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D Pontier

Publications and source records attributed to D Pontier.

36 records · Page 2Linked to original sources
PubMed2000

Detection, identification, and correction of a bias in an epidemiological study.

The relative lack of epidemiological studies of natural populations is partly due to the difficulty of obtaining samples that are both large enough and representative of the population. Here, we present the result of an epidemiological study (December 1992-August 1995) of feline immunodeficiency virus (FIV) in a free-roaming population of domestic cats (Felis catus), with a special emphasis on sample bias. Over five trapping periods, the prevalence of FIV in sampled cats steadily declined. Across these samples we consistently achieved a very large sampling fraction (approximately 60% of the population), the sex ratio, age and weight distributions remained stable with time in the samples, and the sex ratio was similar in the samples and the population. These indices would normally indicate that our samples were representative, suggesting the decline in FIV prevalence to be real. However, a concomitant ecological study of the whole population revealed an important bias in the samples, with an initial high probability of capturing a few individuals, which appeared significantly more likely to be FIV-infected, and then a lower probability of recapturing them. Since our protocol resulted in a non-random sampling, subsequent trappings were designed to avoid this bias, by also capturing individuals who had previously learned to escape capture. This modified capture regime revealed that FIV prevalence was in fact constant in the population. This study shows how samples of large size, which are stable and appear representative of the population, can still be biased. These results may have major implications for other studies based on trapping.

Age Distribution↗
PubMed1999

High variation in multiple paternity of domestic cats (Felis catus L.) in relation to environmental conditions.

Paternity was analysed in two domestic cat (Felis catus) populations differing in habitat structure (rural versus urban) and density (234 cats km-2 versus 2,091 cats km-2). A total of 312 offspring, 76 mothers and 65 putative fathers were typed at nine microsatellite loci in the two populations. Our data showed a high rate of multiple paternity in the urban population (70-83% of litters with more than one father), whereas it was much lower in the rural population (0-22% of litters with more than one), as most males were able to monopolize the entire litter. However, males reproduced as soon as they reached sexual maturity (i.e. ten months of age) in the urban population, whereas most males delayed reproduction to age three years in the rural population.

Animals↗
PubMed1999

Die and let live - programmed cell death in plants.

Cysteine and serine proteases are prominent players in the control of developmental and pathogen-activated cell deaths in plants. Ethylene, salicylic acid, the small G-protein Rac, calcium and reactive oxygen species are recurring mediators of death signaling. Lastly, the mitochondrion has emerged in both plant and animal systems as a 'central depot' that interprets multiple signals and in some instances determines the fate of the cell.

Apoptosis↗
PubMed1999

Markers for hypersensitive response and senescence show distinct patterns of expression.

Controlled cellular suicide is an important process that can be observed in various organs during plant development. From the generation of proper sexual organs in monoecious plants to the hypersensitive response (HR) that occurs during incompatible pathogen interactions, programmed cell death (PCD) can be readily observed. Although several biochemical and morphological parameters have been described for various types of cell death in plants, the relationships existing between those different types of PCD events remain unclear. In this work, we set out to examine if two early molecular markers of HR cell death (HIN1 and HSR203J) as well as a senescence marker (SAG12) are coordinately induced during these processes. Our result indicates that although there is evidence of some cross-talk between both cell death pathways, spatial and temporal characteristics of activation for these markers during hypersensitive response and senescence are distinct. These observations indicate that these markers are relatively specific for different cell death programs. Interestingly, they also revealed that a senescence-like process seems to be triggered at the periphery of the HR necrotic lesion. This suggests that cells committed to die during the HR might release a signal able to induce senescence in the neighboring cells. This phenomenon could correspond to the establishment of a second barrier against pathogens. Lastly, we used those cell death markers to better characterize cell death induced by copper and we showed that this abiotic induced cell death presents similarities with HR cell death.

Apoptosis↗
PubMed1998

Dynamics of a feline retrovirus (FeLV) in host populations with variable spatial structure.

