Evolution, maintenance and ecological consequences of genetic caste determination in " Pogonomyrmex " harvester ants

Summary Division of labor between reproducers (queens) and helpers (workers) is the main characteristic of social insect societies and at the root of their ecological success. Kin selection models predict that phenotypic differences between queens and workers should result from environmental rather than from genetic differences. However, genetic effects on queen and worker differentiation were found in two populations-of Pogonomyrmex harvester ants. Each of the two populations is composed of two genetically distinct lineages. Queens (which can be of either lineage) generally mate with males of their own and of the alternate lineage and produce two types of female offspring, those fertilized by males of the queens' lineage which develop into queens and those fertilized by males of the alternate lineage which develop into workers. All four lineages were further suggested to be themselves of hybrid origin between-the species P: barbatus and P. rugosus, in which queens and workers do not differ genetically. In a first set of experiments, we tested if female caste determination (the differentiation into queens and workers) in the lineages was genetically hardwired and if it was associated with costs in terms of the ability to optimally allocate resources to the production of queens and workers. To this end we first mated queens of-two lineages to a single male. Queens mated to a male of the alternate lineage successfully raised worker offspring whereas queens mated to a male of their own lineage almost always failed to produce workers. This reveals that pure-lineage individuals have lost the ability to develop into workers. Second, we analyzed offspring produced by naturally mated queens. During the stage of colony founding when only workers are produced, naturally mated queens laid a high proportion of pure-lineage eggs but the large majority of these eggs failed to develop. As a consequence, the number of offspring produced by incipient colonies decreased linearly with the proportion of pure-lineage eggs laid by queens. Moreover, queens of the lineage most commonly represented in a given population produced more pure-lineage eggs, in line with the view that they mate randomly with the two types of males and indiscriminately use their sperm. Altogether these results predict frequency-dependent founding success for pairs of lineages because queens of the more common lineage will produce more pure-lineage eggs and their colonies be less successful during the stage of colony founding. To describe the distribution of populations characterized with genetic caste determination relative to the populations with environmental caste determination we genotyped queens and workers collected during a large survey of -additional populations. Genetic caste determination associated with pairs of interbreeding lineages was frequent and widespread in the studied range and we identified four additional lineages displaying genetic caste determination. Overall, there were thus eight highly differentiated lineages with genetic caste determination. These lineages always co-occurred in the same complementary lineage pairs. Three of the four lineage pairs appeared to have a common origin, while their relationship with the forth could not be resolved. The genetic survey also revealed that, in addition to being genetically isolated from one another, all eight lineages were genetically distinct from P. rugosus and P. barbatus, even when colonies of interbreeding lineages co-occurred with colonies of either putative parent at the same site. This raised the question of the mechanisms involved in the reproductive isolation between the lineages and the parental species and between the two lineages of a lineage pair. At a site where one lineage pair co-occurred with P. rugosus, we identified two pre-zygotic mechanisms (differences in timing for mating flights between P. rugosus and the lineage pair and assortative mating) and one post-zygotic mechanism (high levels of hybrid unviablility) which in combination may largely account for the reproductive isolation between the lineages and their parental species. The mechanisms accounting for the reproductive isolation between the two lineages of a lineage pair varied across lineage pairs. In one lineage pair, inter-lineage individuals exclusively occurred in the sterile worker caste, raising the possibility that inter-lineage eggs have completely lost the ability to develop into queens in this lineage pair and that there is thus no opportunity for gene flow. In each of the three remaining lineage pairs, inter-lineage queens were produced by a minority of colonies. In these lineage pairs, colonies headed by inter-lineage queens failed to grow sufficiently to produce reproductive individuals which may account for the reproductive isolation between co-occurring lineages in three lineage pairs. In conclusion, the results of this thesis show that genetic caste determination is costly but widespread in Pogonomyrmex harvester ants. Reproductive isolation among the lineages and between the lineages and the parental species as well as frequency-dependent founding success for co-occurring lineages may contribute to the persistence of this extraordinary system. Résumé La division du travail entre individus reproducteurs (les reines) et individus non-reproducteurs (ouvrières) représente la caractéristique principale des sociétés d'insectes et est à la base de leur succès