Search

Background: The human female reproductive lifespan is regulated by the dynamics of ovarian function, which in turn is influenced by several factors: from the basic molecular biological mechanisms governing folliculogenesis, to environmental and lifestyle factors affecting the ovarian reserve between conception and menopause. From a broader point of view, global and regional demographic trends play an additional important role in shaping the female reproductive lifespan, and finally, influences on an evolutionary scale have led to the reproductive senescence that precedes somatic senescence in humans.Objective and Rationale: The narrative review covers reproductive medicine, by integrating the molecular mechanisms of ovarian function and aging with short-term demographic and long-term evolutionary trends.Search Methods: PubMed and Google Scholar searches were performed with relevant keywords (menopause, folliculogenesis, reproductive aging, reproductive lifespan and life history theory). The reviewed articles and their references were restricted to those written in English.Outcomes: We discuss and summarize the rapidly accumulating information from large-scale population-based and single-reproductive-cell genomic studies, their constraints and advantages in the context of female reproductive aging as well as their possible evolutionary significance on the life history trajectory from foetal-stage folliculogenesis until cessation of ovarian function in menopause. The relevant environmental and lifestyle factors and demographic trends are also discussed in the framework of predominant evolutionary hypotheses explaining the origin and maintenance of menopause.Wider Implications: The high speed at which new data are generated has so far raised more questions than it has provided solid answers and has been paralleled by a lack of satisfactory interpretations of the findings in the context of human life history theory. Therefore, the recent flood of data could offer an unprecedented tool for future research to possibly confirm or rewrite human evolutionary reproductive history, at the same time providing novel grounds for patient counselling and family planning strategies. [ABSTRACT FROM AUTHOR]

Costly reproductive competition among females is predicted to lead to strategies that reduce these costs, such as reproductive schedules. Simultaneous births of coresident women in human families can reduce their infant survival, but whether such competition also affects overall birth rates and whether females time their pregnancies to avoid simultaneous births remain unknown, despite being key questions for understanding how intrafemale competition affects reproductive strategies. Here, we used detailed parish registers to study female reproductive competition in historical Finnish joint-families, where brothers stayed on their natal farms and sisters married out, and consequently unrelated daughters-in-law often coresided and competed for household resources. We quantified the time-varying effects of having reproductive-aged competitor(s) on a woman's interval from marriage to first childbirth, on age-specific fertility, and on birth scheduling. Contrary to our hypothesis, the presence of one or several potential female competitors did not lead to longer first birth intervals or lower age-specific probability of reproduction. We also found no evidence that women would schedule their reproduction to avoid the real cost of simultaneous births on their offspring mortality risk; age-specific reproductive rates were unaltered by changes in the presence of other infants in the household. These results raise interesting questions regarding the evolution of fertility suppression in social mammals in different contexts, the costs and benefits of extended families for female reproductive success and strategies deployed, and the cultural practices that may help to avoid the negative outcomes of female reproductive competition in human families. [ABSTRACT FROM AUTHOR]

Lack of maternal milk commonly leads to Asian elephant calves' death in captivity. Currently, available supplements seem inefficient. Hence, we aimed at characterizing the composition of Asian elephant milk to provide information on calves' nutritional needs. Seventy milk samples from 22 Asian elephants living in semi-captivity in their natural environment in Myanmar were collected. Samples were analysed through various techniques including liquid chromatography tandem mass spectrometry, gas chromatography-flame ionization detector, and bicinchoninic acid assay to determine total protein content and various metabolites. Associations with lactation stage (months postpartum) were investigated through repeated measure mixed models. We identified 160 compounds: 22 amino acids, 12 organic acids of the tricarboxylic acid cycle, 27 fatty acids, 15 acyl-carnitines and 84 phospholipids. The milk contained substantial amounts of free glutamate (median: 1727.9, interquartile range (IQR): 1278.4 µmol l -1 ) and free glycine (2541.7, IQR: 1704.1 µmol l -1 ). The fatty acid profile was mostly constituted by saturated fatty acids, particularly capric acid (40.1, IQR: 67.3 g l -1 ). Milk samples also contained high amounts of carnitines, phospholipids and organic acids. The wide array of metabolites identified and quantified, some of which present high concentrations in the milk from this species as opposed to other species, suggests underpinning physiological functions that might be crucial for the survival of Asian elephant calves., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

Background: The transition to retirement is a significant turning point in life, which may lead to changes in food habits., Objective: To examine changes in red meat, fish, vegetables and fruit consumption during the retirement transition and whether these changes vary between sociodemographic groups., Methods: The data were from the Whitehall II study, a cohort of 10 308 British civil servants aged 35-55 years at study induction (1985-1988). Data collection has taken place every 2-3 years. Food consumption (n=2484-2491) was assessed with the Food Frequency Questionnaire in the periods before (max. 16 years) and after retirement (max. 16 years). Changes in preretirement and postretirement consumption were compared in the total cohort and subgroups by sex, marital status, preretirement occupation status and financial hardship using linear regression analyses with generalised estimating equations., Results: Weekly red meat consumption was stable before retirement but increased after retirement (p=0.02), especially among women, single and lower occupational status participants. Fish consumption increased during the follow-up and the increase was steeper before retirement than postretirement period (p=0.02). Vegetable and fruit consumption also increased during the entire follow-up, but more strongly during preretirement than postretirement period (p<0.001 for both)., Conclusion: The transition to retirement is accompanied by favourable (increase in fruit, vegetable and fish) and unfavourable (increase in red meat) dietary changes, varied to some extent by sex, marital status and preretirement occupational status. Our findings suggest that attention should be paid to this transitional phase to promote eating habits in accordance with the recommendations for retirement., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY. Published by BMJ.)

Preferential treatment of kin is widespread across social species and is considered a central prerequisite to the evolution of cooperation through kin selection. Though it is well known that, among most social mammals, females will remain within their natal group and often bias social behaviour towards female maternal kin, less is known about the fitness consequences of these relationships. We test the fitness benefits of living with maternal sisters, measured by age-specific female reproduction, using an unusually large database of a semi-captive Asian elephant ( Elephas maximus) population. This study system is particularly valuable to an exploration of reproductive trends in a long-lived mammal, because it includes life-history data that span multiple generations, enabling a study of the effects of kinship across a female's lifespan. We find that living near a sister significantly increased the likelihood of annual reproduction among young female elephants, and this effect was strongest when living near a sister 0-5 years younger. Our results show that fitness benefits gained from relationships with kin are age-specific, establish the basis necessary for the formation and maintenance of close social relationships with female kin, and highlight the adaptive importance of matriliny in a long-lived mammal. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.