Despite the large body of research devoted to understanding the role of Quaternary glacial cycles in the genetic divergence of European trees, the differential contribution of geographic isolation ...and/or environmental adaptation in creating population genetic divergence remains unexplored. In this study, we used a long-lived tree (Taxus baccata) as a model species to investigate the impact of Quaternary climatic changes on genetic diversity via neutral (isolation-by-distance) and selective (isolation-by-adaptation) processes.
We applied approximate Bayesian computation to genetic data to infer its demographic history, and combined this information with past and present climatic data to assess the role of environment and geography in the observed patterns of genetic structure.
We found evidence that yew colonized Europe from the East, and that European samples diverged into two groups (Western, Eastern) at the beginning of the Quaternary glaciations, c. 2.2 Myr before present. Apart from the expected effects of geographical isolation during glacials, we discovered a significant role of environmental adaptation during interglacials at the origin of genetic divergence between both groups.
This process may be common in other organisms, providing new research lines to explore the effect of Quaternary climatic factors on present-day patterns of genetic diversity.
Palynological long sequences offer a unique possibility to study the effect of pronounced climate change on vegetation dynamics over several glacial-interglacial cycles. Such long sequences are rare, ...especially outside of the Mediterranean realm. Additionally, they often lack robust chronologies, which are a precondition for comparisons across records and proxies. In this study we present a refined chronology of the Velay pollen sequence (0–423 ka) from south-central France by tuning it to the recently published Lake Ohrid pollen sequence from the southern Balkans, which itself has a vegetation-independent, numerical chronology. Furthermore, we use ordination techniques in combination with independent palaeo-temperature proxies and seasonality as explanatory variables for both sites. This allows us to infer climatic responses of interglacial vegetation over a broad ecological gradient, i.e., from a cool-temperate to a submediterranean site. Our analysis shows that temperature is a significant determinant for interglacial vegetation composition at both sites but explains slightly more variance at cool-temperate Velay compared to submediterranean Lake Ohrid, where precessional-driven moisture availability might have had a greater influence. Temperate oceanic taxa such as Abies and Taxus were most affected by comparably cool or warm interglacials at Velay, whereas at Lake Ohrid, the same accounts for Mediterranean taxa such as Quercus ilex, Q. cerris, or Ostrya/Carpinus orientalis. Responses of single taxa and vegetation groups to seasonality changes over the last five interglacials suggest that species-specific niche preferences have remained stable since 423 ka. Additionally, we suggest that unless a future climate exceeds the MIS 5e anomaly of c. +1.3 °C (if compared to the Holocene), evergreen Mediterranean taxa such as Quercus ilex will not expand into temperate biomes north of the Alps. However, even temperature rises below +1.3 °C will cause a restructuring of the current vegetation in both areas.
•We present a novel age-depth model for the palynological long sequence of Velay, Massif Central, France.•We use climate proxy data to quantify the impact of temperature on interglacial vegetation across two biomes.•Temperate oceanic vegetation was most affected interglacial intensity in the Massif Central.•Our results suggest that species-specific responses to seasonality have remained constant since 423 ka.
New investigations performed with a multi-proxy approach provide a robust climate reconstruction for the Late-Glacial in the Massif Central, France. The temperature reconstruction from Coleoptera is ...obtained from the Mutual Climatic Range Method, or “MCR” method, based on the range of climates corresponding to the area occupied today by the species identified in fossil assemblages. The Weighthed Averaging Partial Least Squared (WA-PLS) method is used to produce mean July temperature estimates from Chironomid assemblages. Climate reconstruction from pollen data is performed using an assemblage approach, the Modern Analogue Technique. During the Late-Glacial the July temperature (Tmax) reconstructed from beetles (Coleoptera) was lower than the current Tmax of 18.9 °C. Summer conditions were close to the present at the beginning of the Oldest Dryas (17400–14600 cal. BP), and during most of the Allerød (13900–12800 cal. BP). During the Younger Dryas (12800–11700 cal. BP) Tmax estimates ranged from 12 to 13 °C, much lower than today. The Tmax increased at the onset of the Holocene (11700 cal. BP), reaching values close to the modern conditions from the beginning of the period. Tmax reconstructed from chironomids shows an initial warming around 15000 cal. BP, with a Tmax rise from 7 °C to 11 °C. A maximum (13.5 °C) was reached around 13800 cal. BP. A second optimum of 16 °C occurred after 10800 cal. BP. The Late-Glacial Interstadial (LGI) is marked by temperature decreases (from 13 to 12 to 10–9 °C) around 13200–12900 cal. BP. A second climate minimum was reached around 12600 cal. BP, during the Younger Dryas (Tmax about 10 °C). The end of the Younger Dryas seems to have been warmer, with a Tmax of about 13 °C, just before the early Holocene climate improvement. Pollen-inferred results showed that the Late-Glacial climate at Roustières was characterized by colder and drier winter and summer seasons than today, and by conditions close to the modern ones around 11700 cal. BP, at the onset of the Holocene. Climate conditions comparable to the modern ones were also evidenced at the end of the Allerød, with colder than today conditions evidenced from both Tmax and Tmin (January temperature). During the Oldest and Younger Dryas the coldest month showed a temperature of −13 °C, while summers appeared more moderate (warmest month around 16 °C). Cold conditions were also reconstructed during the Bølling, while temperatures comparable to present-day values were reached during the Allerød. A cold oscillation occurred around 13400 cal. BP. Particularly dry conditions were reconstructed during the Oldest Dryas (17000–15800 cal. BP). From 15800 to the end of the Younger Dryas, the precipitation oscillated around 750 mm, but increased during the Allerød and the Holocene periods. These climatic trends reconstructed by the three proxies allowed identifying the temperate periods (LGI and the Holocene) and the cold events (Younger Dryas) of the Late-Glacial period. However, difficulties due to different sampling resolutions emerged, and several discrepancies linked to the proxy or the methods used are discussed.
