Period Of Cohabitation Research Articles

Effects of Losulazine on Rat Reproduction and Development

Losulazine, a hypotensive agent, was given orally by gastric intubation to Sprague-Dawley rats in doses of 0, 2, 4, or 8 mg/kg/day in a study of fertility and general reproductive performance. Eighteen males per group were treated for 67 days before cohabitation, then daily until killed. Thirty-six females per group were treated for only 14 days because estrous cycles had been disrupted. Females remained untreated for 7 days before cohabitation; treatment was resumed after insemination was confirmed or when the cohabitation period ended. Males were cohabited on a 1:2 basis with females from the same treatment group for up to 14 days, then for 14 days with untreated females. The conception rate of both treated and untreated females was statistically significantly decreased as the dose increased. Mean body weights were statistically significantly greater and mean gestation periods were statistically significantly longer in losulazine-treated females than in females of the vehicle control group. Throughout the preweaning period mean body weights were significantly less in offspring from treated dams than in offspring of dams in the vehicle control group. This adverse effect on weight gain continued in male offspring until at least postpartum day 79. Functional development was significantly delayed in the offspring of losulazine-treated dams tested for pinna detachment, auditory startle, negative geotaxis, eye opening, and learning (swimming M-maze). Delays in development were generally greater in offspring of dams and sires treated with higher doses of losulazine. Fertility of male offspring from dams and sires treated with losulazine at 4 and 8 mg/kg/day was also affected adversely.

Review of Sexual Selection and Chemical Communication in the Lobster, Homarus americanus

Field and laboratory observations have shown that female lobsters, Homarus americanus, are the active searching partner in courtship, choosing locally dominant males. The attractive features of the male are suspected to be intrasexual aggressive behavior and chemical cues. Size-based dominance is an important factor allowing males to secure a suitable mating shelter. In nature, male and female lobsters often approach and check shelters of other lobsters. This behavior may allow the animals to monitor the observed daily and seasonal changes in their physical and social environment. Premolt females approach the dominant male's shelter frequently in the weeks before the female's molt. Indirect evidence indicates that the female then "blows" a urine-related sex pheromone into the male shelter. One to several days before molting, a female enters the male shelter. Female intrasexual competition increases the premolt, but not the postmolt, cohabitation period. During cohabitation, males fan with their pleopods blowing a strong current through the shelter and into the environment. This chemical advertisement attracts other females, including future mating partners, to his shelter entrance. Females spent 1–2 wk in the male shelter. Mating takes place 30 min after the female molts. Another female may start cohabitation with the male immediately. In one 10-wk period a dominant male in the laboratory cohabited and mated with five females in sequence; females ignored a second male of equal size. Theoretically, by allowing a female to spend time in his shelter the male foregoes other mating opportunities, but this is balanced—and hence a stable strategy—by his protection of a vulnerable postmolt female who carries his offspring. Females must choose males who can protect them efficiently from prédation and, perhaps more importantly, from competing lobsters.

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting. In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.

Behavioural, physiological and immunological consequences of social status and aggression in chronically coexisting resident-intruder dyads of male rats

The behavioural and physiological consequences of social status and reciprocal fighting in resident-intruder dyads of Long Evans male rats were evaluated. Before a chronic cohabitation of 10 days, residents and intruders were individually housed for one month to increase their aggressiveness. Control animals included isolates, i.e., animals kept individually housed throughout the experiment and pair-housed rats, i.e., pairs of rats housed together from their rats in the laboratory. In 19 out of 20 dyads, a clear dominance relationship developed with an advantage to the resident in 68% of the cases. Dominants showed more exploratory activity than subordinates in an open-field test at the end of the cohabitation period; subordinates groomed longer than animals from other experimental groups. Dominants had lower pain thresholds than individually and pair-housed animals. Both dominants and subordinates had higher tyrosine hydroxylase enzymatic activities in the left adrenal than isolated and pair-housed rats. Subordinates lost body weight and had higher plasma corticosteroid concentrations than animals from the other experimental groups. In addition, they had smaller thymus glands and reduced spleen lymphocyte responses to mitogenic stimulation in vitro, in comparison to dominant animals. These results show that subordination in the dyadic resident-intruder paradigm leads to a complex syndrome of behavioural and physiological changes, some of which may be modulated by the intensity of aggressive interactions.

