147 resultados para Mysticism--Judaism--History
Evolutionary history and its relevance in understanding and conserving southern African biodiversity
Resumo:
Abstract : Understanding how biodiversity is distributed is central to any conservation effort and has traditionally been based on niche modeling and the causal relationship between spatial distribution of organisms and their environment. More recently, the study of species' evolutionary history and relatedness has permeated the fields of ecology and conservation and, coupled with spatial predictions, provides useful insights to the origin of current biodiversity patterns, community structuring and potential vulnerability to extinction. This thesis explores several key ecological questions by combining the fields of niche modeling and phylogenetics and using important components of southern African biodiversity. The aims of this thesis are to provide comparisons of biodiversity measures, to assess how climate change will affect evolutionary history loss, to ask whether there is a clear link between evolutionary history and morphology and to investigate the potential role of relatedness in macro-climatic niche structuring. The first part of my thesis provides a fine scale comparison and spatial overlap quantification of species richness and phylogenetic diversity predictions for one of the most diverse plant families in the Cape Floristic Region (CFR), the Proteaceae. In several of the measures used, patterns do not match sufficiently to argue that species relatedness information is implicit in species richness patterns. The second part of my thesis predicts how climate change may affect threat and potential extinction of southern African animal and plant taxa. I compare present and future niche models to assess whether predicted species extinction will result in higher or lower V phylogenetic diversity survival than what would be experienced under random extinction processes. l find that predicted extinction will result in lower phylogenetic diversity survival but that this non-random pattern will be detected only after a substantial proportion of the taxa in each group has been lost. The third part of my thesis explores the relationship between phylogenetic and morphological distance in southern African bats to assess whether long evolutionary histories correspond to equally high levels of morphological variation, as predicted by a neutral model of character evolution. I find no such evidence; on the contrary weak negative trends are detected for this group, as well as in simulations of both neutral and convergent character evolution. Finally, I ask whether spatial and climatic niche occupancy in southern African bats is influenced by evolutionary history or not. I relate divergence time between species pairs to climatic niche and range overlap and find no evidence for clear phylogenetic structuring. I argue that this may be due to particularly high levels of micro-niche partitioning. Rsum : Comprendre la distribution de la biodiversit reprsente un enjeu majeur pour la conservation de la nature. Les analyses se basent le plus souvent sur la modlisation de la niche cologique travers l'tude des relations causales entre la distribution spatiale des organismes et leur environnement. Depuis peu, l'tude de l'histoire volutive des organismes est galement utilise dans les domaines de l'cologie et de la conservation. En combinaison avec la modlisation de la distribution spatiale des organismes, cette nouvelle approche fournit des informations pertinentes pour mieux comprendre l'origine des patterns de biodiversit actuels, de la structuration des communauts et des risques potentiels d'extinction. Cette thse explore plusieurs grandes questions cologiques, en combinant les domaines de la modlisation de la niche et de la phylogntique. Elle s'applique aux composants importants de la biodiversit de l'Afrique australe. Les objectifs de cette thse ont t l) de comparer diffrentes mesures de la biodiversit, 2) d'valuer l'impact des changements climatiques venir sur la perte de diversit phylogntique, 3) d'analyser le lien potentiel entre diversit phylogntique et diversit morphologique et 4) d'tudier le rle potentiel de la phylognie sur la structuration des niches macro-climatiques des espces. La premire partie de cette thse fournit une comparaison spatiale, et une quantification du chevauchement, entre des prvisions de richesse spcifique et des prdictions de la diversit phylogntique pour l'une des familles de plantes les plus riches en espces de la rgion floristique du Cap (CFR), les Proteaceae. Il rsulte des analyses que plusieurs mesures de diversit phylogntique montraient des distributions spatiales diffrentes de la richesse spcifique, habituellement utilise pour dicter des mesures de conservation. La deuxime partie value les effets potentiels des changements climatiques attendus sur les taux d'extinction d'animaux et de plantes de l'Afrique australe. Pour cela, des modles de distribution d'espces actuels et futurs ont permis de dterminer si l'extinction des espces se traduira par une plus grande ou une plus petite perte de diversit phylogntique en comparaison un processus d'extinction alatoire. Les rsultats ont effectivement montr que l'extinction des espces lies aux changements climatiques pourrait entraner une