• Here, palaeobotanical and genetic data for common beech (Fagus sylvatica) in Europe are used to evaluate the genetic consequences of long-term survival in refuge areas and postglacial spread. • ...Four large datasets are presented, including over 400 fossil-pollen sites, 80 plant-macrofossil sites, and 450 and 600 modern beech populations for chloroplast and nuclear markers, respectively. • The largely complementary palaeobotanical and genetic data indicate that: (i) beech survived the last glacial period in multiple refuge areas; (ii) the central European refugia were separated from the Mediterranean refugia; (iii) the Mediterranean refuges did not contribute to the colonization of central and northern Europe; (iv) some populations expanded considerably during the postglacial period, while others experienced only a limited expansion; (v) the mountain chains were not geographical barriers for beech but rather facilitated its diffusion; and (vi) the modern genetic diversity was shaped over multiple glacial-interglacial cycles. • This scenario differs from many recent treatments of tree phylogeography in Europe that largely focus on the last ice age and the postglacial period to interpret genetic structure and argue that the southern peninsulas (Iberian, Italian and Balkan) were the main source areas for trees in central and northern Europe.
Human activities are known to modify soil properties; however, the associated modifications to soil processes are poorly documented, as they must be studied over long time scales. Lake Verney, which ...is on the Italian side of the Petit Saint-Bernard Pass in the French-Italian Alps (2188ma.s.l.) provides a sediment record of the last 11,000cal.yrs BP. Analysis of multiple proxies within this sediment sequence, including sedimentological characteristics, mineral geochemistry (as determined using XRF and extractable Fe fractions), pollen and non-pollen palynomorphs (NPPs) and sediment DNA (sedDNA) analysis, is compared with analyses of current soils and paleosols within this mountain ecosystem in order to understand the main drivers of long-term pedogenesis. We performed principle component analysis on both the sediment proxies and the soil geochemical properties to identify different sediment endmembers that reflect different types of soil horizons, mainly stagnic and spodic. These horizons are characteristic of specific soil processes and their associated land uses.
During the first part of the Holocene, a decrease in the carbonate fraction in the sediment reflects the loss of carbonate material from soils that occurred as early as postglacial vegetation became established. The migration of Fe-complexes until 6000cal.yrs BP indicates the development of Podzols in the catchment. The first signs of human land use are detected at 4300cal.yrs BP according to analyses of sedDNA and NPPs. Increases in the input of terrestrial organic matter, associated with forest clearance suggests degradation of the surface horizons of the Podzols. Erosion increased during the Roman Period due to sheep grazing. Then, while erosion was still increasing, Podzols developed into Stagnosols after the Middle Ages with cow grazing which is consistent with the current functioning of the soils. The history of the paleosols and archaeological stratigraphy within the study area confirm the model of soil evolution inferred from the lake sediments and allow us to characterize the human-induced “metapedogenetic phase” of the evolution of the soil cycle. Anthropo-pedogenesis may define the development of soils during the Anthropocene. The main consequence of this change in the functioning of the soils is a reduced sequestration of soil carbon.
•Forest clearing since the mid-Holocene was associated with sheep then cattle grazing.•Grazing activities triggered the erosion of soils and modified soil evolution.•Podzols were eroded and Stagnosols developed from the degraded spodic horizons.•Podzolization and forest seem to have been briefly recovered during the “Dark ages”.•Soil cycle evolution evidence suggest anthropo-pedogenetic phases since ca. 4ka.
Glacial refuge areas are expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. To test this hypothesis, we studied chloroplast DNA variation in 22 widespread ...European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. However, the genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugia.
