SEARCH · PubMed Health

Results for “Reproduction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources

PubMed1980

An estimation of reproductive performance in the women of Punjab.

This paper reports the preliminary findings on the reproductive performance of 325 Punjabi women between the age limits 35 and 55 years. The total amount of time available for reproduction and total time used for effective reproduction and the period which has been wasted as a result of socio-cultural and biological factors have been calculated in the study in hand. For the purpose of the present study it has been assumed that the time period between menarche and menopause represents the maximum possible length of potential reproductive life. A mean age at menarche of 14.31 years and mean age at menopause of 44.6 years gives an average length of menstrual life of 30.3 years for the cases studied. The mean age at marriage in this sample is 14.60 years. A total of 10,084.20 years were all the reproductive periods of 325 individuals. It has been observed that out of this period only 8,782.90 years (87.08 per cent) have been used for effective reproduction and 1,201.3 years (12.92 per cent) have been wasted as a result of socio-cultural and biological factors. All pregnancies, as well as breast feeding operate to reduce fecusidability. The various contraceptive measures used by mankind also lower reproductive performance.

Adult↗

PubMedDate not supplied

Reproductive issues for men with cancer: technology and nursing management.

PURPOSE/OBJECTIVES: To review the current medical technologies available to protect the reproductive potential of adult males undergoing sterilizing cancer treatments; to describe the attributes and limitations of these technologies and how oncology nurses can access them for the patient; and to discuss psychosocial elements, including the legal considerations of oncology nurses who counsel patients. DATA SOURCES: Quantitative data from personal clinical records; personal clinical experience; published articles, abstracts, and books identified by bibliographic data base searches; and consultation with lawyers. DATA SYNTHESIS: Cancer treatment can have severe and adverse long-term iatrogenic effects on male fertility. Medical technologies that protect male reproduction potential from sterilizing procedures have progressed from unreliable to clinically practical over a period of 20 years. The present clinical means for preserving the potential reproductive capacity of men at risk is cryopreservation of sperm before treatment begins, followed by assisted reproductive technology when pregnancy is desired. Medical, legal, and religious issues relevant to counseling are involved. CONCLUSIONS: Current reproductive technology provides realistic hope for future procreation by men facing sterilizing cancer treatment. IMPLICATIONS FOR NURSING PRACTICE: Nursing intervention primarily involves providing patient counseling and arranging patient access to cryopreservation facilities. Oncology nurses can assist men making these types of reproductive decisions by assessing their medical and psychological need for information and by counseling them in regard to human sexuality, the fertility risk of oncologic therapy, the availability of reproductive interventions, and the social ramifications of using stored semen.

Adolescent↗

PubMed2003

Interictal EEG discharges, reproductive hormones, and menstrual disorders in epilepsy.

We evaluated reproductive endocrine function in women with unilateral temporolimbic epilepsy and normal control subjects to assess the effects of epilepsy, epilepsy laterality, and antiepileptic drug use on the cerebral regulation of hormonal secretion. The findings indicate that reproductive endocrine function differs between women with epilepsy and normal control subjects. Significant differences exist at all levels of the reproductive neuroendocrine axis, that is, hypothalamus, pituitary, and peripheral gland. Differences show significant relationships to the epilepsy itself as well as to medication use. Reproductive neuroendocrine changes occur in a stochastic manner such that the laterality of unilateral temporolimbic discharges is associated with predictable directional changes in hormonal secretion at all levels of the reproductive neuroendocrine axis. These directional changes are consistent with the finding that different reproductive disorders may develop in relation to left- and right-sided temporolimbic epilepsy. Hormonal changes can show close temporal relationship to the occurrence of interictal epileptiform discharges and may vary in relation to the laterality of the discharges. Antiepileptic drugs differ in their effects on reproductive hormone levels. There are notable differences between enzyme-inducing and noninducing drugs. Menstrual disorders are more common among women with interictal discharges as well as women with abnormal hormonal findings.

Adolescent↗

PubMed2000

Social control of reproduction in banded mongooses.

