Parental Cohort Research Articles

How does gender equality progress link to alcohol care and death? A registry study of the Swedish parental cohort of 1988/1989

This article examines how gender equality during early parenthood (1988-1991) associates with alcohol-related inpatient care or mortality (1992-2006). We categorised all Swedish couples having had a first child together in 1988-1989 (N=118,595) as traditional, or gender equal, or untraditional based on income and occupational position (bread-winning indicators), parental leave and temporary child care (child-care indicators). Overall, traditional women run lower risk, whereas traditional men and untraditional women (those opposing the traditional division of parenthood responsibilities) run higher risks of alcohol harm than their gender-equal counterparts.

Influence of family environment and social group on smoking among Brazilian youth aged 15 to 24 years

To estimate the prevalence of smoking among Brazilian youth, examining individual, family, and social group factors associated with this habit. Data from youth aged 15 to 24 years living in 17 Brazilian state capitals and the Federal District, obtained from the Household Survey on Risk Factors for Chronic Diseases and Reported Morbidity carried out in 2002 and 2003 by the National Cancer Institute was analyzed. Individual variables (sex, age, schooling, alcohol consumption, self-rated health, physical activity, current school attendance), family variables (age and education of head of household and father, mother, or sibling smoking), and social group variables (best friend smoking, most friends smoking, boyfriend/girlfriend smoking) were analyzed. Generalized estimating equations (GEE) approach to evaluate the factors associated with smoking were used. Considering the effect of the sampling design, smoking prevalence was 12.8%, ranging from 6.8% in Aracaju to 24.1% in Porto Alegre. The following factors were predictors of smoking: male sex, older age, less schooling, not attending school at the time of the survey, poorer health perception, and alcohol consumption. Peer smoking (friends or boyfriend/girlfriend) and smoking among family members (father/mother or sibling) were associated with smoking. There was an effect of parental birth cohort on smoking, with a higher prevalence of smoking among youth whose parents were born in the 1930s. Individual characteristics and the influence of peers and family were relevant for smoking by the youth. Increasing the dialogue among teenagers, school, schoolmates, friends, and parents could lead to a reduction of substance use among youth.

Prevention of Adolescent Reoccurring Violence and Alcohol Abuse: A Multiple Site Evaluation

“Prevention of Adolescent Reoccurring Violence and Alcohol Abuse: A Multiple Site Evaluation” is a multiple component alcohol abuse and violent behavior prevention strategy, targeted to adolescents ages 16–21 who have high levels of anger, or who are victims/perpetrators of violence, and their families. Three community centers located in upstate New York provided group participants (N = 210) known to have conduct disorder and substance abuse history. The centers were used as the intervention sites over a seven-week period with the youth assessment staff using objective screening measures. The participants were exposed to a two-pronged intervention, using a parental involvement cohort with approximately half of the study participants. The Teams, Games, and Tournaments strategy was the intervention method. Teams, Games, and Tournaments is a Social Learning Theory-based intervention with demonstrated empirical evidence of the model's effectiveness. A 2 × 3 factorial design with two follow-up points encompassed: anger control, alcohol/substance abuse, and family interactive education. The goals of the study were to help adolescents reduce their alcohol use, to increase productive family interaction, and ultimately to reduce the adolescents' aggression levels and subsequently reduce the possibility of their becoming victims or perpetrators of a violent crime. Consistent with Social Learning Theory, the Teams, Games, and Tournaments treatment intervention makes use of adolescents as peer counselors. The practical implications include that professionals or students in our public schools, juvenile courts, correctional institutions, and residential treatment centers can easily implement this program. A standardized treatment manual is available. It offers a complete, ready-to-use, and cost-effective tool for reducing adolescent violence and alcohol abuse. Further, the data provide support for a hypothesis of social learning theory, that is: interventions using multiple components are more effective than single treatments on their own.