écologique. Des modèles de sélection de parentèle prédisent que les différences phénotypiques entre reines et ouvrières devraient provenir d'effets environnementaux plutôt que de différences génétiques. Malgré ce fait, des effets génétiques sur la différentiation entre reines et ouvrières ont été montrés dans deux populations de fourmis moissonneuses du genre Pogonomyrmex. Chacune des deux populations est composée de deux lignées génétiquement distinctes. Les reines de chaque lignée s'accouplent en général avec des mâles de leur propre lignée ainsi qu'avec des mâles de l'autre lignée et produisent deux types d'oeufs, ceux qui sont fécondés par les mâles de leur propre lignée qui se développent en nouvelles reines et ceux qui sont fécondés par les mâles de l'autre lignée qui se développent en ouvrières. Il a été suggéré que les lignées sont elles-mêmes des hybrides entre les deux espèces P. barbatus et P. rugosus. Dans ces deux espèces, les reines et ouvrières ne sont pas génétiquement distinctes. Dans une première série d'expériences, nous avons testé si la détermination de la caste femelle (le développement en reine ou en ouvrière) est génétiquement rigide et si elle est associée à des coûts en terme de capacité à allouer de façon optimale les ressources pour la production de reines et d'ouvrières. Pour cela nous avons accouplé des reines de deux lignées avec un seul mâle. Les reines accouplées avec un mâle de l'autre lignée ont élevé de nouvelles ouvrières avec succès alors que les reines accouplées avec un mâle de leur propre lignée ont presque toujours échoué à produire des ouvrières. Ceci montre que les individus de lignée pure ont perdu la capacité de se développer en ouvrière. Deuxièmement, nous avons analysé la descendance de reines qui se sont accouplées naturellement. Durant le stade de fondation de la colonie, où seules des ouvrières sont élevées, les reines accouplées naturellement ont pondu une grande proportion d'oeufs de lignée pure mais la majorité de ces derniers ne se sont pas développés. En conséquence, le nombre de descendants produits par des colonies fondatrices diminuait linéairement avec la proportion des oeufs de lignée pure pondus par la reine en accord avec l'hypothèse que les reines s'accouplent au hasard avec les deux types de mâles et utilisent leur sperme aléatoirement. Dans l'ensemble; ces résultats prédisent un succès de fondation fréquence-dépendant pour les deux lignées, car les reines de la lignée la plus fréquente produiront .plus d'oeufs de lignée pure et leurs colonies auront moins de succès lors de la fondation de colonies par rapport aux colonies de la lignée la moins fréquente. Pour décrire la distribution des-populations caractérisées par une détermination génétique des castes par rapport aux populations caractérisées par une détermination environnementale des castes, nous avons génotypé des reines et des ouvrières qui ont été collectées lors d'une analyse de populations supplémentaires. La détermination génétique des castes associée à des croisements entre lignées est fréquente et largement répartie dans l'aire étudiée. Nous avons identifié quatre lignées supplémentaires, ayant une détermination génétique des castes, pour un total de huit lignées. Ces huit lignées forment quatre paires de lignées et on ne trouve jamais deux lignées de paires différentes, dans une population. Trois des quatre paires de lignées s'avèrent avoir une origine commune alors que leur relation avec la quatrième paire de lignées n'a pas pu être résolue. L'analyse génétique de populations supplémentaires a également révélé qu'en plus d'être génétiquement isolées les unes des autres, les huit lignées sont génétiquement distinctes de P. rugosus et P. barbatus même si les colonies d'une paire de lignées se trouvent en sympatrie avec l'une ou l'autre des espèces parentales. Ceci relève la question des mécanismes impliqués dans l'isolation reproductive entre les lignées et les espèces parentales ainsi qu'entre les deux lignées d'une paire. En étudiant un site où une paire de lignées se trouve en sympatrie avec P. rugosus, nous avons identifié deux mécanismes pré-zygotiques (des différences dans le timing du vol nuptial entre P. rugosus et les lignées et des accouplements assortis) ainsi qu'un mécanisme post-zygotique (un niveau élevé de non-viabilité des hybrides). En combinaison, ces mécanismes peuvent largement expliquer l'isolement reproductif entre les lignées et leurs espèces parentales. Les mécanismes contribuant à l'isolement reproductif entre les deux lignées d'une paire variaient entre paires de lignées. Dans une paire, les individus de génotype inter-lignée se trouvent uniquement dans la caste stérile des ouvrières, suggérant qu'il n'y a pas d'opportunité pour avoir du flux de gènes entre les deux lignées ce cette paire. Dans chacune des trois autres paires de lignées des nouvelles reines de génotype inter-lignée sont produites par une minorité de colonies. Par contre, les colonies avec une reine mère de génotype inter-lignée ne se développent pas suffisamment pour produire des individus reproducteurs. Ceci peut donc expliquer pourquoi il n'y a pas de flux de gènes entre les deux lignées de trois paires. En conclusion, les résultats de cette thèse montrent que la détermination génétique de la caste est coûteuse mais très répandue chez les fourmis. moissonneuses du genre Pogonomyrmex. L'isolement reproductif des lignées entre elles et avec les espèces parentales, ainsi qu'un succès de fondation fréquence-dépendant contribuent à la persistance de ce système extraordinaire.

