Subsequent Reproductive Behavior Research Articles

How does the timing of weapon loss influence reproductive traits and trade-offs in the insect Narnia femorata?

A longstanding goal of evolutionary biology is to understand among-individual variation in resource allocation decisions and the timing of these decisions. Recent studies have shown that investment in elaborate and costly weapons can result in trade-offs with investment in testes. In this study, we ask the following questions: At what point plasticity in resource allocation to these different structures ceases during development, if at all? Furthermore, can individuals tailor their reproductive behavior to accompany structural changes? We experimentally addressed these questions in the insect Narnia femorata, quantifying resource reallocation across development for the first time, using a phenotypic engineering approach. To investigate whether allocation plasticity diminishes throughout ontogeny, we induced weapon loss at a range of different developmental stages and examined subsequent testes mass and reproductive behavior. We found that relative testes mass increased as weapon investment decreased, implying a direct trade-off between testes and weapon investment. However, autotomy postadulthood ceased to induce larger testes mass. Intriguingly, losing a weapon while young was associated with extended adult mating duration, potentially enabling compensation for reduced fighting ability. Our results highlight the importance of examining the ontogeny of trade-offs between reproductive traits and the flexibility of the relationship between reproductive morphology and behavior.

Emergence and Reproductive Rhythm of Clostera anastomosis (Lepidoptera: Notodontidae)

Abstract Clostera anastomosis L. (Lepidoptera: Notodontidae) is a serious defoliator of poplar, Populus spp., trees in China. To establish a baseline of information for possible ecological management of this pest, we studied its emergence, courtship, mating, and oviposition behaviors in the laboratory at 27 ± 1°C and 60 ± 10% relative humidity under a 14:10-h (light:dark) photoperiod. Under these conditions, peak emergence of female adults occurred in the sixth day after pupation, and peak emergence of males was in the seventh day after pupation. Emergence for both sexes occurred throughout the day. Courtship behavior began at the sixth hour of scotophase, reaching peak activity between the 10th hour of scotophase and the first hour of photophase. The courtship and mating success rate were highest for 1-d-old females, and then gradually decreased with age until no mating was observed after females were 4 d old. With 1-d-old females, mating was only observed from the seventh hour of scotophase to the first hour of photophase, with peak activity at 0.5 h after the onset of photophase. Oviposition primarily occurred within 3 d after mating, with 49.8% of the eggs being deposited during the first day after mating. These results demonstrate that there are distinct circadian rhythms in adult emergence and subsequent reproductive behavior of C. anastomosis, thus providing a basis for development of monitoring and management strategies of this pest.

Caesarean deliveries, subsequent reproductive behaviour and children ever born in India.

Against the backdrop of the alarming rise in Caesarean section (C-section) births in India, this study aimed to examine the association between C-section births, fertility decline and female sterilization in the country. A cross-sectional design was used to investigate the association between C-section delivery and subsequent reproductive behaviour in women in India. Data were from the National Family Health Survey (NFHS-4). The study sample comprised 255,726 currently married women in the age group of 15-49 years. The results showed a strong positive relationship between C-section births and female sterilization. The predicted probabilities (PP) from the multivariate regression model indicated a higher chance of female sterilization in women with C-section births (PP = 0.39, p<0.01) compared with those with non-C-section births (PP = 0.20, p<0.01). Both state-level correlation plots and Poisson regression estimates showed a strong negative relationship between C-section births and mean children ever born (CEB). Based on the results, it may be concluded that the use of C-sections and sterilization were strongly correlated in India at the time of the NFHS-4, thus together contributing to fertility decline. A strong negative association was found between the occurrence of C-sections and CEB. The increased and undesired use of C-section births and consequent female sterilization is a regressive socio-demographic process that often violates women's rights. Fertility decline should happen through informed choice of family planning and must protect the reproductive rights of women.

Early-life exposure to Tris(1,3-dichloroisopropyl) phosphate induces dose-dependent suppression of sexual behavior in male rats.