The predictions of epidemic models are remarkably affected by the underlying assumptions concerning host population dynamics and the relation between host density and disease transmission. Furthermore, hypotheses underlying distinct models are rarely tested. Domestic cats (Felis catus) can be used to compare models and test their predictions, because cat populations show variable spatial structure that probably results in variability in the relation between density and disease transmission. Cat populations also exhibit various dynamics. We compare four epidemiological models of Feline Leukaemia Virus (FeLV). We use two different incidence terms, i.e. proportionate mixing and pseudo-mass action. Population dynamics are modelled as logistic or exponential growth. Compared with proportionate mixing, mass action incidence with logistic growth results in a threshold population size under which the virus cannot persist in the population. Exponential growth of host populations results in systems where FeLV persistence at a steady prevalence and depression of host population growth are biologically unlikely to occur. Predictions of our models account for presently available data on FeLV dynamics in various populations of cats. Thus, host population dynamics and spatial structure can be determinant parameters in parasite transmission, host population depression, and disease control.

Animals↗
PubMed1998

Retroviruses and sexual size dimorphism in domestic cats (Felis catus L.).

Hochberg and co-workers have predicted that an increase in host adult mortality due to parasites is balanced by an earlier age at first reproduction. In polygynous species we hypothesize that such a pattern would lead to diverging selection pressure on body size between sexes and increased sexual size dimorphism. In polygynous mammals, male body size is considered to be an important factor for reproductive success. Thus, under the pressure of a virulent infection, males should be selected for rapid growth and/or higher body size to be able to compete successfully as soon as possible with opponents. In contrast, under the same selection pressure, females should be selected for lighter adult body size or rapid growth to reach sexual maturity earlier. We investigated this hypothesis in the domestic cat Felis catus. Orange cats have greater body size dimorphism than non-orange cats. Orange females are lighter than non-orange females, and orange males are heavier than non-orange males. Here, we report the extent to which orange and non-orange individuals differ in infection prevelance for two retroviruses, feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). FIV is thought to be transmitted almost exclusively through aggressive contacts between individuals, whereas FeLV transmission occurs mainly through social contacts. The pattern of infection of both diseases is consistent with the higher aggressiveness of orange cats. In both sexes, orange cats are significantly more infected by FIV, and tend to be less infected by FeLV than other cats. The pattern of infection is also consistent with an earlier age at first reproduction in orange than in non-orange cats, at least for females. These results suggest that microparasitism may have played an important role in the evolution of sexual size dimorphism of domestic cats.

Animals↗
PubMed1998

Fast game theory coupled to slow population dynamics: the case of domestic cat populations.

We study a deterministic model of a population where individuals alternatively adopt hawk and dove tactics. It is assumed that the hawk and dove individuals compete for some resources at a fast time scale. This fast part of the model is coupled to a slow part that describes the growth of the population. It is shown that, in a constant game matrix, the population grows according to a logistic curve whose r and K parameters are related to the payoff of the tactics. Results show that the highest population density is obtained when all individuals are dove. We also study a density-dependent game matrix for which the gain is a function of the population density. In this case, we show that two stable equilibria can occur, a first one at low density with a high proportion of hawk individuals and a second one at large density with a low proportion of hawk individuals. Our model is applied to domestic cat populations for which the behavior of individuals in competition with one another can be modeled by two tactics: hawk and dove. Such tactics change with density of population. The results of the model agree well with observed data: high-density populations of domestic cats are mainly doves, whereas low-density populations are mainly hawks.

Animals↗
PubMed1998

The hypersensitive response. A programmed cell death associated with plant resistance.

In plants, the hypersensitive response (HR) is defined as a rapid cell death occurring in response to pathogen attack, and is closely related to active resistance. Initiation of the HR process begins with the recognition of the pathogen by the plant, which is mediated mainly by the pathogen avirulence genes and the plant resistance genes. Then, complex signal transduction pathways intervene, involving changes in protein phosphorylation, production of reactive oxygen species and modification of ion fluxes. Components required for the regulation of the HR cell death are now being identified genetically by the isolation of mutants, in contrast to those involved in the execution of the cell death programme, which are still largely unknown. Further genetic and biochemical analyses will undoubtedly answer the question as to whether this form of programmed cell death (PCD) can be compared with other forms of PCD in plants and with apoptosis in animals.

Apoptosis↗
PubMed1998

At-risk individuals in Feline Immunodeficiency Virus epidemiology: evidence from a multivariate approach in a natural population of domestic cats (Felis catus).