Reproductive and developmental toxicity of ethylene glycol in the mouse

The effects of ethylene glycol on reproduction of CD-1 mice were tested in a protocol which permitted continuous breeding during a specified interval. The dosage amounts of 0, 0.25, 0.5, or 1% ethylene glycol by continuous administration in drinking water for male and female mice were selected from the general toxic responses observed in a 14-day pilot study. After the first week of administration, begun at 11 weeks of age, the animals were housed one male and one female per cage for 14 weeks during which time any offspring were examined, sexed, weighed, and killed to allow continuous mating of the first generation. At the end of the 14-week cohabitation period, the males and females were separated and any litters delivered after that time were kept until weaning. Those second-generation animals were mated at about 70 days of age. Slight, but statistically significant, decreases were found in the numbers of litters per fertile pair and live pups per litter in the 1% dose group and live pup weight at the 1% dose groups compared to control F 0 mice. Facial anomalies were noted in a number of offspring of high-dose-treated mice and an examination for skeletal defects demonstrated a pattern including reduction in the size of bones in the skull, fused ribs, and abnormally shaped sternebrae and vertebrae in the high-dose-treated, but not the untreated, mice. Neither the 0.25 nor 0.5% dose groups were significantly affected. No clinical signs of toxicity or significant adverse effects on body weight or water consumption were seen at the doses used, but two deaths occurred at the 0.5% quantity which may have been related to oxalate crystal deposition in the kidney.

Distortions caused by nonobservation of periods of cohabitation before the latest

Abstract In retrospective studies of individual life histories, some or all of the information pertaining to periods prior to the latest event interval of interest will sometimes be left out. This simplifies data collection, and it may improve the reliability of the data actually obtained by reducing misreporting. Unfortunately, it may also introduce serious distortion in estimates based on such data. This paper investigates the extent of such distortion in a retrospective study of nonmarital cohabitation, marriage, and childbearing when information on consensual unions is restricted.

Legalization of consensual unions in Latin America.

In Latin America, socially sanctioned conjugal unions take 2 forms: legal marriage and consensual unions. While legal marriage is more prestigious, consensual unions offer practical advantages. An examination of the legalization of consensual unions in rural areas in Colombia, Peru, Costa Rica, and Mexico is undertaken using data from the 1969 Centro Latinoamericano de Demografia's (CELADE) comparative survey of fertility. The survey in each country is based on a self weighted sample of 2000-3000 women aged 15-49 living in areas with fewer than 20,000 inhabitants. The union histories addressed types of unions, duration, and age and date of onset and of termination. The samples consisted of 881 unions in Colombia, 646 in Costa Rica, 865 in Mexico, and 1009 in Peru. The risk of legalization was measured by life table procedures, using only single decrement values for comparisons among subgroups. Between 32-41% of the unions are consensual in the rural areas of these countries. With the exception of Peru, consensual unions are higher among 2nd and later unions than among 1st unions. As expected from previous studies, they are more prevalent among younger women, those without education and among non-Catholics or non-practicing Catholics. About 30% of the consensual unions become legalized in Colombia, Costa Rica, and Mexico, and in Peru the rate of conversion is about 50%. Less than 20% in Colombia and Peru remain intact for more than 25 years; about 25% are terminated within the 1st 2 years. The single decrement values suggest that in the absence of separation or death of a partner, almost 50% of the unions would eventually be legalized in Colombia, Costa Rica, and Mexico, about 65% in Peru. The probability of conversion is highest among women in their 1st union and in the 1st year. Only 2-8% of the women legalize higher order unions. Of the factors related to the probability of legalization, age is an important differential in Costa Rica, education in Mexico, and religious observance in Colombia, Costa Rica, and Peru. The occurrence of a pregnancy does not substantially increase the frequency of legalization. This may be due to the absence of social disapproval of illegitimate children. In all 4 countries, marriages preceded by a period of cohabitation were less likely to end in separation. The higher age at marriage for couples who lived together before marriage explains some of the greater stability. The results do not support the widely held assumption that legalization occurs to legitimize births. Education and age are factors that account for some difference in frequency. Because the analysis is restricted to rural areas, additional research is needed to illuminate relationships in urban areas.