Exposure to endocrine-disrupting chemicals may adversely affect animals, particularly during development. Tris(1,3-dichloroisopropyl) phosphate (TDCIPP) is an organophosphate with anti-androgen function in vitro that is present in indoor dust at relatively high concentrations. In male rats, androgens are necessary for the development of reproductive organs, as well as the endocrine and central nervous systems. However, we currently do not know the exact effects of TDCIPP exposure through suckling on subsequent reproductive behavior in males. Here, we show that TDCIPP exposure (25-250mg kg-1 via oral administration over 28 consecutive days post-birth) suppressed male sexual behavior and reduced testes size. These changes were dose-dependent and appeared first in adults rather than in juveniles. These results demonstrate that TDCIPP exposure led to normal body growth and appearance in juveniles, but disrupted the endocrine system and physiology in adults. Therefore, assays should be performed using adult animals to ensure accuracy, and to confirm the influence of chemical substances given during early mammalian life.

Region-specific rapid regulation of aromatase activity in zebra finch brain.

Recent studies demonstrate that rapid modulation of the estrogen synthetic enzyme aromatase, regulates hypothalamic (HYP) estrogen production, and subsequent neurophysiology and reproductive behavior. In songbirds, in addition to expression in the HYP, aromatase is expressed at high levels in several brain regions notably in the hippocampus (HP) and caudomedial nidopallium (NCM), where estrogens affect learning and memory and auditory processing, respectively. Previous studies, largely in quail HYP, show that aromatase activity is acutely down-regulated by Ca2+ -dependent phosphorylation. Here, using zebra finches (Taeniopygia guttata), we ask if similar mechanisms are at work in the songbird HYP and if there are sex as well as regional differences in aromatase modulation. Using invitro assays to measure activity in homogenates or in partially purified supernatants containing microsomes and synaptosomes of the HP, HYP, and NCM, we examined effects of Ca2+ , Mg2+ , ATP, NADPH, and an inhibitor of kinase activity. We report a rapid down-regulation of aromatase activity in the presence of phosphorylating conditions across all three brain regions and both sexes. However, regional differences were seen in response to some phosphorylating factors, some of which were improved by partial purification of the homogenates. Furthermore, while low concentrations of ATP inhibited aromatase activity, unexpectedly, inhibition was no longer seen with high ATP concentrations. These results provide evidence for a regional and temporal specificity in the rapid modulation of aromatase activity that may bear on local neuroendocrine function. Aromatase activity in male and female zebra finch hippocampus, hypothalamus, and caudomedial nidopallium is rapidly regulated by Ca2+ -dependent phosphorylation. Low ATP and Mg2+ decrease activity, whereas nicotinamide adenine dinucleotide phosphate (NADPH), high ATP, and inhibition of protein kinase C increase activity. Evidence suggests this may occur at the synapse. These results provide a mechanism for rapid regulation of behavior via brain estrogen synthesis.

Impact of child health and disability on subsequent maternal fertility

The prevalence of chronic conditions among children has been rising in the past four decades. Despite the policy relevance and plausible mechanisms through which child disability and severe early life health conditions can impact subsequent maternal reproductive behavior, there has been limited investigation of this question particularly in the US. Child disability or severe early life health problems such as very preterm birth (VPTB) and very low birth weight (VLBW) can constrain household resources to have another child but may also increase parental demand for healthy children and modify allocation of resources between children. Empirical assessment of this question is complicated by unobservables such as maternal health and preferences. We examine whether giving birth to a child with disabilities or severe adverse birth outcomes including VPTB and VLBW impacts subsequent maternal fertility. We employ a mother fixed-effect duration model for maternal fertility over time as a function of the proportion of previously born children with disabilities/health conditions in order to account for time-invariant unobservables, using merged data from the 1993 National Health Interview Survey and 1995 National Survey of Family Growth. We find no evidence that having disabled children reduces subsequent live births when using the mother fixed-effect model, in contrast to the classical model using within and between mother variation which suggests a fertility decline. Similarly, we find no evidence that having VPTB or VLBW children reduces fertility. Overall, our findings indicate no impact of child disability or health conditions on subsequent maternal fertility. Additional analyses excluding women who may qualify for AFDC show overall a similar pattern of results, suggesting that the findings may be generalizable post the AFDC. Time-varying unobservables may still be at work, but they likely result in an opposite (negative) bias toward reduction in fertility.