Restriction site-associated DNA sequencing, genotyping error estimation and de novo assembly optimization for population genetic inference.

Restriction site-associated DNA sequencing (RADseq) provides researchers with the ability to record genetic polymorphism across thousands of loci for nonmodel organisms, potentially revolutionizing the field of molecular ecology. However, as with other genotyping methods, RADseq is prone to a number of sources of error that may have consequential effects for population genetic inferences, and these have received only limited attention in terms of the estimation and reporting of genotyping error rates. Here we use individual sample replicates, under the expectation of identical genotypes, to quantify genotyping error in the absence of a reference genome. We then use sample replicates to (i) optimize de novo assembly parameters within the program Stacks, by minimizing error and maximizing the retrieval of informative loci; and (ii) quantify error rates for loci, alleles and single-nucleotide polymorphisms. As an empirical example, we use a double-digest RAD data set of a nonmodel plant species, Berberis alpina, collected from high-altitude mountains in Mexico.

Factors associated with clinical leptospirosis: a population-based case-control study in the Seychelles (Indian Ocean).

BACKGROUND: In Western countries, leptospirosis is uncommon and mainly occurs in farmers and individuals indulging in water-related activities. In tropical countries, leptospirosis can be up to 1000 times more frequent and risk factors for this often severe disease may differ. METHODS: We conducted a one-year population-based matched case-control study to investigate the frequency and associated factors of leptospirosis in the entire population of Seychelles. RESULTS: A total of 75 patients had definite acute leptospirosis based on microagglutination test (MAT) and polymerase chain reaction (PCR) assay (incidence: 101 per 100,000 per year; 95% confidence interval [CI]: 79-126). Among the controls, MAT was positive in 37% (past infection) and PCR assay in 9% (subclinical infection) of men aged 25-64 with manual occupation. Comparing cases and controls with negative MAT and PCR, leptospirosis was associated positively with walking barefoot around the home, washing in streams, gardening, activities in forests, alcohol consumption, rainfall, wet soil around the home, refuse around the home, rats visible around the home during day time, cats in the home, skin wounds and inversely with indoor occupation. The considered factors accounted for as much as 57% of the variance in predicting the disease. CONCLUSION: These data indicate a high incidence of leptospirosis in Seychelles. This suggests that leptospires are likely to be ubiquitous and that effective leptospirosis control in tropical countries needs a multifactorial approach including major behaviour change by large segments of the general public.

