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PubMed2004

Prediction of the reproductive status of cattle on the basis of milk progesterone measures: model description.

Reproductive management, in particular timely oestrus detection, is important for profitable dairy production. The aim of this study was to develop a biological model to predict reproductive state on the basis of milk progesterone measures. A number of additional inputs were incorporated to make use of other known effectors of reproductive performance that are not reflected in progesterone levels. These are: days from calving, breed, parity, signs of behavioural oestrus, insemination dates, pregnancy determinations, energy status, body fat status, milk urea content and reproductive disorders associated with calving. A dynamic, deterministic model was developed. It is designed to run each time a new trigger input (progesterone, behavioural oestrus, inseminations, pregnancy determinations) occurs using the current and previous values and can run in the absence of the additional inputs. The milk progesterone values are smoothed using an extended Kalman filter before being processed in the biological component of the model. The model predicts the reproductive status of the cow, which can be one of three mutually exclusive states: postpartum anoestrus, oestrus cycling, and potentially pregnant. The other model outputs are all reproductive status specific with the exception of days to next sample (DNS), which is calculated in each model run regardless of reproductive status. DNS is designed to feedback to the sampling system so that the frequency of milk sampling (i.e. progesterone measurement) can be varied according to the predicted likelihood of a future reproductive event, such as onset of oestrus cycling. The other model outputs are: risk of prolonged postpartum anoestrus, risk and type of ovarian cyst, onset of oestrus, likelihood of a potential insemination succeeding, and likelihood of being pregnant (following oestrus). The model was evaluated using three simulated datasets consisting of a timeseries of progesterone values centred on each of the three reproductive statuses and including relevant additional information. Test runs were carried out on the full datasets and then on reduced data. The data reductions were made by using only those values that would have been available if the model days to next sample function was used to control sampling frequency. The sensitivity of the model to noise in the raw progesterone data was examined by adding 1, 2, or 3 residual standard deviations (1.85 ng/ml) random variation to the original data and evaluating model performance. The model was found to be able to readily identify and distinguish reproductive states. A reduction in sampling frequency to 36% of original sample resulted in an average increase in days to detection of oestrus of 0.36. The addition of 1 S.D. noise did not cause additional oestruses to be detected and all oestruses were correctly identified. However, when 2 or 3 S.D. noise were added, the model found on average 1.4 and 3 extra oestruses. It was concluded that reproductive status can be predicted from milk progesterone values using a biological model and that such a model is robust to reductions in sampling frequency number and to a doubling in the random variation in the raw progesterone values. It therefore has the potential to provide the basis for a useful reproductive management tool.

Anestrus↗

PubMed2000

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

Enhancing male reproductive health, and increasing men's participation in it, involves encouraging a range of positive reproductive health and social behaviour by men to help ensure women's and children's well-being. More intellectual work-including research programmes-is urgently needed to clarify the conceptual framework for male reproductive health. At the Asia and the Pacific Symposium 'Intra-regional Cooperation in Reproductive Health Research' (Shanghai, China, 12-13 October 1998) the Symposium participants identified regional research needs and recommended a regional reproductive health research agenda, which addresses six key issues related to male reproductive health: (i) male contraceptive technology; (ii) reproductive tract infections/sexually transmitted diseases and male infertility; (iii) male involvement in reproductive health; (iv) male adolescent reproductive health; (v) male reproductive ageing; and (vi) environment and male reproductive health. One of the major challenges now facing us is the elaboration of a comprehensive, yet realistic, male reproductive health research agenda that reflects the needs and demands of Asian developing countries. Making full use of an interdisciplinary approach is of strategic importance to achieve this.

Adolescent↗

PubMed2005

Respiration and reproductive effort in Xanthium canadense.

