Refugia, differentiation and postglacial migration in arctic-alpine Eurasia, exemplified by the mountain avens (Dryas octopetala L.)

Many arctic-alpine organisms have vast present-day ranges across Eurasia, but their history of refugial isolation, differentiation and postglacial expansion is poorly understood. The mountain avens, Dryas octopetala sensu lato, is a long-lived, wind-dispersed, diploid shrub forming one of the most important components of Eurasian tundras and heaths in terms of biomass. We address differentiation and migration history of the species with emphasis on the western and northern Eurasian parts of its distribution area, also including some East Greenlandic and North American populations (partly referred to as the closely related D. integrifolia M. Vahl). We analysed 459 plants from 52 populations for 155 amplified fragment length polymorphisms (AFLP) markers. The Eurasian plants were separated into two main groups, probably reflecting isolation and expansion from two major glacial refugia, situated south and east of the North European ice sheets, respectively. Virtually all of northwestern Europe as well as East Greenland have been colonized by the Southern lineage, whereas northwest Russia, the Tatra Mountains and the arctic archipelago of Svalbard have been colonized by the Eastern lineage. The data indicate a contact zone between the two lineages in northern Scandinavia and possibly in the Tatra Mountains. The two single populations analysed from the Caucasus and Altai Mountains were most closely related to the Eastern lineage but were strongly divergent from the remaining eastern populations, suggesting survival in separate refugia at least during the last glaciation. The North American populations grouped with those from East Greenland, irrespective of their taxonomic affiliation, but this may be caused by independent hybridization with D. integrifolia and therefore not reflect the true relationship between populations from these areas.     

Chloroplast DNA variation,postglacial recolonization and hybridization in hazel,Corylus avellana

To unravel the postglacial migration history of hazel, Corylus avellana, the genetic variation at two types of chloroplast DNA markers, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and microsatellites, was assessed in 26 natural hazel populations distributed across the range of C. avellana. In addition a sequence of 2468 base pairs, which contains the matK gene, was analysed in seven individuals. Very little variation was detected overall [hT:PCR-RFLP= 0.091, hT:microsatellite= 0.423, pi (nucleotide diversity) = 0.00093] but the microsatellite markers, which have the highest levels of variation, show a clear geographical structure that divides Europe into two areas: (i) Italy and the Balkans, on one hand and (ii) the rest of Europe, on the other hand. These data exclude Italy and the Balkans as possible origins of the postglacial recolonization but cannot unambiguously show which other area is the origin, since the genetic data does not indicate the direction of spread. If we take the pollen record into account, the most likely scenario would be an expansion from southwestern France into most of Europe except Italy and the Balkans, and then a local expansion in the latter area. The two main haplotypes identified with both PCR-RFLP and sequencing, A and B, were found not only in C. avellana but also in other European Corylus species and cultivars. Haplotype A, which is dominating all investigated natural populations of C. avellana, is also found in the European tree hazel (C. colurna) and haplotype B, which is rare in C. avellana, has been identified in the filbert (C. maxima) and C. avellana cultivars. This pattern seems to indicate a history of past hybridization among the European Corylus species and cultivars.     

Environmental dependence of population dynamics and height growth of a subalpine conifer across its vertical distribution: an approach using high‐resolution aerial photographs

Many studies have reported shifts in the altitudinal ranges of plant species in response to recent global warming. However, most studies of tree species have been conducted on a small scale and have focused on tree line ecotones by examining tree rings and age structure on account of the long life spans of the trees. To examine the impact of climate change on forest dynamics at a regional scale, we investigated differences in the population density and canopy height of a Japanese subalpine coniferous species, Abies mariesii, between 1967 and 2003 by analysis of high‐resolution aerial photographs of the Hakkoda Mountains, Honshu, Japan. In 712 plots within the photographs we analyzed which environmental variables (including elevation, aspect, wetness, and distance from moorlands) account for these changes. The population density of A. mariesii decreased below 1000 m a.s.l. and increased above 1300 m a.s.l. It also increased around moorlands, which may provide refugia at low elevations. The rate of increase in canopy height was lowest on the southeastern slopes and on the periphery of the moorlands. The distinct changes in the population density of A. mariesii at its distribution limits probably reflect the responses of the population to climatic changes during three decades. Areas surrounding the moorlands may offer refugia in spite of the poor growing conditions there.     

