.

Black-capped chickadees (Poecile atricapillus) use temperature as a cue for reproductive timing.

Reliable environmental cues, such as photoperiod, act as initial predictive cues that allow birds to time reproduction to match peak food abundance for their offspring. More variable local cues, like temperature, may, however, provide more precise information about the timing of food abundance. Non-migratory birds, in particular, should be sensitive to temperature cues and use them to modulate their reproductive timing. We conducted two experiments to examine the effect of temperature on reproductive condition (gonad size and circulating androgen levels) in non-migratory black-capped chickadees (Poecile atricapillus). First, we exposed groups of birds in outdoor aviaries to three different over-winter temperature treatments and assessed gonad size in the spring. Second, we manipulated temperature in environmental chambers under photostimulatory and non-photostimulatory photoperiodic conditions and assessed gonad size and circulating testosterone levels. Temperature had no independent effect on gonad size or testosterone levels, but when photostimulated birds exposed to warmer conditions became reproductively ready earlier than birds experiencing cooler conditions. We conclude that temperature acts as a supplementary cue that modulates the photoperiod-driven timing of reproduction.

Adverse childhood experiences and reproductive strategies in a contemporary U.S. population.

OBJECTIVES: Stressful experiences may initiate developmentally plastic responses toward a faster reproductive strategy. This study tests whether adverse childhood experiences (ACEs) are associated with characteristics of faster reproductive strategies: earlier menarche and reduced prenatal investment in offspring in a well-nourished, low-immune system burden population. MATERIALS AND METHODS: We analyzed the first 214 enrollees of the prenatal-birth Albany Infant and Mother Study. Mother's menarcheal age, offspring gestational age at birth, and cephalization index (head circumference/weight, cm/g) were derived from medical records. Linear regression models tested the contribution of self-reported ACEs from 0 to 18 years of age to menarcheal age and the contribution of menarcheal age to offspring gestational age and cephalization index. Birth outcome models included covariates self-reported maternal race, education, prenatal smoking, prenatal diet, newborn sex, parity, delivery method, and labor induction derived from medical records. RESULTS: More ACEs were associated with earlier age at menarche, controlling for covariates (ß = -.18, SE = 0.048, p < .001), though timing of ACEs relative to menarche is unknown. Earlier menarcheal age was associated with offspring higher cephalization index (ß = -.01, SE = 0.006, p < .05). Stratified models showed a significant relationship in high (≥2) ACEs group (ß = -.02, SE = 0.009, p < .05), not present among low ACEs. Menarcheal age predicted gestational age only among those with high ACEs (ß = .22, SE = 0.091, p < .05). DISCUSSION: In a well-nourished population, early life stress can result in faster reproductive strategies, initiating sexual maturation earlier, and reducing prenatal investment in individual offspring. Early age at menarche following childhood stress has a stronger relationship with adverse birth outcomes than early menarche without exposure to adverse childhood stress.

Fine-tuning of seasonal timing of breeding is regulated downstream in the underlying neuro-endocrine system in a small songbird.

The timing of breeding is under selection in wild populations as a result of climate change, and understanding the underlying physiological processes mediating this timing provides insight into the potential rate of adaptation. Current knowledge on this variation in physiology is, however, mostly limited to males. We assessed whether individual differences in the timing of breeding in females are reflected in differences in candidate gene expression and, if so, whether these differences occur in the upstream (hypothalamus) or downstream (ovary and liver) parts of the neuroendocrine system. We used 72 female great tits from two generations of lines artificially selected for early and late egg laying, which were housed in climate-controlled aviaries and went through two breeding cycles within 1 year. In the first breeding season we obtained individual egg-laying dates, while in the second breeding season, using the same individuals, we sampled several tissues at three time points based on the timing of the first breeding attempt. For each tissue, mRNA expression levels were measured using qPCR for a set of candidate genes associated with the timing of reproduction and subsequently analysed for differences between generations, time points and individual timing of breeding. We found differences in gene expression between generations in all tissues, with the most pronounced differences in the hypothalamus. Differences between time points, and early- and late-laying females, were found exclusively in the ovary and liver. Altogether, we show that fine-tuning of the seasonal timing of breeding, and thereby the opportunity for adaptation in the neuroendocrine system, is regulated mostly downstream in the neuro-endocrine system.

On the sunny side of (new) life: Effect of sunshine duration on age at first reproduction in Japanese macaques (Macaca fuscata).

To produce offspring early in life is energetically demanding and depends greatly on environmental conditions. In female primates, age at first reproduction (AFR) has been associated with social parameters (e.g., population density and social rank), food availability and meteorological conditions (e.g., photoperiod, rainfall patterns, and temperature). Regarding the latter, less attention has been given to the influence of sunshine. In nonhuman primates, including the northern-most distributed Japanese macaque (Macaca fuscata), sunbathing is an effective thermoregulatory strategy to maintain sufficient energy intake during harsh winter months. Furthermore, the energetic value of sunshine and its role in the synthesis of essential vitamins important for sexual development and overall fertility is well investigated using human and animal models. In the present study, we hypothesized that female's AFR is influenced by the amount of sunshine in a semi-free-ranging, provisioned a group of Japanese macaques. To test this, we gathered data on sunshine duration in the year females theoretically experienced the onset of puberty. This phase of the female life cycle is particularly prone to the effects of environmental conditions. In addition to the investigation of sunshine duration and other meteorological conditions (i.e., rainfall and temperature) we controlled for social parameters (i.e., group size and sex ratio) as potential covariates. We found a clear effect of sunshine duration on female AFR: Females who entered puberty in years with more sunshine reproduced for the first time at significantly younger ages than females who experienced less sunshine during this specific period of their development. Possible mechanisms for how the sunshine influences sexual maturation in Japanese macaques are discussed.