Prevalence of Feline Immunodeficiency Virus (FIV) infection was measured during 6 consecutive years in a natural rural population of domestic cats. Sex, age, weight, origin, group size and presence of antibodies to FIV were recorded for each sampled cat. Logistic regressions were used to estimate the influence of the recorded parameters on infection. FIV prevalence rates are as high as 19.6% in the total population, and do not statistically change between years, after controlling for changes in samples' age structure. FIV infection is characterized by risk factors linked to aggressive behaviour: old mature male adults having dispersed are more likely to be infected. A study of the cats group size and of the spatial distribution of infected individuals indicates the absence of infection clusters in males, and suggests the importance of roaming in the spreading of FIV. In conclusion, FIV infection spreads, with low contagiousness, mainly between particularly aggressive individuals, and the virus is endemic in this population.

Animals↗
PubMed1998

Activation of hsr203, a plant gene expressed during incompatible plant-pathogen interactions, is correlated with programmed cell death.

hsr203J is a tobacco gene whose activation is rapid, highly localized, and specific for incompatible interactions between tobacco and the bacterial pathogen Ralstonia solanacearum. The effect of other hypersensitive response (HR)-inducing pathogens and elicitors has been tested with transgenic plants containing the hsr203J promoter-GUS reporter gene fusion, and confirms the generality of the preferential inducibility of the hsr203J gene promoter during incompatible interactions: bacterial and viral pathogens inducing an HR in tobacco were able to induce the promoter fusion, as were inducers of HR-like responses such as harpin, elicitins, and PopA1 proteins. A tomato hsr203 homologous cDNA was isolated (Lehsr203) and used to examine the effect of avr gene products on the expression of such genes. Lehsr203 was shown to be rapidly and transiently induced in leaves of the tomato Cf-9 line, following Avr9 product infiltration, but not in those of the Cf-0 line. Among potential effectors of HR or resistance such as H2O2, salicylic acid, methyl jasmonate, and 2,6-dichloro-isonicotinic acid (INA), none is able to induce a significant increase in promoter activation. In contrast, heavy metals that cause leaf necrosis can trigger such an activation. In addition, hsr203-GUS fusion expression is detected in transgenic tobacco lines expressing the bO gene and exhibiting spontaneous HR-like lesions. Taken together, these results demonstrate a strong correlation between hsr203 and genetically controlled cell death in tobacco and tomato. The expression of this gene should be a useful marker for programmed cell death occurring in response not only to diverse pathogens, but also to diverse death-triggering extracellular agents.

Amino Acid Sequence↗
PubMed1997

Variation in growth form and precocity at birth in eutherian mammals.

Using the flexible Chapman-Richards model for describing the growth curves from birth to adulthood of 69 species of eutherian mammals, we demonstrate that growth form differs among eutherian mammals. Thereby the commonly used Gompertz model can no longer be considered as the general model for describing mammalian growth. Precocial mammals have their peak growth rate earlier in the growth process than altricial mammals. However, the position on the altricial-precocial continuum accounts for most growth-form differences only between mammalian lineages. Within mammalian genera differences in growth form are not related to precocity at birth. This indicates that growth form may have been associated with precocity at birth early in mammalian evolution, when broad patterns of body development radiated. We discuss four non-exclusive interpretations to account for the role of precocity at birth on the observed variation in growth form among mammals. Precocial and altricial mammals could differ according to (i) the distribution of energy output by the mother, (ii) the ability of the young to assimilate the milk yield, (iii) the allocation of energy by the young between competing functions and (iv) the position of birth between conception and attainment of physical maturity.

Animals↗
PubMed1997

Modelling the feline leukemia virus (FeLV) in natural populations of cats (Felis catus).

A compartmental model was built in order to study the circulation and impact of Feline Leukemia Virus (FeLV) in populations of domestic cats. The model was tested with data from a long-term study of several feline populations. The study of stability shows that FeLV is maintained in the population with a stable equilibrium and a slight reduction of population size. Estimation of the transmission rate allows us to make a comparison with the values previously estimated in the literature. We compare the impact of mass vaccination or removal programmes in controlling FeLV infection, and conclude that vaccination is more efficient.

Animals↗
PubMed1996

Frequency-dependent maintenance of left handedness in humans.