Recent theoretical work suggests that the distribution of reproduction, or degree of reproductive skew, in animal societies depends crucially on (1) whether dominant individuals can fully control subordinate reproduction, and (2) how subordinate reproduction affects the fitness of dominants. I investigated these two factors in cooperatively breeding banded mongooses, Mungos mungo. Female packmates entered oestrus together and were closely guarded by dominant males. These males were aggressive to subordinate males who attempted to mate, but females still managed to mate with males other than their mate guard. Older females were guarded and mated a few days before their younger packmates, yet all females usually gave birth on the same day, suggesting that older females may have a longer gestation period. Moreover, older females carried more fetuses. Overall, ca. 83% of adult females conceived in each breeding attempt and 71% carried to term. These results indicate that, among males, dominant individuals did not have full control over the mating attempts of subordinates (since they could not fully control the mating behaviour of the females they guarded), while among females there was little or no attempt to prevent subordinates from breeding (at least, prior to parturition). Two within-group infanticides by males suggested that some control over reproduction may be exercised postpartum. Per capita survivorship of young in the den increased with the number of females who gave birth. Thus, dominant females may benefit from subordinate reproduction, providing a possible explanation for the lack of reproductive suppression among females in this species. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1995

Estrogen and progesterone receptor mRNA are expressed in distinct pattern in male primate reproductive organs.

PURPOSE: The role(s) of estrogens (E) and progesterone (P) in male reproductive physiology remain unclear. Estrogens are used in the treatment of prostatic cancer. Progestins have been used to control excessive sexual behavior in men, and proposed as a male contraceptive. Previous immunohistochemical studies have shown that E receptors (ER) are present in the reproductive tract of male nonhuman primates. METHOD: We examined the expression pattern of ER and progesterone receptor (PR) mRNA in adult primate male reproductive tract. mRNA was extracted from male pituitary, testis, prostate and different regions of the epididymis of three intact adult cynomolgous monkeys. Ovarian, myometrial and spleen mRNA were used as controls. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to amplify ER and PR mRNA; beta-actin mRNA was used as a reference. Primers for ER, PR and beta-actin were designed using the most conserved areas in the corresponding human cDNA sequences, and the identity of the PCR products was verified using Southern hybridization. Semiquantitative analysis of ER and PR mRNA content in different parts of the male reproductive tract was carried out by spiking the PCR reaction with 33P-dCTP, and amplifying the samples for 20 cycles with the beta-actin primers, whereas 30 cycles were used for ER and PR. RESULTS: The results are expressed as cpm ratios of ER or PR/beta-actin. All the male reproductive organs studied revealed a strong signal for ER and PR mRNA. The results of the semiquantitative analysis indicate that the expression of both ER and PR was highest in testis (mean +/- SE 6.4 +/- 1.3 and 0.5 +/- 0.1, respectively). The mean figures for prostate were 0.5 and 0.4, respectively. The mean content of ER and PR in the different areas of epididymis was 0.5 and 0.1, respectively. The epididymal ER mRNA was highest in the corpus region (ER/beta-actin 0.7), the ratio being 0.4 for the caput and cauda regions. The expression pattern of PR mRNA was different, and the caput of epididymis being the most intense (0.2). Surprisingly, the pituitary content of ER and PR mRNA was close to that seen in the ovary, the mean +/- SE values being 7.6 +/- 0.5 and 1.3 +/- 0.1, respectively. CONCLUSIONS: We, therefore, conclude that male monkey reproductive tract contains mRNA for ER and PR, and there appears to be regional variation in their expression. Thus the role(s) of Es and P in male reproductive physiology, specifically in sperm maturation, warrants further investigations.

Actins↗

PubMed2004

Unpredictable food supply modifies costs of reproduction and hampers individual optimization.

Investment into the current reproductive attempt is thought to be at the expense of survival and/or future reproduction. Individuals are therefore expected to adjust their decisions to their physiological state and predictable aspects of environmental quality. The main predictions of the individual optimization hypothesis for bird clutch sizes are: (1) an increase in the number of recruits with an increasing number of eggs in natural broods, with no corresponding impairment of parental survival or future reproduction, and (2) a decrease in the fitness of parents in response to both negative and positive brood size manipulation, as a result of a low number of recruits, poor future reproduction of parents, or both. We analysed environmental influences on costs and optimization of reproduction on 6 years of natural and experimentally manipulated broods in a Central European population of the collared flycatcher. Based on dramatic differences in caterpillar availability, we classified breeding seasons as average and rich food years. The categorization was substantiated by the majority of present and future fitness components of adults and offspring. Neither observational nor experimental data supported the individual optimization hypothesis, in contrast to a Scandinavian population of the species. The quality of fledglings deteriorated, and the number of recruits did not increase with natural clutch size. Manipulation revealed significant costs of reproduction to female parents in terms of future reproductive potential. However, the influence of manipulation on recruitment was linear, with no significant polynomial effect. The number of recruits increased with manipulation in rich food years and tended to decrease in average years, so control broods did not recruit more young than manipulated broods in any of the year types. This indicates that females did not optimize their clutch size, and that they generally laid fewer eggs than optimal in rich food years. Mean yearly clutch size did not follow food availability, which suggests that females cannot predict food supply of the brood-rearing period at the beginning of the season. This lack of information on future food conditions seems to prevent them from accurately estimating their optimal clutch size for each season. Our results suggest that individual optimization may not be a general pattern even within a species, and alternative mechanisms are needed to explain clutch size variation.