Reproductive behavior following evacuation to foster care during World War II

BACKGROUND Family disruption and separation form parents during childhood may have long-lasting effects on the child. Previous literature documents associations between separation from parents and cognitive ability, educational attainment, and health, but little is known about effects on subsequent reproductive behavior. OBJECTIVE We evaluate the associations between unaccompanied evacuation to foster care and subsequent marriage and fertility behavior by comparing Finnish children who were evacuated to Swedish foster families during World War II to their non-evacuated siblings. METHODS In total, some 49,000 children were evacuated for a period ranging from months to years. We analyze a nationally representative sample of 2,009 evacuees born in 1933-1944 by combining data collected from war time government records with 1950 and 1971 censuses and 1971-2011 population registers. RESULTS Comparison of evacuated and nonevacuated same-sex siblings suggests no associations between evacuation and the probability of ever marrying, timing of first birth, and completed family size, although some associations are found in naive means comparisons. This difference in results across models is suggestive of negative selection of evacuee families. CONCLUSIONS We do not find consistent evidence of any causal effect of family disruption on family formation and reproductive behavior. The results are sensitive to controlling for unobserved selection and suggest that some of the adverse outcomes documented in earlier literature could change if selection was accounted for.

Effects of a Neonatal Immune Challenge on Reproductive Development and Associated Behaviors in Siberian Hamsters (Phodopus sungorus)

Environmental stressors have the potential to disrupt early development in ways that could adversely impact fitness. Studies have demonstrated that animals exposed to postnatal lipopolysaccharide (LPS) show signs of delayed puberty, such as delayed vaginal opening and first estrus. This study investigated the effects of a neonatal immune challenge on subsequent adult reproductive physiology and behavior, and explored possible mediating mechanisms. Hamsters received LPS or saline injections on postnatal day (pnd) 3 and 5, as there is heightened sensitivity of the GnRH pulse generator at these time points. Female reproductive maturity was determined by monitoring for vaginal patency, beginning on pnd 25 and every five days thereafter until maturity. Male reproductive maturity was determined by using the left testis length and width to estimate testis weight beginning on pnd 25 and each subsequent week until reproductive maturity. At pnd 75 animals were placed in staged mating pairs with reproductively mature individuals of the opposite sex. Rejection, grooming and sniffing behaviors were scored for all females, and the lordosis quotient was calculated for receptive females. Mounting, intromission and ejaculation were scored in males. Preliminary data showed a decrease in food intake and body mass, as well as delay in reproductive maturity for animals treated with LPS. Female receptivity and other reproductive behaviors were varied by the LPS challenge. The results of this study contribute to a greater understanding of the behavioral responses to early immune challenges and possible ways in which animals may adjust to this common stressor.

Abdominally implanted satellite transmitters affect reproduction and survival rather than migration of large shorebirds