Late‐glacial recolonization and phylogeography of European red deer (Cervus elaphus L.)

The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion–contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40 000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South‐East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South‐Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North‐West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas.     

Dispersal differences predict population genetic structure in Mormon crickets

Research investigating the geographical context of speciation has primarily focused on abiotic factors such as the role of Pleistocene glacial cycles, or geotectonic events. Few study systems allow a direct comparison of how biological differences, such as dispersal behaviour, affect population genetic structure of organisms that were subdivided during the Pleistocene. Mormon crickets exist in solitary and gregarious 'phases', which broadly correspond with an east-west mtDNA division across the Rocky Mountains. Gregarious individuals form bands that can move up to 2 km daily. This study assessed whether population genetic structure results mainly from deep Pleistocene vicariance or if we can also detect more recent genetic patterns due to phase and dispersal differences superimposed on the older, deeper divisions. We found that separation in refugia was a more important influence on genetic divergence than phase, with the Rockies acting as a barrier that separated Mormon cricket populations into eastern and western refugia during Pleistocene glacial cycles. However, patterns of isolation by distance differ between eastern and western clades for both mitochondrial and nuclear DNA, with greater divergence within the eastern, solitary clade. An mtDNA haplotype mismatch distribution is compatible with historical population expansion in the western clade but not in the eastern clade. A persistent (and possibly sex-biased) difference in dispersal ability has most likely influenced the greater population genetic structure seen in the eastern clade, emphasizing the importance of the interaction of Quaternary climate fluctuations and geography with biotic factors in producing the patterns of genetic subdivision observed today.     

Eastward Ho: phylogeographical perspectives on colonization of hosts and parasites across the Beringian nexus

The response of Arctic organisms and their parasites to dramatic fluctuations in climate during the Pleistocene has direct implications for predicting the impact of current climate change in the North. An increasing number of phylogeographical studies in the Arctic have laid a framework for testing hypotheses concerning the impact of shifting environmental conditions on transcontinental movement. We review 35 phylogeographical studies of trans-Beringian terrestrial and freshwater taxa, both hosts and parasites, to identify generalized patterns regarding the number, direction and timing of trans-continental colonizations. We found that colonization across Beringia was primarily from Asia to North America, with many events occurring in the Quaternary period. The 35 molecular studies of trans-Beringian organisms we examined focused primarily on the role of glacial cycles and refugia in promoting diversification. We address the value of establishing testable hypotheses related to high-latitude biogeography. We then discuss future prospects in Beringia related to coalescent theory, palaeoecology, ancient DNA and synthetic studies of arctic host–parasite assemblages highlighting their cryptic diversity, biogeography and response to climate variation.     

Phylogeographic analysis reveals a deep lineage split within North Atlantic Littorina saxatilis

Phylogeographic studies provide critical insight into the evolutionary histories of model organisms; yet, to date, range-wide data are lacking for the rough periwinkle Littorina saxatilis, a classic example of marine sympatric speciation. Here, we use mitochondrial DNA (mtDNA) sequence data to demonstrate that L. saxatilis is not monophyletic for this marker, but is composed of two distinct mtDNA lineages (I and II) that are shared with sister species Littorina arcana and Littorina compressa. Bayesian coalescent dating and phylogeographic patterns indicate that both L. saxatilis lineages originated in the eastern North Atlantic, around the British Isles, at approximately 0.64 Ma. Both lineages are now distributed broadly across the eastern, central and western North Atlantic, and show strong phylogeographic structure among regions. The Iberian Peninsula is genetically distinct, suggesting prolonged isolation from northeastern North Atlantic populations. Western North Atlantic populations of L. saxatilis lineages I and II predate the last glacial maximum and have been isolated from eastern North Atlantic populations since that time. This identification of two distinct, broadly distributed mtDNA lineages further complicates observed patterns of repeated incipient ecological speciation in L. saxatilis, because the sympatric origins of distinct ecotype pairs on eastern North Atlantic shores may be confounded by admixture of divergent lineages.     

