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Biomedical subjects

M Tatar

Publications and source records attributed to M Tatar.

At least 37 records · Page 2Linked to original sources
PubMed2001

Juvenile hormone regulation of longevity in the migratory monarch butterfly.

Monarch butterflies (Danaus plexippus) of eastern North America are well known for their long-range migration to overwintering roosts in south-central Mexico. An essential feature of this migration involves the exceptional longevity of the migrant adults; individuals persist from August/September to March while their summer counterparts are likely to live less than two months as adults. Migrant adults persist during a state of reproductive diapause in which both male and female reproductive development is arrested as a consequence of suppressed synthesis of juvenile hormone. Here, we describe survival in monarch butterflies as a function of the migrant syndrome. We show that migrant adults are longer lived than summer adults when each are maintained under standard laboratory conditions, that the longevity of migrant adults is curtailed by treatment with juvenile hormone and that the longevity of summer adults is increased by 100% when juvenile hormone synthesis is prevented by surgical removal of its source, the corpora allatum. Thus, monarch butterfly persistence through a long winter season is ensured in part by reduced ageing that is under endocrine regulation, as well as by the unique environmental properties of their winter roost sites. Phenotypic plasticity for ageing is an integral component of the monarch butterflies' migration-diapause syndrome.

Animal Migration↗
PubMed2001

A mutant Drosophila insulin receptor homolog that extends life-span and impairs neuroendocrine function.

The Drosophila melanogaster gene insulin-like receptor (InR) is homologous to mammalian insulin receptors as well as to Caenorhabditis elegans daf-2, a signal transducer regulating worm dauer formation and adult longevity. We describe a heteroallelic, hypomorphic genotype of mutant InR, which yields dwarf females with up to an 85% extension of adult longevity and dwarf males with reduced late age-specific mortality. Treatment of the long-lived InR dwarfs with a juvenile hormone analog restores life expectancy toward that of wild-type controls. We conclude that juvenile hormone deficiency, which results from InR signal pathway mutation, is sufficient to extend life-span, and that in flies, insulin-like ligands nonautonomously mediate aging through retardation of growth or activation of specific endocrine tissue.

Aging↗
PubMed2001

Comparing adolescents' considerations for self-referral and counsellors' perceptions of these considerations: an exploratory study.

This study investigated the considerations of adolescents for self-referral to counsellors as reported by 421 senior-high school students and 123 school counsellors. Participants were asked to assess the extent to which different considerations affect adolescent willingness to self-refer to a counsellor. While the most important consideration for both samples was the counsellor's trustworthiness, some differences were found. Counsellors attributed more importance than adolescents to counsellor and adolescent gender and age, to adolescent academic and social status and to the conditions of the presenting problem, whereas the adolescents emphasized counsellor expertness. The results are discussed in terms of the strategies that can be implemented for motivating adolescents to independently approach counsellors with their problems.

Adolescent↗
PubMed2001

Age-specific mortality and reproduction respond to adult dietary restriction in Drosophila melanogaster.

Adult dietary yeast modulates mortality rate and reproduction of the Mediterranean fruit fly, Ceratatis capitata. In the medfly, a sugar-only diet leads to low mortality rates and reduced reproduction; addition of dietary yeast increases both mortality and egg laying. In Drosophila melanogaster low availability of dietary yeast is known to increase life span and reduce the rate of reproduction. Despite these similarities, because of differences in experimental design it remains unclear whether a common physiological mechanism modulates the effect of diet on survival. Here, we investigate how mortality rate and reproduction in D. melanogaster respond to the treatment regime used to study the medfly: no-yeast versus full diet. We find that adult medfly and D. melanogaster have opposite responses to the absence of yeast: D. melanogaster have high mortality when on no-yeast diet; when switched to full diet, D. melanogaster reduce mortality rates to the level presented by females continuously maintained on yeast. This reduction in mortality is accompanied by increased fecundity. These patterns are observed in all tested wildtype stocks, but flies made sterile by mutation in the gene oo18 RNA-binding protein (orb) lack this response. D. melanogaster, unlike medflies, appear to require adult dietary yeast to maintain maximal survival, and the capacity to assimilate yeast for somatic processes is one wildtype function of the gene orb.

