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PubMed1999

Male reproductive health research needs and research agenda: Asian and Chinese perspective.

Research that addresses male reproductive health should assist in the development of reproductive health programmes and policy; identify and test new leads in male contraceptive technology; establish effective male involvement initiatives which are likely to have a positive impact on the reproductive health of men and women; guide the allocation of health care resources to ensure cost-effectiveness of interventions; generate new knowledge, develop diagnostic technology in reproductive health and offer optimal treatment/care regimens. In considering the needs and demands of male reproductive health research in Asia and the Pacific, the following six research topics are recommended as the priority research areas: male contraceptive technology; male reproductive health behaviour and male adolescent reproductive health; male reproductive aging including male menopause and other diseases; male RTIs, STDs, HIV/AIDS; prevalence, management and prevention of male infertility; environment and semen quality and other male reproductive problems. One of the major challenges now facing us is the elaboration of a comprehensive, yet realistic male reproductive health research agenda that reflect the needs and demands of Asian developing countries. To this end, to make use of an interdisciplinary approach is of strategic importance. The most creative insights and productive leads are likely to emerge from a research team that is interdisciplinary especially in the field of reproductive health.

Adolescent↗

PubMed2025

Unisexual reproduction in the global human fungal pathogen Cryptococcus neoformans.

The human fungal pathogen Cryptococcus species complex (encompassing C. neoformans, C. deneoformans, and the C. gattii species complexes) exhibit diversity in sexual reproduction, including α-a mating, pseudosexual reproduction, as well as unisexual reproduction initiated from a single isolate or between isolates of the same mating type. A central conundrum is that while most Cryptococcus natural populations exhibit significant α mating-type bias, genetic and genomic analyses show recombination occurs in nature. The discovery of unisexual reproduction in C. deneoformans provided insight; however, thus far unisexual reproduction has never been directly observed in the predominant global pathogenic species C. neoformans. Here, we provide evidence that mutating the RIC8 gene, which encodes a conserved guanine nucleotide exchange factor (GEF) involved in both chaperoning and activating Gα proteins, enables unisexual reproduction in C. neoformans. Additionally, we show that genetic variation in the natural population promotes unisexual reproduction, and unisexual reproduction in C. neoformans involves canonical meiotic recombination. Finally, we found that deletion of both GPA2 and GPA3 in the MATα background leads to self-filamentation without sporulation, suggesting that differential modulation of the Gα proteins, likely involving Ric8, could underlie the switch between different modes of sexual reproduction in Cryptococcus. Our study further highlights that the highly conserved Ric8 GEF can act as an important regulator of cellular development in response to environmental stimuli and could modulate sexual reproduction in nature. We hypothesize that unisexual reproduction occurs much more frequently in nature than currently appreciated, and possibly in other fungi and microbial eukaryotes as well.

G protein↗

PubMedDate not supplied

A delay in age at first mating results in the loss of future reproductive potential via apoptosis.

Women who delay childbearing risk subfertility. However, this loss of fertility is not a simple function of aging. Women who have had children early in life tend to maintain fertility longer, measured as a later age at menopause. But why should otherwise healthy women lose reproductive capacity? Loss of fertility independent of senescence, menopause, has been approached from two perspectives: evolution and development. Evolutionary biologists focus on how natural selection favors survival after reproductive ability has ceased, whereas reproductive biologists examine mechanisms by which women lose fertility with age and factors that influence the rate of reproductive aging. Combining mechanistic studies with evolutionary theory should allow us to define principles of the evolution of postembryonic development of ovaries, including the role of reproductive timing relative to sexual maturation. Achieving this will require identifying appropriate, and more experimentally tractable, taxa in which to study how early reproductive events influence lifetime fertility. We work with an invertebrate species, the cockroach Nauphoeta cinerea, with a complex reproductive biology in which females experience reproductive cycles, give live birth, and show age-related decline in fertility. Thus, N. cinerea provides an opportunity to use an experimental approach to examine mechanisms by which females lose reproductive potential as they delay reproduction. Our results demonstrate that the loss of both oocytes ready for fertilization and future oocytes in females that delay mating is because of apoptosis. We suggest that loss of fertility because of delayed mating may originate in a nonadaptive response in control of apoptosis through mistiming of reproduction.