Population Biology of Rhodnius domesticus Neiva & Pinto, 1923 (Hemiptera: Reduviidae) under Laboratory Conditions

The entire life cycle of Rhodnius domesticus, fed weekly on mice, was studied under controlled conditions. Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of the insect life-cycle were evaluated. The hatching rate observed in 100 eggs was 57% and the mean time of hatching was 15.6 days. Forty-six nymphs (80.7%) completed the cycle and the mean time from NI to adult was 93.8 days. The average span in days for each stage was 12.4 for NI, 9.8 for NII, 14.2 for NIII, 16.8 for NIV and 25.0 for NV. The number of bloodmeals in each nymphal stage varied from 1 to 3. The mortality rate was 12.3% for NI, 3.5% for NII and 1.7% for NIII and NV nymphs. The mean number of eggs laid per female in a 9-month period was 333.1. Average adult survival rates were 287.6 +133 and 328 +73 days for males and females respectively.

Evolution démographique d'une population de musaraignes aquatiques (Neomys fodiens) en Suisse romande

Studies on water shrews, Neomy fodiens, showed a significant decrease of capture rates throughout the winter period. Thereafter, during reproduction, animals dispersed along the stream as far as one kilometer from their original site. In this work, we assess the extension of their dispersion movements. We suppose that very small populations persist wintertime at localized spots and from their recolonize the empty habitats

Le burnout concerne 20 pour cent de la population active

Epuisement émotionnel, déshumanisation progressive de la relation avec l'autre et un sentiment d'échec professionnel. Le burnout est tout ça à la fois. La difficulté est de déceler à temps ces symptômes qui peuvent mettre parfois des mois, voire des années à se déclarer. Définition et tour d'horizon du burnout.

THE USE OF SIMULATIONS IN EVOLUTIONARY POPULATION GENETICS: APPLICATIONS ON HUMANS, OWLS AND VIRTUAL ORGANISMS

Summary (in English) Computer simulations provide a practical way to address scientific questions that would be otherwise intractable. In evolutionary biology, and in population genetics in particular, the investigation of evolutionary processes frequently involves the implementation of complex models, making simulations a particularly valuable tool in the area. In this thesis work, I explored three questions involving the geographical range expansion of populations, taking advantage of spatially explicit simulations coupled with approximate Bayesian computation. First, the neutral evolutionary history of the human spread around the world was investigated, leading to a surprisingly simple model: A straightforward diffusion process of migrations from east Africa throughout a world map with homogeneous landmasses replicated to very large extent the complex patterns observed in real human populations, suggesting a more continuous (as opposed to structured) view of the distribution of modern human genetic diversity, which may play a better role as a base model for further studies. Second, the postglacial evolution of the European barn owl, with the formation of a remarkable coat-color cline, was inspected with two rounds of simulations: (i) determine the demographic background history and (ii) test the probability of a phenotypic cline, like the one observed in the natural populations, to appear without natural selection. We verified that the modern barn owl population originated from a single Iberian refugium and that they formed their color cline, not due to neutral evolution, but with the necessary participation of selection. The third and last part of this thesis refers to a simulation-only study inspired by the barn owl case above. In this chapter, we showed that selection is, indeed, effective during range expansions and that it leaves a distinguished signature, which can then be used to detect and measure natural selection in range-expanding populations. Résumé (en français) Les simulations fournissent un moyen pratique pour répondre à des questions scientifiques qui seraient inabordable autrement. En génétique des populations, l'étude des processus évolutifs implique souvent la mise en oeuvre de modèles complexes, et les simulations sont un outil particulièrement précieux dans ce domaine. Dans cette thèse, j'ai exploré trois questions en utilisant des simulations spatialement explicites dans un cadre de calculs Bayésiens approximés (approximate Bayesian computation : ABC). Tout d'abord, l'histoire de la colonisation humaine mondiale et de l'évolution de parties neutres du génome a été étudiée grâce à un modèle étonnement simple. Un processus de diffusion des migrants de l'Afrique orientale à travers un monde avec des masses terrestres homogènes a reproduit, dans une très large mesure, les signatures génétiques complexes observées dans les populations humaines réelles. Un tel modèle continu (opposé à un modèle structuré en populations) pourrait être très utile comme modèle de base dans l'étude de génétique humaine à l'avenir. Deuxièmement, l'évolution postglaciaire d'un gradient de couleur chez l'Effraie des clocher (Tyto alba) Européenne, a été examiné avec deux séries de simulations pour : (i) déterminer l'histoire démographique de base et (ii) tester la probabilité qu'un gradient phénotypique, tel qu'observé dans les populations naturelles puisse apparaître sans sélection naturelle. Nous avons montré que la population actuelle des chouettes est sortie d'un unique refuge ibérique et que le gradient de couleur ne peux pas s'être formé de manière neutre (sans l'action de la sélection naturelle). La troisième partie de cette thèse se réfère à une étude par simulations inspirée par l'étude de l'Effraie. Dans ce dernier chapitre, nous avons montré que la sélection est, en effet, aussi efficace dans les cas d'expansion d'aire de distribution et qu'elle laisse une signature unique, qui peut être utilisée pour la détecter et estimer sa force.