Satellite telemetry has become a common technique to investigate avian life-histories, but whether such tagging will affect fitness is a critical unknown. In this study, we evaluate multi-year effects of implanted transmitters on migratory timing and reproductive performance in shorebirds. Shorebirds increasingly are recognized as good models in ecology and evolution. That many of them are of conservation concern adds to the research responsibilities. In May 2009, we captured 56 female Black-tailed Godwits Limosa limosa limosa during late incubation in The Netherlands. Of these, 15 birds were equipped with 26-g satellite transmitters with a percutaneous antenna (7.8 % ± 0.2 SD of body mass), surgically implanted in the coelom. We compared immediate nest survival, timing of migration, subsequent nest site fidelity and reproductive behaviour including egg laying with those of the remaining birds, a comparison group of 41 females. We found no effects on immediate nest survival. Fledging success and subsequent southward and northward migration patterns of the implanted birds conformed to the expectations, and arrival time on the breeding grounds in 2010–2012 did not differ from the comparison group. Compared with the comparison group, in the year after implantation, implanted birds were equally faithful to the nest site and showed equal territorial behaviour, but a paucity of behaviours indicating nests or clutches. In the 3 years after implantation, the yearly apparent survival of implanted birds was 16 % points lower. Despite intense searching, we found only three eggs of two implanted birds; all were deformed. A similarly deformed egg was reported in a similarly implanted Whimbrel Numenius phaeopus returning to breed in central Alaska. The presence in the body cavity of an object slightly smaller than a normal egg may thus lead to egg malformation and, likely, reduced egg viability. That the use of implanted satellite transmitters in these large shorebirds reduced nesting propensity and might also lead to fertility losses argues against the use of implanted transmitters for studies on breeding biology, and for a careful evaluation of the methodology in studies of migration.

Avoir un deuxième enfant en Italie : de l'intention à la réalisation

Résumé En Italie, l’indice synthétique de fécondité est largement au-dessous du niveau de remplacement des générations, mais la plupart des femmes envisagent toujours d’avoir deux enfants. Il y a donc un décalage entre les intentions de fécondité et les comportements observés. Les auteures cherchent à évaluer, au niveau individuel, le degré de concordance entre les intentions de fécondité des mères d’un enfant et leur fécondité ultérieure, et à mettre en évidence quelles caractéristiques affectent à la fois les intentions positives de fécondité et leur réalisation à court terme. Cette analyse est élaborée à partir d’une base de données ad hoc construite en reliant l’édition 2002 de l’Enquête par sondage sur les naissances (où étaient recueillies les intentions de fécondité des mères) aux naissances vivantes inscrites dans le Registre de la population entre 2002 et 2008. Les résultats montrent que les intentions de fécondité des mères d’un enfant ont une influence déterminante sur leur comportement reproductif futur. Les hypothèses de l’influence du statut socioéconomique de ces femmes et de la charge des tâches ménagères sur leur intention d’avoir un autre enfant et la réalisation de ce projet ont été testées : les auteures constatent que le statut socioéconomique affecte moins les intentions positives de fécondité que leur réalisation, et que la charge de travail domestique ne paraît pas avoir d’effet significatif.

RECENT SOCIAL HISTORY ALTERS MALE COURTSHIP PREFERENCES

Phenotypically plastic mating behavior may allow males to modify their reproductive behavior to suit the prevailing social conditions, but we do not know if males only react to immediate social stimuli or change their inherent mate preferences according to their social history. Here we examine the effect of social experiences on the subsequent reproductive behavior of male guppies under standard conditions, allowing us to distinguish the effect of past and immediate social conditions. Males experienced experimental conditioning periods during which they interacted with three females, either of variable size or of similar size. Females arrived either simultaneously or consecutively. In subsequent standard assays, only males that had experienced females of variable size preferentially courted large females. Further, males exposed to sequential female arrival courted subsequent females more vigorously than males that had experienced simultaneous female arrival. In contrast, males did not alter their coercive mating attempts in relation to their recent social history. These results demonstrate that males use past experiences to modify their subsequent reproductive behavior rather than reacting only to immediate stimuli, and reveal the sophisticated ways in which males alter their reproductive tactics to suit the social environment and maximize fitness across changing selective landscapes.

