Parasitism in plants is often accompanied by a suite of morphological and physiological changes resulting in a condition known as the ‘parasitic reduction syndrome’. With changes including extreme vegetative reduction, frequently beyond any resemblance to its photosynthetic relatives, accompanied by significant losses of genes linked to photosynthesis, the study of parasitic plants can be challenging. Conopholis (Orobanchaceae) is a small holoparasitic genus distributed across eastern and southwestern North America and Central America. This genus has never been the subject of a molecular phylogenetic or morphometric analyses. In addition, very little is known of the relationships among populations and of their post-glacial history. To investigate the species limits and phylogenetic relationships in Conopholis, we conducted a comprehensive molecular phylogenetic study of the genus as well as a fine-scale morphometric study. Based on plastid and nuclear sequences, Conopholis was found to contain three distinct and well-supported lineages which have varying degrees of overlap with previously proposed taxa. The clustering and ordination analyses of the morphometric study corroborated the molecular data, demonstrating the morphological differentiation between the three lineages detected within Conopholis. A taxonomic re-alignment is proposed for the genus that recognizes three species, C. americana, C. panamensis, and C. alpina. To address genetic diversity and phylogeographic structure of C. americana in eastern North America, microsatellite markers were developed and characterized for the first time in this species. Using these newly generated markers along with sequences from the plastid genome, the persistence of a minimum of two glacial refugia at the last glacial maximum were inferred, one in Florida and southern Alabama and another in the Appalachian Mountains near the southern tip of Blue Ridge Mountains. The diversity seen across the southern Appalachian Mountains supports the hypothesis that populations derived from the southern and northern refugia come together in this area.

No description available.

Este estudo apresenta indicações de mudanças paleoceanográficas ao longo dos últimos 25.000 anos na porção oeste do Oceano Atlântico Sul a partir do registro da variação de nanofósseis calcários em dois testemunhos de sedimento marinho da margem continental nordeste do Brasil. Outros indicadores foram incorporados às análises de nanofósseis calcários no intuito de melhor compreender as alterações observadas nas assembléias fósseis: 1) dados isotópicos de oxigênio de testas de foraminíferos planctônicos e bentônicos; 2) índice de temperatura e de nutrientes; 3) equação de paleoprodutividade e 4) análises estatísticas multivariadas. Os índices de temperatura e nutrientes foram, pela primeira vez, aplicados a nanofósseis calcários do Quaternário em amostras do Atlântico Sul. A integração dos resultados sugere que as principais características oceanográficas não sofreram alterações significativas nos últimos 25.000 anos, embora condições ambientais instáveis tenham sido registradas a partir da transição do Último Máximo Glacial - Holoceno. Durante o Último Máximo Glacial a região estudada sofreu pouca variação de temperatura, funcionando como um reservatório de calor. A variação da profundidade da termoclina/nutriclina foi considerada a principal resposta às oscilações climáticas, sendo relacionada às mudanças de intensidade dos ventos alísios. / This study focuses on changes in calcareous nannofossil assemblages as an evidence of paleoceanographic variability during the last 25,000 years in two deep sea piston cores from the northeastern Brazilian continental margin. To support reconstructing ancient marine environment others proxies have been applied along with the calcareous nannofossil analysis: 1) oxygen isotopic data from planktonic and benthic foraminifers\' tests; 2) temperature and nutrient indices; 3) paleoproductivity equation and 4) multivariate analysis. For the first time the temperature and nutrient indices were employed to Quaternary calcareous nannofossil from the South Atlantic Ocean. According to presented results major oceanographic features were stable in the last 25,000 years, although instable environmental conditions were recorded in the Last Glacial Maximum - Holocene boundary. During the Last Glacial Maximum the western tropical Atlantic seems to have experienced slight temperature changes and served as a heat and salt reservoir. Nutricline and thermocline depth variation was considered the most important response to climate changes largely related to Trade Winds strength oscillation.