BACKGROUND AND AIMS: The proportion of resources devoted to reproduction in the plant is called the reproductive effort (RE), which is most commonly expressed as the proportion of reproductive biomass to total plant biomass production (RE(W)). Reproductive yield is the outcome of photosynthates allocated to reproductive structures minus subsequent respiratory consumption for construction and maintenance of reproductive structures. Thus, RE(W) can differ from RE in terms of photosynthates allocated to reproductive structures (RE(P)). * METHODS: Dry mass growth and respiration of vegetative and reproductive organs were measured in Xanthium canadense and the amount of photosynthates and its partitioning to dry mass growth and respiratory consumption were determined. Differences between RE(W) and RE(P) were analysed in terms of growth and maintenance respiration. * KEY RESULTS: The fraction of allocated photosynthates that was consumed by respiration was smaller in the reproductive organ than in the vegetative organs. Consequently, RE(P) was smaller than RE(W). The smaller respiratory consumption in the reproductive organ resulted from its shorter period of existence and a seasonal decline in temperature, as well as a slower rate of maintenance respiration, although the fraction of photosynthates consumed by growth respiration was larger than in the vegetative organs. * CONCLUSIONS: Reproductive effort in terms of photosynthates (RE(P)) was smaller than that in terms of biomass (RE(W)). This difference resulted from respiratory consumption for maintenance, which was far smaller in the reproductive organ than in vegetative organs.

Ecosystem↗

PubMed1992

Does seasonal reproductive state affect the neuroendocrine response of the ewe to a long-day pattern of melatonin?

This study examined whether or not the reproductive response of female sheep to photoperiod varies with seasonal reproductive state. The specific objective was to test the hypothesis that the reproductive response to a long-day pattern of melatonin varies with the reproductive state of the ewe. The response examined was the synchronization of reproductive neuroendocrine induction (rise in serum luteinizing hormone, or LH) following nocturnal infusion of melatonin into pinealectomized ewes for 35 consecutive nights. This infusion restored a pattern of circulating melatonin similar to that in pineal-intact ewes maintained in a long photoperiod (LD 16:8). The ewes had been pinealectomized and without melatonin replacement for 16-25 months prior to the study. They were in differing reproductive states at the start of the infusion, as their endogenous reproductive rhythm had become desynchronized among individuals and with respect to time of year. Noninfused pinealectomized ewes served as controls. Regardless of the reproductive state at the start of the 35-day infusion of the long-day pattern of melatonin, all treated ewes exhibited the same reproductive neuroendocrine response after the infusion was ended. This consisted of a synchronized rise in LH some 6-8 weeks after the infusion was terminated, the maintenance of a high level of serum LH for some 15 weeks, and a subsequent precipitous fall in LH to a very low level. These results provide evidence that a long-day pattern of melatonin can synchronize reproductive neuroendocrine induction in the ewe, regardless of reproductive condition, and thus do not support the hypothesis that this response differs with seasonal reproductive state.

Animals↗

PubMed1998

Evaluation of overall reproductive performance of dairy herds.

Reproductive efficiency was assessed in 106 commercial dairy herds in Ontario. Herds that were similar in historical calving interval or projected calving interval varied widely in reproductive culling rate. The correlation between the reproductive culling rate and the historic calving interval and between the reproductive culling rate and the projected calving interval were -0.23 and were not significant. The coefficient of variation associated with the reproductive culling rate (75.7%) was much higher than that of the historical calving interval (3.8%) or the projected calving interval (4.5%). The repeatability of the reproductive culling rate (0.26) was much lower than that of the historical calving interval (0.81) or the projected calving interval (0.60) because culling rate was not only influenced by the overall herd reproductive performance, but also by the differences in the maximal allowable days open for rebreeding and the estimation of which cows were culled for reproductive failure. Additionally, a high coefficient of variation for the reproductive culling rate is unavoidable because this variable has a binomial distribution and a low mean value (7.5%). These disadvantages are not sufficient to exclude this measure from a comprehensive assessment of overall herd reproductive performance. The projected calving interval and the reproductive culling rate can be combined into the adjusted calving interval and thus interpreted jointly. On 40.5% of the farms providing data for this study, fertility assessment based on the projected calving interval indicated better reproductive performance than that based on adjusted calving interval. Hence, the assessment of herd fertility on the basis of projected calving interval can lead to a different and erroneous conclusion regarding the level of herd fertility than that obtained with the evaluation based on adjusted calving interval.

Animals↗

PubMed2001

Male involvement in reproductive health care.