perte plus grande de diversit phylogntique. Cependant, cette perte ne serait plus grande que celle lie un processus d'extinction alatoire qu' partir d'une forte perte de taxons dans chaque groupe. La troisime partie de cette thse explore la relation entre distances phylogntiques et morphologiques d'espces de chauves-souris de l'Afrique australe. ll s'agit plus prcisment de dterminer si une longue histoire volutive correspond galement des variations morphologiques plus grandes dans ce groupe. Cette relation est en fait prdite par un modle neutre d'volution de caractres. Aucune vidence de cette relation n'a merg des analyses. Au contraire, des tendances ngatives ont t dtectes, ce qui reprsenterait la consquence d'une volution convergente entre clades et des niveaux levs de cloisonnement pour chaque clade. Enfin, la dernire partie prsente une tude sur la rpartition de la niche climatique des chauves-souris de l'Afrique australe. Dans cette tude je rapporte temps de divergence volutive (ou deux espces ont diverg depuis un anctre commun) au niveau de chevauchement de leurs niches climatiques. Les rsultats n'ont pas pu mettre en vidence de lien entre ces deux paramtres. Les rsultats soutiennent plutt l'ide que cela pourrait tre I d des niveaux particulirement levs de rpartition de la niche chelle fine.
Resumo:
Hatching is an important niche shift, and embryos in a wide range of taxa can either accelerate or delay this life-history switch in order to avoid stage-specific risks. Such behavior can occur in response to stress itself and to chemical cues that allow anticipation of stress. We studied the genetic organization of this phenotypic plasticity and tested whether there are differences among populations and across environments in order to learn more about the evolutionary potential of stress-induced hatching. As a study species, we chose the brown trout (Salmo trutta; Salmonidae). Gametes were collected from five natural populations (within one river network) and used for full-factorial in vitro fertilizations. The resulting embryos were either directly infected with Pseudomonas fluorescens or were exposed to waterborne cues from P. fluorescens-infected conspecifics. We found that direct inoculation with P. fluorescens increased embryonic mortality and induced hatching in all host populations. Exposure to waterborne cues revealed population-specific responses. We found significant additive genetic variation for hatching time, and genetic variation in trait plasticity. In conclusion, hatching is induced in response to infection and can be affected by waterborne cues of infection, but populations and families differ in their reaction to the latter.
Resumo:
During the past 20 years, BOLD fMRI has developed towards a central and fundamental tool in neuroscience. It has been shown that the BOLD response provides an indicator of neuronal activity in the brain. Consequently, for an accurate interpretation of findings in BOLD MRI experiments and to draw meaningful conclusions about the temporal evolution of neural events, a deep understanding of the nature of the BOLD contrast has become of essential importance. Since the dynamics of the major direct determinants of the BOLD signal (CBF, CBV and CMRO(2)) range between seconds and minutes, long duration stimulation was an early key strategy needed to study and understand the BOLD characteristics. This paper summarizes and discusses the thoughts and rationales of the long duration stimulation studies.
Resumo:
New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Monad transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55 Ma and metamorphosed by ca. 48-40 Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10 km) by 40-30 Ma in the Tso Monad dome (northern section of the transect) and by 30-20 Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.
Resumo:
Abstract Macroevolutionary and microevolutionary studies provide complementary explanations of the processes shaping the evolution of niche breadth. Macroevolutionary approaches scrutinize factors such as the temporal and spatial environmental heterogeneities that drive differentiation among species. Microevolutionary studies, in contrast, focus on the processes that affect intraspecific variability. We combine these perspectives by using macroevolutionary models in a comparative study of intraspecific variability. We address potential differences in rates of evolution of niche breadth and position in annual and perennial plants of the Eriogonoideae subfamily of the Polygonaceae. We anticipated higher rates of evolution in annuals than in perennials owing to differences in generation time that are paralleled by rates of molecular evolution. Instead, we found that perennial eriogonoid species present greater environmental tolerance (wider climate niche) than annual species. Niche breadth of perennial species has evolved two to four times faster than in annuals, while niche optimum has diversified more rapidly among annual species than among perennials. Niche breadth and average elevation of species are correlated. Moreover, niche breadth increases more rapidly with mean species elevation in perennials than in annuals. Our results suggest that both environmental gradients and life-history strategy influence rates and patterns of niche breadth evolution.