As assembléias dos foraminíferos planctônicos fósseis de dois testemunhos amostrados do Atlântico tropical oeste representativo dos últimos 30.000 anos foram analisadas junto com estimativas de paleotemperatura superficial e ∂18O e ∂13C do foraminífero planctônico Globigerinoides ruber \'branca\'. Estes resultados mostraram que durante o Último Máximo Glacial e durante os eventos de resfriamento de curta duração Heinrich 1 and Younger Dryas o Atlântico tropical oeste manteve altas paleotemperaturas superficiais. Este estudo sugere que durante este período o Atlântico tropical oeste ocorreu uma acumulação de sal e clor nesta porção do Atlântico como conseqüência do enfraqueciemnto do transporte de calor e sal através do equador. Ao final destes eventos a intensificação do transporte de calor e sal foi restabelecido, baixando a temperatura superficial aos valores conhecidos atuamente. Este estudo sugere que o Atlântico tropical oeste atuou como um reservatório de calor e sal durante a deglaciação. / The planktonic foraminiferal assemblages of two piston cores from western tropical Atlantic covering the last 30,000 years have been analysed together with paleoceanographic ANN sea surface temperature reconstruction and ?18O and ?13C of the shallow dwelling planntonic foraminifera Globigerinoides ruber \'white\'. These proxies reveal that during the Last Glacial Maximum and during the Heinrich 1 and Younger Dryas cold events, the western tropical experienced warm periods. This study suggest that during these warm intervals a pronounced accumulation of heat and salt occurred at western tropical Atlantic, as a result of cross-equatorial heat and salt transport decrease. At the end of these events, the intensification of cross-equatorial heat and salt transport cooled and freshened the western tropical surface waters. This study suggests the western tropical Atlantic served as a heat and salt reservoir during deglaciation.

High resolution dating of loess on the Chinese Loess Plateau (CLP) using Optically Stimulated Luminescence (OSL) has increased the understanding of past monsoon climate but also raised questions regarding dust mass accumulation rate (MAR), the presence of disturbances or gaps in the sediment record, a possible teleconnection between North Atlantic and East Asian monsoon climate, and whether these events are due to climate variability, local settings, or age model uncertainties. This study undertakes a detailed (<20cm sampling resolution) -OSL investigation of the Lingtai section to create an independent age model using linear regression, to reconstruct monsoon climate changes using magnetic susceptibility(MS) and grain size (GS) proxies, as well as to calculate MAR for the site. The data shows that between 44-15 ka climate changes from a period of strong summer monsoon to a strong winter monsoon. GS data show variable trends attributed to changes in dust storm activity and local environmental conditions. MAR data does not correlate with grain size and is different from other loess records on the CLP. Such differences are either due to local variations or age model uncertainties. No clear correlation with Heinrich events or teleconnection with North Atlantic climate is visible in the records over the Last Glacial period, and hiatuses or gaps are not obviously present at this site. It is suggested that using linear regression for continuous age model construction from the luminescence ages comes with uncertainties due to subjective bias when fitting the lines and determining shifts in the data, especially during MAR calculations. Further studies are needed to ascertain optimal methods for creating age models, and to constrain the reasons behind the variability between different sites and loess records on the CLP. / Högupplöst OSL-datering av loessjordar från CLP har ökat förståelsen av dåtida monsunklimat, men har även lyft frågan gällande MAR, närvaron av avbrott eller småskaliga event i jordsektionerna, möjligheten av en relation mellan de Nordatlantiska och Ostasiatiska monsunklimaten, och om dessa förändringar sker till följd av faktisk klimatvariation, lokala förutsättningar, eller osäkerheter i åldersmodellen. Studien genomförde en detaljerad (<20cm) OSL-undersökning av Lingtai-sektionen för att skapa en oberoende åldersmodell, återge monsunklimatförändringarna genom tillämpning av MS och GS proxies, samt beräkna MAR från platsen. Resultaten påvisar att mellan 44-15 ka förändrades klimatet från en period av stark sommar- till en stark vinter-monsun. Kornstorleks-resultaten påvisar stora variationer vilka kan kopplas till en förändring i sandstormsaktivitet samt de lokala förutsättningarna för deposition av sediment. MAR-resultaten överensstämmer inte med kornstorleksdatan och skiljer sig från den övriga empirin, detta kan bero på lokala variationer i regionen eller osäkerheter i åldermodellen. Det finns ingen klar korrelation mellan "Heinrich events" eller en "teleconnection" i sektionen, och avbrott samt störningar i sektionen är inte förekommande. Avsaknaden av korrelation antyder att användningen av regressionslinjer för att skapa kontinuerliga åldermodeller kommer innebära fortsatta osäkerheter i empirin, speciellt gällande beräking av MAR. Ytterligare studier krävs för att bestämma optimala metoder för att framställa åldersmodeller, samt att utröna orsaken till skillnaden mellan resultat från olika platser på plat