Adaptation, Physiological↗

PubMed1983

Male reproductive tract sensitivity to ethanol: a critical overview.

While endocrinological effects of acute and chronic ethanol ingestion have been extensively reviewed, a survey of ethanol induced functional and physical perturbations of the male reproductive tract remains lacking. A brief overview of recent literature concerned with ethanol sensitivity of various components of the reproductive tract is presented. Clinical findings are reviewed as they relate to the possible pathogenesis of alcohol-related testicular atrophy. Currently available animal models for the study of ethanol-induced male reproductive failure are discussed. Attempts have been made to separate the contribution of ethanol per se from secondary factors, such as hepatic dysfunction and nutritional deficiency, to manifestations of male infertility. Studies directed toward elucidating the mechanism(s) by which ethanol exerts its inhibitory effect on testicular steroidogenesis are discussed. Finally, evidence suggesting an effect of ethanol on the functional integrity of other components of the reproductive tract is reviewed. It is concluded that ethanol is a male reproductive tract toxin. Future clinical studies of alcoholics afflicted with testicular atrophy, but having normal liver histology, will be of great value in efforts to identify the mechanisms by which chronic ethanol ingestion results in reproductive impairment. Similar benefits will be realized in laboratory experimentation, in which models are employed that describe ethanol-induced infertility, while minimizing nutritional factors and hepatic involvement, and control for the reproductive maturity of the organism.

Acetaldehyde↗

PubMed1997

Ethical issues relating to reproduction control and women's health.

There are many ethical aspects which derive from the application of reproduction control in women's health. Women's health can be enhanced if women are given the opportunity to make their own reproduction choices about sex, contraception, abortion and application of reproductive technologies. The main issues that raise ethical dilemmas following the development of assisted reproduction techniques are: the right to procreate or reproduce; the process of in vitro fertilization itself-is it morally acceptable to interfere in the reproduction process?; the moral status of the embryo; the involvement of a third party in the reproductive process by genetic material donation; the practice of surrogacy, cryopreservation of pre-embryos; genetic manipulation; experiments on pre-embryos, etc. Induced abortion raises ethical issues related to the rights of the woman versus the rights of the fetus. For those who consider life to begin at conception abortion always equals murder and is therefore forbidden. Those who believe in the absolute autonomy of the woman over her body take the other extreme approach. The discussion surrounding abortion usually centers on whether it should be legal or illegal. Access to safe abortion is critical to the health of women and to their autonomy. The development of new effective contraceptive methods has a profound impact on women's lives. By the use of contraception it is possible to lessen maternal, infant and child mortality and to reduce the prevalence of sexually transmitted diseases. Research and development of new effective reversible contraceptives for women and men is needed. Dissemination of information about the safety and effectiveness of contraceptive methods is of great importance. Female genital mutilation is still practiced worldwide due to customs and tradition among various ethnic groups. The procedure is considered to be medically detrimental to the physical and mental health of women and girls, and is considered by many as oppression of women. The practice has to be stopped. Recognition of the fetus as a 'patient' has a potential effect on women's right for autonomy; they have no legal obligation to undergo invasive procedures and to risk their health for the sake of their fetuses. The woman carries ethical obligations toward her fetus. This obligation should not be enforced by the law. At present women bear most of the burden of reproductive health. All of them have a right of access to fertility regulation. Governments and society must ensure the women's equal rights to health care just as men have in the regulation of their fertility.

Abortion, Induced↗

PubMed2000

An intuitive formulation for the reproductive number for the spread of diseases in heterogeneous populations.