The programme of action globally endorsed at the International Conference on Population and Development (ICPD) emphasised the need for equity in gender relations with a special focus on men's shared responsibility and active involvement to promote reproductive and sexual health. If men are brought into a wide range of reproductive health services in such a way that they are supported as equal partners and responsible parents, as well as clients in their own right, better outcomes are expected in reproductive health indicators such as contraception acceptance and continuation, safer sexual behaviours, use of reproductive health services, and reduction in reproductive morbidity and mortality. This paper focuses on these key questions. What does men's involvement mean and how should it be operationalised? What does shared responsibility mean for various reproductive health problems subsumed within the reproductive health framework? Programmes to involve men should be designed to address three major goals: (1) Improve sexual and reproductive health of men and women, (2) generate men's support for women's actions related to reproduction and respect for women's reproductive and sexual rights, and (3) promote responsible and healthy reproductive and sexual behaviour in young men and boys. Gender inequality is a major barrier that must be overcome if these goals are to be met. Improving the reproductive well-being of women and men requires freeing them both from restricted gender roles.

Contraception↗

PubMed1997

The effects of photoperiod and food intake on reproductive development in male deer mice (Peromyscus maniculatus).

Seasonal breeding is a tactic that has evolved in rodents that limits reproduction to specific times of the year to increase reproductive success. In order to time breeding accurately, many animals respond to changes in daily photoperiod. Short day lengths inhibit breeding in many nontropical rodent species. Restricted food availability can also inhibit reproductive function among some individuals in these so-called "photoperiodic" populations. Rodents born at the end of the breeding season typically delay sexual maturation until the following spring. Prepubertal rodents exposed to day lengths that are < 12 h light/day will not undergo puberty for 4-7 months in the laboratory. Food restriction can also affect the timing of puberty onset. Reproductive function of food-restricted juvenile mice may remain inhibited until food availability improves. Alternatively, reproductive function of food-restricted juvenile mice might eventually develop despite restricted food intake. This study examined the effects of chronic food restriction and photoperiod on reproductive development in male deer mice (Peromyscus maniculatus bairdii). Short-day mice fed ad lib delayed gonadal development for 5-7 months, but eventually achieved reproductive maturity. The reproductive function of short-day mice fed ad lib was indistinguishable from long-day control animals when assessed at week 32. Long-day food-restricted mice exhibited an intermediate level of gonadal development and function. Short-day food-restricted deer mice also inhibited reproductive growth, but failed to demonstrate reproductive maturity by week 32 of the study. Taken together, these results suggest that retardation of reproductive development by food restriction is only superficially similar to the delay in reproductive maturation imposed by short day exposure. It does not appear that male deer mice escape from the inhibitory effects of food restriction to attain sexual development.

Animals↗

PubMed2006

Environmental control of kisspeptin: implications for seasonal reproduction.

The KiSS-1 gene encodes the peptide hormone kisspeptin, which acts as a principal positive regulator of the reproductive axis by directly stimulating GnRH neuron activity. To gain insight into a potential role for kisspeptin in integrating and relaying reproductively relevant stimuli to the GnRH system, we investigated changes in kisspeptin peptide expression associated with photoperiodic changes in reproductive state as well as pituitary and gonadal responses to peripheral kisspeptin injections. Seasonally breeding rodents undergo pronounced fluctuations in reproductive state in response to changing day lengths. In common with other rodent species, a majority of male Siberian hamsters (Phodopus sungorus) exhibit reproductive decline after exposure to short-day lengths. A subset of individuals fails to respond to day length information, however, and maintains their reproductive function. We exploited these individual differences to examine whether kisspeptin may act at the interface between external stimuli and the reproductive system. After extended exposure to short days, animals with a quiescent reproductive axis displayed a marked reduction in kisspeptin cell labeling in the anteroventral periventricular nucleus but robust kisspeptin-immunoreactive staining in the arcuate nucleus. In contrast, animals with functional reproductive systems displayed high numbers of kisspeptin-immunoreactive neurons in the anteroventral periventricular nucleus but a paucity of expression in the arcuate nucleus. Kisspeptin injections significantly elevated LH over preinjection levels regardless of photoperiod or reproductive state. Collectively, these findings suggest an important role for kisspeptin in coordinating and relaying environmentally relevant information to the reproductive axis as well as a role for this peptide in regulating seasonal changes in reproductive function.