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Several internally fertilizing hermaphroditic animals can only perform one sexual role at a time. In such species, two individuals that engage in a copulation may have different interests in acting as male or female. A gender choice must be made which, if both individuals have the same preference, may give rise to a severe sexual conflict. Here we tested the hypothesis that gender choice could be influenced by mating history, using the freshwater snail, Physa acuta. We recorded the copulatory behaviour of 240 pairs composed of a focal individual and a partner, each either short- or long-isolated. We found that the time to the first copulation was unaffected by isolation status, suggesting that first contacts in this species are random processes. In contrast, the duration of copulations and the frequency of rejection behaviours suggested that individual gender preference switches from male biased to female biased as isolation increases. In addition, snails rejected copulations more frequently when presented to a partner with the same isolation status. Reciprocity, measured as the rate of gender swapping between the first and second copulations, was high irrespective of gender status. We suggest possible evolutionary causes for this gender preference switch and discuss its potential importance in natural population as well as its consequences for the maintenance of hermaphroditism
Resumo:
Rsum Les changements climatiques du Quaternaire ont eu une influence majeure sur la distribution et l'volution des biota septentrionaux. Les Alpes offrent un cadre spatio-temporel bien tudi pour comprendre la ractivit de la flore et le potentiel d'adaptation d'une espce vgtale face aux changements climatiques. Certaines hypothses postulent une diversification des espces en raison de la disparition complte de la flore des Alpes et d'un isolement important des espces dans des refuges mridionaux durant les dernires glaciations (Tabula Rasa). Une autre hypothse stipule le maintien de poches de rsistance pour la vgtation au coeur des Alpes (Nunataks). Comme de nombreuses espces vgtales prsentant un grand succs cologique semblent avoir ragi aux glaciations par la multiplication de leur gnome (autopolyplodie), leur tude en milieu naturel devrait permettre de comprendre les avantages inhrents la polyplodie. Biscutella laevigata est un modle emblmatique de biogographie historique, diverses tudes ayant montr que des populations diplodes sont actuellement isoles dans les zones restes dglaces durant le dernier maximum glaciaire, alors que des ttraplodes ont recolonis l'ensemble des zones alpines mises nu par le retrait des glaciers. Si le contexte priglaciaire semble avoir favoris ce jeune complexe autopolyplode, les circonstances et les avantages de cette mutation gnomique ne sont pas encore clairs. Y a-t-il eu de multiples vnements de polyplodisation ? Dans quelle mesure affecte(nt)il(s) la diversit gntique et le potentiel volutif des polyplodes ? Les polyplodes ont-ils une grande flexibilit gnomique, favorisant une radiation adaptative, ou doivent-ils leur succs une grande plasticit cologique ? Cette tude aborde ces questions diffrentes chelles spatiales et temporelles. L'chelle rgionale des Alpes occidentales permet d'aborder les facteurs distaux (aspects historiques), alors que l'chelle locale cherche apprhender les facteurs proximaux (mcanismes volutifs). Dans les Alpes occidentales, des populations ont t densment chantillonnes et tudies grce (1) leur cytotype, (2) leur appartenance taxonomique, (3) leur habitat et (4) des marqueurs molculaires de l'ADN chloroplastique, en vue d'tablir leurs affinits volutives. l'chelle locale, deux systmes de population ont t tudis : l'un o les populations persistent en priphrie de l'aire de distribution et l'autre au niveau du front actif de colonisation, en marge altitudinale. Les rsultats l'chelle des Alpes occidentales rvlent les sites d'intrt (refuges glaciaires, principales barrires et voies de recolonisation) pour une espce reprsentative des pelouses alpines, ainsi que pour la biodiversit rgionale. Les Pralpes ont jou un rle important dans le maintien de populations proximit immdiate des Alpes centrales et dans l'volution du taxon, voire de la vgtation. Il est aussi dmontr que l'poque glaciaire a favoris l'autopolyplodie polytopique et la recolonisation des Alpes occidentales par des lignes distinctes qui s'hybrident au centre des Alpes, influenant fortement leur diversit gntique et leur potentiel volutif. L'analyse de populations locales en situations contrastes l'aide de marqueurs AFLP montre qu'au sein d'une ligne prsentant une grande expansion, la diversit gntique est faonne par des forces volutives diffrentes selon le contexte cologique et historique. Les populations persistant prsentent une dispersion des