The thresholds for mathematical epidemiology models specify the critical conditions for an epidemic to grow or die out. The reproductive number can provide significant insight into the transmission dynamics of a disease and can guide strategies to control its spread. We define the mean number of contacts, the mean duration of infection, and the mean transmission probability appropriately for certain epidemiological models, and construct a simplified formulation of the reproductive number as the product of these quantities. When the spread of the epidemic depends strongly upon the heterogeneity of the populations, the epidemiological models must account for this heterogeneity, and the expressions for the reproductive number become correspondingly more complex. We formulate several models with different heterogeneous structures and demonstrate how to define the mean quantities for an explicit expression for the reproductive number. In complex heterogeneous models, it seems necessary to define the reproductive number for each structured subgroup or cohort and then use the average of these reproductive numbers weighted by their heterogeneity to estimate the reproductive number for the total population.

Disease Outbreaks↗

PubMed1997

Returns to service after mating and removal of sows for reproductive reasons from commercial swine farms.

We studied the records of 30 herds with an average inventory of 11,705 sows, 25,719 farrowings and 25,040 daily feed intake logs. Production events were recorded by producers using the PigCHAMP production information system. Of 21,505 matings, 7.2% of sows subsequently returned to estrus after service. The proportionate rates of intervals from service to the subsequent post service event were 0 to 17 d, 2.1%; 18 to 25 d, 27.9%; 26 to 37 d, 13.8%; 38 to 46 d, 15.8%; 47 to 108 d, 30.4%; and >108 d, 10.0%. Sows returned to service after mating were categorized into groups that either regularly or irregularly returned to service after mating. Of a total inventory of 19,076 sows, 10.0% were removed following weaning for reproductive reasons. The reasons for removal included those of anestrus (25.2%), failure to conceive (37.0%), failure to farrow (15.0%), not pregnant (1.4%), negative pregnancy check (14.0%), and abortion (7.4%). The last 5 types of post weaning reproductive failure were grouped into the category of did not farrow. Categorical additive models and comparisons using contrasts were used to analyze the influence of risk factors on reproductive failure. Parity 1 sows had a higher proportion (P < 0.01) of returns to service and a greater proportion of sows remaining anestrous post weaning relative to Parity 3 sows. The proportion of sows that did not farrow was higher (P < 0.01) in Parities 9 and 10 than in Parity 3. More sows were removed for anestrus during the spring (P < 0.01) and summer (P = 0.06) than during the winter. All categories of lactation length had similar rates of reproductive failure except for the lactation length 1 to 7 d, which had a higher (P < 0.05) proportion of reproductive failure. Lower lactational feed intake was associated with an increased risk of occurrence of each reproductive failure category. The odds ratios of lactation feed intake in logistic regression analyses were 0.84, 0.89, 0.82 and 0.88 for regularly and irregularly returned to service, anestrus, and did not farrow groups, respectively. This means, for example, that a sow was 0.88 times less likely to have an occurrence of not farrowing for each 1 kg increase in average daily feed intake during lactation. Our results indicate that lower and higher parities, spring and summer seasons, a lactation length of less than 8 d and lower feed intake during lactation affect the occurrence of return to service after mating and of herd removal for reproductive reasons.

Journal Article↗

PubMed1999

MUC1/episialin: a critical barrier in the female reproductive tract.

The female reproductive tract must resist microbial infections as well as support embryonic development, implantation and placentation. Reproductive tract mucins, in general, and Muc1/episialin, in particular, play key roles in implantation related events and in protection from microbial infection. High levels of mucin expression in the lower reproductive tract presumably affords protection against infection while down-regulation of uterine mucins has been suggested to provide access to the uterine surface. The present studies demonstrate that mucins, particularly Muc1, are effective barriers to embryo attachment. Furthermore, a strain of female Muc1 null mice in normal housing displays chronic infection and inflammation of the lower reproductive tract and markedly reduced fertility rates. This phenotype is not observed when Muc1 nulls are housed in a pathogen-free environment indicating that this phenotype results from chronic microbial exposure. Only normal endogenous flora were isolated from the reproductive tracts of affected Muc1 null mice, suggesting that these bacterial species become opportunistic with loss of the mucin barrier. Staphylococcal adherence to lower reproductive tract epithelia was found to be mediated by cell surface mucin carbohydrates. Collectively, these studies demonstrate a critical barrier role for Muc1 in various aspects of female reproductive tract physiology.

Animals↗

PubMed2002

Health-seeking behavior of Karachi women with reproductive tract infections.