Association of age at menarche with adult leg length and trunk height: Speculations in relation to breast cancer risk

Background: It seems paradoxical that both increased height and earlier age at menarche (which predicts for shorter stature) are both associated with increased breast cancer risk.Methods: Retrospective data from a parental cohort coupled with prospective interviews with and anthropometric measurements from their daughters were used. Multivariable linear regression analyses were conducted using mixed regression models to account for same-family participants.Results: Controlling for birth weight, maternal height, and birth cohort, and analyzed as a group, a 1—year increase in the age at menarche predicted an increase in standing height, leg length, and trunk height of 0.76, 0.41, and 0.35 cm, respectively. However, when stratifying by birth year (prior to 1966 vs 1966 or after), these relationships were true only for those born prior to 1966.Conclusion: Given the height–breast cancer risk association, the emerging evidence linking breast cell proliferation to hormones associated with growth, and the finding in this study that the relationship between age at menarche and adult height no longer exists for women born in 1966 or later, it is possible that the long-established relationship between age at menarche and breast cancer risk may also no longer exist.

Low rates of transmission of SRV‐2 and STLV‐I to juveniles in a population of Macaca fascicularis facilitate establishment of specific retrovirus‐free colonies

Prevalence of simian retrovirus-2 (SRV-2) and simian T lymphotropic virus type I (STLV-I), was unknown in 337 captive cynomolgus macaques. Molecular assays identified 29% of animals as SRV-2 mono-infected, 4% of animals as STLV-I mono-infected and 9% of animals as dual-infected. Of 108 juvenile animals, 83% were SRV-2-negative and no juvenile animal was STLV-I-positive. A subsequent study of juvenile macaques over a period of 2.5 years detected no STLV-I and 10 SRV-2 infections, six of which occurred between testing and day of colony formation. The study also highlighted that an anti-SRV-2 serological response does not presuppose infection. Tissue reservoirs of latent SRV-2 were not identified in suspected SRV-2 infections. Low transmissibility of the viruses present in the parental cohort and improved knowledge of the host response to SRV-2 has facilitated the creation of specific-retrovirus-free colonies of cynomolgus macaques.

Cultural transmission of ethnobotanical knowledge and skills: an empirical analysis from an Amerindian society

The modeling of cultural transmission is of great importance for understanding the maintenance, erosion, and spread of cultural traits and innovations. Researchers have hypothesized that, unlike biological transmission, cultural transmission occurs through at least three different, non-mutually exclusive paths: (1) from parents (vertical); (2) from age peers (horizontal); and (3) from older generations (oblique). We used data from 270 adults in a society in the Bolivian Amazon to estimate the association between a person's knowledge and skills and the knowledge and skills of the (1) same-sex parent, (2) age peers (or individuals born in the same village as the subject within ±4 years of the subject's year of birth), and (3) parental cohort (excluding parents). We found a statistically significant association between personal and parental and old cohort knowledge. The magnitude of the association is larger for old cohort knowledge than for parental knowledge, suggesting that, for the studied population, the transmission of ethnobotanical knowledge and skills is mostly oblique.

Missingness in the T1DGC MHC fine‐mapping SNP data: association with HLA genotype and potential influence on genetic association studies

The absence or 'missingness' of single nucleotide polymorphism (SNP) assay values because of genotype or related factors of interest may bias association and other studies. Missingness was determined for the Type 1 Diabetes Genetics Consortium (T1DGC) Major Histocompatibility Complex (MHC) data and was found to vary across the region, ranging up to 11.1% of the non-null proband SNPs, with a median of 0.3%. We consider factors related to missingness in the T1DGC data and briefly assess its possible influence on association studies. We assessed associations of missingness in the SNP assay data with human leucocyte antigen (HLA) genotype of the individual and with SNP genotypes of the parents. Within-cohort analyses were combined (over all cohorts) using (i) Mantel-Haenszel tests for two-by-two tables or (ii) by combining test statistics for larger tables and regression models. Mixed effect regression models were used to assess association of the SNP genotypes with affected status of the offspring after adjustment for parental SNP genotypes, cohort membership and HLA genotypes. Log-linear models were used to assess association of missingness in the unaffected sib assays with SNP genotypes of the probands. Missingness of SNP values near the HLA class I (A, B and C) and class II (DR, DQ and DP) loci is strongly associated with carriage of corresponding HLA genotypes within these groups. Similar associations pertain to missing values among the microsatellite data. In at least some of these cases, regions of missingness coincided with known deletion regions corresponding to the associated HLA haplotype. We conjecture that other regions of associated missingness may point to similar haplotypic deletions. Analysis of association patterns of SNP genotypes with affected status of offspring does not indicate strong informative missingness. However, association of missingness in proband data with parental SNP genotypes may impact transmission disequilibrium test (TDT)-type analyses. Comparisons of affected and unaffected siblings point to possible susceptibility regions additional to the classical HLA-DR3/4 alleles near BAT4-LY6G5B-BAT5 and NOTCH4. Potentially informative missingness in SNP assay values in the MHC region may impact on association and related analyses based on the T1DGC data. These results suggest that it would be prudent to assess the degree to which missingness may abrogate assessed SNP disease markers in such studies. Initial analyses based on comparison of affected and unaffected status in offspring suggest that at least these may be little affected.

