Escherichia coli population structure and antibiotic resistance at a buffalo/cattle interface in Southern Africa

At a human/livestock/wildlife interface, Escherichia coli populations were used to assess the risk of bacterial and antibiotic resistance dissemination between hosts. We used phenotypic and genotypic characterization techniques to describe the structure and the level of antibiotic resistance of E. coli commensal populations and the resistant Enterobacteriaceae carriage of sympatric African buffalo (Syncerus caffer caffer) and cattle populations characterized by their contact patterns in the southern part of Hwange ecosystem in Zimbabwe. Our results (i) confirmed our assumption that buffalo and cattle share similar phylogroup profiles, dominated by B1 (44.5%) and E (29.0%) phylogroups, with some variability in A phylogroup presence (from 1.9 to 12%); (ii) identified a significant gradient of antibiotic resistance from isolated buffalo to buffalo in contact with cattle and cattle populations expressed as the Murray score among Enterobacteriaceae (0.146, 0.258, and 0.340, respectively) and as the presence of tetracycline-, trimethoprim-, and amoxicillin-resistant subdominant E. coli strains (0, 5.7, and 38%, respectively); (iii) evidenced the dissemination of tetracycline, trimethoprim, and amoxicillin resistance genes (tet, dfrA, and blaTEM-1) in 26 isolated subdominant E. coli strains between nearby buffalo and cattle populations, that led us (iv) to hypothesize the role of the human/animal interface in the dissemination of genetic material from human to cattle and toward wildlife. The study of antibiotic resistance dissemination in multihost systems and at anthropized/natural interface is necessary to better understand and mitigate its multiple threats. These results also contribute to attempts aiming at using E. coli as a tool for the identification of pathogen transmission pathway in multihost systems. (Résumé d'auteur

Escherichia coli population structure and antibiotic resistance at a buffalo/cattle interface in southern Africa

At a human/livestock/wildlife interface, Escherichia coli populations were used to assess the risk of bacterial and antibiotic resistance dissemination between hosts. We used phenotypic and genotypic characterization techniques to describe the structure and the level of antibiotic resistance of E. coli commensal populations and the resistant Enterobacteriaceae carriage of sympatric African buffalo (Syncerus caffer caffer) and cattle populations characterized by their contact patterns in the southern part of Hwange ecosystem in Zimbabwe. Our results (i) confirmed our assumption that buffalo and cattle share similar phylogroup profiles, dominated by B1 (44.5%) and E (29.0%) phylogroups, with some variability in A phylogroup presence (from 1.9 to 12%); (ii) identified a significant gradient of antibiotic resistance from isolated buffalo to buffalo in contact with cattle and cattle populations expressed as the Murray score among Enterobacteriaceae (0.146, 0.258, and 0.340, respectively) and as the presence of tetracycline-, trimethoprim-, and amoxicillin-resistant subdominant E. coli strains (0, 5.7, and 38%, respectively); (iii) evidenced the dissemination of tetracycline, trimethoprim, and amoxicillin resistance genes (tet, dfrA, and blaTEM-1) in 26 isolated subdominant E. coli strains between nearby buffalo and cattle populations, that led us (iv) to hypothesize the role of the human/animal interface in the dissemination of genetic material from human to cattle and toward wildlife. The study of antibiotic resistance dissemination in multihost systems and at anthropized/natural interface is necessary to better understand and mitigate its multiple threats. These results also contribute to attempts aiming at using E. coli as a tool for the identification of pathogen transmission pathway in multihost systems.This study was implemented within the framework of the research Platform Conservation and Production in Partnership (www.rp-pcp.org) and in collaboration with CNRS within the framework of the Zone Atelier in the Hwange area.Agence Nationale de la Recherche (ANR) http://dx.doi.org/10.13039/501100001665ANR-11-CEPL-003.http://aem.asm.org2017-06-30Mammal Research Institut

Boire ou ne pas boire ? : l'influence de la disponibilité en ressource sur l'approvisionnement et la sélection de l'habitat d'éléphants dans une savanne semi aride

