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PubMed2001

The basic depression ratio of the host: the evolution of host resistance to microparasites.

The basic reproduction ratio R0 occupies a central position in the theory of host pathogen interactions. However, this quantity stresses the role of the pathogen. This paper proposes an additional, more host-centred char acterization using the basic depression ratio D0. This quantity is the number of host individuals per infected by which the infected host population is depressed below its uninfected level. This paper shows that a baseline criterion for the evolution of host resistance to microparasites is that resistance evolves to minimize D0. This parallels the result for pathogen virulence where R0 is maximized. The tension between these two criteria is noted. The framework established allows a discussion of trade-offs between aspects of the pathogen-free host biology and the host pathogen interaction. For certain linear and convex trade-offs it is shown that the strain with the lowest transmission parameter beta wins (despite the fact that it has the lowest intrinsic birth rate a). For corresponding concave trade-offs, either the strain with minimum beta and a or the strain with maximum beta and a wins. Finally the connection with the techniques of adaptive dynamics is made. Evolutionary singular points are shown to occur at extrema of D0. The evolutionary attainment of the results is discussed.

Adaptation, Physiological↗

PubMed1984

Congenital craniofacial malformations: issues and perspectives.

Congenital craniofacial malformations represent an extremely fascinating and complex set of biomedical problems. The complexity includes early detection, diagnosis, treatment, habilitation, and prevention. Genetic and environmental issues that appear to interact and result in congenital craniofacial malformations are becoming better understood. Advances in mouse and human immunogenetics now suggest several possible explanations for why some individuals acquire certain birth defects and others do not. Recent discoveries concerning the MHC and its association with a number of human birth defects have stimulated interesting speculations concerning genetic and environmental factors that might be responsible for predispositions to congenital malformations. Of particular interest is the possible function of the MHC of the mother during early stages of embryogenesis (the first trimester) and how this assembly of genes may infer susceptibility to environmentally induced birth defects in mouse and human reproduction. A number of environmental chemicals have been implicated in causing birth defects. A large amount of exciting information regarding the genetic regulation of certain drug-metabolizing enzymes (for example, the cytochrome P-450 system) has developed. Basic research and biotechnology continue to advance our appreciation for and knowledge of craniofacial development biology.

Abnormalities, Drug-Induced↗

PubMed2005

The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis.

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.

DNA, Plant↗

PubMed2005

Illegal births and legal abortions--the case of China.

BACKGROUND: China has a national policy regulating the number of children that a woman is allowed to have. The central concept at the individual level application is "illegal pregnancy". The purpose of this article is to describe and problematicize the concept of illegal pregnancy and its use in practice. METHODS: Original texts and previous published and unpublished reports and statistics were used. RESULTS: By 1979 the Chinese population policy was clearly a policy of controlling population growth. For a pregnancy to be legal, it has to be defined as such according to the family-level eligibility rules, and in some places it has to be within the local quota. Enforcement of the policy has been pursued via the State Family Planning (FP) Commission and the Communist Party (CP), both of which have a functioning vertical structure down to the lowest administrative units. There are various incentives and disincentives for families to follow the policy. An extensive system has been created to keep the contraceptive use and pregnancy status of all married women at reproductive age under constant surveillance. In the early 1990s FP and CP officials were made personally responsible for meeting population targets. Since 1979, abortion has been available on request, and the ratio of legal abortions to birth increased in the 1980s and declined in the 1990s. Similar to what happens in other Asian countries with low fertility rates and higher esteem for boys, both national- and local-level data show that an unnaturally greater number of boys than girls are registered as having been born. CONCLUSION: Defining a pregnancy as "illegal" and carrying out the surveillance of individual women are phenomena unique in China, but this does not apply to other features of the policy. The moral judgment concerning the policy depends on the basic question of whether reproduction should be considered as an individual or social decision.

Journal Article↗

PubMed2002

Providing research and research training infrastructures for clinical research in the reproductive sciences.