Trends in human birth weight across two successive generations.

To determine the correlation between parental and offspring birthweight (BW) in India. The study involved two birth cohorts of successive generations. The parental cohort comprised of 472 fathers and 422 mothers from an earlier study. Details of their anthropometry at birth and in adulthood were available. 1525 children born to them comprised the offspring cohort. BW was obtained from hospital records for the offspring cohort. Odds ratios and regression coefficients were calculated to estimate the risks of a low birth weight (LBW) parent producing a LBW baby and quantitate the effects after adjusting for confounders. A LBW mother had a 2.8 times risk (95%CI 1.2-6.4) of delivering a LBW baby (p=0.02) and a LBW father was twice as likely to produce a LBW baby (OR 2.2; 95%CI 1.0 - 4.8; p=0.05). Every 100g increase in maternal BW was associated with an increase in offspring BW of 14 g; the equivalent figure for paternal BW was 18.1g (p< 0.001 for both). Between the generations, the incidence of LBW decreased from 19.7% to 17.2% (p=0.1). Mean BW increased in males (2846 g vs 2861 g; p=0.59) but not in females (2790 g vs 2743 g; p=0.08). Both maternal and paternal BW are strong determinants of offspring BW. The effect of mothers' BW on offspring BW is weaker than that seen in developed nations. Stronger intrauterine constraint exhibited by Indian women secondary to a higher prevalence of growth restriction in utero may be responsible. Paternal effects may be governed by paternal genes inherited by the offspring.

Trivalent Inactivated Influenza Vaccine Compliance Rate in Neonatal Intensive Care Unit Parents

The American Academy of Pediatrics (AAP) recommends injected, inactivated influenza vaccine for all close contacts of high-risk infants. This population includes parents of infants younger than 59 months of age, with an emphasis on children 0-6 months who are not direct candidates for immunization. This 0-6 month age group is a major component of the neonatal intensive care unit (NICU) population. No data exist on the compliance rate with influenza vaccine in this specific parent population. The purpose of this study was to assess the compliance rate among this parent population and compare it with vaccine use in the general adult population at the time, which has traditionally ranged from 25% to 32%. The study also sought reasons for poor compliance with flu vaccine. Answering this question is important in determining whether programs directly aimed at NICU parents are required to achieve compliance or if simply informing parents of the need to be immunized results in sufficient vaccination rates. For 14 weeks during the 2004-2005 influenza season, 92 randomly selected parents (from 56 inborn infants) underwent an informational program regarding influenza vaccine and the risks and benefits of vaccination. Parents were surveyed in the spring to assess if they obtained the injection the previous winter. Subjects were parents of NICU patients admitted to the New York University NICU during the 14-week study period. The main outcome measure was the influenza vaccination rate of the parental cohort that underwent the informational program. For those who intended to receive influenza vaccination but did not, reasons for noncompliance were assessed via standardized telephone interview. After the information session, 85 parents (92%) indicated they intended to obtain the vaccine; however 30 parents (32.6%) actually received it by the following spring. The most commonly cited reason for failing to obtain influenza vaccine was convenience. No correlation between parents who obtained the vaccine and infant birth weight, gestational age, or length of stay was observed. Compliance with national recommendations to obtain trivalent inactivated influenza vaccine in this highly specified parent population is roughly equivalent to the national average of all adults in the general population. Caregivers of high-risk neonates must encourage/offer immunization to this targeted population.

