Effets de la fragmentation forestière sur l'activité des coléoptères coprophages : dispersion secondaire des graines en Guyane française

The effect of seed burial by dung beetles on seed survival and seedling establishment in Tetragastris altissima (Burseraceae) was measured on 3 sites of continuous forest and 7 islands in the man-inundated rain forest of Saint-Eugène, French Guiana. Experiments using a total of 250 seeds were performed using wire enclosures open to dung beetles but excluding terrestrial seed predators. Fragmentation had no effect on the rate of dung disappearance at 12, 24 and 48 h because there was a high variability between sites. On average, 24 % of seeds were buried by dung beetles after 72 h. Overall, there was no effect of fragmentation due to variation between sites. Dung burial rates were positively correlated with rarefaction of the dung beetle samples collected on the different sites. They were also positively correlated with weighted abundances of large diurnal tunneliers after 12 h and to total tunneliers after 24 h. Seed burial was positively correlated to weighted abundance of large noctumal tunneliers and of total tunneliers. The species diversity and abundance were positively related to area that did not involve a correlation between seed burial rates and area. After 72 h, survival rate of protected seeds at ground surface was significantly larger (78 %) than for non protected seeds (22 %), which were attacked by rodents. There was no difference between continuous forest and islands. Eight percent of buried seeds emerged, i.e. 2 % of all seeds deposited. Burial depth significantly affected the rate of emergence of buried seeds. Ninety percent of seeds at surface gerrninated versus 0 % at 10 and 15 cm. The effects of seed burial by dung beetles on early recruitment of T. altissima was low and highly variable between sites in relation with the structure of the community of Scarabaeidae and intensity of seed predationL'effet de l'enfouissement des graines contenues dans les excréments par les coléoptères coprophages sur la survie des graines et l'établissement des plantules a été mesuré chez Tetragastris altissima (Burseracées) sur 3 sites en forêt continue et 7 îles résultant de l'inondation de la forêt dense par l'homme à Saint-Eugène en Guyane française. Des expériences utilisant un total de 250 graines ont été menées avec un dispositif fait d'enclos laissant agir les coléoptères coprophages à l'abri des prédateurs terrestres de graines. Il n'a pas été détecté d'effet de la fragmentation sur les taux de disparition des excréments après 12, 24 et 48 h en raison de la grande variabilité entre sites. Un pourcentage moyen de 24 % des graines a été enfoui par les coprophages après 72 h. La fragmentation n'a pas eu d'effet sur l'enfouissement des graines qui a montré une grande variabilité entre sites. La disparition des excréments était positivement corrélée à la raréfaction des échantillons de coprophages capturés sur les sites, à l'abondance pondérée des grands fouisseurs diurnes après 1 2 h et avec celle du total des fouisseurs après 24 h. L'enfouissement des graines a été positivement corrélé aux abondances pondérées des grands fouisseurs nocturnes et du total des grands fouisseurs. La diversité spécifique et l'abondance des coprophages était positivement corrélée à la superficie des sites mais il n'y avait aucune corrélation entre l'enfouissement des excréments ou des graines et la superficie. Après 72 h, le taux de survie des graines protégées en surface (78 %) a été significativement supérieur à celui des graines non protégées (22 %), soumises à la prédation des rongeurs. Il n'a pas été observé de différences de survie entre la terre ferme et les îles. Huit pour cent des graines enfouies protégées ont émergé, soit 2 % de l'effectif initial. Le taux d'émergence des graines enfouies est significativement affecté par la profondeur. Il a été de 90 % en surface mais il a été nul à 10 et 15 cm de profondeur. L'effet des coprophages sur le succès de la régénération précoce de T. altissima a été faible et a varié selon les sites en relation avec la structure de la communauté de Scarabéidés et l'intensité de la prédation des graines au so

The sperm of aging male bustards retards their offspring's development.

9 pagesInternational audienceUnderstanding whether the sperm of older males has a diminished capacity to produce successful offspring is a key challenge in evolutionary biology. We investigate this issue using 10 years of reproductive data on captive long-lived houbara bustards (Chlamydotis undulata), where the use of artificial insemination techniques means parents can only influence offspring quality via their gametes. Here we show that paternal aging reduces both the likelihood that eggs hatch and the rate at which chicks grow, with older males producing the lightest offspring after the first month. Surprisingly, this cost of paternal aging on offspring development is of a similar scale to that associated with maternal aging. Fitting with predictions on germline aging, the sperm of immature males produce the fastest growing offspring. Our findings thus indicate that any good genes benefit that might be offered by older 'proven' males will be eroded by aging of their germline DNA

Does recognized genetic management in supportive breeding prevent genetic changes in life-history traits?

