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At least 1,585 records · Page 88Linked to original sources
PubMed1988

Competition and genotypic variability in Drosophila melanogaster.

It has been claimed that in competitive conditions larval viabilities of Drosophila melanogaster depend on the similarity of genotypes coexisting. Two types of experimental populations were established: homogeneous (low genotypic variability) and heterogeneous (high genotypic variability). Under conditions of moderate larval competition productivity was similar, in each although the developmental time was shorter in the heterogeneous series. Under conditions of high larval competition the productivity of heterogeneous populations exceeded that of the homogeneous and attained the adult stage in shorter period of time.

Animals↗
PubMed1992

Natural selection on body size in Tribolium: possible genetic constraints on adaptive evolution.

To determine whether genetic constraints on adaptive evolution were operating in a laboratory population of a flour beetle, Tribolium castaneum, we first estimated the direct selection acting on each of several body size traits. Strong selection in males for an increase in pupal weight and a decrease in the ratio of adult to pupal weight occurred. In addition, a non-significant trend for a decrease in adult width was found. No significant selection on females was detected, although there were trends toward an increase in pupal weight and a decrease in adult width. These estimates were then combined with estimates of the genetic variances and covariances of the traits to predict the multivariate response to selection, that is, the evolutionary change in the traits across one generation. These projections showed only a small predicted change in male pupal weight in spite of the strong selection on pupal weight, and a relatively large predicted increase in width in spite of the possible negative direct selection on this trait. Both of these results were due in part to the positive genetic covariance between pupal weight and width, and they therefore suggest the possibility of genetic constraints on adaptive evolution of these traits.

Animals↗
PubMed2002

Children by choice: reproductive technologies and the boundaries of personal autonomy.

Unlike other countries that regulate assisted reproduction, the US has largely left this field to the domain of professional self-regulation and market preferences. The reason lies both in the confused jurisprudence of reproductive liberty and the paralysing effect of the abortion debate on US politics. The debate surrounding cloning, however, has galvanized both activists and the government to revisit the question of regulation, and recent cases in the US Supreme Court suggest that if the political will to regulate this field is found, governmental authority to intervene in areas such as pre-implantation diagnosis, gamete donation and surrogacy might well be upheld, even in the face of constitutional challenges.

Abortion, Induced↗
PubMed2002

The economic impact of the assisted reproductive technologies.

Thousands of cycles of in vitro fertilization (IVF) are performed each year. In the US, multiple births occur after 39% of IVF cycles, whereas in Europe, the figure is 26%. Indeed, multiple births are a major factor in the costs attributable to IVF. Reducing the multiple birth rate may reduce the overall costs of IVF, and providing insurance coverage of IVF may contribute to lowering multiple birth rates. The use of IVF is likely to expand in response to increases in infertility and scientific advances.

Female↗
PubMed2005

Population structure and coil dimorphism in a tropical land snail.

Tree snails of the subgenus Amphidromus s. str. are unusual because of the chiral dimorphism that exists in many species, with clockwise (dextrally) and counter-clockwise (sinistrally) coiled individuals co-occurring in the same population. Given that mating in snails is normally impeded when the two partners have opposite coil, positive frequency-dependent selection should prevent such dimorphism from persisting. We test the hypothesis that a strong population structure with little movement between tree-based demes may result in the fixation of coiling morphs at a very small spatial scale, but apparent dimorphism at all larger scales. To do so, we describe the spatial structure in a Malaysian population of A. inversus (Müller, 1774) with 36% dextrals. We marked almost 700 juvenile and adult snails in a piece of forest consisting of 92 separate trees, and recorded dispersal and the proportions of dextrals and sinistrals in all trees over a 7-day period. We observed frequent movement between trees (155 events), and found that no trees had snail populations with proportions of dextrals and sinistrals that were significantly different from random. Upon recapture 1 year later, almost two-thirds of the snails had moved away from their original tree. We conclude that population structure alone cannot stabilise the coil dimorphism in Amphidromus.

Animal Structures↗
PubMed2000

Gene flow and selection balance in haplodiploid social insects.

Understanding the joint effects of gene flow and selection is one of the more important but difficult areas of evolutionary genetics. A method is presented to describe cases of gene flow-selection balance while accounting for the life history of haplodiploid social insects (eusocial Hymenoptera). A continent-island model is used to estimate gene flow rates from allele frequency data and provide variance formulae. The occurrence of unequal yet stable allele frequencies among social insect castes is explained and the usefulness of models with discrete generations for eusocial insects is explained. Gene flow and selection balance has been demonstrated for the fire ant Solenopsis invicta at two allozyme loci. This continent-island model gives results that well describe the system. Issues fundamental to the differences between X-linked and haplodiploid genetic systems and diploid genetic systems are also discussed.