The remnant montane forests of southern Lebanon provide habitat to a rich diversity of endemic, rare and threatened plant and animal species. Prior to the intensification of human activity during the mid-Holocene period these forests covered most of the Lebanon and Anti-Lebanon Mountain ranges. What is not known is how the dynamics of these forests changed in response to major shifts in climate. The aim of this DPhil thesis was to document changes in vegetation composition in southern Lebanon during the last glacial period (~112 to 35 ka BP). To achieve this aim, a palynological study was conducted on a sedimentary sequence recovered from Aammiq Wetland located in the Bekaa Valley, Lebanon. Fossil pollen was analysed to reconstruct variability in vegetation composition and abundance. Energy dispersive spectroscopy, magnetic susceptibility and loss-on-ignition were used to reconstruct the geomorphological and hydrological processes acting within the wetland and its watershed. Macro and microcharcoal were analysed to reconstruct local and regional fire histories respectively. A chronology was established for this sequence using a combination of radiocarbon and optically stimulated luminescence dating (OSL) techniques. The results indicate significant variability in the composition and abundance of vegetation through the time interval ~ 112 to ~ 35 ka BP closely aligned in time to global and regional climatic events. Changes in the chemical and physical properties of the sediments indicate significant variability in landscape erosion processes and hydrological conditions in the watershed and within the wetland over the similar interval in time. Peaks in local and regional fire activity were concurrent with periods of precession minima and Dansgaard-Oeschger warming events and had a significant impact on the composition of vegetation within the Aammiq region. These findings provide the first account of environmental change in the southern Bekaa Valley and adjacent slopes of the Lebanon Mountains during the last glacial period.