Journal Article↗
PubMed2001

Slow aging during insect reproductive diapause: why butterflies, grasshoppers and flies are like worms.

Diapause is a state of arrested development accompanied by physiology for somatic persistence. Diapause is common in many invertebrates and is familiar to biogerontology in the context of Caenorhabditis elegans dauer. Among insects, diapause may occur in embryos, larvae, pupae or adults. At the adult stage, reproductive diapause arrests development of oogenesis, vitellogenesis, accessory gland activity, and mating behavior. Reproductive diapause has been well studied in monarch butterflies, several grasshoppers, and several Diptera, including Drosophila and Phormia. In monarchs and in grasshoppers, reproductive diapause physiology has been experimentally induced by the surgical removal of the corpora allata, the source of adult juvenile hormone; allatectomy in each case was found to double adult longevity. Among Drosophila, the endemic D. triauraria of Japan, and D. littoralis of Finland over-winter as adults in reproductive diapause. How D. melanogaster winter is poorly understood, but reproductive diapause can be cued by cool temperature. In laboratory studies, the mortality rates of post-diapause D. melanogaster are similar to rates of newly enclosed, young flies. This implies that senescence during diapause is slow or negligible. Slow aging during the diapause period may involve elevated somatic stress resistance as well as reallocation of resources to somatic maintenance. Reproductive diapause in Drosophila is proximally controlled by down regulation of juvenile hormone, a phenotype that is also produced by mutants of the insulin-like receptor InR, homologue of C. elegans daf-2. We propose neuroendocrine control of reproductive diapause in D. melanogaster that includes phenotypic plasticity for rates of senescence.

Aging↗
PubMed2000

Parental expectations of their adolescents' teachers.

In spite of increasing parental participation in their children's education, and the growing research interest in this trend, the study of one of the central components of parental involvement, namely, parental expectations of teachers, has been scarce. The present research focuses on this important, albeit neglected, topic. We examined the effects of the sex of the parent and the sex and grade level of the specific child on parental expectations of teachers. Seven hundred and sixty-five Israeli parents of students attending 31 educational institutions participated in the study. They completed the Expectations of Teachers questionnaire, consisting of 12 items describing behavioural characteristics of teachers subsumed under three broad categories: Help and Assistance, Teaching Competence, and Fairness. Greater expectations for Help and Assistance were reported by the parents, followed by Teaching Competence and Fairness on the part of the teacher. Mothers hold higher Fairness and Help and Assistance expectations as compared with fathers. Help and competence expectations were higher for parents of female students as compared with parents of boys. Conclusions from our study call for increasing efforts geared toward the building of a sustainable and beneficial partnership between teachers and parents for the best interest of the students and for the further elucidation of teachers' expectations of parents.

Achievement↗
PubMed2000

Transgenic organisms in evolutionary ecology.

Evolutionary ecology aims to understand how phenotypes are designed for reproductive success and survival. Perhaps the most powerful approach towards this goal is to alter a character genetically and observe the resulting change in reproduction, survival, growth, defense or competitive ability. Until recently, this strategy was not practical. Transgenic manipulation now offers a solution - novel genes are introduced into the germ line and are then expressed in the developing organism. This technique is already available in model and agricultural organisms. The challenge for molecular evolutionary ecologists is to find ways to adopt these powerful systems to understand the mechanisms underlying adaptive traits and their evolution.

Journal Article↗
PubMed2000

Women's perceptions of caesarean section: reflections from a Turkish teaching hospital.

Caesarean section as a contentious topic has attracted attention world-wide and different dimensions of the issue has been investigated. The primary reason behind these initiatives have been the upsurge of caesarean sections both in the developed and developing world and the realisation that the operation may not always contribute positively to the mother's and baby's health. By contrast, several studies have demonstrated both the short and long term negative effects. Research has also revealed that factors other than medical necessity play an important role in the decision to perform a caesarean section. Turkey, although reliable data does not exist, can be classified among the countries experiencing the caesarean epidemic, at least among highly educated and wealthy mothers. This research, exploring the perceptions of mothers in a teaching hospital with a high caesarean rate, is a rare example of its kind in Turkey. The main finding is the dissatisfaction of the mothers undergoing caesareans during their stay in the hospital.