Animals↗

PubMed2025

Unisexual reproduction in the global human fungal pathogen Cryptococcus neoformans.

The human fungal pathogen Cryptococcus species complex (encompassing Cryptococcus neoformans, Cryptococcus deneoformans, and the Cryptococcus gattii species complexes) exhibits 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.

Cryptococcus neoformans↗

PubMed2003

Phenotypic plasticity of reproductive effort in a colonial ascidian, Botryllus schlosseri.

Phenotypic plasticity is the capability of a genotype to produce different phenotypes in different environments. Previous studies have indicated phenotypic variability in asexual, male, and female reproduction in Botryllus schlosseri, a hermaphroditic, colonial ascidian, but not explicitly tested for genotype by environment interactions that indicate genetic variation in plastic responses. Consequently, clones derived from an estuarine population were deployed at their native site and a warmer, higher productivity site 10 km up-river. Male reproduction was assayed by testis size, female reproduction by the number of eggs produced, and asexual reproduction by colony growth rate. To test for ontogenetic effects, data were collected from two different generations of zooids born in the field. Analyses of variance indicated plasticity in asexual and female reproduction during the first zooid generation and plasticity in all three traits during the third zooid generation. Reaction norms varied significantly among genotypes in direction and magnitude for asexual reproduction at both times, implying that selection on asexual reproduction is weak. Sperm production during the third zooid generation was significantly lower at the nonnative site, but there was no genotype by environment interaction. The reaction norms for female reproduction varied significantly among genotypes in direction and magnitude during the first zooid generation, but only varied in magnitude during the third generation, with egg production being higher in all genotypes at the nonnative site. Comparisons of weighted frequency distributions between sites demonstrated that differences in egg production in the third generation were due to increases in the proportion of reproductive zooids within a colony. The greater emphasis on female reproduction at a site associated with higher food availability and temperature, and the greater emphasis on male reproduction at a colder, food-limited site, supports predictions from sex allocation theory.

Adaptation, Physiological↗

PubMedDate not supplied

Reproductive and teratologic effects of electromagnetic fields.

The reproductive risks of electromagnetic fields (EMF) were evaluated based on an extensive review of the scientific literature pertaining to human epidemiologic studies, secular trend data, in vivo animal studies and in vitro studies, and biologic plausibility. The epidemiologic studies involving the reproductive effects of EMF exposures to human populations have included populations exposed to: (1) video display terminals (VDTs), and (2) power lines and household appliances. The clinical use of diagnostic MRI (magnetic resonance imaging) has been increasing, but there are few reports or studies of pregnant women or individuals of reproductive age who have been exposed to MRI, and whose reproductive performance has been evaluated. The population that has been studied most frequently are women exposed to VDTs, but their EMF exposures are extremely low and frequently are at the level of the ambient EMF in a house or office. The results of epidemiologic studies involving VDTs are generally negative for the reproductive effects that have been studied. Based on the number of studies, the exposure levels, and the fairly consistent results, it can be argued that VDT epidemiologic studies should no longer be given priority. There have been fewer studies concerned with the reproductive risks of power lines, electric substations, and home appliances. In some publications, positive findings for reproductive risks were reported, but the more consistent findings indicate that EMF, even at these higher exposures, do not generate a measurable increase in reproductive failures in the human population. When compared to other fields of human epidemiology, it is obvious that these studies have many difficulties. Exposures are rarely determined. Studies frequently involve small sample sizes and the investigators rarely have a combined expertise in EMF physics, engineering, and reproductive biology. Because of the allegation that there may be particular windows of frequency, wave shape, and intensity that may be deleterious, it is impossible to disregard low frequency EMF exposures as having no deleterious reproductive effects. Yet the epidemiologic data that are available would point in that direction. Secular trend data analysis of birth defect incidence data indicate that increasing generation of electric power during this century is not associated with a concomitant rise in the incidence of birth defects. There are over 70 EMF research projects dealing with animal and in vitro studies that are concerned with some aspect of reproduction and growth. Unfortunately, a large proportion of the embryology studies utilized the chick embryo and evaluated the presence or absence of teratogenesis after 48 to 52 hours of development.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Women's reproductive health: monotheistic religious perspectives.

