Past Climatic Events Research Articles

Mitochondrial DNA reveals high genetic divergence between populations of Chalcides mertensi Klausewitz, 1954 (Reptilia: Scincidae) from Tunisia

Genetic diversity of four populations of Chalcides mertensi (Klausewitz, 1954) from Tunisia was analyzed by means of the Restriction Fragment Length Polymorphism (RFLP) analysis of two fragments of mitochondrial DNA (mtDNA) encompassing NADH dehydrogenase subunits 1 and 2 (ND-1/2) and NADH dehydrogenase subunits 3, 4 and 4L (ND-3/4). Phylogenetic relationships between haplotypes were inferred by analysing the sequence of 396 base pairs at the 5′ end of the mitochondrial gene encoding cytochrome b and a segment of 12S rRNA gene (386 bp). The results of this study highlighted a pronounced genetic divergence between the populations from northern (Ain Soltane and Tabarka) and southern (Kasserine and Sidi Bouzid) Tunisia, that the phylogenetic analysis recovered as two distinct taxonomic entities. These two groups of populations can therefore be ascribed to two distinct taxa, with southern populations probably representing the typical C. mertensi, whereas northern individuals are likely to represent a new species of grass swimming Chalcides. The divergence between these two taxonomic entities can be referred to palaeogeographic and palaeoclimatic events that have affected northwestern Africa during the last 10 Million years. The analysed populations show a low genetic variability that can be related to the past climatic and geologic events and the colonization processes that took place with environmental amelioration, and to the peripheral position of these populations in the distributional range of the species. However, a more exhaustive study, including Algerian and Moroccan skink populations will be necessary in order to clarify these issues.

What is the climate system able to do ‘on its own’?

ABSTRACTThe climate of the Earth, like planetary climates in general, is broadly controlled by solar irradiation, planetary albedo and emissivity as well as its rotation rate and distribution of land (with its orography) and oceans. However, the majority of climate fluctuations that affect mankind are internal modes of the general circulation of the atmosphere and the oceans. Some of these modes, such as El Niño-Southern Oscillation (ENSO), are quasi-regular and have some longer-term predictive skill; others like the Arctic and Antarctic Oscillation are chaotic and generally unpredictable beyond a few weeks. Studies using general circulation models indicate that internal processes dominate the regional climate and that some like ENSO events have even distinct global signatures. This is one of the reasons why it is so difficult to separate internal climate processes from external ones caused, for example, by changes in greenhouse gases and solar irradiation. However, the accumulation of the warmest seasons during the latest two decades is lending strong support to the forcing of the greenhouse gases. As models are getting more comprehensive, they show a gradually broader range of internal processes including those on longer time scales, challenging the interpretation of the causes of past and present climate events further.This paper is part of a Thematic Cluster in honor of the late Professor Bert Bolin for his outstanding contributions to climate science.

Arctic Ocean Benthic Foraminiferal Faunae Change Associated with the Onset of Perennial Sea Ice in the Middle Miocene

Research Article| January 01, 2013 Arctic Ocean Benthic Foraminiferal Faunae Change Associated with the Onset of Perennial Sea Ice in the Middle Miocene Sev Kender; Sev Kender 4 1 British Geological Survey, Keyworth, Nottingham, NG12 5GG, U.K. 4 Correspondence author. E-mail: sev.kender@bgs.ac.uk Search for other works by this author on: GSW Google Scholar Michael A. Kaminski Michael A. Kaminski 2 Earth Sciences Department, King Fahd University of Petroleum and Minerals, P.O. Box 701, Dhahran 31261, Saudi Arabia3 Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, U.K. Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2013) 43 (1): 99–109. https://doi.org/10.2113/gsjfr.43.1.99 Article history received: 05 May 2012 accepted: 09 Oct 2012 first online: 13 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Sev Kender, Michael A. Kaminski; Arctic Ocean Benthic Foraminiferal Faunae Change Associated with the Onset of Perennial Sea Ice in the Middle Miocene. Journal of Foraminiferal Research 2013;; 43 (1): 99–109. doi: https://doi.org/10.2113/gsjfr.43.1.99 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Understanding how Arctic Ocean deep-water ecology responded to past climatic events is of importance in assessing the region’s sensitivity to environmental change. Here we present the first quantitative Miocene-Pliocene benthic foraminiferal records from the central Arctic Ocean, Lomonosov Ridge, IODP Hole M0002A. Despite significant dissolution and the absence of calcareous tests, these data show a significant faunal change occurred at ~14 Ma, characterized by a change from an older, relatively diverse assemblage including Reticulophragmium pusillum, Ammolagena clavata, and Recurvoides brideauxi, associated with open-ocean environments and a paleodepth probably >200 m, to a younger assemblage dominated by Rhabdammina spp. and the endemic Arctic benthic foraminifera Alveolophragmium polarensis. Sedimentologic proxies indicate the onset of perennial sea ice in the central Arctic Ocean likely occurred in conjunction with the faunal change, suggesting that this onset and increased ice rafting had a long-term impact on bottom-water ecology in the central Arctic Ocean. This ecologic change may have been related to changes in the type, quantity, and duration of organic carbon flux, which may also explain the documented increase in total sedimentary organic carbon at the same time, possibly indicative of increased productivity. In the younger section of M0002A, from ~12.6 Ma, abundances are too low for clear paleoecologic interpretations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

