Alexandre Robert

Plasmodium relictum infection and MHC diversity in the house sparrow (Passer domesticus)

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasite populations. In particular, the high level of genetic diversity usually observed at the major histocompatibility complex (MHC) is generally thought to be maintained by parasite-driven selection. Among the possible ways through which parasites can maintain MHC diversity, diversifying selection has received relatively less attention. This hypothesis is based on the idea that parasites exert spatially variable selection pressures because of heterogeneity in parasite genetic structure, abundance or virulence. Variable selection pressures should select for different host allelic lineages resulting in population-specific associations between MHC alleles and risk of infection. In this study, we took advantage of a large survey of avian malaria in 13 populations of the house sparrow (Passer domesticus) to test this hypothesis. We found that (i) several MHC alleles were either associated with increased or decreased risk to be infected with Plasmodium relictum, (ii) the effects were population specific, and (iii) some alleles had antagonistic effects across populations. Overall, these results support the hypothesis that diversifying selection in space can maintain MHC variation and suggest a pattern of local adaptation where MHC alleles are selected at the local host population level.

Molecular biology of elastin as related to aging and atherosclerosis

Abstract The authors consider in some detail the structure of elastin at the molecular level as related to its normal function and to the modifications accompanying aging and atherosclerosis. 1. (1) The peculiar physicochemical properties of elastin can be best explained by assuming the prevalence of hydrophobic interactions as the main stabilizing forces of its tertiary and quaternary structure. Detailed investigation of the acceleration of alkalin hydrolysis of elastin by a variety of organic solvents confirms this assumption (Kornfeld-Poullain and Robert, 1968). It is postulated that lipidic substances do share with organic solvents their affinity for elastin and many accelerate its “unfolding” and degradation through such “denaturing” effect. Elastin surface are measurements with 85 Kr and by flow calorimetry confirmed the direct accessibility of elastin in native stroma of aorta to small molecules (Robert et al. , 1970b; Stack and Robert, 1970). 2. (2) The study of the sugar components of elastin suggested the presence of structural glycoproteins (SGP) as “impurities” in all purified elastin samples investigated. These SGP-components are very probably identical with the “microfibrils” seen on electron-micrograms of elastin. 3. (3) In vitro incorporation of 14 C-lysine were carried out in aortas of rabbits immunized with purified elastin and SGP or fed on cholesterol rich diet. A strong labelling of the SGP-fraction was obtained and a significant labelling of the polymeric collagen and elastin fractions also. Incorporation was higher in strongly atheromatous aortas. It is concluded that at least a partial “derepression” of elastin synthesis may occur in such conditions. 4. (4) The antigenic properties of elastin can be ascribed also to the presence of both components, polymerized pro- or tropoelastin and SGP-s (microfibrils). The presence of anti-elastin antibodies in human sera was described (Stein et al. , 1965; Crouzet et al. , 1970). These antibodies appear at about 20 yr of age and decrease or disappear at 70–80 yr. The lower titres found in severely atheramatous sera was ascribed to the adsorbtion of these antibodies to degrading elastic fibers in the aorta and elsewhere. Arguments in favor of our immunological theory of atheromatosis are discussed (see Fig. 6) in the light of recent experiments. Such recent findings are the production of atheromatosis in rabbits immunized with elastin or aorta SGP-preparations and the isolation of a platelet protease capable of attacking elastin (Robert et al. , 1969).

Host and habitat specialization of avian malaria in Africa

Studies of both vertebrates and invertebrates have suggested that specialists, as compared to generalists, are likely to suffer more serious declines in response to environmental change. Less is known about the effects of environmental conditions on specialist versus generalist parasites. Here, we study the evolutionary strategies of malaria parasites (Plasmodium spp.) among different bird host communities. We determined the parasite diversity and prevalence of avian malaria in three bird communities in the lowland forests in Cameroon, highland forests in East Africa and fynbos in South Africa. We calculated the host specificity index of parasites to examine the range of hosts parasitized as a function of the habitat and investigated the phylogenetic relationships of parasites. First, using phylogenetic and ancestral reconstruction analyses, we found an evolutionary tendency for generalist malaria parasites to become specialists. The transition rate at which generalists become specialists was nearly four times as great as the rate at which specialists become generalists. We also found more specialist parasites and greater parasite diversity in African lowland rainforests as compared to the more climatically variable habitats of the fynbos and the highland forests. Thus, with environmental changes, we anticipate a change in the distribution of both specialist and generalist parasites with potential impacts on bird communities.