gnes restreinte, engendrant une diversit gntique assez faible, mais semblent adaptes aux conditions locales de l'environnement. l'inverse, les populations colonisant la marge altitudinale sont influences par les effets de fondation conjugus une importante dispersion des gnes et, si ces processus impliquent une grande diversit gntique, ils engendrent une rpartition alatoire des gnotypes dans l'environnement. Les autopolyplodes apparaissent ainsi comme capables de persister face aux changements climatiques grce certaines facults d'adaptation locale et de grandes capacits maintenir une importante diversit gntique lors de la recolonisation post-glaciaire. Summary The extreme climate changes of the Quaternary have had a major influence on species distribution and evolution. The European Alps offer a great framework to investigate flora reactivity and the adaptive potential of species under changing climate. Some hypotheses postulate diversification due to vegetation removal and important isolation in southern refugia (Tabula Rasa), while others explain phylogeographic patterns by the survival of species in favourable Nunataks within the Alps. Since numerous species have successfully reacted to past climate changes by genome multiplication (autopolyploidy), studies of such taxa in natural conditions is likely to explain the ecological success and the advantages of autopolyploidy. Early cytogeographical surveys of Biscutella laevigata have shed light on the links between autopolyploidy and glaciations by indicating that diploids are now spatially isolated in never-glaciated areas, while autotetraploids have recolonised the zones covered by glaciers- during the last glacial maximum. A periglacial context apparently favoured this young autopolyploid complex but the circumstances and the advantages of this genomic mutation remain unclear. What is the glacial history of the B. laevigata autopolyploid complex? Are there multiple events of polyploidisation? To what extent do they affect the genetic diversity and the evolutionary potential of polyploids? Is recolonisation associated with adaptive processes? How does long-term persistence affect genetic diversity? The present study addresses these questions at different spatiotemporal scales. A regional survey at the Western Alps-scale tackles distal factors (evolutionary history), while local-scale studies explore proximal factors (evolutionary mechanisms). In the Western Alps, populations have been densely sampled and studied from the (1) cytotypic, (2) morphotaxonomic, (3) habitat point of views, as well as (4) plastid DNA molecular markers, in order to infer their relationships and establish the maternal lineages phylogeography. At the local scale, populations persisting at the rear edge and populations recolonising the attitudinal margin at the leading edge have been studied by AFLPs to show how genetic diversity is shaped by different evolutionary forces across the species range. The results at the regional scale document the glacial history of a widespread species, representative of alpine meadows, in a regional area of main interest (glacial refugia, main barriers and recolonisation routes) and points out to sites of interest for regional biodiversity. The external Alps have played a major role in the maintenance of populations near the central Alps during the Last Glacial Maximum and influenced the evolution of the species, and of vegetation. Polytopic autopolyploidy in different biogeographic districts is also demonstrated. The species has had an important and rapid radiation because recolonisation took place from different refugia. The subsequent recolonisation of the Western Alps was achieved by independent lineages that are presently admixing in the central Alps. The role of the Pennic summit line is underlined as a great barrier that was permeable only through certain favourable high-altitude passes. The central Alps are thus viewed as an important crossroad where genomes with different evolutionary histories are meeting and admixing. The AFLP analysis and comparison of local populations growing in contrasted ecological and historical situations indicate that populations persisting in the external Alps present restricted gene dispersal and low genetic diversity but seem in equilibrium with their environment. On the contrary, populations colonising the attitudinal margin are mainly influenced by founder effects together with great gene dispersal and genotypes have a nearly random distribution, suggesting that recolonisation is not associated with adaptive processes. Autopolyploids that locally persist against climate changes thus seem to present adaptive ability, while those that actively recolonise the Alps are successful because of their great capacity to maintain a high genetic diversity against founder effects during recolonisation.
