Cryptic northern refugia and the origins of the modern biota
TL;DR: Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugias in northern Europe during the Late Pleistocene, which could partially explain the ‘nonanalogue' mammalian assemblages of the Late pleistocene.
Abstract: Viewed from a geological perspective, present-day animal and plant communities in many parts of the world have a remarkably short history. The environmental revolution at the end of the Pleistocene, a mere 10 000 years ago, triggered major shifts in the ranges of species and hence composition of communities. Present-day communities in the boreal and temperate zones assembled at this time by combining species that survived the northern environment of the Last Cold Stage with those returning from more temperate refugia. Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugia in northern Europe during the Late Pleistocene. These northern refugia would have been in areas of sheltered topography that provided suitable stable microclimates, and could partially explain the ‘nonanalogue' mammalian assemblages of the Late Pleistocene. They also have implications for phylogeography and speciation.
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TL;DR: Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking, and a better fusion of experimentation and theory will advance understanding of the causes of range limits.
Abstract: Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.
1,534 citations
TL;DR: Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them, which has implications for the role ofRefugia in the evolution of species and their genetic diversity.
Abstract: Climate change in the past has led to significant changes in species' distributions. However, how individual species respond to climate change depends largely on their adaptations and environmental tolerances. In the Quaternary, temperate-adapted taxa are in general confined to refugia during glacials while cold-adapted taxa are in refugia during interglacials. In the Northern Hemisphere, evidence appears to be mounting that in addition to traditional southern refugia for temperate species, cryptic refugia existed in the North during glacials. Equivalent cryptic southern refugia, to the south of the more conventional high-latitude polar refugia, exist in montane areas during periods of warm climate, such as the current interglacial. There is also a continental/oceanic longitudinal gradient, which should be included in a more complete consideration of the interaction between species ranges and climates. Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them. This has implications for the role of refugia in the evolution of species and their genetic diversity.
1,036 citations
Cites background or methods from "Cryptic northern refugia and the or..."
...The problem, in our view, with assigning glacial refugia to coldadapted species is that they generally have a larger distribution during cold stages than during periods of warm climate (e.g. Stewart & Lister 2001; Dalén et al. 2005; Stewart & Dalén 2008)....
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...The concept, as originally conceived by Stewart & Lister (2001) was applied to taxa that were not generally accepted as living in central or northern Europe during the last glaciation....
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...Cryptic northern refugia may often comprise sheltered habitats located in deeply incised valleys that provided microclimates for temperate species, allowing them to survive at latitudes where they would normally have perished (Stewart & Lister 2001)....
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...An important category of refugia are the cryptic refugia as defined by Stewart & Lister (2001)....
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...In fact, the original inclusion of pine (Pinus sylvestris) living on the Norwegian coast during the last glaciation (Stewart & Lister 2001), was already stretching the definition of a cryptic northern refugium as this taxon is not strictly temperate and is relatively cold-tolerant....
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TL;DR: Many of the insights into the glacial histories of species in cryptic refugia gained through phylogeographic approaches are summarised.
Abstract: The glacial episodes of the Quaternary (2.6 million years ago–present) were a major factor in shaping the present-day distributions of extant flora and fauna, with expansions and contractions of the ice sheets rendering large areas uninhabitable for most species. Fossil records suggest that many species survived glacial maxima by retreating to refugia, usually at lower latitudes. Recently, phylogeographic studies have given support to the existence of previously unknown, or cryptic, refugia. Here we summarise many of these insights into the glacial histories of species in cryptic refugia gained through phylogeographic approaches. Understanding such refugia might be important as the Earth heads into another period of climate change, in terms of predicting the effects on species distribution and survival.
980 citations
TL;DR: In this paper, a detailed analysis of the scientific literature (1993-2007) in order to identify refugia in the Mediterranean region, based on intraspecific phylogeographical studies of plant species, is presented.