川西米亚罗林区不同海拔岷江冷杉生长对气候变化的响应

Tree rings which can record the past climatic events allows for retrospective analyses of climate-growth relationship.Generally,it is assumed that the relationships between tree growth and climate are elevation-independent and age-independent if the biological growth trend related to elevation and age is removed from the tree-ring data.However,if tree growth of different elevations or ages responds differently to climatic conditions,a dendroclimatic analysis based on samples at different elevations or with different ages may be biased in capturing climatic variability throughout the length of the chronology. In our study,tree cores of Abies faxoniana were taken from three different elevations(High altitude;Middle altitude;Low altitude) to represent the trees growth in Miyaluo of western Sichuan,China(total 132 cores,37 at Low altitude;51 at Middle altitude and 44 at High altitude).Three residual chronologies were developed from the cross-dated ring width series using the program ARSTAN,the longest was 170 years(1842—2011).Response analysis showed that the correlation between temperature and chronologies was almost negative,at low altitude there was the highest correlation coefficient.The positive correlation between PDSI(April and May of the current year) and the chronologies of Middle altitude and Low altitude showed that drought stresses inhibited the tree growth.In addition,a significantly positive response to precipitation(April of the current year) found at Low altitude explained that the precipitation was quite important for the tree growth. Furthermore,analysis of different age classes(old or young) showed that the response of old tree growth to climate change were more obvious than that of the young tree growth.It revealed that climate conditions would affect tree growth differently between different ages.Physiological processes and hydraulic constraints related to tree ages could possibly be the main causes of these age-dependent responses,so the relative sampling strategies should be considered.

Effects of species biology on the historical demography of sharks and their implications for likely consequences of contemporary climate change

Climate variation is an important factor shaping the demographic histories of many marine species, though impacts likely differ depending on species life history, habitat preferences and ecology. Investigating how species responded to historic climate fluctuations may provide critical insights into a species’ response to current climate change. Despite their ecological diversity, shark species share many similar life history characteristics and may be especially vulnerable to anthropogenic and climate impacts. We compared patterns of genetic variability, mismatch distributions and demographic reconstructions from coalescence approaches among temperate and tropical shark species with differing ecological characteristics, to investigate the effect of the past glaciation cycles on population abundance. Genetic diversity at two mitochondrial DNA regions (ND2 and control region) was assayed in four North Pacific species, Pacific spiny dogfish, Pacific sleeper sharks, salmon shark, and bluntnose sixgill shark. In addition, control region sequences acquired from GenBank for five shark species [tope shark (California/Australia), white shark (California), blacktip shark (eastern and western Gulf of Mexico), lemon shark (Bahamas), and whale shark] were analyzed. General patterns in genetic diversity, mismatch analyses and Bayesian skyline plots supported our hypothesis that species biology affected the impact of climate variation on demographic history. Consequently, our results suggest that effects of contemporary climate change on sharks may be to some degree predictable from species biology, distribution, habitat and the impact of past climate events.