Strategies of Pomatoschistus minutus and Pomatoschistus microps to cope with environmental instability

The populations of Pomatoschistus minutus and Pomatoschistus microps were studied from June 2003 to May 2006 in the Mondego estuary, in order to understand the ability of these species to withstand environmental variability. During this period a severe drought occurred (2005), with consequent lower freshwater runoff and higher salinity incursion into the estuary. Occasional abnormal high water temperatures were observed in 2003 and 2005. The fish populations were sampled monthly along an estuarine gradient, from which population density, structure, growth and biomass production was assessed. Pomatoschistus minutus distributed mainly at the most saline downstream area, while P. microps distributed within the whole estuary, in accordance to the salinity and temperature tolerances for the species. A clear decrease in density and production was observed for P. minutus in the dry year, with non-expressive recruitments and the quick disappearance of the parental cohort. For P. microps, the decrease was not so pronounced. No direct effects were attributable to the salinity and temperatures variations (resulting from the drought and high temperatures). Yet, higher predation pressure on P. minutus hypothesis was raised, as the salinity incursion increased the piscivorous marine adventitious species in the downstream areas. Pomatoschistus microps benefited from a wider temperature and salinity range tolerance, allowing the species to occupy different areas in the estuary and by this seemed better able to cope with the environmental conditionings during the 3-year studied period.

Carotid intima-media thickness is associated with premature parental coronary heart disease: the Framingham Heart Study.

A family history of coronary heart disease (CHD) is an independent risk factor for cardiovascular events. However, the mechanisms underlying this susceptibility have not been fully elucidated. We hypothesized that an important mediator of the familial predisposition to CHD is subclinical atherosclerosis, which is detectable by noninvasive imaging. We studied 1662 subjects (mean age 57, 51% women) in the Framingham Offspring Study who underwent carotid ultrasonography and had both biological parents in the original (parental) cohort. Parental CHD events were validated prospectively by a physician endpoint committee. The associations of carotid intima-media thickness (IMT) with premature parental CHD (occurring before age 60) and any parental CHD (no age restriction) were examined in age- and multivariable-adjusted analyses. Age-adjusted mean internal carotid IMT was higher in subjects who had at least one parent with premature CHD than in those without a validated parental history of premature CHD (men 1.13 versus 1.04 mm, P<0.01; women 0.92 versus 0.85 mm, P=0.03). In both sexes, these differences remained significant after adjustment for cardiovascular risk factors. In analyses without a restriction on parental age of CHD onset, the association between carotid IMT and parental CHD was not statistically significant. There was also no significant association of common carotid IMT with premature or any parental CHD. These findings suggest that subclinical atherosclerosis, assessed in the carotid arteries, is more prevalent in individuals with a family history of CHD. Early-onset parental CHD, in particular, identifies offspring with a strong familial predisposition to atherosclerosis.

Pertussis infection in childhood and subsequent type 1 diabetes mellitus.

Pertussis has been implicated but not proven as a risk for Type 1 diabetes mellitus (DM). Previous studies have investigated paediatric, but not adult-onset Type 1 DM. We investigated association of pertussis exposures and Type 1 DM with follow-up into adulthood. Longitudinal analysis of 16 820 members (100 with Type 1 DM) of two nationally representative British birth cohorts (the 1970 British Cohort Study (BCS70) and the National Child Development Study (NCDS)) followed from birth to ages 30 years (BCS70) and 42 years (NCDS). Cox regression analysis with age of onset for Type 1 DM as the dependent variable investigated relationships with pertussis infection and immunization, modelled as time-dependent co-variates. Simultaneous adjustment was made for Wild measles, mumps and chickenpox infections; tetanus and smallpox immunizations; sex, parental social class and cohort. The potential confounding factors were modelled as fixed co-variates. Cox regression analysis produced adjusted odds ratios (ORs) (with 95% confidence intervals (CIs)) of 2.21 (1.35-3.59) and 0.73 (0.49-1.05) for Type 1 DM (with onset at any age) associated with pertussis infections and immunization (trend over number of vaccinations), respectively. Adjusted ORs from Cox regression for Type 1 DM with onset after age 10 years are 2.59 (1.56-4.30) for pertussis infection and 0.63 (0.42-0.94) for pertussis immunization. None of the other infections or immunizations are notably associated with Type 1 DM. Some pertussis infections may be a risk for Type 1 DM and immunization may confer protection. Further research should consider delayed Type 1 DM following pertussis exposures.