Systematics and Population Level Analysis of Anopheles darlingi

A new phylogenetic analysis of the Nyssorhynchus subgenus (Danoff-Burg and Conn, unpub. data) using six data sets {morphological (all life stages); scanning electron micrographs of eggs; nuclear ITS2 sequences; mitochondrial COII, ND2 and ND6 sequences} revealed different topologies when each data set was analyzed separately but no heterogeneity between the data sets using the arn test. Consequently, the most accurate estimate of the phylogeny was obtained when all the data were combined. This new phylogeny supports a monophyletic Nyssorhynchus subgenus but both previously recognized sections in the subgenus (Albimanus and Argyritarsis) were demonstrated to be paraphyletic relative to each other and four of the seven clades included species previously placed in both sections. One of these clades includes both Anopheles darlingi and An. albimanus, suggesting that the ability to vector malaria effectively may have originated once in this subgenus. Both a conserved (315 bp) and a variable (425 bp) region of the mitochondrial COI gene from 15 populations of An. darlingi from Belize, Bolivia, Brazil, French Guiana, Peru and Venezuela were used to examine the evolutionary history of this species and to test several analytical assumptions. Results demonstrated (1) parsimony analysis is equally informative compared to distance analysis using NJ; (2) clades or clusters are more strongly supported when these two regions are combined compared to either region separately; (3) evidence (in the form of remnants of older haplotype lineages) for two colonization events; and (4) significant genetic divergence within the population from Peixoto de Azevedo (State of Mato Grosso, Brazil). The oldest lineage includes populations from Peixoto, Boa Vista (State of Roraima) and Dourado (State of São Paulo).

Association between circulating cytokine levels, diabetes and insulin resistance in a population-based sample (CoLaus study).

OBJECTIVE: The associations between inflammation, diabetes and insulin resistance remain controversial. Hence, we assessed the associations between diabetes, insulin resistance (using HOMA-IR) and metabolic syndrome with the inflammatory markers high-sensitive C-reactive protein (hs-CRP), interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α). DESIGN: Cross-sectional study. PARTICIPANTS: Two thousand eight hundred and eighty-four men and 3201 women, aged 35-75, participated in this study. METHODS: C-reactive protein was assessed by immunoassay and cytokines by multiplexed flow cytometric assay. In a subgroup of 532 participants, an oral glucose tolerance test (OGTT) was performed to screen for impaired glucose tolerance (IGT). RESULTS: IL-6, TNF-α and hs-CRP were significantly and positively correlated with fasting plasma glucose (FPG), insulin and HOMA-IR. Participants with diabetes had higher IL-6, TNF-α and hs-CRP levels than participants without diabetes; this difference persisted for hs-CRP after multivariate adjustment. Participants with metabolic syndrome had increased IL-6, TNF-α and hs-CRP levels; these differences persisted after multivariate adjustment. Participants in the highest quartile of HOMA-IR had increased IL-6, TNF-α and hs-CRP levels; these differences persisted for TNF-α and hs-CRP after multivariate adjustment. No association was found between IL-1β levels and all diabetes and insulin resistance markers studied. Finally, participants with IGT had higher hs-CRP levels than participants with a normal OGTT, but this difference disappeared after controlling for body mass index (BMI). CONCLUSION: We found that subjects with diabetes, metabolic syndrome and increased insulin resistance had increased levels of IL6, TNF-α and hs-CRP, while no association was found with IL-1β. The increased inflammatory state of subjects with IGT is partially explained by increased BMI.