Glacial refugia of temperate, Mediterranean and Ibero-North African flora in south-eastern Spain: new evidence from cave pollen at two Neanderthal man sites

Aim To locate glacial refugia of thermophilous plant species in Spain. Location Two south‐eastern Spanish Neanderthal man sites in Murcia; namely, the inland Cueva Negra del Estrecho del Río Quípar and the coastal Sima de las Palomas del Cabezo Gordo. Methods We use pollen found in cave sediments as a source of palaeobotanical and palaeoecological information. The findings are discussed with regard both to animal remains from both sites, and also to other refugia in south‐eastern Spain and elsewhere in the Iberian Peninsula. Results Both sequences show persistence of abundant mesothermophilous trees during the last glacial stage, suggesting both localities were reservoirs of phytodiversity and woodland species. At both sites, deciduous and evergreen oaks are the most abundant components, followed by a wide variety of deciduous trees and sclerophyllous shrubs, including Ibero‐North African xerothermic scrub near the coast. Conclusions Incomplete information underlies a common misapprehension that Iberian glacial refugia were confined to southernmost parts of the peninsula. A rather different picture of Quaternary refugia emerges from consideration of pollen sequences from caves (and other inputs such as macroscopic charcoal, spatial genetic structure of present‐day populations, faunal remains, and present‐day distribution of thermophilous species). This picture offers a view of numerous viable areas for woodland species in southern Spain, in addition to others in the mountain ranges, both in continental central Spain and those of northern Spain: these stretch from the Mediterranean coast of Catalonia to the westernmost extent of the Bay of Biscay.     

Multi‐species distribution modelling highlights the Adelaide Geosyncline,South Australia,as an important continental‐scale arid‐zone refugium

The mainland portion of the Adelaide Geosyncline (Mount Lofty and Flinders Ranges) has been postulated as an important arid‐zone climate refugium for Australia. To test the sensitivity of this putative Australian arid biome refugium to contemporary climate change, we compared Generalized Additive Modelling and MaxEnt distribution models for 20 vascular plant species. We aimed to identify shared patterns to inform priority areas for management. Models based on current climate were projected onto a hypothetical 2050 climate with a 1.5°C increase in temperature and 8% decrease in rainfall. Individual comparisons and combined outputs of logistic models for all 20 species showed range contraction to shared refugia in the Flinders Ranges and southern Mount Lofty Ranges. Modelling suggests the Flinders Ranges will experience species turnover while suitable climatic habitat will be retained in the Mount Lofty Ranges for the current suite of species. Fragmentation of the southern Mount Lofty Ranges poses management challenges for conserving species diversity with warming and drying. Although projected models must be interpreted carefully, they suggest the region will remain an important but threatened refugium for mesic species at a continental scale.     

A review of the subspecies status of the Icelandic Purple Sandpiper Calidris maritima littoralis

The Icelandic Purple Sandpiper Calidris maritima littoralis (C.L. Brehm, 1831) represents one member of a poorly understood subspecies complex. Currently, differences in size define two other subspecies: Calidris maritima belcheri Engelmoer & Roselaar, 1998, which breeds in north‐eastern Canada along the Hudson Bay and James Bay, and Calidris maritima maritima (Brunnich, 1764), which breeds along the Arctic coasts elsewhere in northern Canada, Greenland, Svalbard, Scotland, and Fennoscandia, to northern central Siberia. There are large size differences amongst populations of C. m. maritima, however. As an Arctic/Alpine breeding bird, C. m. littoralis could provide an interesting perspective on the evolutionary changes following a northwards expansion of a species after glacial retreat. Considering the extent of the ice sheet in the northern hemisphere during the last glaciation, and the short period of time since it ended, the correct attribution of subspecies status for C. m. maritima may reflect either rapid diversification from a single population or ancestral splits of distinct evolutionary lineages that survived in isolation at southern latitudes. We applied morphometric subspecies criteria, diagnosability by Amadon's rule, and genetic analysis of five nuclear introns, and the mitochondrial DNA markers cytochrome oxidase c subunit I (COI) and NADH dehydrogenase subunit 2 (ND2), to geographically separate breeding populations in order to examine the subspecies status of the Icelandic population. The results do not provide support for the subspecies status of the Icelandic population because the nominate and Icelandic subspecies fail to uphold Amadon's rule, and genetic analyses indicate that the study populations derive from a single shared refugium. © 2015 The Linnean Society of London