Age Factors↗

PubMed2000

Genetic variation and evolutionary trade-offs for sexual and asexual reproductive modes in Allium vineale (Liliaceae).

Populations of Allium vineale commonly include individuals with very different allocation patterns to three modes of reproduction: sexual flowers, aerially produced asexual bulbils, and belowground asexual offsets. If selection is currently acting to maintain these different allocation patterns there must be a genetic basis for variation in allocation to these three reproductive modes. In addition, negative genetic correlations between reproductive traits would imply evolutionary trade-offs among reproductive strategies. We evaluated the heritability of these allocation patterns by growing 16 clones from a single population in the greenhouse at two levels of fertilization. Bulb mass and the mass and number of bulbils, offsets, and flowers were used as response variables, in addition to the proportion allocated to each reproductive mode. We found evidence of substantial heritable variation in allocation to sexual reproduction and in allocation within the two modes of asexual reproduction, indicating high sensitivity of these allocation patterns to natural selection. We also found evidence of strong negative genetic correlations between bulbil and flower traits, as well as between bulbil and offset traits, with one group of genotypes allocating greater resources to aerial asexual bulbils and the second group allocating more resources to belowground asexual offsets and aerial flowers. Phenotypic plasticity in allocation to above- vs. belowground asexual reproduction and sexual vs. asexual aerial reproduction was limited, indicating that plants are unlikely to change reproductive mode in response to nutrient availability. Together, then, we have demonstrated strong heritability for, and trade-offs in, the reproductive allocation patterns within this plant population.

Journal Article↗

PubMed2005

Toxic effects of bisphenol A on sexual and asexual reproduction in Hydra oligactis.

Hydra oligactis, an evolutionarily primitive invertebrate, produced eggs or testes (sexual reproduction) when starved at 10 degrees C, and produced buds (asexual reproduction) when fed at 20 degrees C. Bisphenol A (BPA) at 2-4 mg/L given to male or female hydra had adverse effects on both sexual and asexual reproduction. Despite the estrogenic nature of BPA, testis formation and egg formation were similarly affected. The doses causing these acute toxicities were comparable to those reported earlier in aquatic invertebrates and were much higher than environmentally detected doses, at which the disruption of the endocrine system has been reported in fishes. All these facts indicate that the adverse effects are the results of general toxicity and may not be due to the estrogenic function of the compound. On the other hand, we found that BPA at 1 mg/L (a dose still much higher than environmental doses) stimulated asexual reproduction. No such stimulation of sexual reproduction was seen. When male hydras were fed at 10 degrees C, they produced both buds and testes simultaneously. BPA at 0.5 and 1 mg/L under this condition also stimulated asexual reproduction, whereas it suppressed sexual reproduction more severely than BPA at 2-3 mg/L. There may be some interaction between processes involved in sexual and asexual reproduction under this condition, and the stimulation of asexual reproduction by BPA may cause suppression of sexual reproduction.

Animals↗

PubMed1997

Trends in reproductive health knowledge following a health education intervention among adolescents in Zimbabwe.