A Study of Cryptosporidium parvum Genotypes and Population Structure

Genetic evidence for the occurrence of two Cryptosporidium parvum subgroups is presented. This evidence is based on restriction fragment length polymorphism analysis of several independent loci. Sequence analysis of the b -tubulin intron revealed additional polymorphism. The stability of the genetic profiles following passage of C. parvum isolates between different hosts was investigated.

Conservation of a threatened European tree frog (Hyla arborea) metapopulation

Summary: Amphibians are among the most vulnerable animals of the world. One third of all species are currently threatened with extinction. Habitat loss is the major menace to pond- and stream-breeding species in the old world. In highly urbanized landscape like the Swiss Plateau, most species suffer from habitat reduction and fragmentation. Among all indigenous species, the European tree frog (Hyla arborea L., 1758) is one of the most endangered. It experienced an alarming decline during the last century and its regional long-term persistence is not guaranteed. We developed a monitoring framework based on calling male counts which included multiple visits to each wetland during the reproduction period in order to precisely determine its distribution on the Lemanic coast. Our results indicate that visiting populations 3 limes under suitable climatic conditions (temperature >20°C) provides reliable presence/absence data. Based on our monitoring data, we analyzed the species requirements regarding its breeding habitat. It appeared that anthropogenic activities had paradoxical effects on the species. On one hand, urbanization, traffic and intensive agriculture had a strong detrimental effect on tree frog distribution. On the other hand, large tree frog populations were frequently associated with gravel pits and military training grounds. Our results allowed us to create a habitat suitability map taking into account detrimental landscape elements around ponds (>1100m away from urban areas and >500m away from first class roads). In parallel, we developed a metapopulation model of the European tree frog in order to identify the critical threats to the long term persistence of the species. Our results indicated that suitable pond density is at the low end of the species requirements. Pond creation must therefore be considered an essential complementary approach to pond conservation and restoration. Our model also provided a mapping solution permitting the location of the must suitable area for pond creation from a metapopulation perspective. As many other amphibians, the European tree frog is not only exposed to an aquatic habitat (breeding and larval period), but also to a terrestrial stage (summer and overwintering habitats). Unfortunately, animals in their terrestrial phase are less conspicuous and, as a consequence, their terrestrial needs are relatively unknown. Using a recent tracking method (the Harmonic Direction Finder), we followed post-breeding frogs and identified favored terrestrial habitats, thus providing another practical conservation tool. We conclude that only the combination of multiple spatially explicit approaches (landscape-scale habitat suitability, metapopulation dynamics and terrestrial needs) is likely to provide wildlife managers with effective tools for the conservation of highly endangered amphibians. Résumé: Les amphibiens font partie des animaux les plus vulnérables du monde. Un tiers des espèces est actuellement menacé d'extinction. Dans l'ancien monde, la disparition des habitats constitue la principale menace pour les grenouilles, crapauds, tritons et salamandres. Dans les paysages fortement urbanisés comme le Plateau Suisse, la plupart des espèces souffrent d'une réduction et d'une fragmentation de leurs habitats. Parmi toutes les espèces indigènes, la rainette verte (Hyla arborea L., 1758) est l'une des plus menacée. Sa distribution a régressé de manière alarmante durant le siècle passé et sa survie régionale à long terme n'est pas assurée. Nous avons développé une méthode de suivi des populations se basant sur le comptage des mâles chanteurs durant la période de reproduction. Cette méthode requiert plusieurs visites à chaque plan d'eau de manière à déterminer précisément la distribution de l'espèce. Nos résultats démontrent que 3 visites par population dans des conditions climatiques favorable (température >20°C) permettent d'obtenir des données de présence/ absence valables. Sur la base de nos comptages sur la Côte lémanique, nous avons analysé les exigences de l'espèce concernant ses sites de reproduction. Il est apparu que les activités humaines avaient un effet paradoxal sur l'espèce. D'une part, l'urbanisation, le trafic routier et l'intensification de l'agriculture ont un effet fortement préjudiciable, tandis que d'autre part les plus grandes populations sont souvent associées à des gravières et autres places d'armes. Nos résultats ont permis de créer une carte de qualité d'habitat prenant en compte les éléments paysagers préjudiciables à la rainette (situé à plus de 1100m de zones urbaines et à plus de 500m de routes de première classe). En parallèle, nous avons développé un modèle métapopulationnel (incluant l'ensemble des populations) de manière à identifier les menaces prépondérantes sur la survie à long terme de l'espèce. Nos résultats ont permis de déterminer que la densité actuelle de plans d'eau adéquats est à la limite inférieure des exigences de l'espèce. La création d'étangs doit donc être considérée comme une approche indispensable et complémentaire à la protection et à la restauration des sites existants. Notre modèle a également fourni des résultats cartographiables permettant l'identification des sites les plus appropriés dans une perspective métapopulationnelle. Comme de nombreux autres amphibiens, la rainette verte est exposée à un habitat aquatique (reproduction et développement larvaire) ainsi qu'à un habitat terrestre (été et hiver). Les animaux étant particulièrement cryptiques dans cette seconde phase, leurs besoins terrestres sont relativement mal connus. Nous avons donc développé une nouvelle méthode de télémétrie basée sur le goniomètre harmonique. Cette méthode nous a permis de suivre des rainettes dans leurs migrations jusqu'à leurs habitats d'été et d'établir ainsi des recommandations pratiques pour la conservation de la rainette. Nous concluons que la combinaison de multiples approches spatialement explicites (qualité d'habitat, dynamique de métapopulation et habitats terrestres) est seule à même de produire des outils efficaces pour la conservation des espèces menacées d'amphibiens.