Water and forage are key non-substitutable resources for herbivores in arid and semi-arid ecosystems. The distribution of surface water determines the distribution and abundance of water dependent animal species yet little is known about the processes involved at the individual level. Thirteen African savanna elephant family groups and ten bulls (Loxodonta Africana) were tracked with GPS collars within and on the outskirts of Hwange National Park, Zimbabwe. Elephants behave as multiple central place foragers: They visit waterholes periodically every 5h, 24h, 48h or 72h and travel further from water during longer trips. During the dry season, temperatures increase and forage becomes depleted closer to water. Elephant family groups visit waterholes more often by increasing the proportion of briefer trips and abandoning 72h trips. However, they forage further during 24h trips by increasing travelling speed. Elephant movement patterns revealed locomotional and navigational abilities are at the core of their coping strategies although they are seldom allowed to vary in most foraging models of animal's use of heterogeneously distributed resources. During these foraging trips, family herds select for areas with low waterhole density at multiple scales. Selection strength for low density areas increases with both distance to water and the advancement of the dry season. Although scaling effects are widely recognized, the effects of the spatial distribution of multiple central places constraining foraging have been ignored yet they determine depletion effects and their feedbacks on habitat selection. I also showed that wildlife strongly avoid livestock and people that herd them at the boundary of a protected area during the rainy season yet avoidance decreases during the dry season when foraging and drinking resources become scares. Elephants are increasingly constrained by surface water availability during the dry season as their drinking requirements increase while they strive to main their forage intake. This study provides quantitative assessment of individual water dependence and of landscape effects of surface water distribution on a large herbivore. These findings can inform surface water management in contexts of aridification resulting from climate change.L’eau et le fourrage sont deux ressources non substituables pour les herbivores dans les écosystèmes arides et semi-arides. La distribution spatiale de l’eau de surface détermine la distribution et l’abondance des espèces dépendantes de l’eau. Cependant les processus impliqués à l’échelle individuelle demeurent méconnus. Treize groupes familiaux d’éléphants d’Afrique (Loxodonta africana) et dix mâles ont été équipé de colliers GPS dans le parc National de Hwange, au Zimbabwe, et à sa périphérie. Les éléphants fourragent autour de multiples points centraux : ils visitent un point d’eau périodiquement toutes les 5h, 24h, 48h ou 72h et s’éloignent plus de l’eau lorsque ils font des trajets de plus longue durée. Pendant la saison sèche, la température augmente et les ressources fourragères s’épuisent à proximité de l’eau. Les groupes familiaux d’éléphants visitent les points d’eau plus souvent en augmentant la fréquence des trajets courts et en abandonnant les trajets de 72h. Cependant, ils parviennent à se rendre plus loin de l’eau pendant les trajets de 24h en augmentant la vitesse de déplacement. Ainsi les patrons de déplacement révèlent que les capacités de locomotion et de navigation des éléphants sont au cœur de leur stratégie d’adaptation à la saison sèche. Malgré cela, ces capacités sont rarement incluses dans les modèles d’approvisionnement dans des environnements hétérogènes. Pendant ces trajets, les groupes familiaux sélectionnent les zones de faible densité de points d’eau à des échelles multiples. La force de la sélection pour ces zones de faible densité augmente avec la longueur du trajet et au cours de la saison. Malgré le fait que l’importance des échelles spatiales soit bien établie dans la littérature, les contraintes associées à l’utilisation de multiples points centraux distribués de manière hétérogène dans le paysage ont été négligé alors que cette distribution détermine le degré d’épuisement des ressources fourragères et les rétroactions sur la sélection de l’habitat. J’ai aussi montré que la faune sauvage évite fortement le bétail et les humains qui les conduisent en périphérie d’une zone protégée pendant la saison des pluies. Cependant cet évitement décline au cours de la saison sèche en raison de l’assèchement des points d’eau et de la raréfaction des ressources fourragères. Les éléphants sont de plus en plus contraints par la distribution de l’eau de surface en saison sèche en raison de l’augmentation de leur besoins en eau tandis qu’ils tentent de maintenir leur approvisionnement en fourrage. Cette étude donne une évaluation quantitative de la contrainte en eau à l’échelle individuelle ainsi que les effets de la distribution en eau dans le paysage sur un grand herbivore. Ces résultats peuvent guider les politiques de gestion de l’eau dans un contexte d’aridification dû au changement climatique

Temperature as a constraint on the timing and duration of African elephant foraging trips