Cette recherche doctorale entend caractériser les fluctuations morphologiques des rennes paléolithiques du Sud-Ouest de la France consécutives aux changements climatiques. En effet, le dernier Pléniglaciaire et le Tardiglaciaire (entre 21 500 - 13 000 cal. BP) ont constitué des périodes de contraintes paléoclimatiques et paléoenvironnementales particulièrement fortes, qui ont occasionné, directement ou indirectement, des répercussions sur la taille corporelle des populations de rennes. Les séries analysées dans le cadre de ce travail proviennent tant du registre actuel que fossile. Plusieurs échantillons de populations actuelles (Norvège, Finlande, Groenland) ont ainsi été analysés, afin de tester notre méthodologie et d’envisager des comparaisons morphologiques avec les populations passées. Le corpus paléolithique comporte 29 assemblages naturels et anthropiques du Sud-Ouest de la France, datés majoritairement du dernier Pléniglaciaire et du Tardiglaciaire. La méthode du Variability Size Index appliquée récemment sur le Renne paléolithique posant des problèmes, s’agissant notamment de la détermination du sex-ratio d’un assemblage, du caractère significatif ou non des différences morphologiques -isométriques et allométriques - observées..., nous avons eu recours à une nouvelle méthodologie combinant plusieurs outils statistiques appliqués à un nouvel indice de taille (VSI* : Variability Size Index modifié). Les analyses ostéométriques et statistiques que nous avons effectuées tendent à identifier des fluctuations morphologiques temporelles attestant d’adaptations de l’espèce. D’un point de vue synchronique, nos résultats permettent de rejeter l’hypothèse précédemment soutenue de différences entre les rennes tardiglaciaires des Landes d’une part et du secteur Dordogne/Gironde d’autre part. Les données saisonnières tendent toutefois à indiquer une absence de migrations de grande ampleur des rennes selon cet axe Nord/Sud. L’existence de populations distinctes est toutefois proposée entre les rennes des Landes et ceux du Bassin de l’Aude. Le Sud-Ouest de la France, à la fin du Paléolithique supérieur, aurait été occupé de manière pérenne par des troupeaux de rennes, dont le comportement migratoire reste cependant à déterminer plus précisément. / This doctoral research aims at characterizing morphological fluctuations resulting from climate change in palaeolithic reindeers from Southwest France. Indeed, the Last Pleniglacial and the Last Glacial (between 21 500 - 13 000 cal. BP) constituted periods of particularly strong palaeoclimatic and palaeoenvironmental constraints, which ended, either directly or indirectly, in repercussions on the body size of reindeer populations. The series analyzed within the framework of this work result from both current and fossil registers. Several samples of current populations (Norway, Finland, and Greenland) were thus analyzed, in order to experiment our methodology and envisage morphological comparisons with the past populations. The palaeolithic corpus is composed of 29 natural and anthropological assemblages of Southwest France, dated mainly from the Last Pleniglacial and the Last Glacial. Since the Variability Size Index method recently applied to palaeolithic Reindeer raises issues, particularly relating to the determination of an assemblage’s sex-ratio, to the characterization or not of observed morphological differences –either isometric and allometric–, we decided to use a new methodology combining several statistical tools applied to a new size index (VSI*: modified Variability Size Index). Osteometric and statistical analyses that we performed tend to identify temporal morphological fluctuations, demonstrating adaptations of the specie. From a synchronic standpoint, our results allow to reject the hypothesis previously asserted regarding differences between Last Glacial reindeers from Landes on the one hand and the Dordogne/Gironde sector, on the other hand. Seasonal data however tend to indicate an absence of large-scale migrations of reindeers according to such a North/South axis. Nonetheless, the existence of different populations between reindeers of Landes and those of the Aude basin is proposed. Hence, Southwest France, at the end of the upper Palaeolithic, would have been occupied continuously by reindeer herds, the migratory behaviour of which however remains to determine more exactly.

No description available.

No description available.

How long has the extant flora been present in the Antarctic? Glaciological reconstructions propose that most areas in Antarctica were covered by thick ice sheets throughout the Last Glacial Maximum (LGM; ~22-18 kya) as well as previous glaciations, suggesting terrestrial life must have been extremely limited during these periods. In contrast, recent biogeographic and genetic studies support most extant groups of Antarctic terrestrial fauna having survived past glaciations in situ. However, studies on the origin and age of the Antarctic flora remain sparse. Applying population genetic, phylogeographic and divergence time analyses I assessed the global biogeography, origin and age of several abundant Antarctic moss species, including: four Polytrichaceae mosses, characterised by having bipolar distributions, the most common (~45% of species) distribution pattern amongst Antarctic mosses; the globally widespread moss Ceratodon purpureus; the bank-forming moss Chorisodontium aciphyllum, also known for its old sub-fossils in Antarctica and long-term viability from revival experiments; and, lastly, the genus Schistidium, the most species-rich moss genus in Antarctica, including many endemic species. Genetic analyses revealed evidence of long-term (multi-million year) survival of plants in Antarctica (several species of Schistidium, Ceratodon purpureus, and possibly Polytrichum juniperinum). However, evidence for a likely more recent (< 100 ky) arrival of Chorisodontium aciphyllum was also found. Some species revealed multiple separate dispersal events to the Antarctic, suggesting the region may be less isolated for spore-dispersed organisms than previously thought. Evidence for increased genetic diversity in the northern maritime Antarctic compared to other regions point at it including potential refugial areas. Furthermore, genetic patterns revealed geographic features that enable and limit the connectivity of bryophytes globally as well as in Antarctica. This study suggests that, despite the harsh polar climate during glaciation periods, many bryophytes have had a much longer presence in Antarctica than previously thought.