The Reproductive Sciences Branch of the National Institutes of Child Health and Human Development has created pioneering new research and research training programs that address the impending shortage of physician-scientists in obstetrics, gynecology, and women's health and the need to bolster translational and clinical research. This article provides a brief overview of the Specialized Cooperative Centers Program in Reproduction Research, the National Cooperative Program for Infertility Research, the Reproductive Medicine Network, the Reproductive Scientist Development Program, the Women's Reproductive Health Research Career Development Program, and the Contraception and Infertility Research Loan Repayment Program and describes how these programs collectively create an infrastructure to promote the next generation of physician-scientists and to provide an information exchange between basic and clinical investigators. A key component in increasing the number of clinical investigators is the Contraception and Infertility Research Loan Repayment Program. This program has enabled clinicians to be involved in research without having to be concerned about educational loan debt. Other component programs provide basic/translational, clinical hypothesis-oriented research and clinical trials research infrastructure. The programs created are individually strong and collectively poised to support translational and clinical research efforts and to build a well-trained cadre of physician-scientists. The collective use of these types of programs is proposed as a model for the National Institutes of Health.

Contraception↗

PubMed2000

The influence of self-fertilization and pairing on life-history traits in the freshwater snail Bulinus forskalii (Gastropoda, planorbidae).

This study analyses the basic reproductive biology of the schistosonie-vector snail Bulinus forskalli. This hermaphroditic species can self-fertilize. Variation of the mating system was analysed in two populations from Cameroon in a three-step experiment. (i) The fecundity (number of eggs and of egg capsules) of isolated virgin individuals from both populations was followed over a month, as well as the survival of offspring from these individuals. Estimates of these parameters were intermediate. Our results also indicate that inbreeding depression has a maximum value of about one-half in both populations. No difference was observed between populations for both the overall fecundity of adults and survival of offspring. (ii) Individuals were then paired either within, or between populations over three successive days, and the number of copulations recorded. Copulations were observed in all situations, including between-population pairs. No significant dlifference in the number of copulations per pair was detected. However, this value decreased with time, and reciprocal copulations were significantly less numerous between than within populations. (iii) Individuals that successfully copulated as female in (ii) were isolated, and their fecundity was followed over 3 weeks. The fecundity of individuals that had been maintained isolated over the whole experiment served as a control. No significant difference was on the whole detected. Our results collectively suggest that the individuals from the two populations studied are rather selfers, confirming that B. forskalii is a preferentially selfing species. There is also some pre-zygotic isolation against crosses between populations.

Animals↗

PubMed2005

Ernst Mayr and the modern concept of species.

Ernst Mayr played a central role in the establishment of the general concept of species as metapopulation lineages, and he is the author of one of the most popular of the numerous alternative definitions of the species category. Reconciliation of incompatible species definitions and the development of a unified species concept require rejecting the interpretation of various contingent properties of metapopulation lineages, including intrinsic reproductive isolation in Mayr's definition, as necessary properties of species. On the other hand, the general concept of species as metapopulation lineages advocated by Mayr forms the foundation of this reconciliation, which follows from a corollary of that concept also advocated by Mayr: the proposition that the species is a fundamental category of biological organization. Although the general metapopulation lineage species concept and Mayr's popular species definition are commonly confused under the name "the biological species concept," they are more or less clearly distinguished in Mayr's early writings on the subject. Virtually all modern concepts and definitions of the species category, not only those that require intrinsic reproductive isolation, are to be considered biological according to the criterion proposed by Mayr. Definitions of the species category that identify a particular contingent property of metapopulation lineages (including intrinsic reproductive isolation) as a necessary property of species reduce the number of metapopulation lineages that are to be recognized taxonomically as species, but they cause conflicts among alternative species definitions and compromise the status of the species as a basic category of biological organization.

Animals↗

PubMed2005

The influence of different factors on selenium levels in dairy cow herds in the central-eastern region of Poland.

Selenium has been recognised as a basic bioelement that determines normal development and health of animals and humans alike. Studies of many authors revealed the influence of selenium deficiency on immunity, health, reproduction and production of dairy cows. Selenium deficiency have been reported in a number of countries, for example in different regions of Poland. The aim of the study was to determine the Se levels in blood serum of dairy cows in the Lublin region. In the periods: autumn 2003, winter 2003 and autumn 2004 selenium concentrations were investigated in serum samples from 180 dairy cows. The samples were obtained from 11 farms. The selenium concentrations were estimated with the ASA method. The monitoring studies have found that Se serum levels are dependent on season of the year, physiological period, maintenance systems and methods of feeding. Mean selenium serum levels observed in the study were between 0.21-0.92 micromol/l, especially (micromol/l): lactation 0.74 +/- 0.13, drying-off period 0.67 +/- 0.15, autumn 2003 0.38 +/- 0.17, winter 2003 0.48 +/- 0.16, autumn 2004 0.69 +/- 0.18. These results suggest that selenium should be supplemented, especially in high-producing dairy cow herds.