Anticipation in inflammatory bowel disease: A phenomenon caused by an accumulation of confounders

Inflammatory bowel disease (IBD) has a definite genetic component as documented by epidemiological and linkage evidence. It shows an earlier onset of disease in children of affected patients than in their parents. This has lead to speculations about genetic anticipation in this disorder. 2,007 IBD patients with sporadic disease and 472 multiplex familial cases (including 103 affected parents and 99 children of affected patients) were evaluated with a multi-item questionnaire as part of a study of inflammatory bowel disease genetics. The Mann-Whitney U-test and the general linear model were used for analysis. Clinical characteristics such as presence of fistulae, stenoses, extraintestinal manifestations, and other parameters, which are related to the severity of the disease, were found to be similar between familial and sporadic cases of IBD (corrected P > or = 0.31 for all tests). The mean-age-of onset in children of affected patients was 19.4 years earlier than in their parents. However, the age of the parental cohort was significantly higher (27 years) and the diagnostic interval also longer (1.7 years). If these confounders are corrected in a general linear model, no significant difference is evident for the age-of-onset between the groups (P > or = 0.52). There is no evidence for genetic anticipation in inflammatory bowel disease. The absence of genetic anticipation is consistent with the clinical similarity of familial and sporadic inflammatory bowel disease. This finding justifies the primary genetic analysis of familial disease under the assumption that their genetic background will be representative for all presentations of IBD.

Race, socioeconomic factors, and area of residence are associated with asthma prevalence.

Asthma prevalence in the United States has been reported to be higher in minority groups such as Blacks and Hispanics. Because a disproportionate number of individuals from such minority groups are of low socioeconomic status (SES), it is unclear how much of the racial/ethnic differences in asthma prevalence is related to low SES. We investigated the effect of SES on the relationship between race/ethnicity and asthma prevalence in a cohort of families with a history of asthma or allergies from the Boston, Massachusetts area. From 499 families, a cohort of 998 parents and 307 children was identified. We used total yearly family income (<$50,000 vs. > or = $50, 000), highest level of education (< or = high school vs. > or = college), and residence in high-poverty areas vs. low-poverty areas as measures of SES. Yearly family income <$50,000, < or = high school education, and residence in high poverty areas were all associated with increased risks for asthma in both cohorts. In the parental cohort, Blacks and Hispanics (OR = 2.1, 95% CI = 1.5, 2.8; and OR = 2.2, 95% CI = 1.5, 3.2, respectively) were at greater risk for asthma than Whites. In the cohort of children, Black and Hispanic children (OR = 2.9, 95% CI = 1.0, 8.0; and OR = 5.3, 95% CI = 1.6, 17.5, respectively) were also at increased risk for asthma. When the three measures of SES were included in the multivariable models, the risks associated with Blacks and Hispanics decreased in both cohorts: OR = 1.4, 95% CI = 0.9, 2.0; and OR = 1.6, 95% CI = 1.0, 2. 6, respectively, for the parents; and OR = 0.8, 95% CI = 0.2, 3.0; and 2.5, 95% CI = 0.5, 11.7, respectively, for the children. We conclude that a large proportion of the racial/ethnic differences in asthma prevalence in our study is explained by factors related to income, area of residence, and level of education.