BACKGROUND: Unwanted teenage pregnancy, sexually transmitted infections and the attendant morbidity and mortality necessitate the need for understanding factors influencing adolescent sexuality and the implementation of programmes designed to improve their knowledge, reproductive behaviour, sexual and reproductive health. OBJECTIVE: To determine the impact of an intervention package on knowledge levels of various reproductive health issues through trend analysis. DESIGN: Randomized controlled trial of a health education intervention in schools stratified for representativeness. SETTING: Rural and urban secondary schools in Zimbabwe. SUBJECTS: 1,689 students recruited from 11 secondary schools in Mashonaland Central. MAIN OUTCOME MEASURE: Knowledge level before and after intervention. RESULTS: The demographic characteristics of the pupils at baseline, five months and nine months were comparable between the two groups. There was an overall increase in knowledge on menstruation. Students from the intervention schools were more likely to have correct knowledge over time on aspects of reproductive biology. A significant linear trend (p = 0.017) was observed in the area of family planning and contraception. A linear decreasing trend (p = 0.001) was observed on pregnancy risk. Though not significantly linear, the general trend of knowledge levels in all the areas of reproductive health, pregnancy risk, STDs and HIV/AIDS showed an upward trend, from 20% to 96%. Worth noting was that in all the areas the intervention group had knowledge above that in the control group. CONCLUSION: The reproductive health education intervention had an impact on aspects of reproductive biology and contraception as measured by the increased scoring at follow up when comparing intervention and control schools. The overall findings point to the need for early school based reproductive health education programmes incooperating correct information on reproductive biology and the prevention of subsequent reproductive morbidity by imparting information on non-risk behaviour during the early developmental years.

Adolescent↗

PubMed1992

A survey of infertility, surgical sterility and associated reproductive disability in Perth, Western Australia.

Infertility, surgical sterility and associated reproductive disability were studied in a stratified cluster sample of 1,511 couples with women aged 16 to 44 years resident in metropolitan Perth in 1988. Sixteen couples were omitted from analysis because of missing data. The proportion of couples affected by current infertility was 3.5 per cent (53 of 1,495), and 67.9 per cent of these (36 of 53) had a reproductive disability, meaning that they were unable to achieve their desired level of reproductive function. Those affected by surgical sterility accounted for 37.1 per cent (555 of 1,495), and of these couples 2.0 per cent (11 of 555) had a reproductive disability. Empirically, the prevalence of both infertility and reproductive disability peaked at ages 30 to 34 years in the female partner. Of the factors studied, infertility was associated with surgery for a ruptured appendix, a history of pelvic inflammatory disease and number of sexual partners. In 10 of the 47 couples with reproductive disability, contraceptive sterilisation had been a cause of later regret. Most other cases were due to infertility. Almost one half of couples with reproductive disability had sought treatment. The affected couples had at least one child from the current union in 23 of the 47 cases of reproductive disability. The results support the need for development of a strategy to prevent infertility and other causes of reproductive disability.

Adolescent↗

PubMed2001

Reproductive period and risk of dementia in postmenopausal women.

CONTEXT: Exogenous estrogen use may lower risk of dementia in postmenopausal women. A relationship between long-term exposure to endogenous estrogens and incident dementia has been hypothesized but not studied. OBJECTIVE: To determine whether a longer reproductive period, as an indicator of longer exposure to endogenous estrogens, is associated with lower risk of dementia and Alzheimer disease (AD) in women who have natural menopause. DESIGN AND SETTING: The Rotterdam Study, a population-based prospective cohort study conducted in the Netherlands. PARTICIPANTS: A total of 3601 women aged 55 years or older who did not have dementia at baseline (1990-1993) and had information on age at menarche, age at menopause, and type of menopause. Participants were reexamined in 1993-1994 and 1997-1999 and were continuously monitored for development of dementia. MAIN OUTCOME MEASURES: Incidence of dementia, based on Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition criteria, and AD, based on National Institute of Neurological Disorders and Stroke/Alzheimer's Disease and Related Disorders Association criteria, compared by quartiles of reproductive period among women with natural menopause. RESULTS: During 21 046 person-years of follow-up (median follow-up, 6.3 years), 199 women developed dementia, including 159 who developed AD. After adjusting for age, dementia was not clearly associated with length of reproductive period. However, after adjusting for multiple covariates, women with natural menopause and more reproductive years had an increased risk of dementia (adjusted rate ratio [RR] for women with >39 reproductive years [highest quartile] compared with <34 reproductive years [lowest quartile], 1.78; 95% confidence interval [CI], 1.12-2.84). The adjusted RR per year of increase was 1.04 (95% CI, 1.01-1.08). For risk of AD, the adjusted RRs were 1.51 (95% CI, 0.91-2.50) and 1.03 (95% CI, 1.00-1.07), respectively. Risk of dementia associated with a longer reproductive period was most pronounced in APOE epsilon4 carriers (adjusted RR for >39 reproductive years compared with <34 reproductive years, 4.20 [95% CI, 1.97-8.92] for dementia and 3.42 [95% CI, 1.51-7.75] for AD), whereas in noncarriers, no clear association with dementia or AD was observed. CONCLUSION: Our findings do not support the hypothesis that a longer reproductive period reduces risk of dementia in women who have natural menopause.