To explore the contextual factors influencing health-seeking behavior of women in Karachi regarding reproductive tract infections, 18 women with reproductive tract infections from different clinics and community settings were identified and in-depth interviews were conducted. Physicians in our study diagnosed a woman to have lower reproductive tract infection if she complained of malodorous vaginal discharge with or without perineal itching; and to have pelvic inflammatory disease or upper reproductive tract infection if she had any two of the following complaints: malodorous vaginal discharge, menstrual irregularities, lower abdominal pain or dyspareunia. Women consulted a variety of healthcare providers in their pursuit for treatment, mainly allopathic doctors and hakims. The different treatments prescribed to women ranged from oral and intravaginal medications to various home remedies including refraining from specific foods. Causes of reproductive tract infections reported were "melting bones", consuming foods with perceived hot composition, poor personal hygiene and procedures like dilatation and curettage, delivery and induced abortions. None reported sexually transmitted diseases as the perceived cause of their problem. Interference with religious activities, sexual relationships or socializing was reported as consequences of reproductive tract infections, in addition to lower abdominal pain, menstrual irregularities, backache and kamzori (weakness). Pakistani women seek care for reproductive tract infections and visit a variety of providers, though causes and treatments offered are usually not related to sexually transmitted diseases. We therefore suggest training of healthcare providers for appropriate counseling and that treatment management protocols be advocated.

Adult↗

PubMed2000

Seasonal effects on puberty and reproductive characteristics of female Chios sheep and Damascus goats born in autumn or in February.

Ten Chios ewe lambs and 10 Damascus she-kids born in October-November and similar numbers born in February along with eight multiparous females from each species, were used to examine pubertal events and reproductive seasonality. Reproductive activity was monitored by determining serum progesterone concentrations once a week for 12 months. The mean date of onset of ovulation (puberty) in autumn-born Chios females (7 August) was earlier (p<0.05) than in February-born ones (11 September) though the onset of regular cyclicity was not significantly different between the two groups (30 August and 19 September, respectively). The age and live weight at puberty in autumn-born females was higher (p<0.01) than in February-born ones, the respective values being 43.3 weeks and 50.1kg, versus 29.9 weeks and 42.0kg. All animals, irrespective of time of birth, started ovulating after the summer equinox. Multiparous Chios ewes had reproductive cycles covering most time of the year with acyclic periods during spring and summer. In ewe lambs, about half of the animals ceased cycling during the second half of winter and in spring, while the rest continued cycling. The total number of cycles detected over the experimental period was lower (p<0.05) for February-born (n=9.4) compared with autumn-born females (n=13.7) and adult ewes (n=17.1). In Damascus she-kids born in autumn or in February, onset of puberty was at the same time in the following autumn, the respective mean date for the two groups being 1 November and 27 October. For autumn-born animals, age (48.4 weeks) and live weight (53.8kg) at puberty were higher (p<0.01) than for those born in February (37.3 weeks, 42.9kg). Reproductive cycles in adult goats started in the second half of September and continued until the end of March. Most young goats (75%) had their last seasonal cycle in February and the rest in March. The total number of cycles was higher (p<0.01) in adult (n=8.1) than in young goats born either in autumn (n=6.3) or in February (n=5.7). It is concluded that reproductive development and puberty in Chios female sheep are mostly under seasonal influences though age and body weight are also contributing factors. This breed has a long reproductive season with some animals cycling throughout the year. The Damascus female goat is strictly seasonal with distinct periods of reproductive cyclicity and inactivity. Puberty attainment of Damascus females born in autumn or in February is at the same time the following autumn.

Journal Article↗

PubMed2002

Thyroid issues in reproduction.

Observations in people and animals demonstrate relationships between thyroid and reproductive functions. Thyroid issues of importance to small animal reproduction are twofold. First, some thyroid disorders, such as lymphocytic thyroiditis and some forms of congenital hypothyroidism, appear to be heritable. Those traits might be considered undesirable. If so, to eliminate the trait affected animals would not be selected as breeding stock. Second, thyroid disorders may adversely affect fertility, pregnancy, or neonatal health. If a causal relationship existed between thyroid and reproductive disorders, correction of one would be expected to result in resolution of the other. This is often not the case. Although animals and people with thyroid disorders may also have reproductive disorders, usually disorders other than thyroid disease are the cause of reproductive abnormalities. It appears that euthyroidism supports optimal reproductive performance, but clinically significant reproductive dysfunction is manifested only under certain uncommon conditions of thyroid disease in dogs and cats.