Possible hybridization of Brazilian planorbid snails and its importance in population dynamics

This study focuses on the possibility of experimental hybridization among host snail species for Schistosoma mansoni in Brazil, with morphological characterization of the hybrids found. By using albinism as a genetic marker, intraspecific crossbreedings were performed between two strains of each species involved, in addition to interspecific crossbreedings; the only viable crossbreeding was between pigmented Biomphalaria glabrata (Paulista, PE) and albino B. tenagophila (Joinville, SC), with the formation of F1 and F2 generations. All offspring in F1 displayed black eyes and a renal ridge on the mantle, while F2 displayed dissociated morphological traits. With regard to reproduction, F1 was more efficient than F2. The experiment's results suggest post-zygotic reproductive isolation.

Population pharmacokinetic modelling and evaluation of different dosage regimens for darunavir and ritonavir in HIV-infected individuals.

OBJECTIVES: Darunavir is a protease inhibitor that is administered with low-dose ritonavir to enhance its bioavailability. It is prescribed at standard dosage regimens of 600/100 mg twice daily in treatment-experienced patients and 800/100 mg once daily in naive patients. A population pharmacokinetic approach was used to characterize the pharmacokinetics of both drugs and their interaction in a cohort of unselected patients and to compare darunavir exposure expected under alternative dosage regimens. METHODS: The study population included 105 HIV-infected individuals who provided darunavir and ritonavir plasma concentrations. Firstly, a population pharmacokinetic analysis for darunavir and ritonavir was conducted, with inclusion of patients' demographic, clinical and genetic characteristics as potential covariates (NONMEM(®)). Then, the interaction between darunavir and ritonavir was studied while incorporating levels of both drugs into different inhibitory models. Finally, model-based simulations were performed to compare trough concentrations (Cmin) between the recommended dosage regimen and alternative combinations of darunavir and ritonavir. RESULTS: A one-compartment model with first-order absorption adequately characterized darunavir and ritonavir pharmacokinetics. The between-subject variability in both compounds was important [coefficient of variation (CV%) 34% and 47% for darunavir and ritonavir clearance, respectively]. Lopinavir and ritonavir exposure (AUC) affected darunavir clearance, while body weight and darunavir AUC influenced ritonavir elimination. None of the tested genetic variants showed any influence on darunavir or ritonavir pharmacokinetics. The simulations predicted darunavir Cmin much higher than the IC50 thresholds for wild-type and protease inhibitor-resistant HIV-1 strains (55 and 550 ng/mL, respectively) under standard dosing in >98% of experienced and naive patients. Alternative regimens of darunavir/ritonavir 1200/100 or 1200/200 mg once daily also had predicted adequate Cmin (>550 ng/mL) in 84% and 93% of patients, respectively. Reduction of darunavir/ritonavir dosage to 600/50 mg twice daily led to a 23% reduction in average Cmin, still with only 3.8% of patients having concentrations below the IC50 for resistant strains. CONCLUSIONS: The important variability in darunavir and ritonavir pharmacokinetics is poorly explained by clinical covariates and genetic influences. In experienced patients, treatment simplification strategies guided by drug level measurements and adherence monitoring could be proposed.