Aged↗

PubMed1998

Validity of an estimator of reproductive success.

Lifetime reproductive success is a major component of individual fitness and a central dependent variable for the study of natural selection. For long-lived animals, such as apes or baboons, assessment of lifetime reproductive success requires observations of identified individuals in continuous, long-term studies from which it is difficult and often impossible to obtain an adequate sample of necessary reproductive and survival data. This situation can be alleviated by the availability of a valid measure that uses incomplete reproductive histories to estimate the lifetime reproductive success of individuals. The validity of one such estimator was tested by determining if, after 10.5 years of studying free-ranging female baboons, it predicted lifetime reproductive success obtained from full reproductive histories after 21.5 years. Validity was evaluated for seven criteria of success, ranging from the number of a female's live births to the number of her offspring that reached the age of 72 months. Moderate to good prediction of lifetime reproductive success by the estimator was found for criteria of offspring living to 36 months or more. After 10.5 years, complete reproductive life spans were available for only eight females. Using the estimator, analytic potential, via sample representativeness and size, was improved at 10.5 years by an increase from a sample of eight to between 34 and 62, depending upon the criterion used, and at 21.5 years from 39 to 70. With a valid estimator, the opportunity to study lifetime reproductive success of a long-lived species is substantially improved without having to depend upon rarely available, uninterrupted data collection for 20-60 years.

Animals↗

PubMed2004

Reproductive output, maternal age, and survivorship in captive common marmoset females (Callithrix jacchus).

Common marmosets (Callithrix jacchus) demonstrate significant variation in reproductive output on both a yearly and lifetime basis in comparison to other anthropoid primates. We explore the factors that may be most important in determining reproductive variation in captive common marmosets. Studies have found that maternal age, maternal condition, and dam survivorship are related to reproductive output; however, these reports are not in agreement and are far from conclusive. With the use of a large, multicolony, demographic database pooling data across five marmoset colonies, we examined litter information for 1,649 litters, and reproductive summaries for 400 dams to assess 1) how reproductive output variation (total production, total weaned production) is determined by litter size, interbirth interval (IBI), age at first birth, and dam survival age; 2) the relationship between maternal age and reproductive output variables; and 3) relationship between the reproductive output variables and survival. We used stepwise regression procedures to describe the amount of variation in lifetime reproductive output among dams, and found that mean litter size accounted for 18% of the variance in total production, survival age accounted for 10.6%, age at first birth accounted for 8.8%, and mean IBI accounted for 5%. For total (nonzero) weaned production, survival age accounted for 7.6% of variance, age at first birth accounted for 7.2%, mean IBI accounted for 2%, and mean litter size accounted for 1.6%. We identified significant effects (P<0.05) of maternal age on litter size and IBI length, but no effect of dam age on weaned litter size. Cox proportional hazards regression analyses revealed significant effects (P<0.01) of number of litters, age at first birth, and site on dam survivorship. Dams that produced more litters showed higher survivorship. Age at first birth showed a positive relationship with dam survivorship, i.e., dams that delayed first reproduction had higher survival. Our findings about reproductive variation in marmosets may have practical applications for the management of marmoset breeding colonies.

Animals↗

PubMed2005

Mixed reproductive strategy in Tubifex tubifex (Oligochaeta, Tubificidae)?