Reconstruction of past climatic events using principal comp-onent analysis of the trace element profiles in a sediment core (Joides Basin, Antarctica)

Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ∼100 to ∼400 m on proceeding downslope from ∼600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ∼35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (<−1 °C), salty (>34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (−1.9 °C; 34.79) and approaching 1.5 m s−1 at descent angles as large as ∼60° relative to the isobaths. Such events were most common during November–May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real, may reflect the influence of the large iceberg C-19 over Drygalski Trough until its departure in mid-May 2003, when there was a marked decrease in the coldest, saltiest gravity current adjacent to Drygalski Trough. Northward transport of cold, saline, recently ventilated Antarctic Bottom Water observed in March 2004 off Cape Adare was ∼1.7 Sv, including ∼0.4 Sv of High Salinity Shelf Water.

Response of a desert shrub to past geological and climatic change: A phylogeographic study of Reaumuria soongarica (Tamaricaceae) in western China

Abstract Past geological and climatic events have promoted intraspecific divergence and range shifts in numerous plant species. This is particularly true for temperate species in climate‐sensitive regions. Few previous studies have examined whether such genetic footprints were also shaped in desert plants, which can survive in arid habitats and might be “static” under the past climatic oscillations. We therefore studied the phylogeographical history of Reaumuria soongarica, a shrub species that is widely distributed across the deserts of western China. We sequenced chloroplast DNA (cpDNA) fragments of 27 natural populations across western China. Eight cpDNA haplotypes were identified, which clustered into three clades. The clades were located in the western (clade II) or eastern regions (clades I and III) of western China. Analysis of molecular variance also supported this major partitioning (∼67%) of the cpDNA variation between regions. However, within each region, genetic differentiation was low (29%–37%) and a single dominant haplotype was fixed; this indicated past regional range expansion. The deep divergence and regional range expansions of this species may have corresponded to the most recent uplift of the Qinghai–Tibet Plateau and the development of desert ecosystems during the last glacial age in western China. This is the first study to show that the evolutionary history of plants in desert habitats has been seriously affected by past geological and climatic change.

Bioenergetic Response by Steelhead to Variation in Diet, Thermal Habitat, and Climate in the North Pacific Ocean

AbstractEnergetic responses of steelhead Oncorhynchus mykiss to climate‐driven changes in marine conditions are expected to affect the species’ ocean distribution, feeding, growth, and survival. With a unique 18‐year data series (1991–2008) for steelhead sampled in the open ocean, we simulated interannual variation in prey consumption and growth efficiency of steelhead using a bioenergetics model to evaluate the temperature‐dependent growth response of steelhead to past climate events and to estimate growth potential of steelhead under future climate scenarios. Our results showed that annual ocean growth of steelhead is highly variable depending on prey quality, consumption rates, total consumption, and thermal experience. At optimal growing temperatures, steelhead can compensate for a low‐energy diet by increasing consumption rates and consuming more prey, if available. Our findings suggest that steelhead have a narrow temperature window in which to achieve optimal growth, which is strongly influenced by climate‐driven changes in ocean temperature.

Loss of Genetic Diversity Means Loss of Geological Information: The Endangered Japanese Crayfish Exhibits Remarkable Historical Footprints

Intra-specific genetic diversity is important not only because it influences population persistence and evolutionary potential, but also because it contains past geological, climatic and environmental information. In this paper, we show unusually clear genetic structure of the endangered Japanese crayfish that, as a sedentary species, provides many insights into lesser-known past environments in northern Japan. Over the native range, most populations consisted of unique 16S mtDNA haplotypes, resulting in significant genetic divergence (overall F ST = 0.96). Owing to the simple and clear structure, a new graphic approach unraveled a detailed evolutionary history; regional crayfish populations were comprised of two distinct lineages that had experienced contrasting demographic processes (i.e. rapid expansion vs. slow stepwise range expansion) following differential drainage topologies and past climate events. Nuclear DNA sequences also showed deep separation between the lineages. Current ocean barriers to dispersal did not significantly affect the genetic structure of the freshwater crayfish, indicating the formation of relatively recent land bridges. This study provides one of the best examples of how phylogeographic analysis can unravel a detailed evolutionary history of a species and how this history contributes to the understanding of the past environment in the region. Ongoing local extinctions of the crayfish lead not only to loss of biodiversity but also to the loss of a significant information regarding past geological and climatic events.