Impacts of Early Life Exposure to Estrogen on Subsequent Breeding Behavior and Reproductive Success in Zebrafish

Impacts of exposure to environmental estrogens on reproductive development are well documented, but recently wider concern has been raised due to evidence that such exposures can disrupt normal patterns of reproductive behavior, dominance, and parentage, with potential population level implications. It is fundamental therefore to understand any such effects for effective risk assessment. This study investigated the impact of a transient exposure to ethinylestradiol (EE(2)) during early life (from 20-60 days post fertilization), including at a dosing level within the environmental range, on the subsequent reproductive behavior and success in both male and female zebrafish (Danio rerio) in competitive breeding scenarios. There were no obvious effects of the early life EE(2) exposures on the subsequent gonadal phenotypes in either mature males or females. In fact, reproductive success in males exposed to 2.76 ng EE(2)/L was increased in competitive spawning scenarios. In contrast, exposure of females to EE(2) (9.86 ng/L) during early life reduced their subsequent reproductive success in competitive spawning scenarios. Mate choice experiments suggested this was a consequence of the females' diminished courting behavior toward males, rather than any male preference for unexposed females. Reproductive capability of females is generally considered a key determinant in population demographics and dynamics, and therefore the effect of exposure to EE(2) on female reproductive success may have significant implications for exposed fish populations.

Calling and Courtship Behaviors Initiated by Male-Male Contact Via Agonistic Encounters in the CricketGryllus bimaculatus

We investigated the stridulatory courtship initiated by male-male contact after agonistic encounters and the effect of dominance status on subsequent reproductive behavior in the cricket Gryllus bimaculatus. When two male crickets were kept together in a small area, their dominance status was quickly established through fighting or non-fighting interactions. Approximately 10 min after pairing, most dominant males produced calling and/or courtship songs in the presence of subordinate males. This behavior appeared to be triggered by some contact chemicals on the body surface of the males. Stimulation using the forewing of a neutral male induced courtship in dominant males at a higher level compared with neutral males which were not previously paired with males. These observations suggest that the sexual motivation in dominant males increased because of previous agonistic interactions. In contrast, subordinate males remained silent. Stimulation using the male forewing induced stridulation to a lesser degree in subordinate males than in neutral males, suggesting decreased sexual motivation in subordinate males. Furthermore, only 40% of subordinate males exhibited courtship behavior under triadic conditions (dominant male, subordinate male and female) in contrast with 100% in male-female pairs. This result reveals that subordinate males, being less sexually motivated, are continuously suppressed in their courtship by intermittent attacks by the nearby dominant males. In the other triadic condition where the males were allowed to copulate, 65% of the dominant males copulated, while none of the subordinates did. These results suggest that dominant males have a greater chance to copulate and produce offspring.

Effects of mating experience on subsequent reproductive behaviour and sperm release in the spider Nesticodes rufipes

During a mating season, individuals encounter potential mates that have varied copulatory experiences. Such experience may influence the likelihood and nature of subsequent reproductive behaviour and sperm release within a female/male dyad. We examined the influence of an individual's sexual experience on its subsequent mating activities and that of a potential partner in a cobweb spider, Nesticodes rufipes. Our results suggest that an individual's prior sexual experience influenced its own subsequent motivation, but had little effect on that of the potential partner. For females, their prior experience decreased receptivity and increased aggressiveness towards the second male, while having little effect on the subsequent male's motivation (i.e. approach). Specific aspects of a female's initial mating experience (i.e. plug formation) did however influence the nature of subsequent copulation, which in turn influenced sperm release. For males, their prior experience decreased the latency to approach the female and increased the efficiency of pedipalp insertion, but male experience had little effect on the behaviour of the female. Our results suggest that mating experience may benefit both sexes in that (1) females that are not sperm limited may incur high costs from remating (time) and (2) males show experience-related improvement in copulatory efficiency.