Despite the wide use of the tubificid oligochaete Tubifex tubifex in eco-toxicological studies, the reproductive strategy adopted by the species, that can reasonably be assumed to be the key to its ecological success, is still not well investigated. This study reports on breeding experiments analysed by allozyme markers (Pgi, Pgm, and Idh), accompanied by a study of the sperm production in the species, with the aim to: (1) clarify the type of uniparental reproduction adopted by the species, (2) test the hypothesis that uniparental reproduction is reversible, (3) investigate the occurrence of biparental reproduction in laboratory cultures. Studies of parent-offspring comparison at polymorphic allozyme loci showed parthenogenetic reproduction and maintenance of asexuality in the parthenogenetic individuals. A cross-breeding test performed with couples made up of randomly assorted individuals, whose genotype combinations were suitable for discriminating between sexual and asexual reproduction, failed to show biparental reproduction in laboratory cultures: T. tubifex always reproduced parthenogenetically. Unexpectedly, spermiogenetic analysis indicated that both kinds of sperm produced by the species (eusperm and parasperm) were differentiated in individuals raised either in cohort cultures or in isolation (first, second, and third parthenogenetic generations), with a similar pattern of sperm production correlated to the sexual stage. Interestingly, there was no avoidance of mating in any of the collective cultures analysed. Concomitance between parthenogenetic reproduction and a "normal" male functionality, which is typical of a sexually reproducing species, could be justified by a mixed reproductive strategy or a pseudogamy process occurring in T. tubifex. However, several aspects of the reproductive behaviour of the species deserve further investigation.

Animals↗

PubMed2004

The social context of reproductive health in an Egyptian hamlet: a pilot study to identify female genital schistosomiasis.

This pilot study is the first to identify female genital schistosomiasis (FGS) in an Egyptian community setting. The year-long interdisciplinary study, in a small hamlet (ezba), combined clinical assessment with an in-depth study of the social context of reproductive health. Schistosoma haematobium ova were found in 16.7% of women in the study (21/126). Half of the women who agreed to a full gynecological examination (43 of 86) had evidence of reproductive morbidity due to schistosomiasis, either schistosome eggs in the cervix or sandy patches, tissue changes in the reproductive tract. Other reproductive tract morbidities included infections (vaginitis 40%, chronic cervicitis 75%, pelvic inflammation 9%) and prolapse (54%). FGS was associated with dysparunia, abnormal vaginal discharge, vaginal or cervical polyps, contact bleeding, vulval itching and chronic cervicitis. Community members recognized S. haematobium as a health problem, but did not believe that it affected reproductive health. Indeed, they had little awareness of reproductive health and the possible impact of reproductive morbity on women's arduous daily tasks. There was no discussion of any reproductive health issues (except infertility) between women or between spouses. The study identified a number of factors that would affect the identification and treatment of FGS, and reproductive health care in general; (1) the neglect of women's health: (2) misconceptions about reproductive health and family planning; and (3) limited access to, and use of formal health care. The paper ends with a brief discussion of the significance of our findings about FGS, strategies to increase awareness of FGS, and the need for future research.

Egypt↗

PubMed2000

Reproduction in female reindeer.

Reindeer are either wild or kept under very extensive farming systems. They are seasonal breeders, with mating coinciding with the decreasing photoperiod in the autumn, and with calving in the spring. Little is known regarding the factors that influence reproduction in reindeer or of their reproductive physiology. Studies carried out to date have mainly focused on issues related to the population dynamics of wild populations and semi-domestic herds, and to a limited extent on the reproductive physiology of the female. Nor is much known about reproductive disorders and their medical treatment, or of the possibilities to manipulate or control reproduction by the use of hormones. Modern reproductive techniques such as artificial insemination and in vitro fertilisation, maturation and transfer of embryos have so far received scant attention.In the future, it is possible that reindeer under certain conditions might be kept in more intensive production systems. Limited access to high-quality winter pastures and increased demands for productivity have resulted in artificial feeding becoming a common practice in various reindeer herding areas in Scandinavia. In efforts to enhance the productivity of reindeer herds, attention has been focused on factors affecting reproduction in the female and survival of the offspring. Further knowledge on these issues seems necessary when developing strategies for optimalization of meat production in domestic herds and the harvesting of wild populations. This paper puts a broad focus on various aspects of reproduction, including factors influencing the fecundity of reproductively active females. In order to understand these effects it is important also to have a basic understanding of the reproductive physiology of these animals.