Climate and refugial origin influence the mitochondrial lineage distribution of weasels (Mustela nivalis) in a phylogeographic suture zone

Overarching trends can be seen in European mammalian phylogeography, yet it is clear that species responded differently depending on adaptations to past environments. We built upon previous work on the phylogeography of weasels (Mustela nivalis) in Europe by using well-preserved museum specimens from a proposed phylogeographic suture zone. The complete cytochrome b gene was amplified from 49 individuals from present-day Poland and analyzed with previously published data on a European scale to identify glacial refugia and infer recolonization processes. Bayesian coalescent analysis revealed the importance of the Last Glacial Maximum and the Younger Dryas in the diversification of, and demographic changes in, identified mitochondrial lineages. Our analysis, in conjunction with the available fossil data, strongly points to a Carpathian origin for one of the lineages, and further highlights the importance of this region as a refugium for European mammals. Mustela nivalis originating from this refugium appear to have a selective advantage over M. nivalis from other lineages in certain environments in the suture zone in central Europe, with climate clearly influencing the distribution of mitochondrial DNA lineages. This has important implications not only for our understanding of how past climatic events shaped the genetic architecture of species, but also how they will respond to current and future climatic changes. (c) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 5769.

Phylogeographic patterns of decapod crustaceans at the Atlantic–Mediterranean transition

Comparative multispecies studies allow contrasting the effect of past and present oceanographic processes on phylogeographic patterns. In the present study, a fragment of the COI gene was analyzed in seven decapod crustacean species from five families and with different bathymetric distributions. A total of 769 individuals were sampled along the Atlantic–Mediterranean transition area in order to test the effect of three putative barriers to gene flow: Strait of Gibraltar, Almeria–Oran Front and Ibiza Channel. A significant effect of the Strait of Gibraltar was found in the crabs Liocarcinus depurator and Macropipus tuberculatus. The Ibiza Channel had a significant effect for L. depurator. However, the Almeria–Oran front was not found to have a significant effect on any of the studied species. Higher levels of population structure were found in shallow-water species, although the number of species sampled should be increased to obtain a conclusive pattern. The haplotypes within the different species coalesced at times that could be related with past climatic events occurring before, during and after the last glacial maximum. Given the large diversity of phylogeographic patterns obtained within decapods, it is concluded that both historical and contemporary processes (marine current patterns, bathymetry and life-history traits) shape the phylogeographic patterns of these crustaceans.

Why Analyze Mental Models of Local Climate Change? A Case from Southern Mozambique

AbstractPeople construct mental models of local climate change based on their observations and experiences of past climate events and changes. These mental models offer critical insight into locally important factors that trigger responses to new climate conditions and can be used to ground-truth regional climate models. In this paper, the authors explore mental models of changes to local climate patterns and climate-associated environmental changes over the past 45 years (1963–2008) in two rural communities in Matutúine District, Mozambique. Interview results are compared to data from a regional weather station. Residents discuss temperature increases, short-term and long-term precipitation changes, and altered seasonal timing. Measurable climate change in this region includes increasing temperatures and more erratic rainfall leading to drought and altered season timing. The climate-associated environmental changes residents observed draw attention to links between local livelihood practices and climate, as well as emphasize changes that would not necessarily appear in regional climate models. Such changes include reduced crop and wild fruit production, fewer cattle, variable forest size, increased wildfires and elephant conflict, drying up of water sources, poor health, and cultural change. Differences between adjacent communities highlight the potential interaction of landscape and vegetation variability, gender, and livelihoods in observations and experiences of climate change and demonstrate how mental models can provide insight into local ecological patterns and processes.

Molecular evidence of cryptic speciation, historical range expansion, and recent intraspecific hybridization in the Neotropical seasonal forest tree Cedrela fissilis (Meliaceae)