Animals↗

PubMed2003

Reproduction of seen actions: stimulus-selective learning.

Subjects observed and reproduced abstract, irregular stimulus models generated by the steady movement of a disk across two-dimensional paths. The paths comprised 3 to 7 randomly oriented linear segments linked head-to-foot. Reproductions were expressed by moving a stylus over the surface of a graphics tablet while the disk was tracing its trajectory (concurrent reproduction), or soon after the disk had finished (delayed reproduction). For both concurrent and delayed conditions, fidelity of reproduction fell with increasing number of segments in the model. Overall quality of reproduction did not differ between the two conditions. When a few models were repeated, interspersed among non-repeated ones, performance improved but only when reproduction was delayed. This improvement was stimulus-selective, not a general improvement with practice. Two additional experiments showed that (i) memory for a seen model is well preserved for at least 6 s, with relatively modest need for rehearsal, and (ii) successful reproduction is possible with remarkably little information having been extracted from key points in the model's trajectory.

Adolescent↗

PubMed1997

Regulation of reproductive tract immunoglobulins by oestradiol-17beta in the European Red Fox.

The effect of the ovarian hormone, oestradiol-17beta, on reproductive tract immunity in the female fox was investigated. Reproductive tract antibody responses were induced by either Peyer's patch immunization with a recombinant fox sperm protein, or by oral immunization with live, attenuated Salmonella typhimurium. The effect of exogenous oestradiol-17beta or the stage of the oestrous cycle on reproductive tract immunity was assessed. The secretion of specific vaginal IgA, but not vaginal IgG, antibodies was reduced by exogenous treatment with oestradiol-17beta, while both specific vaginal IgA and vaginal IgG levels declined during the period of natural oestrus. It is concluded that oestradiol-17beta, and probably other reproductive hormones, are involved in the regulation of antibody-secretion in the fox reproductive tract, and that reproductive status is an important factor to consider in the design and application of vaccines which aim to induce immunity within the female reproductive tract.

Animals↗

PubMedDate not supplied

Reproductive versus chronologic age as a predictor of low birth weight, preterm delivery and intrauterine growth retardation in primiparous women.

The effect of reproductive age (chronologic age at conception minus menarcheal age) and chronologic age on the risks of low birth weight, preterm delivery and intrauterine growth retardation were studied in 1198 primiparous women whose pregnancies ended in singleton live births at Yale-New Haven Hospital, 1980-1982. After adjustment for maternal race and other important confounding variables, neither young reproductive age (less than 8 years) nor young chronologic age (less than 20 years) were strongly related to any of the reproductive outcomes. Older chronologic age (greater than 29 years) was also not strongly related to any of these outcomes, but older reproductive age (greater than 15 years) was moderately associated with low birth weight (OR 1.9; 95% CI 0.9, 3.8) after adjusting for maternal race, religion and smoking status. In addition, extremely young reproductive age (less than 2 years) appeared to be associated with an increased risk of preterm delivery (OR 3.1; 95% CI 0.7, 14.6), but our sample was too small to adjust for confounding factors in this group of women. Reproductive age appears to reflect extremes in menarcheal age, whereas chronologic age does not, and this association may account for any relationship between reproductive age and pregnancy risk in primiparous women.

Adolescent↗

PubMed1989

On the origin of meiotic reproduction: a genetic modifier model.

We study the conditions under which a rare allele that modifies the relative rates of meiotic reproduction and apomixis increases in a population in which meiotic reproduction entails selfing as well as random outcrossing. A distinct locus, at which mutation maintains alleles that are lethal in homozygous form, determines viability. We find that low viability of carriers of the lethal alleles, high rates of selfing, dominance of the introduced modifier allele, and lower rates of recombination promote the evolution of meiosis. Meiotic reproduction can evolve even in the absence of linkage between the modifier and the viability locus. The adaptive value of meiotic reproduction depends on the relative viabilities of offspring derived by meiosis and by apomixis, and on associations between the modifier and the viability locus. Meiotic reproduction, particularly under selfing, generates more diverse offspring, including those with very high and very low viability. Elimination of offspring with low viability generates positive associations between enhancers of meiotic reproduction and high viability. In addition, partial selfing generates positive associations in heterozygosity (identity disequilibrium) between the modifier and the viability locus, even in the absence of linkage. The two kinds of associations together can compensate for initial reductions in mean offspring viability under meiotic reproduction.

Biological Evolution↗