Animals↗

PubMed1998

Oxygen consumption and carbon dioxide production in male prairie deermice (Peromyscus maniculatus bairdii) in different reproductive conditions and group densities.

Natural and laboratory populations of Peromyscus exhibit a profound but reversible reproductive inhibition related to population density. Our earlier studies described the endocrine physiology of inhibited animals which resembles a condition of delayed puberty, but they did not reveal a primary mechanism for the induction and maintenance of the inhibition. These studies indicated that reproductive inhibition could be associated with an overall change in general metabolism. To test this hypothesis, oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in three groups of Peromyscus maniculatus males that were: 1) reproductively-proven, 2) reproductively-inhibited, or 3) recovered from inhibition. We found that the mean of the 2-hr period with the lowest VO2 (the Resting Metabolic Rate, or RMR) was significantly lower, and the mean Respiratory Exchange Ratio (RER) was significantly higher in reproductively-inhibited males compared with reproductively-proven males. In addition, previously inhibited males allowed to recover reproductive function had a significantly higher mean VO2, while the mean RER was not different from reproductively-proven males. Moreover, and contrary to some studies with other species, increasing the ambient carbon dioxide concentration or the caging densities to as high as six animals did not significantly affect oxygen consumption when compared with the corresponding values for individuals. Taken together, these findings indicate that the reproductive inhibition observed in P. maniculatus laboratory populations is causally associated with a significant reduction in general metabolism and that this metabolic reduction which is associated with reproductive-inhibition is not induced by a CO2 signal or induced by absolute density, per se.

Animals↗

PubMed2006

Orchestration of avian reproductive effort: an integration of the ultimate and proximate bases for flexibility in clutch size, incubation behaviour, and yolk androgen deposition.

How much effort to expend in any one bout of reproduction is among the most important decisions made by an individual that breeds more than once. According to life-history theory, reproduction is costly, and individuals that invest too much in a given reproductive bout pay with reduced reproductive output in the future. Likewise, investing too little does not maximize reproductive potential. Because reproductive effort relative to output can vary with predictable and unpredictable challenges and opportunities, no single level of reproductive effort maximizes fitness. This leads to the prediction that individuals possessing behavioural mechanisms to buffer challenges and take advantage of opportunities would incur fitness benefits. Here, we review evidence in birds, primarily of altricial species, for the presence of at least two such mechanisms and evidence for and against the seasonal coordination of these mechanisms through seasonal changes in plasma concentrations of the pituitary hormone prolactin. First, the seasonal decline in clutch size of most bird species may partially offset a predictable seasonal decline in the reproductive value of offspring. Second, establishing a developmental sibling-hierarchy among offspring may hedge against unpredictable changes in resource availability and offspring viability or quality, and minimize energy expenditure in raising a brood. The hierarchy may be a product, in part, of the timing of incubation onset relative to clutch completion and the rate of yolk androgen deposition during the laying cycle. Because clutch size should influence the effects of both these traits on the developmental hierarchy, we predicted and describe evidence in some species that females adjust the timing of incubation onset and rate of yolk androgen deposition to match clutch size. Studies on domesticated precocial species reveal an inhibitory effect of the pituitary hormone prolactin on egg laying, suggesting a possible hormonal basis for the regulation of clutch size. Studies on the American kestrel (Falco sparverius) and other species suggest that the seasonal increase in plasma concentrations of prolactin may regulate both a seasonal advance in the timing of incubation onset and a seasonal increase in the rate of yolk androgen deposition. These observations, together with strong conceptual arguments published previously, raise the possibility that a single hormone, prolactin, functions as the basis of a common mechanism for the seasonal adjustment of reproductive effort. However, a role for prolactin in regulating clutch size in any species is not firmly established, and evidence from some species indicates that clutch size may not be coupled to the timing of incubation onset and rate of yolk androgen deposition. A dissociation between the regulation of clutch size and the regulation of incubation onset and yolk androgen deposition may enable an independent response to the predictable and unpredictable challenges and opportunities faced during reproduction.