Molecular phylogeography can lead to a better understanding of the interaction between past climate events, large-scale vegetation shifts, and the evolutionary history of Neotropical seasonal forests. The endangered timber tree species Cedrela fissilis is associated with seasonal forests and occurs throughout South America. We sampled C. fissilis from 56 sites across the species’ range in Brazil and Bolivia and obtained sequence data for nuclear and chloroplast DNA. Most specimens (149 out of 169) exhibited intraindividual polymorphism for the nuclear internal transcribed spacer (ITS). Cloning and an array of complementary sequence analyses indicated that the multiple copies of ITS were functional paralogs – concerted evolution in C. fissilis appeared to be incomplete. Independent Bayesian analyses using either ITS or cpDNA data revealed two separate phylogenetic lineages within C. fissilis that corresponded to populations located in separate geographic regions. The divergence occurred in the Early Pliocene and Late Miocene. We argue that climate-mediated events triggered dispersal events and split ancestral populations into at least two large refugial areas of seasonal forest that were located to the east and west of the present day Cerrado. Upon recent climate amelioration, formerly isolated lineages reconnected and intraspecific hybridization gave rise to intraindividual polymorphism and incomplete concerted evolution in C. fissilis.

The genetics and genomics of Syngnathidae: pipefishes, seahorses and seadragons

The goal of this review was to provide a historical overview of how molecular techniques have increased the understanding of the ecology and evolution of the family Syngnathidae (pipefishes, seahorses and seadragons). Molecular studies based primarily on mitochondrial DNA markers have proved their worth by elucidating complex phylogenetic relationships within the family. Phylogeographic studies, which have revealed how life-history traits and past climatic events shape geographic distributions and patterns of genetic variation within syngnathid species, also provide interesting case studies for the conservation and management of threatened species. The application of microsatellite DNA markers has opened a floodgate of studies concerned with the breeding biology of these fishes, which are interesting due to their unique reproductive mode of male pregnancy. Research in this area has contributed significantly to the understanding of mating patterns and sexual selection. Molecular markers may also be employed in studies of demography, migration and local breeding population sizes. Genomic studies have identified genes that are probably involved in male pregnancy and promise additional insights into various aspects of syngnathid biology at the level of the gene. Despite these advances, much more remains to be explored. Goals for future research should include: (1) a more inclusive phylogeny to resolve outstanding issues concerning the relationships within the family and higher order taxa, (2) a broader use of molecular studies to aid management and conservation efforts, (3) the inclusion of more genera in comparative behavioural studies and (4) the continued development of genomic resources for syngnathids to facilitate comparative genomic work.

Range-wide chloroplast and mitochondrial DNA imprints reveal multiple lineages and complex biogeographic history for Douglas-fir

The contemporary genetic structure of species offers key imprints of how organisms responded to past geological and climatic events, which have played a crucial role in shaping the current geographical distribution of north-temperate organisms. In this study, range-wide patterns of genetic variation were examined in Douglas-fir (Pseudotsuga menziesii), a dominant forest tree species distributed from Mexico to British Columbia in western North America. Two organelle DNA markers with contrasting modes of inheritance were genotyped for 613 individuals from 44 populations. Two mitotypes and 42 chlorotypes were recovered in this survey. Both genomes showed significant population subdivision, indicative of limited gene flow through seeds and pollen. Three distinct cpDNA lineages corresponding to the Pacific Coast, the Rocky Mountains, and Mexico were observed. The split time of the two lineages from the Rockies lineage was dated back to 8.5 million years (Ma). The most recent common ancestors of Mexican and coastal populations were estimated at 3.2 and 4.8 Ma, respectively. The northern populations of once glaciated regions were characterized by a high level of genetic diversity, indicating a large zone of contact between ancestral lineages. A possible northern refugium was also inferred. The Mexican lineage, which appeared established by southward migration from the Rockies lineage, was characterized by the lowest genetic diversity but highest population differentiation. These results suggest that the effects of Quaternary climatic oscillations on the population dynamics and genetic diversity of Douglas-fir varied substantially across the latitudinal section. The results emphasize the pressing need for the conservation of Mexican Douglas-fir.