Animal Feed↗

PubMed1995

Transmission dynamics of Echinococcus granulosus, Taenia hydatigena and Taenia ovis in sheep in Uruguay.

A base-line survey was carried out on the transmission dynamics of Echinococcus granulosus, Taenia hydatigena and Taenia ovis in sheep in the Department of Florida, Uruguay. Mean life expectancy at birth of the sheep population in this Department was estimated at 3.5 and 4.8 years for male and female sheep, respectively. Both intensity and prevalence of E. granulosus infection increased with age providing no evidence that immunity was acquired in the population. This revealed that E. granulosus was only relatively stable and in an equilibrium endemic steady state with an estimate of the basic reproduction ratio (Ro) of about 1.2. The mature larval population in sheep was over-dispersed with parameter k, from fitting a negative binomial, being 0.199 and 0.556 in 42- and 54-month-old sheep, respectively. The mean number of cysts increased by 1.05 cysts per year and the infection pressure was calculated as 0.174 infections per year, implying that each infection consisted of 693.6 eggs to produce 6.03 cysts. Neither intensity nor prevalence of infection with T. hydatigena or T. ovis increased with age. This indicated that immunity was acquired to reinfection by both parasites and they were in an equilibrium hyperenedemic steady state with an estimated Ro of 4.2-5.8. Viability and fertility of E. granulosus, and viability of T. hydatigena cysts in the older age groups were low. The effects of the different transmission levels of the parasites on potential control strategies are discussed.

Animals↗

PubMed2000

The basic reproductive ratio of a word, the maximum size of a lexicon.

Language is about words and rules. While there is some discussion to what extent rules are learned or innate, it is clear that words have to be learned. Here I construct a mathematical framework for the population dynamics of language evolution with particular emphasis on how words are propagated over generations. I define the basic reproductive ratio of word, R, and show that R > 1 is required for words to be maintained in the lexicon of a language. Assuming that the frequency distribution of words follow Zipf's law, an upper limit is obtained for the number of words in a language that relies exclusively on oral transmission.

Humans↗

PubMed2006

Examining male infertility.

Problems of male infertility can seem like minor issues within the larger realm of urology. But many male infertility diagnoses can be successfully treated, allowing the couple to conceive naturally or with minimal medical assistance. Some patients presenting with male infertility can have more significant disease. Treatments for male infertility will continue to progress, and as an increasing number of couples seek infertility services, the need to provide basic information grows as well.

Clomiphene↗

PubMed2000

The reproductive pattern and efficiency of female buffaloes.

Buffaloes play a prominent role in rural livestock production, particularly in Asia. Reproductive efficiency is the primary factor affecting productivity and is hampered in female buffalo by (i) inherent late maturity, (ii) poor estrus expression in summer, (iii) distinct seasonal reproductive patterns, and (iv) prolonged intercalving intervals. Ovarian function is central to these issues; hence, the focal point of this review is ovarian function in Bubalus bubalis, particularly, in relation to seasonal changes. Ovarian anatomy, follicular and luteal development development, and hormonal profiles during the estrous cycle are discussed. Review of the literature revealed a paucity of critically derived information on follicular and ovulatory patterns in buffalo, particularly, in relation to seasonal estrus/birthing. Efforts may be directed at understanding the process (recruitment, development, atresia) and temporal pattern (follicle selection, dominance, subordinate follicle suppression, follicle numbers, and, preovulatory changes) of follicular dynamics using techniques which permit serial assessment of changes occurring over time. Emphasis may be directed towards investigating follicular "waves" as a functional unit, rather than the estrous cycle, in the context of whole animal endocrinology. The data obtained from such basic studies may then be used to develop and test models for enhancing reproductive efficiency.

Animals↗

PubMed2026

Impact of genomic selection for disease resistance on the spread of infection in a simulated aquaculture population.