Adolescent↗
PubMed2000

Reproductive costs of heat shock protein in transgenic Drosophila melanogaster.

Senescence may evolve when genes have antagonistic effects between early reproduction and later age-specific mortality. Although widely consistent with data of quantitative genetics, this model has yet to be validated with the identification of a specific locus presenting such trade-offs. The molecular chaperone hsp70 may be a candidate for such a gene. Heat induced expression of the Hsp70 protein in adults decreases rates of age-specific mortality during normal aging, while maternally experienced heat shock depresses the production of mature progeny. Here we show that maternal heat shock reduces the proportion of egg hatch but not the viability of successfully hatched offspring. To assess whether heat induced maternal expression of hsp70 causes reduced egg hatch, we measured the proportion of eggs that hatch from females engineered to overexpress hsp70 transgenes. We used the same transgenic strains that extend longevity upon hsp70 expression and found that Hsp70 is sufficient to suppress egg hatch. The proportion of egg hatch as a function of hsp70 expression was not reduced in the first eggs laid after maternal heat shock, but appears in later laid eggs, which were at preoogenic and early vitellogenic stages during the maternal expression of hsp70. The contervailing effects of hsp70 upon fecundity and subsequent age-specific mortality exemplify antagonistic pleiotropy, and this trade-off could contribute to the evolution of Drosophila senescence.

Animals↗
PubMed1999

Toward reconciling inferences concerning genetic variation in senescence in Drosophila melanogaster.

Standard models for senescence predict an increase in the additive genetic variance for log mortality rate late in the life cycle. Variance component analysis of age-specific mortality rates of related cohorts is problematic. The actual mortality rates are not observable and can be estimated only crudely at early ages when few individuals are dying and at late ages when most are dead. Therefore, standard quantitative genetic analysis techniques cannot be applied with confidence. We present a novel and rigorous analysis that treats the mortality rates as missing data following two different parametric senescence models. Two recent studies of Drosophila melanogaster, the original analyses of which reached different conclusions, are reanalyzed here. The two-parameter Gompertz model assumes that mortality rates increase exponentially with age. A related but more complex three-parameter logistic model allows for subsequent leveling off in mortality rates at late ages. We find that while additive variance for mortality rates increases for late ages under the Gompertz model, it declines under the logistic model. The results from the two studies are similar, with differences attributable to differences between the experiments.

Aging↗
PubMed1999

Secondary school pupils' perceptions of burnout among teachers.

BACKGROUND: Numerous studies examined teachers' self-reports concerning their occupational burnout. Given that pupils are in a prime position to assess teachers' burnout, due to their intensive daily contact with their teachers and because some of pupils' behaviours can induce stress, the present study focuses on a relatively unexplored topic, namely the meanings that adolescents attach to burnout among their teachers. AIMS: This study was aimed at examining pupils' perceptions regarding burnout among their teachers, and to investigate the possible recommendations that the pupils would suggest to different constituents of the educational system for coping with burnout among teachers. SAMPLE: A total of 297 Israeli secondary school pupils (approximately 57% girls and 43% boys) studying in 12 tenth grade classes (mean age 15 years 8 months, SD = 0.42 years) participated in this study. METHODS: A questionnaire dealing with pupils' perceptions of burnout among teachers was administered. It included four sections. The first part asked for background of the pupils (sex and age). Next, pupils were asked an open-ended question in which they need to describe the most salient behaviour of a burned-out teacher in the classroom and to indicate the proportion of burned-out teachers among those teaching them. The third section consisted of a list of 14 items describing potential characteristics of burned-out teachers. The respondents were asked to indicate the extent to which, in their opinion, each of the descriptors characterized burned-out teachers. In addition, pupils were asked three open-ended questions in which they were required to describe the most salient way for (a) the students, (b) the teachers themselves and (c) the school principal to cope with teachers' burnout. RESULTS: Findings showed that the most frequently mentioned characteristics of burned-out teachers were: teachers who 'feel that working with pupils for a full day is an oppressive effort', 'feel wiped out at the end of a teaching day', 'feel that teaching is turning them into impatient persons' and 'feel that teaching frustrates them'. No differences were found between girls' and boys' perceptions of burned-out teachers: both emphasize the psychological exhaustion of teachers as the most salient characteristic of burnout among teachers. Pupils suggest that the better ways for coping with this phenomenon include a more positive behaviour of the pupils themselves towards teachers, that burned-out teachers quit their jobs and that better work conditions be offered to them by the educational authorities. CONCLUSIONS: Our findings allude to the importance of analyzing interactional phenomena like burnout among teachers from the perspectives of different actors in the school arena and allow us to broaden our understanding of pupils' perceptions of teachers. Suggestions for further research and for the development of methodological refinements are discussed.