Dosing regimen of gentamicin in neonates: evaluation of current guidelines based on a large population pharmacokinetic analysis

Objectives: Gentamicin is among the most commonly prescribed antibiotics in newborns, but large interindividual variability in exposure levels exists. Based on a population pharmacokinetic analysis of a cohort of unselected neonates, we aimed to validate current dosing recommendations from a recent reference guideline (Neofax®). Methods: From 3039 concentrations collected in 994 preterm (median gestational age 32.3 weeks, range 24.2-36.5) and 455 term newborns, treated at the University Hospital of Lausanne between 2006 and 2011, a population pharmacokinetic analysis was performed with NONMEM®. Model-based simulations were used to assess the ability of dosing regimens to bring concentrations into targets: trough ≤ 1mg/L and peak ~ 8mg/L. Results: A two-compartment model best characterized gentamicin pharmacokinetics. Model parameters are presented in the table. Body weight, gestational age and postnatal age positively influence clearance, which decreases under dopamine administration. Body weight and gestational age influence the distribution volume. Model based simulations confirm that preterm infants need doses superior to 4 mg/kg, and extended dosage intervals, up to 48 hours for very preterm newborns, whereas most term newborns would achieve adequate exposure under 4 mg/kg q. 24 h. More than 90% of neonates would achieve trough concentrations below 2 mg/L and peaks above 6 mg/L following most recent guidelines. Conclusions: Simulated gentamicin exposure demonstrates good accordance with recent dosing recommendations for target concentration achievement.

Evaluation of Insecticide Resistance and Biochemical Mechanisms in a Population of Culex quinquefasciatus (Diptera: Culicidae) from São Paulo, Brazil

To establish an insecticidal resistance surveillance program, Culex quinquefasciatus mosquitoes from São Paulo, Brazil, were colonized (PIN95 strain) and analyzed for levels of resistance. The PIN95 strain showed low levels of resistance to organophosphates [malathion (3.3-fold), fenitrothion (11.2-fold)] and a carbamate [propoxur (3.0-fold)]. We also observed an increase of 7.4 and 9.9 in a and b esterase activities, respectively, when compared with the reference IAL strain. An alteration in the sensitivity of acetylcholinesterase to insecticide inhibition was also found in the PIN95 mosquitoes. The resistant allele (Ace.1R), however, was found at low frequencies (0.12) and does not play an important role in the described insecticide resistance. One year later, Cx. quinquefasciatus mosquitoes were collected (PIN96 strain) at the same site and compared to the PIN95 strain. The esterase activity patterns observed for the PIN96 strain were similar to those of the PIN95 mosquitoes. However the occurrence of the Ace.1R allele was statistically higher in the PIN96 strain. The results show that esterase-based insecticide resistance was established in the PIN95 Cx. quinquefasciatus population and that an acethylcholinesterase based resistant mechanism has been selected for. A continuous monitoring of this phenomenon is fundamental for rational mosquito control and insecticide application programs.