Roles of survival and dispersal in reintroduction success of Griffon vulture (Gyps fulvus).

The success of reintroduction programs greatly depends on the amount of mortality and dispersal of the released individuals. Although local environmental pressures are likely to play an important role in these processes, they have rarely been investigated because of the lack of spatial replicates of reintroduction. In the present study, we analyzed a 25-year data set encompassing 272 individuals released in five reintroduction programs of Griffon Vultures (Gyps fulvus) in France to examine the respective roles of survival and dispersal in program successes and failures. We use recent developments in multi-strata capture-recapture models to take into account tag loss in survival estimates and to consider and estimate dispersal among release areas. We also examined the effects of sex, age, time, area, and release status on survival, and we tested whether dispersal patterns among release areas were consistent with habitat selection theories. Results indicated that the survival of released adults was reduced during the first year after release, with no difference between sexes. Taking into account local observations only, we found that early survival rates varied across sites. However when we distinguished dispersal from mortality, early survival rates became equal across release sites. It thus appears that among reintroduction programs difference in failure and success was due to differential dispersal among release sites. We revealed asymmetrical patterns of dispersal due to conspecific attraction: dispersers selected the closest and the largest population. We showed that mortality can be homogeneous from one program to another while, on the contrary, dispersal is highly dependent on the matrix of established populations. Dispersal behavior is thus of major interest for metapopulation restoration and should be taken into account in planning reintroduction designs.

Lésions artérielles produites chez le lapin par immunisation avec l'élastine et les glycoprotéines de structure de l'aorte Etudes biochimiques et morphologiques

Abstract Arterial lesions produced in rabbits by immunisation with elastin and structural glycoproteins of aorta Biochemical and morphological studies The production of arterial lesions is described by immunisation with purified extracts of human and porcine aorta, as well as the morphological study of the lesions produced. The antigens used are: 1. (a) CTC-extract of human aorta, containing water soluble proteins and proteoglycans of the aorta, 2. (b) 8 M urea-extract of human and porcine aorta, containing the structural glycoprotein (SGP) component and part of the “bound lipids” of the aorta, 3. (c) purified elastin from human and porcine aorta. The chemical (carbohydrate and amino acid composition) and immunochemical properties of these antigens are described. Cross-reactions between these antigens and their antisera indicate the presence of a water soluble form of SGP and of elastin in the CTC extract and the presence of a small amount of SGP in purified elastin. Serum cholesterol rose significantly in the sera of all rabbits (control and treated), during the 1st month, the highest elevation has been observed in sera of rabbits immunised with the urea-extract. β-Lipoprotein rose continuously in the sera of all rabbits. These effects may be attributed to the diet and to aging of the rabbits. The antibody titer was highest in the sera of rabbits immunised with the CTC-extract of aorta, somewhat lower with the urea-extract and lowest with elastin as sensitizing antigen. All antigens produced specific delayed type of hypersensitivity reactions. About 25% of all sensitized rabbits developed macroscopic arterial lesions, covering the whole ascending aorta, the arch and the thoracic aorta, with strongly fibrous, calcifying lesions. More than 70% of the elastin-treated rabbits and 50% of the SGP-treated rabbits showed lesions, macroscopically visible, or detected by optical or electron microscopy. The CTC-extract was much less efficient in inducing such lesions and the control rabbits did not show any of these lesions. All the lesions were characterised by early and massive destruction of the elastic tissue, which became fragmented and calcified. Intercellular fibrosis has been noted in the media and intima, together with cellular necrosis. The pathogenic efficiency of the antigens appeared to be inversely related to the circulating antibody titer they elicited. No signs of a cellular immuno-reaction could be demonstrated in the lesions. These results confirm the pathogenic efficiency of the antigens derived from the insoluble polymeric stroma of the arterial wall in inducing arterial lesions on prolonged immunisation. This result is in agreement with the theory in which we tried to explain the immunological mechanism of atherosclerosis.