Starting Age and Subsequent Birth Intervals in Cohabitational Unions in Current Danish Cohorts, 1975

This paper presents some main results of an investigation by life table methods of birth interval data in cohabitational unions (marriages as well as consensual unions) in current Danish cohorts. Our results confirm previous findings that an early age at the start of recorded exposure to childbearing risk is indicative of a rapid pace and high level of subsequent fertility. The analysis modifies previous results and adds several new details regarding cohort trends and the effect of parity at the start of reported cohabitation. For each parity within a period of cohabitation, fertility differentials by reported starting age seem to have diminished from our older cohorts (of age up to 49 years in 1975) to our younger ones (of age less than 30 years in 1975). There are indications of a dramatic change in childbearing behaviour following the arrival of novel attitudes to non-marital cohabitation and childbearing in Denmark about 1967.

Childlessness and marital instability: a re-examination of the evidence.

Earlier studies have queried whether divorce was associated with childlessness. Evidence from surveys of broken marriages passing through the divorce courts of England and Wales indicates that infertility and divorce are not related in the way supposed. When the duration of de facto marriage is controlled divorcing couples have a higher rate of fertility than that found within those who remain married. The former are also more likely to have a larger family within the same period of time. Similar findings emerge from data relating to broken marriages resorting to the magistrates courts. These results are partly a consequence of the trend whereby working class marriages -- with their earlier start of a family and larger completed family size -- form an increasing proportion of all divorcing couples. Survey results showed that within a divorcing population a shorter period of cohabitation resulted in a higher level of infertility. High infertility rates were also associated with later age at marriage and high social class. Current trends suggest that an increasing proportion of divorcing couples will be childless. It is concluded that there is a need for deeper knowledge of possible relationships and their causes in this and other areas of married life. (Authors)

Childlessness and Marital Instability: A Re-Examination of the Evidence

SummaryEarlier studies have queried whether divorce was associated with childlessness. Evidence from surveys of broken marriages passing through the divorce courts of England and Wales indicates that infertility and divorce are not related in the way supposed. When the duration of de facto marriage is controlled, divorcing couples have a higher rate of fertility than that found within those who remain married. The former are also more likely to have a larger family size within the same period of time. Similar findings emerge from data relating to broken marriages resorting to the magistrates' courts. These results are partly a consequence of the trend whereby working-class marriages—with their earlier start of a family and larger completed family size—form an increasing proportion of all divorcing couples.Survey results showed that within a divorcing population a shorter period of cohabitation resulted in a higher level of infertility. High infertility rates were also associated with later age at marriage and high social class. Current trends suggest that an increasing proportion of divorcing couples will be childless. It is concluded that there is need for a deeper knowledge of possible relationships, and their causes, in this and other areas of married life.

The influence of females upon aggression in domesticated male rats ( Rattus norvegicus)

The aggression of adult male Long-Evans rats ( Rattus norvegicus), toward males of the same strain, was tested before and after a 1-week period of cohabitation with a pair of intact females, ovariectomized females, or intact males, comparable to the females in size. Only cohabitation with intact females increased the aggression of resident males against unfamiliar male intruders. Female enhancement of aggression does not appear to be caused by sexual frustration of males, or a function of dominance-subordinance relations, per se. Increased aggression may be mediated by elevated testosterone production associated with mating.

Morbilità e Mortalità nella Prole di 300 Coppie di Coniugi Consanguinei nel Comune di Firenze

SummaryA family investigation has been carried out on 301 consanguineous and the same number of nonconsanguineous couples, who married in Florence in the years 1939 through 1958. The sample turned out to be homogeneous as regards age of the couple, year of marriage, period of cohabitation, social level, and methods of survey.The average rate of consanguinity in Florence in the above years was of 0.458 × 10−3, with a decrease from 0.595 to 0.327 × 10−3 between the first and the second decade.While the number of pregnancies is not significantly different in the two groups, abortions are more frequent among blood relatives. As a result, the number of stillbirths being not significantly different, the birth rate is higher among the controls. Infant mortality is more than double in blood relatives. As regards morbidity, hereditary defects or anomalies show an average increase of 2.6 times in the offspring of blood relatives: the increase being higher for serious hereditary defects (3.44) than for lighter ones (1.98). The finding of slight delays in mental development was 4.8 times more frequent in the offspring of blood relatives.By applying Morton-Crow-Muller's formula, it was possible to calculate the A and B values, and to find out, in the observed population, the presence of 2.2-2.4 pathological gene equivalents per gamete as to early mortality (abortions + stillbirths + infant mortality); 1.6-1.7 gene equivalents as to hereditary defects in general; and 0.82-0.85 gene equivalents as to slight delays in mental development.