Adolescent↗
PubMed1998

Reproductive cessation in female mammals.

In female mammals, fertility declines abruptly at an advanced age. The human menopause is one example, but reproductive cessation has also been documented in non-human primates, rodents, whales, dogs, rabbits, elephants and domestic livestock. The human menopause has been considered an evolutionary adaptation, assuming that elderly women avoid the increasing complications of continued childbirth to better nurture their current children and grandchildren. But an abrupt reproductive decline might be only a non-adaptive by-product of life-history patterns. Because so many individuals die from starvation, disease and predation, detrimental genetic traits can persist (or even be favoured) as long as their deleterious effects are delayed until an advanced age is reached, and, for a given pattern of mortality, there should be an age by which selection would be too weak to prevent the onset of reproductive senescence. We provide a systematic test of these alternatives using field data from two species in which grandmothers frequently engage in kin-directed behaviour. Both species show abrupt age-specific changes in reproductive performance that are characteristic of menopause. But elderly females do not suffer increased mortality costs of reproduction, nor do post-reproductive females enhance the fitness of grandchildren or older children. Instead, reproductive cessation appears to result from senescence.

Adaptation, Physiological↗
PubMed1998

Friendship expectations among immigrant adolescents and their host peers.

This study investigated differences in friendship expectations between immigrants in early and middle adolescence and their Israeli-born peers. Israeli newcomers from the former Soviet Union and their non-immigrant classmates were asked to rate behavioural characteristics of peers according to the extent of their importance for friendship, and also to assess the importance of these characteristics as friendship expectations of members of the other group. Results indicate that immigrants assign greater importance than their host counterparts to all aspects of friendship expectations (help and assistance, status, similarity, and avoidance of harm). Immigrants also tend to view their host peers as expecting more of their friendship in terms of status and similarity, whereas host adolescents perceive the help and avoidance functions of friendship to be a strong factor in the friendship expectations of their immigrant counterparts. Immigrants' friendship expectations were found to be correlated with social distress, especially among early adolescent girls. The results are discussed in terms of the functions of friendships and friendship expectations in the immigrants' adaptation process, and of institutional differences in allocation of immigrants to integrated or segregated classrooms.

Adolescent↗
PubMed1998

Significant individuals in adolescence: adolescent and adult perspectives.

This study examines the ways in which 360 Israeli adolescents, and 395 midlife adults looking retrospectively perceive significant individuals from their adolescence. Following the methodology developed by Hendry et al. (Journal of Adolescence 1992, 15, 255-270), participants were asked to chose the most significant family and non-family individuals in their adolescent lives, and to indicate which of a number of characteristics applied or did not apply to their chosen significant persons. Our results indicate that most of the adults and the adolescents chose a parent as the most significant relative in their adolescence and that females in both samples chose their mothers more than did males. Compared with adolescents, adults attributed, retrospectively, more negative characteristics to their parents (e.g. as being mollycoddlers and rejectors). Adults were more likely to mention their teachers as significant non-family individuals in their lives and to characterize them in terms of their future impact as teachers and role models. Adolescents referred more positively to their parents, they also chose more friends of the same or opposite sex as significant others, and characterized them in terms of present-oriented features as being supporters and challengers.