Reproductive maturation in the large pine weevil Hylobius abietis: the relative importance of larval and adult diet

Abstract1 Larval and adult Hylobius abietis (L.) can feed and, in the case of the adults, cause commercially significant damage to many species of conifer. The present study aimed to evaluate the impact of larval and adult feeding on different host plants on subsequent reproductive fitness.2 Hylobius abietis larvae were reared on logs of four host species known to vary in suitability for development; Pinus nigra ssp. laricio, Picea sitchensis, Larix kaempferi and Pseudotsuga menziesii. Adult females were collected on emergence and allocated to complete maturation feeding on one of four seedling conifer species, P. nigra spp. laricio, P. sitchensis, P. menziesii and Larix ×marschlinsii. It was assumed that variation in both larval and adult host plant quality had the potential to influence subsequent reproductive behaviour.3 The time taken for females to attain reproductive maturity was assessed, and reproductive output was measured over an average period of 17 days.4 The best predictor of the time to attain reproductive maturity was found to be the initial adult body weight. This was strongly related to the larval host species, with the largest adults emerging from P. nigra ssp. laricio. The time taken to begin oviposition was in the range 10–49 days (mean 23 days). The subsequent mean rate of oviposition for individual females was in the range 0.1–3.7 eggs per day. Egg volumes varied between and within individual females, in the range 0.241–1.079 mm3.5 The species of seedling provided for maturation feeding had no significant impact on reproductive behaviour over the course of the experiment. It is possible, however, that the quality of the adult diet might exert a greater influence on behaviour over a longer period because H. abietis is a relatively long‐lived species.

THE EFFECT OF HUSBANDS’ FERTILITY PREFERENCES ON COUPLES’ REPRODUCTIVE BEHAVIOUR IN RURAL BANGLADESH

Bangladesh society is profoundly gender stratified, and yet male roles in reproductive health processes have not been rigorously investigated. This study examines the association between men's reproductive health knowledge, attitude and behaviour and their wives' subsequent reproductive behaviour using longitudinal data from the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). A total of 4969 matched husband-and-wife data from a 1998 survey and women's contraceptive use history data following this survey are used. Results show a significant association between husbands' fertility preferences and current use of any family planning method. When wives' background characteristics, and husbands' background and socioeconomic characteristics are controlled for, the predicted probability of using a method of contraception among non-educated wives whose husbands want more children is 0.49 compared with 0.64 for those whose husbands do not want more children. However, the net effect of husbands' preference for additional children diminishes as wives' level of education increases. Among wives who had completed high school, the predicted probability of using a method of contraception is 0.70 for those whose husbands want more children compared with 0.69 for those whose husbands do not want more children.

Seminal fluids mediate sexual inhibition and short copula duration in mated female Queensland fruit flies

Molecules in male seminal fluid transferred to female insects during mating can have potent effects on their subsequent sexual and reproductive behaviour. Like many other tephritids, female Queensland fruit flies ( Bactrocera tryoni) typically have diminished sexual receptivity after their first mating. Also, copulations of females that do remate tend to be shorter than those of virgins. We here find that virgin females injected with small doses (0.1, 0.2 or 0.5 male equivalents) of extracts from the male reproductive tract accessory tissues, which consist of male accessory glands, ejaculatory apodeme and ejaculatory duct (AG/EA/ED), have diminished receptivity and short copula duration very similar to naturally mated females. In contrast, virgin females injected with saline or with high doses of AG/EA/ED (1 or 2 male equivalents) that likely exceed the range of natural variation retain the higher levels of sexual receptivity and longer copulations of un-injected virgins. We conclude that reduced sexual receptivity and shorter copulations of mated female Q-flies are mediated by products in the male seminal fluid derived from the male reproductive tract accessory tissues.

Environmental Effects on Family Size Preferences and Subsequent Reproductive Behavior in Nepal

This study investigates the relationship between environmental degradation and men and women’s family size preferences and subsequent reproductive behaviors in Nepal. We draw on unique environmental data at the local level, household and individual-level survey data and individuals reproductive behavior over a 3 year time period in Western Chitwan Valley, Nepal. Results from Ordinary Least Squares (OLS) and logistic regression models show that poorer environmental quality and greater reliance on publicly owned natural resources are associated with higher family size preferences and higher rates of pregnancy. The analyses provide support for the “vicious circle” argument that environmental degradation can lead to rising population growth via positive effects on fertility. As environmental conditions decline and when households rely on public lands for natural resources, men and women desire larger family sizes and women are more likely to get pregnant in the near future.