The interaction between reproductive cost and individual quality is mediated by oceanic conditions in a long‐lived bird

Environmental variability, costs of reproduction, and heterogeneity in individual quality are three important sources of the temporal and interindividual variations in vital rates of wild populations. Based on an 18-year monitoring of an endangered, recently described, long-lived seabird, Monteiros Storm-Petrel (Oceanodroma monteiroi), we designed multistate survival models to separate the effects of the reproductive cost (breeders vs. nonbreeders) and individual quality (successful vs. unsuccessful breeders) in relation to temporally variable demographic and oceanographic properties. The analysis revealed a gradient of individual quality from nonbreeders, to unsuccessful breeders, to successful breeders. The survival rates of unsuccessful breeders (0.90 +/- 0.023, mean +/- SE) tended to decrease in years of high average breeding success and were more sensitive to oceanographic variation than those of both (high-quality) successful breeders (0.97 +/- 0.015) and (low-quality) nonbreeders (0.83 +/- 0.028). Overall, our results indicate that reproductive costs act on individuals of intermediate quality and are mediated by environmental harshness.

Post-Release Dispersal in Animal Translocations: Social Attraction and the “Vacuum Effect”

Animal translocations are human-induced colonizations that can represent opportunities to contribute to the knowledge on the behavioral and demographic processes involved in the establishment of animal populations. Habitat selection behaviors, such as social cueing, have strong implications on dispersal and affect the establishment success of translocations. Using modeling simulations with a two-population network model (a translocated population and a remnant population), we investigated the consequences of four habitat selection strategies on post-translocation establishment probabilities in short- and long-lived species. Two dispersal strategies using social cues (conspecific attraction and habitat copying) were compared to random and quality-based strategies. We measured the sensitivity of local extinctions to dispersal strategies, life cycles, release frequencies, remnant population and release group sizes, the proportion of breeders and the connectivity between populations. Our results indicate that social behaviors can compromise establishment as a result of post-release dispersal, particularly in long-lived species. This behavioral mechanism, the “vacuum effect”, arises from increased emigration in populations that are small relative to neighboring populations, reducing their rate of population growth. The vacuum effect can drive small remnant populations to extinction when a translocated group is large. In addition, the magnitude of the vacuum effect varies non-linearly with connectivity. The vacuum effect represents a novel form of the behaviorally mediated Allee effect that can cause unexpected establishment failures or population extinctions in response to social cueing. Accounting for establishment probabilities as a conditional step to the persistence of populations would improve the accuracy of predicting the fates of translocated or natural (meta)populations.

Meteorological conditions influence short‐term survival and dispersal in a reinforced bird population

A high immediate mortality rate of released animals is an important cause of translocation failure (‘release cost’). Post-release dispersal (i.e. the movements from the release site to the first breeding site) has recently been identified as another source of local translocation failure. In spite of their potential effects on conservation program outcomes, little is known about the quantitative effects of these two sources of translocation failure and their interactions with environmental factors and management designs.[br/] Based on long-term monitoring data of captive-bred North African houbara bustards Chlamydotis undulata undulata (hereafter, houbara) over large spatial scales, we investigated the relative effects of release (e.g. release group size, period of release), individual (e.g. sex and body condition) and meteorological (e.g. temperature and rainfall) conditions on post-release survival (n = 957 individuals) and dispersal (n = 436 individuals).[br/] We found that (i) rainfall and ambient air temperature had, respectively, a negative and a positive effect on houbara post-release dispersal distance; (ii) in interaction with the release period, harsh meteorological conditions had negative impact on the survival of houbara; (iii) density-dependent processes influenced the pattern of departure from the release site; and (iv) post-release dispersal distance was male-biased, as natal dispersal of wild birds (although the dispersal patterns and movements may be influenced by different processes in captive-bred and in wild birds).[br/] Synthesis and applications. Our results demonstrate that post-release dispersal and mortality costs in translocated species may be mediated by meteorological factors, which in turn can be buffered by the release method. As the consequences of translocation programs on population dynamics depend primarily upon release costs and colonization process, we suggest that their potential interactions with meteorological conditions must be carefully addressed in future programs (i) through monitoring of short-term post-release mortality to understand its link with environmental conditions, (ii) by carefully choosing the season of release to minimize exposition of inexperienced individuals to harsh conditions and (iii) by generalizing the use of long-term weather forecast to adapt release effort and staggering releases over several years to buffer meteorological effects.