Assessment of tree response to drought: validation of a methodology to identify and test proxies for monitoring past environmental changes in trees

A thinning experiment stand at Avoca, Ballinvalley, on the east coast of the Republic of Ireland was used to test a developed methodology aimed at monitoring drought stress, based on the analysis of growth rings obtained by coring. The stand incorporated six plots representing three thinning regimes (light, moderate and heavy) and was planted in the spring of 1943 on a brown earth soil. Radial growth (early- and latewood) was measured for the purpose of this study. A multidisciplinary approach was used to assess historic tree response to climate: specifically, the application of statistical tools such as principal component and canonical correlation analysis to dendrochronology, stable isotopes, ring density proxy, blue reflectance and forest biometrics. Results showed that radial growth was a good proxy for monitoring changes to moisture deficit, while maximum density and blue reflectance were appropriate for assessing changes in accumulated temperature for the growing season. Rainfall also influenced radial growth changes but not significantly, and was a major factor in stable carbon and oxygen discrimination, mostly in the latewood formation phase. Stable oxygen isotope analysis was more accurate than radial growth analysis in drought detection, as it helped detect drought signals in both early- and latewood while radial growth analysis only detected the drought signal in earlywood. Many studies have shown that tree rings provide vital information for marking past climatic events. This work provides a methodology to better identify and understand how commonly measured tree proxies relate to environmental parameters, and can best be used to characterize and pinpoint drought events (variously described using parameters such as like moisture deficit, accumulated temperature, rainfall and potential evaporation).

Transformation of tectonic and climatic signals from source to sedimentary archive

Sedimentary rocks reflect past tectonic and climatic events. Numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream.

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

BackgroundReconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (Oreochromis niloticus) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales.ResultsUsing nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (RST = 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (RST = 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (RST = 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (F = 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m ~ 0.094 - 0.097) in the Volta populations.ConclusionsThis study revealed clear hierarchical patterns of the population genetic structuring of O. niloticus in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.

Turbiditic levee deposition in response to climate changes: The Var Sedimentary Ridge (Ligurian Sea)

The Var turbiditic system located in the Ligurian Sea (SE France) is an intermediate mud/sand-rich system. The particularity of the Var deep-sea fan is its single channel with abrupt bends and its asymmetric and hyper-developed levee on the right hand side: the Var Sedimentary Ridge. Long-term sediment accumulation on the Var Sedimentary Ridge makes this an ideal target for studying the link between onshore climate change and deep-sea turbidite stratigraphy. This paper focuses on the establishment of the first detailed stratigraphy of the levee, which is used to analyze the timing of overbank deposition throughout the last deglaciation. Main results indicate that high variability in turbidite frequencies and deposition rates along the Var Sedimentary Ridge are determined by two main parameters: 1) the progressive decrease of the levee height controlling the ability of turbidity currents to spill out from the channel onto the levee, and 2) climatic variations affecting the drainage basin, in particular changes in glacial condition since late Last Glacial Maximum to early Holocene. Compared to other deep-water areas, this study confirms the ability of turbiditic systems to record past climatic events on millennial timescales, and underlines the influence of European deglaciation on the observed decrease in turbidite activity in the Var canyon. The presence of a very narrow continental shelf and a single, large channel-levee system makes the Var Sedimentary Ridge a unique example of climate-controlled turbiditic accumulations.

Evolutionary history of the four-spotted megrim ( Lepidorhombus boscii) and speciation time within the genus based on mitochondrial genes analysis

The evolutionary history and geographic distribution of North-Atlantic and Mediterranean marine taxa has been largely affected by past geological and climatic events, like the Messinian salinity crisis, the opening of the Strait of Gibraltar and the Quaternary glacial cycles. The four-spotted megrim Lepidorhombus boscii is a demersal flatfish of the family Scophthalmidae (Pleuronectiformes), distributed in the Northeast Atlantic and the Mediterranean Sea. During its larval development it is planktonic, being passively drifted by marine currents, while adults are more or less sedentary living near the sea bottom. In order to investigate whether past geological and climatic events have influenced the evolutionary and demographic history of L. boscii, we analyzed a fragment of the highly variable mitochondrial control region in 163 individuals from different North-Atlantic areas and from the Mediterranean Sea. Contemporary processes of moderate gene flow, partially restricted by isolation by distance, as well as recent paleoecological events like the last Pleistocene glaciation, seem to play key roles in shaping the current phylogeographic pattern of the four-spotted megrim. On the other hand, we also analyzed 94 individuals from different North-Atlantic areas of its congeneric species L. whiffiagonis in order to compare genetic variation patterns within this genus. Finally, we used a fragment of the protein-coding mitochondrial gene cytochrome c oxidase I to estimate the time of speciation in megrims. Results suggest that divergence between the two species likely took place 5.3 MYA, which can be correlated with the end of the Messinian salinity crisis.