Prédation

Résumé

La prédation est l'action de prendre, de capturer. Etymologie Ce terme est un emprunt de la Renaissance au latin praedator, « voleur, pilleur », lui-même issu de praeda, « proie » et de prehendō, « prendre », qui exprime le fait de se saisir de quelqu'un ou de capturer une proie déterminée par sa poursuite. Description La prédation est une interaction trophique directe, de nature antagoniste, entre deux organismes, par laquelle une espèce dénommée prédateur, consomme entièrement ou partiellement une ou plusieurs espèces dénommées proies, généralement en les tuant, pour s'en nourrir ou pour alimenter sa progéniture. La définition lato sensu inclut la zoophagie (depuis les micro-organismes procaryotes jusqu'aux superprédateurs, en passant par les hématophages ou les plantes carnivores), la bactériophagie, la microphagie (depuis les mollusques jusqu'aux baleines à fanons), mais aussi la phytophagie (consommation de plantes par les herbivores, de graines par les g

Source officielle

https://fr.wikipedia.org/wiki/Pr%C3%A9dation

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The students will learn the fundamentals in ecology with the goal to perceive the environment beyond its physical and chemical characteristics. Starting from basic concepts, they will acquire mechanistic understanding of biodiversity, ecosystem functioning and global change.

Ce cours introduit les systèmes dynamiques pour modéliser des réseaux biologiques simples. L'analyse qualitative de modèles dynamiques non-linéaires est développée de pair avec des simulations numériques. L'accent est mis sur les exemples biologiques.

The course starts with fundamentals of electrical - and chemical signaling in neurons. Students then learn how neurons in the brain receive and process sensory information, and how other neurons control the behavior of an animal. Furthermore, memory, learning, and brain disorders will be introduced.

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Viral Transfer and Inactivation through Zooplankton Trophic Interactions

Virginie Bachmann, Xavier Fernandez Cassi, Niveen Saad Ismail, Tamar Kohn, Margot Ninon Lauren Olive

Waterborne viruses are responsible for numerous diseases and are abundant in aquatic systems. Understanding the fate of viruses in natural systems has important implications for human health. This research quantifies the uptake of bacteriophage T4 and the enteric virus echovirus 11 when exposed to the filter feeders Tetrahymena pyriformis and Daphnia magna, and also examines the potential of viral transfer due to trophic interactions. Experiments co-incubating each species with the viruses over 72-96 hours showed up to 4-log virus removal for T. pyriformis, while direct viral uptake by D. magna was not observed. However, viral uptake by D. magna occurred indirectly by viral transfer from prey to predator, through D. magna feeding on virus loaded T. pyriformis. This predator-prey interaction resulted in 1-log additional virus removal compared to removal by T.pyriformis alone. Incomplete viral inactivation by D. magna was observed through recovery of infective viruses from daphnid tissue. This research furthers our understanding of the impacts of zooplankton filter feeding on viral inactivation and shows the potential for viral transfer through the food chain. The viral-zooplankton interactions observed in these studies indicate that zooplankton may improve water quality through viral uptake or may serve as vectors for infection by accumulating viruses.

2020

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Collembola is an abundant group of soil organisms playing a major role on litter decomposition process and nutrient cycling in forest ecosystems. Habitat structure strongly influences Collembola assemblages as plant litter physical characteristics and quantity provide structural niches and determine the outcome of their interactions with predators. Collembola are also extremely sensitive to environmental conditions such as soil temperature that control their demographic parameters and activity. In this context, increasing temperature with the ongoing climate change can have strong impact on Collembola assemblages and their responses to predation either directly by altering their behaviour or indirectly by altering their habitat structure. We therefore examined how the increase of temperature combined to the decrease of specific leaf area (SLA, a major functional plant trait) of the European common oak (Quercus robur L.) and the presence of a centipede predator (Chilopoda: Lithobiidae) will affect the abundance of Folsomia candida (Collembola: Isotomidae) in a 5-week microcosm experiment. Increasing temperature, decreasing SLA and presence of centipede altered F. candida abundance. We observed a significant temperature x predation interaction suggesting differential effects of increasing temperature on F. candida abundance with and without predator. We also observed a significant SLA x predation interaction highlighting that lower SLA decreases F. candida abundance only in predator presence. Finally, our findings evidenced that increasing temperature and decreasing SLA amplify the negative effect of centipede predation on F. candida abundance, suggesting that both direct and indirect effects of climate change would conjointly strengthen the top-down control of predators on preys.

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER2018

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The molecular treasure box of environmental Vibrio cholerae strains

Natalia Carolina Drebes Dörr

Cholera pandemics have been affecting humankind for centuries and are still considered a major public health problem, especially in regions around the world with poor access to clean water and sanitation. Cholera pandemics are caused by a specific lineage of the bacterial pathogen Vibrio cholerae, while the vast majority of the species' diversity is found in innocuous environmental strains. The complete set of factors that allowed the emergence and success of the pandemic lineage are still unknown. Importantly, most V. cholerae strains are adapted to aquatic habitats and trigger their behavior accordingly. The aim of this thesis was therefore to gain a better understanding of what is special about the pandemic lineage when contrasted to its environmental counterparts. Specifically, we investigated environmentally important bacterial behaviors in a comparative framework. Firstly, considering the relevance of eukaryotic predation in shaping bacterioplankton structure, we investigated possible strategies used by V. cholerae to avoid grazing by the predatory amoeba Dictyostelium discoideum. We observed that V. cholerae was able to rapidly intoxicate amoebae and that the intoxication dynamics differed when caused by pandemic or environmental strains. Secondly, we compared a well-conserved set of mobile genetic elements (MGEs) of the pandemic lineage, many of which are involved in key aspects of cholera pathogenesis, with the respective counterparts of environmental strains. To do so, we sequenced and de novo assembled the genomes of fifteen environmental isolates and thoroughly described their mobilome. Moreover, transcription profiling demonstrated that most genes located on these MGEs are expressed. Thirdly, we compared environmental and pandemic strains regarding their potential to kill bacterial competitors and to defend themselves against protozoan predation. Specifically, we assessed the role of two molecular weapons: the pore-forming toxin hemolysin and the type six secretion system (T6SS), a molecular killing device that delivers effector toxins into target cells. While environmental strains keep both of these weapons constitutively active, pandemic strains employ regulatory mechanisms to control their expression. We observed that all environmental V. cholerae isolates used their T6SS to efficiently outcompete prey bacteria, while only two clades of the environmental isolates also intoxicated eukaryotic amoebae. Furthermore, we performed a meticulous in silico characterization of the effector and immunity proteins carried by the environmental strains and showed in pairwise killing experiments that a high degree of immunity protein identity was required to allow the strains' coexistence. Finally, we addressed the phenomenon of T6SS constitutive activity in non-pandemic V. cholerae strains, which has puzzled the field since the T6SS' discovery in 2006. Using a transformation-based strain library, we uncovered a genomic region that controls T6SS activity. In summary, work developed in this thesis contributes to a better understanding of V. cholerae's evolution from an innocuous inhabitant of aquatic environments to a pandemic-causing human pathogen.

EPFL2021

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The molecular treasure box of environmental Vibrio cholerae strains

Natalia Carolina Drebes Dörr

EPFL2021