Find the weakest link. A comparison between demographic, genetic and demo-genetic metapopulation extinction times

BackgroundWhile the ultimate causes of most species extinctions are environmental, environmental constraints have various secondary consequences on evolutionary and ecological processes. The roles of demographic, genetic mechanisms and their interactions in limiting the viabilities of species or populations have stirred much debate and remain difficult to evaluate in the absence of demography-genetics conceptual and technical framework. Here, I computed projected times to metapopulation extinction using (1) a model focusing on the effects of species properties, habitat quality, quantity and temporal variability on the time to demographic extinction; (2) a genetic model focusing on the dynamics of the drift and inbreeding loads under the same species and habitat constraints; (3) a demo-genetic model accounting for demographic-genetic processes and feedbacks.ResultsResults indicate that a given population may have a high demographic, but low genetic viability or vice versa; and whether genetic or demographic aspects will be the most limiting to overall viability depends on the constraints faced by the species (e.g., reduction of habitat quantity or quality). As a consequence, depending on metapopulation or species characteristics, incorporating genetic considerations to demographically-based viability assessments may either moderately or severely reduce the persistence time. On the other hand, purely genetically-based estimates of species viability may either underestimate (by neglecting demo-genetic interactions) or overestimate (by neglecting the demographic resilience) true viability.ConclusionUnbiased assessments of the viabilities of species may only be obtained by identifying and considering the most limiting processes (i.e., demography or genetics), or, preferentially, by integrating them.

Heterogeneity of reproductive age increases the viability of semelparous populations

1. One important feature of natural populations is that individuals of the same age or functional class at a given time may vary in their demographic rates, such as their survival probabilities or fecundities. This demographic heterogeneity is due to the plastic response of individuals to spatially variable environmental conditions, to genetic variation or to maternal or cohort effects. Although demographic heterogeneity may have serious consequences, it is generally not included in models of population dynamics. The interactions of demographic heterogeneity with environmental stochasticity and density dependence are poorly understood, as are its consequences for population viability.[br/] [br/] 2. We explored the effect of heterogeneity in age at reproduction on the dynamics and viability of semelparous populations. We developed individual-based models according to which individuals had to follow a particular life path in a multifurcated life cycle. We used data from a well-studied monocarpic plant, Centaurea corymbosa, to calibrate the models with realistic distributions of demographic parameters.[br/] [br/] 3. Disregarding the trivial effect of changing generation time, we found that heterogeneous populations had higher viability than homogeneous populations due to the desynchronization of demographic processes among individuals. [br/] [br/] 4. Heterogeneity buffers the negative impact of environmental stochasticity by reducing the covariation of life histories among individuals (i.e. the bet-hedging effect). In addition, when negative density dependence is implemented, desynchronization in heterogeneous populations reduces intraspecific competition. Indeed, crowded cohorts, occurring randomly due to demographic or environmental stochasticity, can spread their offspring over several years, which limits negative interactions among individuals due to resource limitations (in this study, a fixed number of microsites for seedlings). These effects are likely to occur in every semelparous population. [br/] [br/] 5. Our results allow us to better understand the functional links between the heterogeneity, desynchronization, dynamics and viability of populations facing spatial and temporal variations in their environments. These links suggest that demographic heterogeneity, regardless of its causes (genetic variation or plasticity), is an important component of population dynamics. Neglecting demographic heterogeneity leads to overestimating the level of synchronization among individuals, which may in turn strongly bias viability assessments in realistic environments.