It is important to those who practice reproduction techniques to learn about the different religious attitudes related to reproductive health problems. Religion exerts an influence on civil authorities in the field of reproduction such as prevention or procreation and in issues such as abortion and infertility therapy. The Jewish attitude towards reproduction can be learned from the fact that the first commandment of God to Adam was be fruitful and multiply. Judaism allows the practice of all techniques of assisted reproduction when the oocyte and sperm originate from the wife and husband, respectively. All Rabbinical rulings permit the use of contraception for medical indications. Economic difficulties and inconveniences of raising children are not indications for birth control practice. According to Judaism abortion on demand is forbidden but it may be performed if the mother's life is in danger. The attitude toward reproductive practice is different among the different divisions of Christianity. The practice of assisted reproduction is not accepted by the Vatican, however, it may be practiced by Protestant, Anglican and other Denomination's. According to the Roman Catholic doctrine the primary purpose of marriage is procreation. The contraceptive act destroys the potential of producing new life by sexual intercourse and violates the purpose of marriage and, therefore, is a sin against nature. The Christian tradition views the embryo as a human being since conception and, therefore, abortion is strictly forbidden. According to Islam, the procedure of IVF and ET is acceptable, however, it can be preformed only if it involves the husband and the wife. It allows contraception practice only under some circumstances and only in some special cases abortion can be preformed. Religion, being concerned with affairs that are regarded as extraordinary and as having unique importance in life, is an intrinsic aspect of the culture of all societies, religious groups, however, still exert influence on the civil authorities in issues of reproduction such as contraception, procreation, abortion, and infertility therapy. They have been active in pressing their bioethical positions on the public arena in pluralistic societies. Developments in science and technology in reproduction raise new religious questions that do not always have clear answers. The role of theology in bioethics is foremost to clarify for the different religious communities the perceived attitudes toward these developments. Therefore, it is important to those who practice reproduction techniques to learn about the different religious attitudes related to reproductive health problems.

Abortion, Induced↗

PubMed2003

Longevity cost of reproduction for males but no longevity cost of mating or courtship for females in the male-dimorphic dung beetle Onthophagus binodis.

Life history theory predicts a trade-off between current and future reproduction. Despite a wealth of research on the cost of reproduction for females, there have been very few studies that have looked at the cost of reproduction for males. Longevity is closely related to the opportunity for future reproduction, and thus decreased longevity in response to current reproductive effort has been used as a measure of the cost of reproduction. Here we examine the cost of reproduction for males and females in the dung beetle Onthophagus binodis. Like many onthophagines, O. binodis exhibit dimorphic male morphology; major males develop a large pronotal horn while minor males remain hornless. Alternative morphologies are associated with alternative reproductive tactics. Thus, we ask whether major and minor males pay different costs of reproduction. We found that in contrast to previous work on Diptera, mating is not costly in terms of reduced longevity for female dung beetles. Despite a longevity cost of reproduction for males, we found no evidence for differential longevity costs associated with alternative reproductive tactics.

Animals↗

PubMed1999

Recombinant bovine somatotropin: association with reproductive performance in dairy cows.

A clinical trial was performed to determine the effect of bST on reproductive performance in dairy cows on 4 Michigan dairy farms when bST was used according to labeled directions. Holstein cows (n = 555) at 4 Michigan dairy farms were randomly assigned to receive bovine somatotropin (bST) or to serve as untreated controls. Bovine somatotropin (500 mg, s.c.) was administered every 14 d beginning at 63 to 69 d of lactation and continuing until approximately 21 d prior to the end of lactation or until the producer removed the animal from the herd. A total of 229 (42.57%) animals consisting of 112 (48.91%) controls and 117 (51.09%) bST-treated cows were not diagnosed pregnant and were considered as having reproductive failure by 150 d of lactation and 92 (17.10%) of the animals consisting of 45 (48.91%) controls and 47 (51.09%) bST-treated cows had reproductive failure at the end of their lactation. No significant difference in the incidence of reproductive failure existed between the study treatment groups during either time frame. Cows with cystic ovarian disease had more instances of reproductive failure at 150 d of lactation than cows without this disease. Cows with dystocia, twin births, metritis, displaced abomasum and cystic ovarian disease had more instances of reproductive failure by the end of lactation than cows without these diseases. The bST-treated cows developed more nonspecific off feed conditions during the study lactation and had more twin births at the calving following bST administration compared to control cows. No differences were found between the study treatment groups in calculations of reproductive parameters. Logistic regression analysis found no significant effect of bST on reproductive failure; the odds ratios for the bST treatment effect on reproductive failure at 150 d of lactation and reproductive failure at the end of lactation were 0.95 (95% CI 0.67 to 1.36) and 0.95 (95% CI 0.59 to 1.54), respectively. Overall, bST was not found to have a significant impact on reproductive performance in the herds studied.