International audienceSupportive breeding is one of the last resort conservation strategies to avoid species extinction. Management of captive populations is challenging because several harmful genetic processes need to be avoided. Several recommendations have been proposed to limit these deleterious effects, but empirical assessments of these strategies remain scarce. We investigated the outcome of a genetic management in a supportive breeding for the Houbara Bustard. At the phenotypic level, we found an increase over generations in the mean values of gamete production, body mass and courtship display rate. Using an animal model, we found that phenotypic changes reflected genetic changes as evidenced by an increase in breeding values for all traits. These changes resulted from selection acting on gamete production and to a lesser extent on courtship display. Selection decreased over years for female gametes, emphasizing the effort of managers to increase the contribution of poor breeders to offspring recruited in the captive breeding. Our results shed light on very fast genetic changes in an exemplary captive programme that follows worldwide used recommendations and emphasizes the need of more empirical evidence of the effects of genetic guidelines on the prevention of genetic changes in supportive breeding

Density-dependence of reproductive success in a Houbara bustard population

Although density-dependent processes and their impacts on population dynamics are key issues in ecology and conservation biology, empirical evidence of density-dependence remains scarce for species or populations with low densities, scattered distributions, and especially for managed populations where densities may vary as a result of extrinsic factors (such as harvesting or releases). Here, we explore the presence of density-dependent processes in a reinforced population of North African Houbara bustard (Chlamydotis undulata undulata). We investigated the relationship between reproductive success and local density, and the possible variation of this relationship according to habitat suitability using three independent datasets. Based on eight years of nests monitoring (more than 7000 nests), we modeled the Daily Nest Survival Rate (DNSR) as a proxy of reproductive success. Our results indicate that DNSR was negatively impacted by local densities and that this relationship was approximately constant in space and time: (1) although DNSR strongly decreased over the breeding season, the negative relationship between DNSR and density remained constant over the breeding season; (2) this density-dependent relationship did not vary with the quality of the habitat associated with the nest location. Previous studies have shown that the demographic parameters and population dynamics of the reinforced North African Houbara bustard are strongly influenced by extrinsic environmental and management parameters. Our study further indicates the existence of density-dependent regulation in a low-density, managed population.The study was funded by Emirates Center for Wildlife Propagation (ECWP, Morocco), a project of the International Fund for Houbara Conservation (IFHC, United Arab Emirates)

Quantitative Genetics of the Aging of Reproductive Traits in the Houbara Bustard

International audienceDo all traits within an organism age for the same reason? Evolutionary theories of aging share a common assumption: the strength of natural selection declines with age. A corollary is that additive genetic variance should increase with age. However, not all senescent traits display such increases suggesting that other mechanisms may be at play. Using longitudinal data collected from more than 5400 houbara bustards (Chlamydotis undulata) with an exhaustive recorded pedigree, we investigated the genetics of aging in one female reproductive trait (egg production) and three male reproductive traits (courtship display rate, ejaculate size and sperm viability), that display senescence at the phenotypic level. Animal models revealed an increase in additive genetic variance with age for courtship display rate and egg production but an unexpected absence of increased additive genetic variance for ejaculate size and no additive genetic variance for sperm viability. Our results suggest that the mechanisms behind the senescence of some traits are linked with a change in genetic expression, whereas for some other traits, aging may result from the constraints associated with physiological wear and tear on the organism throughout the life of the individual

Genetic diversity of[i] Rhizoctonia solani[/i] associated with potato tubers in France