The percentage (10-13%) of left handedness in human has apparently not changed since the Neolithic. Left handedness is heritable and appears to be repeatedly associated with some reduced fitness components; the persistence of left handedness implies that left handers have a fitness advantage in some situations. We propose that left handers have a frequency-dependent advantage in fights and for that reason a fitness advantage. To test this hypothesis, left handedness frequencies in the general population and in sporting individuals (both students and the sporting elite) have been compared, as sporting performance is likely to be a good indicator of fighting abilities. The higher proportion of left-handed individuals in interactive sports (reflecting some fighting elements), reaching 50% in some sports categories, but not in noninteractive sports, is consistent with the fighting hypothesis. The greater frequency of left handedness in males than in females is also consistent with this hypothesis, as male-male fights are universally more frequent than other combinations. The frequency-dependent advantage in fights of left handers might explain the stability of left handedness.

Adolescent↗
PubMed1995

Population dynamics of feline immunodeficiency virus within cat populations.

A deterministic model was constructed for studying the circulation of Feline Immunodeficiency Virus (FIV), a feline retrovirus homologous to Human Immunodeficiency Virus (HIV), within populations of domestic cats. The model has been tested with data generated by a long-term study of several natural cat populations. Simulations and a study of stability show that once introduced, the retrovirus is maintained within the population, with a stable equilibrium stage reached by both numbers of susceptible and infected individuals. An estimation of parameters indicates that the transmission rate is low and depends on the structure of the population. In addition, FIV has a low impact on the population in that the total number of cats at equilibrium when this virus is present is almost always equal to the habitat carrying capacity in the absence of the virus. Those results, in agreement with other observations, suggest that FIV originally arose in the distant past.

Animals↗
PubMed1994

hsr203J, a tobacco gene whose activation is rapid, highly localized and specific for incompatible plant/pathogen interactions.

A novel plant defense gene, hsr203J, whose corresponding mRNA accumulates preferentially during the incompatible interaction of tobacco (Nicotiana tabacum L.) with a pathogenic bacterium, Pseudomonas solanacearum, has been isolated and sequenced. No sequence homology of the putative product of this gene has been found in data bases. Evidence is presented here that the hsr203J gene promoter, when fused to the GUS reporter gene, is selectively expressed in response to the hypersensitive response (HR)-inducing bacteria in tobacco protoplasts and that the sequences responsible for this response are contained within 1.4 kb of the 5' noncoding region. The temporal and spatial patterns of hsr203J activation in leaves and roots inoculated with P. solanacearum indicate that the hsr203J promoter exhibits a rapid (3-6 h post-inoculation) and high level of induction only in plant cells inoculated with the HR-inducing bacterial isolate. In addition, this gene promoter which does not respond to various stress conditions and is only very weakly induced during compatible interactions, is strongly dependent on hrp (hypersensitive response and pathogenicity) genes of P. solanacearum. These data indicate that the hsr203J gene promoter exhibits new and original characteristics of activation with regard to the plant defense genes studied so far; its spatial and temporal program of activation together with its specific induction during the HR underline the importance of this gene as a molecular tool for studying the establishment and regulation of the HR.

Amino Acid Sequence↗
PubMed1994

Feline immunodeficiency virus: an epidemiological review.

From a synthesis of 59 serosurveys, we estimate and discuss influence of several parameters on feline immunodeficiency virus (FIV) infection. The overall infection rate estimated from 85,529 tested cats is high, 11.04%, besides the virus seems to be rather endemic. Parameters influencing FIV infection are sex, age and roaming habits. Neutering, breed and group size effects seem to be rather indirect. Prevalence differences between countries and potential cofactors are also discussed. Results show that FIV transmission is influenced by behavior. We highlight the important bias of this kind of surveys and propose to sample rather natural populations of cats, taking into account their dynamical and ecological parameters. This synthesis highlights arguments in accordance with the hypothesis that FIV is not a recent virus.

Age Factors↗
PubMed1989

Sampling properties of the asymptotic behavior of age- or stage-grouped population models.

The discrete-time linear recurrent models proposed by Leslie in 1945 and Usher in 1966 for age-or stage-grouped populations are discussed with emphasis on the random nature, due to sampling variations, of their well-known asymptotic behavior. The statistical properties of the estimated asymptotic multiplication rate, stage, or age stable structures and mean generation time are inspected by both a theoretical approach and a simulation procedure. Illustrative case studies provide some order of magnitudes of the sampling bias and variance of these statistics.

Age Factors↗