Life history, population dynamics and production of eastern mosquitofish, Gambusia holbrooki (Pisces, Poeciliidae), in rice fields of the lower Mondego River Valley, western Portugal

The introduced population of Gambusia holbrooki from the rice fields of the lower Mondego River Valley, Portugal, was studied for 15 months, relating their life cycle and population dynamics with its production, in order to assess the role of the species in the energy flow and secondary production in this type of agro-ecosystem. Two main annual cohorts (1995 and 1996 cohorts) were identified. The females outnumbered males and the average female/male-ratio was 4. The inspection of ovary developmental stages of this viviparous fish, revealed that the most important reproductive period was between April and August. The first recruits were recorded in June and were present thereafter until October. Males from the parental cohort died before August, whereas parental females could survive until October. Mean adjusted fecundity (number of embryos divided by female standard length) peaked in July 1996 (0.95) and in June 1997 (1.05). Females reached greater sizes, had a higher growth rate and lived longer than males. Annual production was estimated at 3.101 g.m–2.year–1 (ash-free dry weight, AFDW), the average biomass at 2.896 g.m–2 (AFDW), and the P/B ratio was 1.071. A conjugation of life history, population dynamics, production and ecological traits (e.g. fast growth, reduced longevity, viviparity, high productivity, an intermediate position in food chain, and no special habitat requirements for reproduction) clearly show that the populations of G. holbrooki, introduced into rice fields all over the world, may play an important role in the structure and functioning of the biological communities of these important agro-ecosystems.

The risk of preterm birth across generations

To examine the risk of preterm birth for mothers who themselves were born before term. Data were taken from a linked data base of birth certificates composed of two cohorts: 1) a parental cohort of women born between 1947 and 1957 and 2) their offspring born between 1970 and 1992. "Preterm mothers" were women in the parental cohort who were born at less than 37 weeks' gestation. "Term mothers" were women in the parental cohort born at or after 38 weeks' gestation. Preterm mothers and term mothers were matched for birth year, county of birth, marital status, parity, and age. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for the risk of preterm delivery in preterm mothers. Multiple logistic regression was used to assess the interaction of concomitant variables with the risk of premature delivery. The risk of preterm birth was significantly higher in preterm mothers than in term mothers (OR 1.18; 95% CI 1.02, 1.37). The risk increased as the gestational age at the mothers' birth decreased (less than 30 weeks'; OR 2.38; 95% CI 1.37, 4.16). The interaction between maternal age and parity increased the risk of preterm delivery at less than 34 weeks in some age and parity strata. An increased risk of preterm delivery exists for women who themselves were born before 37 weeks' gestation. The risk is inversely correlated with the maternal gestational age at birth and is influenced by maternal age and parity.

Life history of Gambusia holbrooki (Pisces, Poeciliidae) in the Ebro delta (NE Iberian peninsula)

We studied age, growth and reproduction of an introduced poeciliid, Gambusia holbrooki (Agassiz, 1859), in the Ebro delta marshes. Maximum ages observed were 2+ in females and 0+ in males. Growth commenced in March and continued until September. Females reached greater sizes, had a higher rate of growth and lived longer than males. The largest sizes found were 63 mm ♀♀ versus 32 mm ♂♂. Multiple spawning occurred throughout the reproductive cycle (from May to September). The average brood size per female reached its maximum in July in the parental cohort (86 embryos/♀) and in August in the offspring cohort (29 embryos/♀). After reproduction the parental cohort decreased drastically. The relationship between fecundity (F) and total length (mm) was calculated for each month of the reproductive period. Sex-ratio deviated significantly from unity. Viviparity, several broods and large larvae provide G. holbrooki with several advantages over oviparous species. The capacity to adjust its life history to a particular environment could explain the life history differences between those in the Ebro delta and other populations.