Androgens↗

PubMed2004

Fitness benefits of prolonged post-reproductive lifespan in women.

Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction.

Adult↗

PubMed2006

Changes in carbohydrate and nutrient contents throughout a reproductive cycle indicate that phosphorus is a limiting nutrient in the epiphytic bromeliad, Werauhia sanguinolenta.

BACKGROUND AND AIMS: This study examined the physiological basis of the cost of reproduction in the epiphytic bromeliad Werauhia sanguinolenta, growing in situ in a tropical lowland forest in Panama. METHODS: Entire mature plants were sampled repeatedly over the course of 2 years, which represents the common interval between reproductive events. Due to the uncertainty concerning the appropriate currency of resource allocation to reproduction, the temporal changes of the contents of total non-structural carbohydrates (TNC) and of all major nutrient elements in different plant parts were studied (stems, green leaves, non-green leaf bases, roots and reproductive structures when present). KEY RESULTS: Although TNC varied with time in all compartments, this variation was more related to seasonal fluctuations than to reproductive status. The contents of the nutrient elements, N, P, K, Mg and S, on the other hand, showed significant differences between reproductive and non-reproductive individuals, while Ca did not change with reproductive status. Differences in nutrient contents were most pronounced in stems. Seeds were particularly enriched in P, much less so in N and the other nutrient elements. Model calculations of nutrient fluxes indicate that a plant needs about 2 years to accumulate the amount of P invested in a fruit crop, while the estimated uptake rates for N were much faster. CONCLUSIONS: Since most mature individuals of this species fruit every other year, it is hypothesized that P is the prime limiting factor for reproduction. These findings therefore add to an increasing body of evidence that P rather than N is limiting growth and reproduction in vascular epiphytes.

Biomass↗

PubMed1985

Mammalian reproduction: an ecological perspective.

The objectives of this paper are to organize our concepts about the environmental regulation of reproduction in mammals and to delineate important gaps in our knowledge of this subject. The environmental factors of major importance for mammalian reproduction are food availability, ambient temperature, rainfall, the day/night cycle and a variety of social cues. The synthesis offered here uses as its core the bioenergetic control of reproduction. Thus, for example, annual patterns of breeding are viewed as reflecting primarily the caloric costs of the female's reproductive effort as they relate to the energetic costs and gains associated with her foraging effort. Body size of the female is an important consideration since it is correlated with both potential fat reserves and life span. Variation in nutrient availability may or may not be an important consideration. The evolutionary forces that have shaped the breeding success of males usually are fundamentally different from those acting on females and, by implication, the environmental controls governing reproduction probably also often differ either qualitatively or quantitatively in the two sexes. Mammals often live in habitats where energetic and nutrient challenges vary seasonally, even in the tropics. When seasonal breeding is required, a mammal may use a predictor such as photoperiod or a secondary plant compound to prepare metabolically for reproduction. A reasonable argument can be made, however, that opportunistic breeding, unenforced by a predictor, may be the most prevalent strategy extant among today's mammals. Social cues can have potent modulating actions. They can act either via discrete neural and endocrine pathways to alter specific processes such as ovulation, or they can induce nonspecific emotional states that secondarily affect reproduction. Many major gaps remain in our knowledge about the environmental regulation of mammalian reproduction. For one, we have a paucity of information about the annual patterns of breeding and about the mechanisms controlling these patterns in the most common mammals on the planet-the small to average-sized mammals living in the tropics. We probably have only a shallow conceptualization of the way available energy and nutrients control reproduction and, likewise, we may have only a narrow view of the potential kinds and uses of seasonal predictors. Finally, we have little appreciation of the way environmental cues interact with each other to control reproduction.

Animals↗