Extinction event | EPFL Graph Search

An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity. The "Big Five" mass extinctions In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five particular geological intervals with excessive diversity loss. They were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic, but as more s

Genetic selection for low glucocorticoid responsiveness recapitulates PTSD-related phenotypes: a behavioral, neuroimaging and sleep-physiology study

Silvia Monari

Humans show inter-individual differences in vulnerability to develop post-traumatic stress disorder (PTSD) following exposure to trauma. Several critical biobehavioral features have been consistently described in PTSD patients, including blunted cortisol levels, smaller hippocampal size, sleep disturbances. However, because of the delay between trauma exposure and the onset of symptoms characteristic of PTSD, only a few longitudinal studies have tried to dissect whether these features constitute pre-trauma risk factors or consequences of the trauma. Enormous effort in animal and human studies has been dedicated to understanding mechanisms of conditioned fear and fear extinction, processes that are at the core of PTSD. However, the same progress has not been translated into psychiatric practice for PTSD. Deepening our understanding of the contribution of key factors to PTSD-related alterations can serve to develop effective treatments.In particular, with regard to low cortisol levels in PTSD pathophysiology, a causative role for blunted glucocorticoid responsiveness in PTSD has not been demonstrated yet.Here, we have addressed this question in lines of Wistar rats genetically-selected for their differential habituation of glucocorticoid responses to stress (LOW-, INTER-, HIGH-CORT Responder rats) and focused on fear extinction, a hallmark of PTSD symptomology, as one of the key features. As a first step, we looked whether divergent trajectories of glucocorticoid responsiveness were associated with brain volume abnormalities, prompted by the influential role of glucocorticoid in brain development. Notably, rats with low or high corticosterone responsiveness exhibit smaller hippocampi, regardless of trauma exposure, compared to rats with normative corticosterone levels. Similarly, the distribution of corticosteroid receptors in the hippocampus presented similarities between the LOW-CR and the HIGH-CR rats with higher mineralocorticoid receptors (MR) and less glucocorticoid receptors (GR). Although LOW- and HIGH-CR rats displayed a similar hippocampal profile at the structural and molecular levels, only LOW-CR male rats exhibited strong deficits in extinction consolidation compared to rats with 'normative' glucocorticoid responses (INTER-CR rats), and showed higher fear response both at few days and at several weeks after trauma exposure. We next tested the causal involvement of corticosterone in the fear extinction consolidation, and found that post-extinction corticosterone treatment markedly prevented the deficits in extinction memory and attenuated fear relapse. In addition, pharmacological inhibition of corticosterone levels during extinction memory consolidation, but not during training, in the INTER-CR rats led to extinction deficits at retrieval one day later. These results indicate that blunted corticosterone levels contribute to confer major vulnerability than having a small hippocampus, and that consolidation processes following extinction are mainly affected by low corticosterone levels.It is well known that glucocorticoids play an important role in memory consolidation processes and that sleep disturbances are a diagnostic criterion of PTSD. Therefore, we investigated in greater detail the sleep architecture in undisturbed condition and during the consolidation period of the extinction phase, which is known to be supported by sleep-dependent processes. In polysomnographic recordings, we found that rats with blunted corticos

EPFL2022

Beyond the patch: on landscape-explicit metapopulation dynamics

Jonathan Giezendanner

Climate change threatens biodiversity and species distribution all over the world at unprecedented rates. Human induced changes to landscape structure and habitat are redefining the relation between species and their environment. Understanding, characterizing and modeling the relation between complex landscape features and geographical species presence, the subject of this thesis, have thus gained paramount importance in order to make informed decisions on near- and far-term management strategies for species and landscape protection. The present thesis pays particular attention to the understanding of how mountain landscapes, described as heterogeneous habitat matrices, govern the presence of a species in space and time. To this end, throughout this thesis a metapopulation model is considered, a spatially-explicit model based on the balance between colonization and extinction events in areas of different suitability. The classical patch-based modelling approach is extended here in various ways in order to incorporate landscape-explicit information about the habitat matrix. A first theoretical study is performed on geometric, realistic, and real landscapes which highlights how different levels of connectivity, the degree to which different areas of similar habitat are actually linked together in the landscape (say, derived from geomorphic structures, such as valleys and peaks or emerging structures shaped by fluvial erosion and tectonic uplift) impact the dynamic of mountain species under climate change. A second, applied, study investigates how different landscape descriptors derived from Earth Observation data can be used in order to dynamically model the spatial, landscape-explicit, presence of two carabid species (Pterostichus flavofemoratus and Carabus depressus) in the Gran Paradiso National Park. In a final study, the consistency of the metapopulation model is investigated when considering different resolutions of the landscape matrix, i.e. different levels of coarse-graining. This last part is fundamental to the understanding of how conclusions drawn from local studies can be made general and extrapolated to larger regions. Overall, this thesis bridges the fields of population and landscape ecology, focusing on modelling metapopulation dynamics in complex landscapes seen as the substrate for ecological interactions. The result from the three studies show that metapopulation ecology can profit from the insights of landscape ecology. The combination of the two fields can be a useful tool in furthering the understanding and monitoring of mountain species.

EPFL2020

An evaluation of new particle formation events in Helsinki during a Baltic Sea cyanobacterial summer bloom

Lubna Dada, Marjan Marbouti

Several studies have investigated new particle formation (NPF) events from various sites ranging from pristine locations, including forest sites, to urban areas. However, there is still a dearth of studies investigating NPF processes and subsequent aerosol growth in coastal yet semi-urban sites, where the tropospheric layer is a concoction of biogenic and anthropogenic gases and particles. The investigation of factors leading to NPF becomes extremely complex due to the highly dynamic meteorological conditions at the coastline especially when combined with both continental and oceanic weather conditions. Herein, we engage in a comprehensive study of particle number size distributions and aerosol-forming precursor vapors at the coastal semi-urban site in Helsinki, Finland. The measurement period, 25 June-18 August 2019, was timed with the recurring cyanobacterial summer bloom in the Baltic Sea region and coastal regions of Finland. Our study recorded several regional/local NPF and aerosol burst events during this period. Although the overall anthropogenic influence on sulfuric acid (SA) concentrations was low during the measurement period, we observed that the regional or local NPF events, characterized by SA concentrations on the order of 10(7) molec. cm(-3), occurred mostly when the air mass traveled over the land areas. Interestingly, when the air mass traveled over the Baltic Sea, an area enriched with algae and cyanobacterial blooms, high iodic acid (IA) concentration coincided with an aerosol burst or a spike event at the measurement site. Further, SA-rich bursts were seen when the air mass traveled over the Gulf of Bothnia, enriched with cyanobacterial blooms. The two most important factors affecting aerosol precursor vapor concentrations, and thus the aerosol formation, were speculated to be (1) the type of phytoplankton species and intensity of bloom present in the coastal regions of Finland and the Baltic Sea and (2) the wind direction. During the events, most of the growth of sub-3 nm particles was probably due to SA, rather than IA or methane sulfonic acid (MSA); however much of the particle growth remained unexplained indicative of the strong role of organics in the growth of particles, especially in the 3-7 nm particle size range. Further studies are needed to explore the role of organics in NPF events and the potential influence of cyanobacterial blooms in coastal locations.

COPERNICUS GESELLSCHAFT MBH2022