International audienceIn arid and semi-arid environments, water is a key resource that is limited in availability. During the dry season, perennial water sources such as water pans often are far apart and shape the daily movement routines of large herbivores. In hot environments, endotherms face a lethal risk of overheating that can be buffered by evaporative cooling. Behavioral adjustments are an alternative way to reduce thermal constraints on the organism. The trade-off between foraging and reaching water pans has been studied widely in arid environments; however, few studies have looked into how ambient temperature shapes individual trips between two visits to water. In this study, we tracked during the dry season the movement of 8 GPS-collared African elephants (Loxodonta africana) cows from different herds in Hwange National Park, Zimbabwe. This species, the largest extant terrestrial animal, is particularly sensitive to heat due to its body size and the absence of sweat glands. We show that most foraging trips depart from water at nightfall, lowering the average temperature experienced during walking. This pattern is conserved across isolated elephant populations in African savannas. We also observed that higher temperatures at the beginning of the trip lead to shorter trips. We conclude that elephants adjust the timing of foraging trips to reduce the thermal constraints, arguing that further considerations of the thermal landscape of endotherms are important to understand their ecology

Resource depletion versus landscape complementation: habitat selection by a multiple central place forager

International audienceThe spatial distribution of non-substitutable resources implies diverging predictions for animal movement patterns. At broad scales, animals should respond to landscape complementation by selecting areas where resource patches are close-by to minimize movement costs. Yet at fine scales, central place effects lead to the depletion of patches that are close to one another and that should ultimately be avoided by consumers. We developed a multi-scale resource selection framework to test whether animal movement is driven by landscape complementation or resource depletion and identify at which spatial scale these processes are relevant from an animal's perspective. During the dry season, surface water and forage are non-substitutable resources for African elephants. Eight family herds were tracked using GPS loggers in Hwange National Park, Zimbabwe. We explained habitat selection during foraging trips by mapping surface water at two scales with gaussian kernels of varying widths placed over each waterhole. Unexpectedly, elephants select areas with low waterhole density at both fine scales (< 1 km) and broad scales (5-7 km). Selection is stronger when elephants forage far away from water, even more so as the dry season progresses. Elephant selection of low waterhole density areas suggests that resource depletion around multiple central places is the main driver of their habitat selection. By identifying the scale at which animals respond to waterhole distribution we provide a template for water management in arid and semi-arid landscapes that can be tailored to match the requirements and mobility of free ranging wild or domestic species

DISTINCT PHYSIOLOGICAL RESPONSES UNDERLIE DEFOLIATION TOLERANCE IN AFRICAN LAWN AND BUNCH GRASSES

<p>Premise of research. African grass communities are dominated by two distinct functional types: tall, caespitose bunch grasses and short, spreading lawn grasses. Functional type coexistence has been explained by differences in defoliation tolerance, because lawn grasses occur in intensively grazed areas while bunch grasses are less associated with heavy grazing. If different responses to tissue loss explain their distribution, expectations are that biomass production and leaf-level physiology will be negatively impacted in bunch relative to lawn grasses.</p><p>Methodology. We tested the influence of defoliation on three lawn and three bunch grasses from Tanzania and South Africa by quantifying growth and measuring physiological response of these grasses to simulated herbivory in a glasshouse experiment. Specifically, we measured photosynthesis, transpiration, stomatal conductance, leaf dry matter content (LDMC), specific leaf area (SLA), leaf nitrogen, and leaf pigment concentrations in leaves of bunch and lawn grasses that were clipped or unclipped.</p><p>Pivotal results. In contrast to our expectations, clipped lawn and bunch grasses did not differ in photosynthesis, leaf nitrogen, or biomass production, and both lawn and bunch grasses upregulated photosynthesis in response to clipping. However, defoliated bunch grasses had higher rates of stomatal conductance and transpiration compared with defoliated lawn grasses. Also, leaf carotenoid concentrations increased in response to clipping for both functional types but much more in bunch than in lawn grasses. An analysis of leaf-level physiological relationships with structural equation modeling showed that lawn and bunch grasses exert control over carbon gain in different ways. In bunch grasses, net carbon gain was associated with leaf-level structural properties (LDMC and SLA) that varied in response to defoliation, while in lawn grasses, increased carbon gain was the result of increased leaf [N] subsequent to defoliation.</p><p>Conclusions. The varied responses of lawn and bunch grasses to defoliation appear to arise from their different investments in defense and carbon assimilation subsequent to defoliation. Bunch grasses invest relatively more in carotenoid production, likely as a mechanism to enhance regrowth and protect costly leaves from photodamage. Moreover, bunch grasses maintain efficient carbon assimilation by structural adjustments in leaves (decreasing LDMC subsequent to defoliation), while lawn grasses maintain efficient water use by increasing leaf [N] subsequent to defoliation. Thus, we conclude that a key difference between lawn and bunch grasses is not defoliation tolerance per se but physiological adaptations that constrain them to environments with different moisture availability subsequent to defoliation.</p>