Animals↗
PubMed2002

The reproductive health of daughters of pregestational diabetic women: Medical Birth Registry of Norway.

Maternal diabetes may have an impact upon a daughter's reproductive health through genetic influences, an altered fetal metabolic environment or both. We examined the reproductive health of daughters of diabetic women using linked generation data from the Medical Birth Registry of Norway. Among all female births between 1967 and 1982 (n = 459182), 739 had a mother with registered pregestational diabetes, a rate of 1.6 per 1000 deliveries. A total of 142904 daughters delivered at least one child by 1998. After taking into account differences in survival, we observed no differences in the percentage of childbearing and in the average number of children born by 1998 between daughters with and without a diabetic mother in age-stratified analyses. In analyses limited to singleton deliveries and stratified by mothers' and daughters' diabetic status, we found a threefold excess stillbirth delivery rate among women who had either a mother with pregestational diabetes (2.6%) or pregestational diabetes themselves (2.6%) compared with the stillbirth delivery rate observed in non-diabetic women with no maternal history of diabetes (0.8%). These findings were unaltered in multivariable analyses adjusting for daughters' maternal age and registered obstetric risk factors. Our results indicate that pregestational diabetes remains a health care challenge in Norway and that further evaluation of the reproductive health of daughters of diabetic pregnancies is warranted.

Adult↗
PubMed2003

Frequency-dependent inbreeding depression in Amsinckia.

If the competitive ability of plants produced by self-pollination differs from that of plants derived by outcrossing, then the magnitude of inbreeding depression may be influenced by the composition of the competitive environment (i.e., the frequency of plants that have arisen from selfing and outcrossing in the neighborhood of "target" plants in which inbreeding depression is expressed). Here, we report the results of experiments designed to examine whether inbreeding depression is influenced by the frequency of inbred plants in the competitive neighborhood. Two species of the annual plant genus Amsinckia were studied, one a near-complete selfer (Amsinckia gloriosa) and the other a partial outcrosser (Amsinckia douglasiana). Competition experiments were conducted in artificial stands composed of different mixtures of inbred and outbred progeny. The fitnesses of progeny were found to be significantly influenced by the composition of the competing neighborhood. The fitness of target plants, however, did not vary monotonically with the frequency of inbred plants in the neighborhood. Rather, for A. gloriosa, maximum performance was observed when there was an intermediate frequency of inbred neighbors. For A. douglasiana, the opposite pattern was found. The results suggest that competition among progeny has the potential to play a role in the selection of self-fertilization and possibly in the maintenance of mixed mating systems.

Amsinckia↗
PubMed2002

Assisted reproductive technology in Europe, 1999. Results generated from European registers by ESHRE.

European results of assisted reproductive techniques from treatments initiated during 1999, are presented in this third report. Data were collected mainly from pre-existing national registers. From 22 countries 538 clinics reported 258 460 cycles: IVF 125 370, ICSI 95 221, frozen embryo replacement (FER) 34 002 and oocyte donations (OD) 3867. In eight countries, where all clinics reported to the register, a total of 99 629 cycles was performed in a population of nearly 106 million, corresponding to 943 cycles per million inhabitants and 3.9 cycles per 1000 women aged 15-49 years. After IVF and ICSI the distribution of transfer of 1, 2, 3 and >or=4 or more embryos was 11.9, 39.2, 39.6 and 9.3% respectively. Huge differences existed between countries. For IVF the clinical pregnancy rate per aspiration and per transfer was 24.2 and 27.7% respectively. For ICSI the corresponding rates were 26.1 and 27.9%. These figures represent relative increases by 2.2 to 5.2% compared with 1998. The distribution of singleton, twin, triplet and quadruplet deliveries for IVF and ICSI combined was 73.7, 24.0, 2.2 and 0.1%. This gives a total multiple delivery rate of 26.3%. Triplet deliveries after IVF and ICSI ranged from 0.3-7.0% between countries. Compared with 1998, the number of reported cycles increased by 11% and the clinical pregnancy rate per transfer increased from 27.0 to 27.7% after IVF and from 26.8 to 27.9% after ICSI. Multiple deliveries after IVF and ICSI remained unchanged at 26.3% in 1999.

Adolescent↗
PubMed2003

Risks and complications in assisted reproduction techniques: Report of an ESHRE consensus meeting.

Assisted reproduction technique (ART) is an efficacious treatment in subfertile couples. So far little attention has been paid to the safety of ART, i.e. to its adverse events and complications. The consensus meeting on Risks and Complications in ART held in Maastricht in May 2002 focused on four topics: multiple pregnancies, long-term effects of ART on women, effects of ART on offspring, and morbidity/mortality registries.

Breast Neoplasms↗