Abortion, Veterinary↗

PubMed1999

Correlation between reproductive efficiency, as determined by new mathematical indexes, and the body condition score in dairy cows.

The aim of this work was to study a new mathematical model based on dynamic indexes designed to evaluate reproductive efficiency in dairy herds and to correlate the new index with the body condition score (BCS) in order to evaluate the reproductive state of the cows post partum. Four groups of dairy cows were used: 1) loose-housed Italian Friesian (loose Friesian, n = 190); 2) stanchioned Italian Friesian (stanchioned Friesian, n = 121); 3) stanchioned Italian Simmental (stanchioned Simmental, n = 120); and 4) loose-housed selected Italian Friesian cows (BCS test, n = 117). The first 3 herds were used to develop the new mathematical model while the fourth was used to correlate the method with the BCS. The new model was developed from the analysis of progesterone (P4) concentrations in whey and the frequency distribution of the cows in 3 reproductive states: cyclicity, acyclicity and pregnancy. The frequency distribution generated 3 curves, the intersections of which form a closed area. The barycenter of this closed area gives a simple static representation of the reproductive efficiency of each herd. We also studied the movement of the barycenter with time (dynamic index) for each reproductive status curve. The dynamic index allowed for evaluation of the reproductive efficiency of a group of cows at 40 d after calving, by analyzing the evolution of the different reproductive states post partum. A reproductive index called Cycle Time was characterized in a 240-d period of observation as the interval needed to bring all the animals from acyclic to pregnant status. The loose Friesian cows had the best reproductive efficiency. The BCS test was used to divide cows into 3 groups depending on the percentage loss of BCS due to the negative energy balance at 30 d post partum. Cows which lost more than 20% in BCS had the lowest reproductive efficiency. The following protocol was devised to monitor herds in order to identify cows that were likely to have reproductive problems: 1) measure BCS 10 d before calving; 2) monitor progesterone in whey starting 5 d after calving; 3) measure BCS 30 d after calving; 4) isolate cows that lost more than 20% of BCS; 5) measure progesterone only in the cows that lose more than 20% of BCS; 6) activate appropriate feeding strategies to help prevent excessive mobilization of body fat reserves.

Animal Feed↗

PubMed1997

African bats: evolution of reproductive patterns and delays.

Patterns of reproduction in African bats can be compared in three taxon-based groups: fruit bats (Megachiroptera), freetailed bats (Microchiroptera: Molossidae) and the nonmolossid Microchiroptera. In the fruit bats and nonmolossid Microchiroptera there is a trend from either seasonal or aseasonal polyestry, with prolonged or continuous spermatogenesis in the tropics, towards seasonal monestry and seasonal spermatogenesis at more temperate latitudes. Reproductive delays (sperm storage, delayed implantation and delayed development) are rare at tropical latitudes, but are the norm in the nonmolossid Microchiroptera away from the tropics. The molossids are mostly polyestrous at tropical and temperate latitudes, although the duration of the reproductive season decreases with increasing latitude. The molossids appear to have escaped the constraints that affect reproduction of the other Microchiroptera. We propose that this may be due to their flight capabilities and foraging behavior, which give them access to year-round food, and to the thermal characteristics of their roots. We suggest that the ancestral reproductive pattern of the Chiroptera was probably aseasonal or seasonal polyestry, as seen in extant tropical species, and therefore that reproductive cycles have evolved from the polyestrous to the monestrous condition. Short periods of reproductive delay occur in some species of tropical bats; we suggest that these reproductive delays originally were not adaptations to temperate latitudes but rather to the long dry season, which is characteristic of African tropical latitudes. With the move away from the tropics, selective pressures, acting on the timing of lactation and spermatogenesis, would have ensured that these processes continued to occur in the warm wet season, and that the length of the reproductive delay increased. This model accommodates the probable evolutionary origin of bats and links the evolution and development of reproductive delays to the differences in climate that occur with changes in latitude. There is evidence that mate choice and sperm competition may be important to modern bats, but we believe that they need not be involved as causal factors in the evolution of reproductive delays, which can be adequately explained using purely energetic arguments.

