Phylogeographical patterns of a generalist acorn weevil: insight into the biogeographical history of broadleaved deciduous and evergreen forests

Background  

Climatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets. We investigated the phylogeographical patterns of the weevil Curculio sikkimensis (Curculionidae), a generalist seed predator of Fagaceae plants living in both deciduous oak and evergreen forests of Japan. Its genetic structure was compared to that of another host-specific seed predator, C. hilgendorfi, inhabiting only evergreen forests.     

Genetic Differentiation and Genetic Diversity of Castanopsis (Fagaceae), the Dominant Tree Species in Japanese Broadleaved Evergreen Forests,Revealed by Analysis of EST-Associated Microsatellites

The broadleaved evergreen forests of the East Asian warm temperate zone are characterised by their high biodiversity and endemism, and there is therefore a need to extend our understanding of its genetic diversity and phylogeographic patterns. Castanopsis (Fagaceae) is one of the dominant tree species in the broadleaved evergreen forests of Japan. In this study we investigate the genetic diversity, genetic structure and leaf epidermal morphology of 63 natural populations of C. sieboldii and C. cuspidata, using 32 Expressed Sequence Tag associated microsatellites. The overall genetic differentiation between populations was low (G _ST = 0.069 in C. sieboldii and G _ST = 0.057 in C. cuspidata). Neighbor-joining tree and Bayesian clustering analyses revealed that the populations of C. sieboldii and C. cuspidata were genetically clearly differentiated, a result which is consistent with the morphology of their epidermal cell layers. This suggests that C. sieboldii and C. cuspidata should be treated as independent species, although intermediate morphologies are often observed, especially at sites where the two species coexist. The higher level of genetic diversity observed in the Kyushu region (for both species) and the Ryukyu Islands (for C. sieboldii) is consistent with the available fossil pollen data for Castanopsis-type broadleaved evergreen trees during the Last Glacial Maximum and suggests the existence of refugia for Castanopsis forests in southern Japan. Within the C. sieboldii populations, Bayesian clustering analyses detected three clusters, in the western and eastern parts of the main islands and in the Ryukyu Islands. The west-east genetic differentiation observed for this species in the main islands, a pattern which is also found in several plant and animal species inhabiting Castanopsis forests in Japan, suggests that they have been isolated from each other in the western and eastern populations for an extended period of time, and may imply the existence of eastern refugia.     

Phylogeography of the Japanese giant flying squirrel, Petaurista leucogenys (Rodentia: Sciuridae): implication of glacial refugia in an arboreal small mammal in the Japanese Islands

To test the association between temperate forest dynamics and glacial refugia for arboreal small mammals, we studied the phylogeography of the Japanese giant flying squirrel ( Petaurista leucogenys ) using complete mitochondrial cytochrome b gene sequences (1140 bp). This squirrel is endemic to three of Japan's main islands: Honshu, Shikoku, and Kyushu. We examined 58 specimens of P. leucogenys collected from 40 localities in Japan. Additionally, two individuals with unknown sampling localities were included in phylogenetic analyses. There were 54 haplotypes of P. leucogenys. We found five major phylogroups (Northern, Central, South-eastern, South-western, and Southern). These phylogroups may have originated from glacial refugia during the Late Pleistocene. After the last glaciation, the Northern phylogroup, widely distributed in eastern Japan, could have extensively expanded northward from its refugia. By contrast, in western Japan, population expansion was restricted to western Japan. All members of four phylogroups existed in western Japan during glaciations. The complicated phylogeographical pattern of P. leucogenys populations originating from western Japan may have resulted from the long history.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 47–60.     

Phylogeography of the component species of broad-leaved evergreen forests in Japan,based on chloroplast DNA variation

In order to elucidate the past distribution and colonization routes of broad-leaved evergreen (lucidophyllous) forests, we investigated the intraspecific phylogeographic patterns of lucidophyllous forests in Japan and surrounding areas. We selected 6 component species with a similar geographic distributions growing in Castanopsis-dominant forests. We defined possible important refugia during the glacial periods as the regions rich in rare haplotypes (with a frequency of 5% or less), or as regions rich in the number of common haplotypes (with a frequency of more than 5%). We then located the sites of refuge by comparing the intraspecific phylogeographic patterns among 6 component species of lucidophyllous forests with respect to these two parameters (i.e., haplotype uniqueness and the number of haplotypes). The following results were obtained during the course of this study: (1) rare haplotypes were distributed among islands around the main islands of Japan; (2) rare subtypes and the greatest numbers of common haplotypes were observed in Kyushu, a finding which agreed with fossilized pollen data demonstrative of the past existence of refugia in southern Kyushu; and (3) rare haplotypes were found on the Muroto Peninsula, and the second greatest numbers of common haplotypes were observed on the Kii Peninsula, a finding which suggested the existence of additional important refugia along the Pacific coast of Japan during the glacial ages.     