The interplay between infant mortality and subsequent reproductive behaviour: evidence for the replacement effect from historical population of Bejsce Parish, 18th-20th centuries, Poland

The paper examines the relationship between in fant mortality and subsequent reproductive behaviour using data from a reconstitution of parish registers from Bejsce (1750-1968, Poland). It is expected that experience of infant death should increase the risk of subsequent parity transi tion due to the replacement effect. Multilevel event history analyses shows that the death of an infant significantly in creases the risk of transition to subsequent birth and short ens the median duration of birth intervals among controlled fertility birth cohorts. The replacement effect is stronger at lower parities and when the previous child dies during the first 12 months of life.

Neonatal screening for inborn errors of metabolism: cost, yield and outcome.

OBJECTIVES. To systematically review the literature on inborn errors of metabolism, neonatal screening technology and screening programmes in order to analyse the costs and benefits of introducing screening based on tandem mass-spectrometry (tandem MS) for a wide range of disorders of amino acid and organic acid metabolism in the UK. To evaluate screening for cystic fibrosis, Duchenne muscular dystrophy and other disorders which are tested on an individual basis. HOW THE RESEARCH WAS CONDUCTED. Systematic searches were carried out of the literature on inborn errors of metabolism, neonatal screening programmes, tandem MS-based neonatal screening technology, economic evaluations of neonatal screening programmes and psychological aspects of neonatal screening. Background material on the biology of inherited metabolic disease, the basic philosophy, and the history and current status of the UK screening programme was also collected. Relevant papers in the grey literature and recent publications were identified by hand-searching. Each paper was graded. For each disease an aggregate grade for the state of knowledge in six key areas was awarded. Additional data were prospectively collected on activity and costs in UK neonatal screening laboratories, and expert clinical opinion on current treatment modalities and outcomes. These data were used to construct a decision-analysis model of neonatal screening technologies, comparing tandem MS with the existing phenylketonuria screening methods. This model determined the cost per additional case identified and, for each disease, the additional treatment costs per case, and the cost per life-year saved. All costs and benefits were discounted at 6% per annum. One-way sensitivity analysis was performed showing the effect of varying the discount rate, the incidence rate of each disorder, the number of neonates screened and the cost of tandem MS, on the cost per life-year gained. RESEARCH FINDINGS. The UK screening programmes for phenylketonuria and congenital hypothyroidism have largely achieved the expected objectives and are cost-effective. Current concerns are the difficulty of maintaining adequate coverage, perceived organisational weaknesses, and a lack of overview. For many of the organic acid disorders it was necessary to rely on data obtained from clinically-diagnosed cases. Many of these diseases can be treated very effectively and a sensitive screening test was available for most of the diseases. Except for cystic fibrosis, there have been no randomised controlled trials of the overall effectiveness of neonatal screening. Despite the anxiety generated by the screening process, there is strong parental support for screening. The effects of diagnosis through screening on subsequent reproductive behaviour is less clear. Conflicts exist between current concepts and the traditional principles of screening. The availability of effective treatment is not an absolute prerequisite: early diagnosis is of value to the family concerned and, to the extent that is leads to increased use of prenatal diagnosis, may help to reduce the overall burden of disease. Neonatal screening is also of value in diseases which present early but with non-specific symptoms. Indeed, almost all of the diseases considered could merit neonatal screening. The majority of economic evaluations failed to incorporate the health benefits from screening, and therefore failed to address the value of the information which the screening programmes provided to parents. The marginal cost of changing from present technology to tandem MS would be approximately 0.60 pounds per baby at a workload of 100,000 samples a year, and 0.87 pounds at 50,000 samples per year. The ability to screen for a wider range of diseases would lead to the identification of some 20 additional cases per 100,000 infants screened, giving a laboratory cost per additional diagnosis of 3000 pounds at an annual workload of 100,000 babies per year.(ABSTRACT TRUNCATED)