Retrospective science such as palaeoecology deeply depends on the preservation of archives in sensitive places. As an example, mountains of medium altitude from Mediterranean peninsulas have long ...been identified by biogeographers as refuges zones allowing the survival of European temperate taxa during the ice ages, but archives to validate this hypothesis are scarce, especially in Southern Italy. Here we present a new sequence from Lago Trifoglietti (1048 m a.s.l.) in the Calabrian Mountains, which covers the Late Glacial Interstadial (LGI, corresponding to the Bölling-Alleröd period in northern-central Europe) and the transition to the Holocene. The independent chronology based on seven radiocarbon dates is supported by the evidence of three tephra layers already identified in other regional sequences. During the LGI, besides the high diversity of non arboreal pollen grains, a great number of pollens of temperate forest trees are present or abundant (mostly deciduous oaks and fir). These assemblages suggest that the site was above but not far from the upper limit of diversified woodland stands. They confirm a local survival during the last glacial. The Younger Dryas is not marked by major changes, and oak percentages are even higher, suggesting a resilient expansion at lower altitude. Surprisingly the site remains above the timberline until an aridity crisis centered at 11,100 cal 14C yr PB, which is correlated with the Preboreal Oscillation (PBO). This event is immediately followed by the local settlement of a dense fir and beech forest around the lake. A comparison with other Italian key sequences aims at explaining the climate forcing factors that governed this original vegetation dynamic. Further investigations using additional proxies are needed for a more robust climate reconstruction.
•As mentioned in the letter to editor out manuscript has been modified, taking into account the useful remarks of our reviewers.•We are still convinced that, beside interesting botanical results, this manuscript opens serious questions on the climate dynamics in Southern Italy at the Lateglacial-Holocene transition and is of interest.•It will be a starting point for the exploration of other proxidata at Trifoglietti to deepen our understanding on this key period.
This study investigates sediment cores from the Mediterranean alpine lakes located in upvalley cirques upper than 1700 metres a.s.l. using sedimentological, palynological and geomorphological ...studies, in order to document environmental changes following the last phase of glacier retreat. These results are considered in the framework of the deglaciation characterized from 16 sediment cores from high-altitude lakes and mires including 104 14C ages and geomorphological studies of the Mediterranean Alps. Considering each sediment core proxy as an independent observation, i.e., comparisons between 14C ages and palynostratigraphy, between 14C ages and lithostratigraphy, between palynostratigraphy and lithostratigraphy, these data are aimed at contributing to a better understanding of the timing of postglacial environmental changes. The 14C ages combined with pollen biostratigraphy indicate that the deglaciation of cirque catchments is dated between 14,500 and 13,000 cal. BP, i.e., during the Lateglacial Interstadial (Greenland Interstadial-1e). The sixteen lacustrine and mire sediment records are systematically characterized by three units from bottom to top: organic-poor blue clay, beige to light-brown silty clay and organic rich dark brown gyttja lithotype. During the Younger Dryas, lakes located below 2300 m a.s.l. were ice-free and their pollen record indicates steppe conditions. The sedimentary facies also informs on the timing of glacial-dominated processes. The onset of organic-rich gyttja is dated at 11,000 cal. BP suggesting the last influence of cirque glaciers in these lakes at the beginning of the Holocene. The timing of the onset of this organic rich unit differs in sites (±2000 years) probably due to an altitudinal and exposure gradient of the glacial cirques. The presence of gyttja from 11,000 cal. BP to Present indicates biogenic infilling lake for all the Holocene. Even though the literature have indicated rock glacier advances occurred during the Holocene (Subboreal and LIA) in the south of the Alps, no significant sedimentological patterns related to glacier fluctuations are recorded in Lake Vens. The glacier fluctuations in the Mediterranean Alps are concomitant with those dated in the non-Mediterranean Alps, thus suggesting a main common climate forcing. However, the increase in terrigenous sediment inputs since 1800 cal. BP is mainly due to human activities.
•Deglaciation of Alpine Mediterranean cirques is dated between 14.5 and 13ka.•No glacier advance is recorded by sediment cores in cirques since the Younger Dryas.•Lake Vens records environmental changes in Mediterranean Alps over the last 14ka.
We present a range-wide synthesis of our own research and related work on the complex postglacial history of
Abies alba Mill. It is based on macroremains, fossil pollen records as well as on ...different genetic markers. The geographic distribution of genetic lineages and allele frequencies together with the fossil records confirm multiple refugia with at least three of them being sources for the Holocene range expansion into Central Europe, representing so-called effective refugia. One is located in the northern Apennines. A long-term refugium in the southern Balkans contributes to northward expansion with a branch along the Carpathians in the East and the Dinaric Alps in the West. Furthermore, new allozyme data indicate a third effective refugium in the northern or western Balkans, respectively. Using different genetic marker categories the differentiation of
A. alba populations could be attributed to different time scales. A separation of maternal lineages took place in previous glacial cycles of the Quaternary, while a second pattern of genetic differentiation is the result of isolation processes during the last glaciation and subsequent gene flow after range expansion. Suture and introgression zones of refugial gene pools were clearly recognised. The patterns of genetic variation and genetic diversity spanning between rear and leading edges of the present range are discussed for evolutionary implications and conservation strategies.
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