Abstract: Aim The aims of this study were to assess the distribution of putative Mediterranean refugia of plants, to compare the locations of refugia and those of regional hotspots of plant biodiversity, and to provide a critical analysis of the Mediterranean refugium paradigm. Furthermore, we consider how biogeographical and genetic results can be combined to guide global conservation strategies. Location The Mediterranean region. Methods We started from a detailed analysis of the scientific literature (1993-2007) in order to identify refugia in the Mediterranean region, based on intraspecific phylogeographical studies of plant species. We used population locations together with gene-pool identity to establish the database, comparing patterns of phylogeographical concordance with the locations of Mediterranean refugia. We then tested the biogeographical congruence between two biodiversity components, namely phylogeographical refugia and regional hotspots. Results We identified 52 refugia in the Mediterranean bioclimatic region and confirmed the role played by the three major peninsulas, with a shared total of 25 refugia. We emphasize the importance of areas that have previously been attributed a lesser role (large Mediterranean islands, North Africa, Turkey, Catalonia). Of the 52 refugia identified, 33 are situated in the western Mediterranean Basin and 19 in the eastern part. The locations of the phylogeographically defined refugia are significantly associated with the 10 regional hotspots of plant biodiversity, with 26 of these refugia (i.e. 50%) occurring within the hotspots. Main conclusions The locations of refugia are determined by complex historical and environmental factors, the cumulative effects of which need to be considered because they have occurred since the Tertiary, rather than solely during the last glacial period. Refugia represent climatically stable areas and constitute a high conservation priority as key areas for the long-term persistence of species and genetic diversity, especially given the threat posed by the extensive environmental change processes operating in the Mediterranean region. The refugia defined here represent 'phylogeographical hotspots'; that is, significant reservoirs of unique genetic diversity favourable to the evolutionary processes of Mediterranean plant species.
968 citations
Cites background from "Cryptic northern refugia and the or..."
...…m year)1 obtained with fossil pollen data sets, the genetic structures of modern tree populations provide evidence that colonization was driven mainly by slower dispersal from disjunct and cryptic glacial refugia, which are quite poorly identified by palynological data (Stewart & Lister, 2001)....
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TL;DR: The largely complementary palaeobotanical and genetic data indicate that beech survived the last glacial period in multiple refuge areas and the modern genetic diversity was shaped over multiple glacial-interglacial cycles.
Abstract: Summary
• 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.
846 citations
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TL;DR: The present genetic structure of populations, species and communities has been mainly formed by Quaternary ice ages, and genetic, fossil and physical data combined can greatly help understanding of how organisms were so affected.
Abstract: Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable markers to examine these. Several good data sets are now available, which provide tests of expectations, insights into species colonization and unexpected genetic subdivision and mixture of species. The genetic structure of human populations may be viewed in the same context. The present genetic structure of populations, species and communities has been mainly formed by Quaternary ice ages, and genetic, fossil and physical data combined can greatly help our understanding of how organisms were so affected.
6,341 citations
TL;DR: The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial-interglacial cycles as discussed by the authors.
Abstract: The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial–interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.
5,109 citations
TL;DR: The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences.
Abstract: The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a rapid expansion would be leptokurtic and lead to homozygosity and spatial assortment of genomes. In Europe and North America, ice age contractions were into southern refugia, which would promote genome reorganization. (2) The present day genetic structure of species shows frequent geographic subdivision, with parapatric genomes, hybrid zones and suture zones. A survey of recent DNA phylogeographic information supports and extends earlier work. (3) The grasshopperChorthippus parallelusis used to illustrate such data and processes. Its range in Europe is divided on DNA sequences into five parapatric races, with southern genomes showing greater haplotype diversity — probably due to southern mountain blocks acting as refugia and northern expansion reducing diversity. (4) Comparison with other recent studies shows a concordance of such phylogeographic data over pleistocene time scales. (5) The role that ice age range changes may have played in changing adaptations is explored, including the limits of range, rapid change in new invasions and refugial differentiation in a variety of organisms. (6) The effects of these events in causing divergence and speciation are explored usingChorthippusas a paradigm. Repeated contraction and expansion would accumulate genome differences and adaptations, protected from mixing by hybrid zones, and such a composite mode of speciation could apply to many organisms.
3,850 citations
TL;DR: A Brooks parsimony analysis produced an unrooted area phylogram, showing that: (i) the northern regions were colonized generally from the Iberic and Balkanic refugia; and (ii) the Italian lineages were often isolated due to the presence of the Alpine barrier.
Abstract: The Quaternary cold periods in Europe are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in both animals and plants. The phylogeographies of 10 taxa, including mammals (Ursus arctos, Sorex spp., Crocidura suaveolens, Arvicola spp.), amphibians (Triturus spp.), arthropods (Chorthippus parallelus), and plants (Abies alba, Picea abies, Fagus sylvatica, Quercus spp.), were analysed to elucidate general trends across Europe. Only a small degree of congruence was found amongst the phylogeographies of the 10 taxa, but the likely postglacial colonization routes exhibit some similarities. A Brooks parsimony analysis produced an unrooted area phylogram, showing that: (i) the northern regions were colonized generally from the Iberic and Balkanic refugia; and (ii) the Italian lineages were often isolated due to the presence of the Alpine barrier. The comparison of colonization routes highlighted four main suture-zones where lineages from the different refugia meet. Some of the intraspecific genetic distances among lineages indicated a prequaternary divergence that cannot be connected to any particular cold period, but are probably related mainly to the date of arrival of each taxon in the European continent. As a consequence, molecular genetics so far appears to be of limited use in dating Quaternary events.
2,855 citations