The intergenerational predisposition to operative delivery

To determine the risk of cesarean delivery for women who themselves were born via operative delivery. A linked data base was constructed between the birth certificates of individuals born in Utah during 1947-1957 (parental cohort) and who subsequently became a parent of offspring born in Utah between 1970-1991 (offspring cohort). Parental cohort women (cases) who had been delivered operatively (cesarean delivery, mid- or high forceps) as well as women who had a sibling delivered by an operative procedure were matched (1:2) with parental-cohort women born by spontaneous vaginal delivery (controls). Both cases and controls were selected based on having a record of at least one delivery in Utah during 1970-1991. Women who were delivered by cesarean were at increased risk of subsequently delivering their children by cesarean (odds ratio [OR] 1.41, 95% confidence interval [CI] 1.18-1.70; P < .001). Progressive risk was associated with parental delivery by mid- or high forceps (OR 1.72, 95% CI 1.20-2.47; P = .004), parental cesarean because of cephalopelvic disproportion alone (OR 1.83, 95% CI 1.16-2.88; P = .01), or parental cesarean for dysfunctional labor (OR 5.97, 95% CI 1.5-23.6; P < .001). The attributable risk for cesarean delivery to the contemporary population is 3.5%. An intergenerational predisposition to cesarean delivery exists.

Life-History Pattern of the Iberian Toothcarp Aphanius Iberus (Pisces, Cyprinodontidae) From a Mediterranean Estuary, the Ebro Delta (Spain)

The life-history pattern was studied of an endangered endemic cyprinodontid from the Iberian peninsula, Aphanius iberus (Cuvier & Valenciennes, 1846), found in a Mediterranean estuary, the Ebro delta. Maximum ages observed were 1 + in both sexes. The seasonal growth period started in March and continued until September. The females reached larger sizes than the males, as they have a higher rate of growth and live longer. The largest sizes found were 45 mm versus 38 mm. A. iberus is a multiple spawner that releases batches of eggs between May and August but with few eggs each time (varying from 10 to 30). Despite this continuous release of eggs two moments appeared to stand out as more important. After the reproduction period the parental cohort reduced drastically. The relationship between fecundity (F) and total length (mm) was represented by the formula: F = 8.358 x 10 -9 x L t 6.343 . The biology of the Iberian toothcarp is characterized by fast growth, early maturity, high reproductive effort, multiple spawning and reduced longevity. This may be a good life strategy for small fish species in unstable environments, such as estuaries, where adult mortality is high, variable or unpredictable. It allows them to exploit favourable environmental conditions, which occur in a specific, reduced period; practically all the population is renewed during this period.

Relative Cohort Size and Fertility: The Socio-Political Context of the Easterlin Effect

The conclusion of this study is that structures of collective social protection and changes in rates of female labor force participation influence cohort relative economic status and thus specify the effect of relative cohort on swings in fertility. Both income potential (affected by entering cohort size) and expected standard of living (affected by previous cohort size) are determined by cohort size. A large youth cohort relative to the parental cohort results in low income and low fertility. The Easterlin thesis that relative cohort size (the ratio of persons aged 30-64 years to persons aged 15-29 years) corresponds to shifts in fertility is supported for the period 1950-80 in the US. Replications of this thesis in Europe were unsuccessful. This study indicates that relative cohort size affects fertility depending on the country and the time period. This study examines 18 high-income countries during 1951-86. Measures of stable institutional characteristics of welfare states which may affect the relationship between relative cohort size and fertility include female labor force participation social security spending consensus democracy (Lijpharts five component scale) corporatism (Pampel Williamson and Stryker) total years of leftist rule commitment to egalitarian social policies (Esping-Andersons index of decommodification) and governability (Schmitter). Principal components factor analysis ordinary least squares (fixed-effects and generalized) models and multivariate analysis are constructed or performed. All mediating influences on fertility are not accounted for. Heterogeneity autocorrelation heteroscedasticity and contemporaneous correlation of residuals are controlled for. Relative cohort size which is lagged two years to allow for the gap between fertility desires and births modestly affects average fertility among 18 countries and at 38 time points. Relative cohort size has weak effects in Europe and in countries with high collectivism scores. High female labor force participation depresses the effect of relative cohort size. Relative cohort size has the strongest effects in the US Canada Ireland and the Netherlands. Effects in Germany Switzerland and Sweden are negligible or negative. The generalized least squares pooled model provides more accurate estimates. Social and institutional characteristics of nations affect the influence of relative cohort size on fertility.