Africa↗

PubMed1996

Reproductive suppression in subordinate, non-breeding female Damaraland mole-rats: two components to a lifetime of socially induced infertility.

The Damaraland mole-rat Cryptomys damarensis exhibits an extreme reproductive division of labour. Reproduction in the colony is restricted to a single breeding pair, resulting from a two-fold control: (i) a reduced pituitary synthesis and/or secretion of luteinizing hormone leading to a block to ovulation in non-reproductive females; and (ii) a strong inhibition to breeding with familiar kin. Circulating basal concentrations of luteinizing hormone as well as luteinizing hormone levels measured in response to a single exogenous gonadotrophin releasing hormone challenge, were significantly lower in non-reproductive females in the presence of the reproductive female than those in colonies lacking a reproductive female. Urinary progesterone concentrations before the removal of the reproductive female were significantly higher in non-reproductives than the post removal values. Behavioural studies from sib-sib and non-sib pairings provide evidence for a strong incest avoidance, probably resulting from an inhibition of breeding with familiar colony members. A total of four pairings of non-sibs resulted in copulatory activity and eventual conception. In contrast, four couples of sib-sib combinations failed to produce any sexual activity or offspring. Thus, suppression of reproduction in these non-reproductive, subterranean bathyergids is complicated by the masking effect of familiarity that prevents incest, in addition to the physiological inhibition of fertility in the presence of the reproductive female.

Animals↗

PubMed1997

Variation in the ability of a long day followed by a short day photoperiod signal to initiate reproductive activity in ewes at different times of the year.

Three experiments examined the importance of the time and duration of exposure to a long day followed by a short day photoperiod signal in initiating reproductive activity in ewes. In Expt 1, ewes were maintained on short days (8.5 h light:15.5 h dark) from 21 December interrupted with either 105 long days (18 h light:6 h dark; LD) from 9 February or 35 LD from 9 February, 16 March or 20 April. Exposure to long days followed by short days advanced the onset of reproductive activity in comparison to control ewes maintained on simulated natural photoperiod. Exposure to long days for 105 days delayed the onset of reproductive activity (August 2 +/- 3 days; P < 0.05) compared with 35 days beginning on the same date (July 13 +/- 5 days). The interval from the end of the long day signal to the onset of reproductive activity was shorter (P < 0.001) however, after 105 LD than after 35 LD. In Expt 2, control ewes were moved from natural photoperiod to simulated natural photoperiod on 1 November and subsequently exposed to short days from 21 December. Four other groups were also exposed to this basic photoperiodic signal sequence but it was interrupted with either 70 LD from 16 November, or 35 LD from 16 November, 21 December or 20 April. More ewes (P < 0.05) initiated reproductive activity after exposure to 70 LD from 16 November and 35 LD from 21 December or 20 April compared with control ewes maintained on short days or ewes given 35 LD from 16 November. The interval from the end of long days to the onset of reproductive activity was less (P < 0.01) in ewes given 70 LD than in ewes given 35 LD. In Expt 3, ewes on natural photoperiod were given either 90 LD from 21 September, 35 LD from 21 September, 26 October, 30 November, 4 January or 8 February followed by short days. The majority of ewes that received long followed by short days after the winter solstice resumed reproductive activity. However, all photoperiod signals given between the autumn equinox and the winter solstice failed to initiate reproductive activity in ewes during the experiment. Thus we conclude that, in ewes, the reproductive neuroendocrine axis is insensitive to long days followed by short days between the autumn equinox and the winter solstice. The reproductive axis of ewes regains sensitivity to the inductive effects of long days followed by short days at a time close to the winter solstice. Between the winter and summer solstices, long days followed by short days maintain the anoestrous state and provide the cue for initiation of reproductive activity.

Animals↗