BACKGROUND: In aquaculture, selection for disease resistance is typically based on mortality records from challenge tests performed on relatives of selection candidates. However, commercial success depends on limiting disease transmission, particularly the incidence and severity of outbreaks. It remains unclear whether selecting for lower mortality also reduces disease transmission. Both these outcomes are influenced by three underlying epidemiological host traits: susceptibility, infectivity, and infection-induced mortality. This simulation study evaluated the impact of genomic selection against mortality on disease transmission in a salmon population exposed to a pathogen with a fast transmission rate. METHODS: Mortality was assumed to be recorded on sibs of selection candidate, either as binary dead/alive status or as time to death during cohabitation/bath challenge tests. Phenotypes were simulated using a stochastic compartmental Susceptible-Infected-Removed epidemiological model, with genetic variation for the three underlying traits. Scenarios were explored by varying the genetic correlations between the three underlying traits. Challenge test designs varied in the number of groups, group sizes, and family distribution across groups. For comparison, a reference scenario with direct selection on the underlying traits was included. Genomic selection was applied over 10 discrete generations, and its impact on disease transmission was assessed using the basic reproductive ratio (R0). RESULTS: When selection was based on dead/alive status, R0 was highly sensitive to both the genetic correlations between the three underlying traits and the challenge test design. In contrast, selection based on time to death consistently reduced R0 across all scenarios (often to below 1 within four generations), regardless of trait correlations or test design. Selection on time to death primarily produced fish with reduced susceptibility to infection, while selection on dead/alive status produced fish with increased resistance and endurance to infection, delaying onset of infection or death without necessarily limiting transmission. Direct selection on the underlying epidemiological traits was the most efficient approach to reduce both mortality and transmission. CONCLUSIONS: Genomic selection for disease resistance, when measured as time to death in cohabitation or bath challenge tests conducted until mortality naturally levels off, reduces both mortality and disease spread. Breeding programs may benefit from challenge test designs that enable estimation of genetic parameters for the underlying traits affecting disease transmission and survival.

Animals↗

PubMed1998

Development and use of genetically uniform strains of common carp in experimental animal research.

Fish are widely used in numerous fields of basic and applied research. Currently, they are the third laboratory animal group in numbers, and will become increasingly important. Common carp is a major species in both aquaculture and research. Inbred strains of carp by gynogenetic (only female inheritance) and androgenetic (only male inheritance) reproduction techniques were developed at our university. With these methods, homozygous animals are produced in one generation and we present the production of homozygous inbred and F1 hybrid strains of common carp. As in mammalian research, using genetically well defined fish is a methodological necessity since in outbred stocks: (1) repeatability between experiments is low, (2) high levels of inbreeding may have accumulated and (3) high intrastrain variability might obscure treatment effects. Within inbred strains, the variation is reduced and as a result, less animals (compared to outbreds) are necessary to obtain statistically significant results. We illustrate this with experimental data from an F1 hybrid and partly outbred strain of common carp, both subjected to an antibiotic treatment resulting in reduced gonadal growth. Results obtained from a single inbred strain should be generalized with the use of a panel of inbred strains. We show that optimal allocation of animals between and within inbred strains depends on the ratio (variation between strains): (variation within strains). When selecting a panel of inbred strains, attention has to be paid to genetic relations between strains to avoid testing within a limited genetic range. It should be considered that in inbred strains, (genic) dominance and interaction effects are absent, due to the absence of heterozygous genotypes. In general, variation within inbred strains will be reduced for traits with a high degree of genetic determination. However, in inbred strains of carp produced by gynogenesis or androgenesis, the chromosome manipulation treatment induces considerable (environmental) variation. By using F1 hybrids of carp, derived from crossing homozygous clonal siblings this source of variation can be avoided. Still, variation in F1 hybrids of carp is relatively large and varies greatly between strains when compared to inbred strains of laboratory rodents. It is assumed that their poikilothermic nature makes them more susceptible to environmental variation. Using inbred fish lines will increase experimental quality and leads to a more efficient use of experimental animals.

Animals↗

PubMedDate not supplied

[Population dynamics in Serbia--present status and problems at the end of the 20th century].