Adolescent↗
PubMed1998

Genetic analysis of extended life span in Drosophila melanogaster. II. Replication of the backcross test and molecular characterization of the N14 locus.

We are interested in localizing chromosomal regions that extend life span in Drosophila. Using stocks artificially selected for long life by Luckinbill and his colleagues, we have identified marker loci that are highly divergent in allelic frequencies between replicated long-lived lines and controls (Curtsinger et al., 1998). Several of the most divergent loci have been found to be associated with effects on life span in segregating backcross populations. Here we report an independent replication of the backcross test for the N14 marker locus, previously reported to extend male life spans by 12 days. The life span effect successfully replicates in males. N14 accounts for 30% of the total selection response in males. Life span extension occurs by a decrease in age-specific mortality rates at all ages, and is not attributable to modification of the slope of the age-specific mortality curve. The effect in females is small or nonexistent. Sequencing of the N14 locus shows that it is non-coding and not obviously regulatory, suggesting that the phenotypic effect arises from linkage disequilibrium with another locus or loci that directly affect life span. N14 DNA hybridizes to 63F/64A on the left arm of chromosome 3. The location is consistent with previous whole-chromosome substitution studies, and suggests new candidate genes for life span extension in Drosophila, including ras2.

Aging↗
PubMed1998

Teachers as significant others: gender differences in secondary school pupils' perceptions.

BACKGROUND: Numerous studies refer to the impact of parents and friends as significant others for adolescents. Given the unique nature of the relationships between teachers and their pupils and their intensive everyday interactions, the present study focuses on a not yet covered topic, namely the meanings that adolescents attach to the significance of their teachers. AIMS: This study was aimed at examining gender differences in secondary school pupils' perceptions regarding positive and negative aspects of the significance of their teachers, and to investigate the possible different domains in which teachers as compared with parents and friends might be significant for the adolescents. SAMPLES: A total of 297 Israeli secondary school pupils (approximately 57 per cent girls and 43 per cent boys) studying in 12 tenth grade classes (age modal 16) participated in this study. METHODS: A questionnaire dealing with pupils' perceptions of significant teachers was administered. Pupils were asked to indicate the extent to which significant teachers are characterised by various descriptors (it was defined for the pupils that a significant teacher is one whom the pupil perceives as having an important influence on her/him). In addition pupils were asked to answer two open-ended questions regarding the domains in which teachers, as compared to their parents and their friends, might be significant for them. RESULTS: Findings showed that the most frequently mentioned characteristics of significant teachers were: teachers who 'take pupils seriously', 'have confidence in them', 'make it easier for them to understand things' and 'push them to do well'. It was also found that girls, more than boys, characterise significant teachers as facilitating learning and relationships; and that boys, more than girls, perceive significant teachers as obstructing their personal development. CONCLUSIONS: Our findings allude to the high potential that teachers may have for impact on their pupils, beyond the domain of learning alone, and provide support for the existence of differential perceptions of significant teachers among boys and girls. These gender differences were explained in terms of the different character of teachers' interaction with the two sexes, and the fact that in the Israeli educational system more than 80 per cent of the teaching staff are women.

Adolescent↗
PubMed1998

Turkish hospital management at a crossroads: prospects for the year 2000.

The Turkish health system has been undergoing a radical reform process since the early 1990s. Reform proposals, based on purchaser/provider split, self-governing hospitals (ultimately leading to full privatization), compulsory health insurance etc., are expected to have a profound effect on hospital management. In such an environment, hospital administrators' views on the domains and issues that will come to the fore in the year 2000 gain importance. In this paper, results of a study undertaken among hospital administrators are presented. The study aimed to find the views of hospital administrators on issues likely to gain prominence in the year 2000 and the skills, knowledge, and abilities required to tackle these issues. It was concluded the autonomous status of hospitals, privatization, competition, and health trusts will become the central domains in the year 2000 in hospital administration. Innovation and following technological developments were considered most critical.

Attitude of Health Personnel↗