Affiche, résuméThe plant pathogenic soil-borne fungus Rhizoctonia solani causes severe damages in crops all around the world. Tubers of potato are frequently affected by R. solani leading to the downgrading of the production. Generally the isolates involved in the sclerotia occurring at the surface of the tuber are assigned to the anastomosis group (AG) 3 but a more precise characterization of the diversity of this deleterious group is needed to set up appropriate control strategies. The diversity of 73 French isolates from the mains potato seed production areas and 31 isolates originating from 9 other countries was assessed according to 3 molecular approaches. Three phylogenetic trees were built up based on the sequences of the internal transcribed spacer (ITS) region and the gene tef-1α as well as the comparison of the total DNA fingerprints of each strain established by amplified fragment length polymorphism (AFLP). The determination of the AGs of R. solani based on the sequencing of the ITS region showed 3 different AGs among our collection (60 AG 3, 8 AG 2-1 and 5 AG 5). Grouping of the isolates belonging to the same AG was confirmed by the sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42 % of the ITS sequences and 73 % of the gene tef-1α sequences contained polymorphic sites where several nucleotides are possible, suggesting that the cells of R. solani strains contain several copies of ITS and gene tef-1α within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α sequences than in ITS sequences. The AFLP analyses showed an even greater diversity among the strains demonstrating that the French strains of R. solani isolated from potatoes were not a clonal population. Moreover, there was no relationship between the geographical origins of the strains or the potato variety from which they were isolated and their genetic diversity. This important and under evaluated genetic diversity as the lack of population structure suggest important genetic mixings leading to a constant evolution within R. solani and could explain the difficulties to control it successfully

Immune-Mediated Change in the Expression of a Sexual Trait Predicts Offspring Survival in the Wild

BACKGROUND: The "good genes" theory of sexual selection postulates that females choose mates that will improve their offspring's fitness through the inheritance of paternal genes. In spite of the attention that this hypothesis has given rise to, the empirical evidence remains sparse, mostly because of the difficulties of controlling for the many environmental factors that may covary with both the paternal phenotype and offspring fitness. Here, we tested the hypothesis that offspring sired by males of a preferred phenotype should have better survival in an endangered bird, the houbara bustard (Chlamydotis undulata undulata). METHODOLOGY/PRINCIPAL FINDINGS: We tested if natural and experimentally-induced variation in courtship display (following an inflammatory challenge) predicts the survival of offspring. Chicks were produced by artificial insemination of females, ensuring that any effect on survival could only arise from the transfer of paternal genes. One hundred and twenty offspring were equipped with radio transmitters, and their survival monitored in the wild for a year. This allowed assessment of the potential benefits of paternal genes in a natural setting, where birds experience the whole range of environmental hazards. Although natural variation in sire courtship display did not predict offspring survival, sires that withstood the inflammatory insult and maintained their courtship activity sired offspring with the best survival upon release. CONCLUSIONS: This finding is relevant both to enlighten the debate on "good genes" sexual selection and the management of supportive breeding programs

Pre-but not post-meiotic senescence affects sperm quality and reproductive success in the North African houbara bustard

Age-dependent reduction in reproductive success can arise due to multiple factors including a deterioration of reproductive physiology. Senescing males have been shown to produce ejaculates with poor sperm quality, which impinges on male reproductive success. In addition to individual age, gamete age can also affect male reproductive success. Accordingly, variance in male reproductive success can be due to pre-meiotic (referring to individual age) and post-meiotic senescence (sperm age). Here, we tested whether male senescence and sperm cell aging have additive or interactive effects on male reproductive success in a bird with a promiscuous mating system, the North African houbara bustard. To assess the effect of pre-meiotic aging, we compared male reproductive success between two age classes (3-6- and 12–16-year-old). To infer the effect of post-meiotic aging, male ejaculates were collected at three-time intervals following a common initial collection (day 1, 5, and 10). Therefore, day 1 ejaculates are supposed to contain younger sperm than day 5 and 10 ejaculates. Following controlled artificial inseminations, reproductive success was assessed using three fitness-linked traits (hatching success, chick growth rate and survival). In addition to reproductive output, we also assessed whether pre- and post-meiotic aging affected a wide range of sperm and ejaculate traits. In agreement with previous reports, we found that males in the older age class produced less sperm with poorer motility compared to young individuals. However, contrary to the prediction, we found that ejaculates collected at day 5 and 10 tended to have better sperm traits such as motility and velocity. The results on sperm traits were generally mirrored in the effect on reproductive success since young males produced offspring that grew faster and had better survival during the first month of life, and eggs fertilized by sperm collected at day 5 had the highest hatching success. In any of the models, there was evidence for interactive effects of male and sperm age. Overall, these results confirm the role of pre-meiotic aging on male reproductive success. The lack of evidence for sperm aging could come from the experimental design but might also reflect the pattern of mating frequency in a species with a lek-based mating system

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men