INTRODUCTION: Population changes in Serbia in the last hundred years were very intensive in all fields of demographic development. They were positive, because the movement trend was basically up-to-date and as such responded to the needs and requirements of the problems in regard to population time. However, what was the intensity of these changes? What kinds of problems does Serbia face at the end of the 20th century? Methodology In order to establish precise data and isolate basic problems the following components were analyzed: fertility, mortality and population growth, age and ethnic distribution, migrations and spatial distribution. Data were taken from official vital statistics, censuses, censuses of people from the territory of former Yugoslavia, population projections and secondary analysis of relevant scientific findings. RESULTS: Serbia is faced with a number of problems in almost all segments of demographic development at the end of the 20th century. This primarily includes dual types of reproduction, open depopulation and fast population growth, reversible mortality trends of certain age-sex groups, a large number of refugees, pronounced emigration, especially of young and educated people, and greater or smaller distortions in the territorial distribution and in the development of certain subpopulations. DISCUSSION: Changes in population of Serbia have been intensive in all areas of demographic development giving it to a lesser or greater extent characteristics of contemporary population of developed countries. These changes, however, were either slow or began later, or too intensive and elemental, causing a series of distortions in the population development. CONCLUSION: The existence of demographic problems poses numerous questions. The basic one is to what extent do demographic distortions slow down the development of a country as a whole; how may the extreme differences in the population fertility levels represent a source of conflict, crises and instability, to questions concerning solutions and probabilities of strong political response. However, there is no dilemma that a population policy is necessary.

Demography↗

PubMed2000

The evolution of syntactic communication.

Animal communication is typically non-syntactic, which means that signals refer to whole situations. Human language is syntactic, and signals consist of discrete components that have their own meanings. Syntax is a prerequisite for taking advantage of combinatorics, that is, "making infinite use of finite means. The vast expressive power of human language would be impossible without syntax, and the transition from non-syntactic to syntactic communication was an essential step in the evolution of human language. We aim to understand the evolutionary dynamics of this transition and to analyse how natural selection can guide it. Here we present a model for the population dynamics of language evolution, define the basic reproductive ratio of words and calculate the maximum size of a lexicon. Syntax allows larger repertoires and the possibility to formulate messages that have not been learned beforehand. Nevertheless, according to our model natural selection can only favour the emergence of syntax if the number of required signals exceeds a threshold value. This result might explain why only humans evolved syntactic communication and hence complex language.

Animal Communication↗

PubMed1999

Training of academic staff in obstetrics and gynaecology in the USA.

As we enter a new century and millennium, departments of obstetrics and gynaecology in American medical schools face a number of challenges. Of primary concern among these is the relative dearth of physician-scientists to explore and connect the basic mechanisms and clinical aspects of the diseases of women. This report reviews some aspects of three programmes designed to educate such investigators: The Reproductive Scientist Development Program, The American Gynecological and Obstetrical Society--American Association of Obstetricians and Gynecologists Foundation Fellowship Program and the Women's Reproductive Health Research Career Development Centers. Based on a decade of experience with the first two of these programmes, the prospects for the relatively new third programme are promising. Nonetheless, the need for and opportunities for obstetrician-gynaecologist reproductive scientists far exceed the supply.

Education, Medical, Graduate↗

PubMed2004

Wildlife conservation and reproductive cloning.

Reproductive cloning, or the production of offspring by nuclear transfer, is often regarded as having potential for conserving endangered species of wildlife. Currently, however, low success rates for reproductive cloning limit the practical application of this technique to experimental use and proof of principle investigations. In this review, we consider how cloning may contribute to wildlife conservation strategies. The cloning of endangered mammals presents practical problems, many of which stem from the paucity of knowledge about their basic reproductive biology. However, situations may arise where resources could be targeted at recovering lost or under-represented genetic lines; these could then contribute to the future fitness of the population. Approaches of this type would be preferable to the indiscriminate generation of large numbers of identical individuals. Applying cloning technology to non-mammalian vertebrates may be more practical than attempting to use conventional reproductive technologies. As the scientific background to cloning technology was pioneered using amphibians, it may be possible to breed imminently threatened amphibians, or even restore extinct amphibian species, by the use of cloning. In this respect species with external embryonic development may have an advantage over mammals as developmental abnormalities associated with inappropriate embryonic reprogramming would not be relevant.

Animals↗