Chloroplast DNA phylogeography of Photinia glabra (Rosaceae) in Japan

Climate changes during glacial periods have had significant effects on the present geographic distribution of plant species. To elucidate the evolutionary history of a plant species with a disjunctive distribution, we investigated the geographic distribution patterns of cpDNA haplotypes in Photinia glabra (Rosaceae) growing in broadleaved evergreen forests in Japan. We examined cpDNA in 42 populations of P. glabra sampled over a geographic range that included Kinki and its surrounding areas and the disjunctive regions in the Amakusa Islands. Both areas had unique cpDNA haplotypes. Moreover, the AMOVA revealed that a large proportion of the total variance (51%, P < 0.001) could be explained by differences among these regions. These results suggest a past fragmentation of this plant species into two separate refugia: southwestern Kyushu and Kinki, including the surrounding area, during the Quaternary glacial periods. A particularly interesting result was that in the southern disjunct distribution in the Amakusa Islands, the genetic subdivision (Φ(CT) = 1.00, P < 0.001) appears to lie between the populations from nearly contiguous islands located across a fairway only approximately 80 to 150 m in width.     

Pleistocene glaciation leaves deep signature on the freshwater crab Aegla alacalufi in Chilean Patagonia

Quaternary glacial cycles have played an important role in shaping the biodiversity in temperate regions. This is well documented in Northern Hemisphere, but much less understood for Southern Hemisphere. We used mitochondrial DNA and nuclear elongation factor 1α intron sequences to examine the Pleistocene glacial impacts on the phylogeographical pattern of the freshwater crab Aegla alacalufi in Chilean Patagonia. Phylogenetic analyses, which separated the glaciated populations on eastern continent into a north group (seven populations) and a south group (one population), revealed a shallow phylogenetic structure in the north group but a deep one in the non-glaciated populations on western islands, indicating the significant influence of glaciation on these populations. Phylogenies also identified the Yaldad population on Chiloé Island as a potentially unrecognized new species. The non-glaciated populations showed higher among population genetic divergence than the glaciated ones, but lower population genetic diversity was not detected in the latter. The two glaciated groups, which diverged from the non-glaciated populations at ~96 800–29 500 years ago and ~104 200–73 800 years ago, respectively, seem to have different glacial refugia. Unexpectedly, the non-glaciated islands did not serve as refugia for them. Demographic expansion was detected in the glaciated north group, with a constant population increase after the last glacial maximum. Nested clade analyses suggest a possible colonization from western islands to eastern continent. After arriving on the continent and surviving the last glacial period there, populations likely have expanded from high to low altitude, following the flood of melting ice. Aegla alacalufi genetic diversity has been primarily affected by Pleistocene glaciation and minimally by drainage isolation.     

Reconciling historical processes and population structure in the sooty tern Sterna fuscata

To test the influence of past vicariant events on population genetic structure of the sooty tern Sterna fuscata , we examined sequence variation in the mitochondrial control region of individuals from the Indo-Pacific and Atlantic Oceans. Our analyses indicate a rapid population expansion at a global scale during the last 100 000 years, consistent with global recolonisation during the interstade following the Pleistocene glacial maxima (125 000–175 000 years bp). We estimate islands of the Great Barrier Reef and Coral Sea were colonised no more than 16 000 years ago, most likely in association with the appearance of new breeding habitat following the final Pleistocene glacial retreat (19 000–22 000 years bp). Our results suggest that ice sheets linked to major glacial events not only impact genetic structuring in temperate seabirds, but that sea level changes in the tropics associated with these same events have also significantly impacted contemporary genetic structuring in tropical seabird species.     

Living on the edge: demographic and phylogeographical patterns in the woodlouse-hunter spider Dysdera lancerotensis Simon, 1907 on the eastern volcanic ridge of the Canary Islands

The Eastern Canary Islands are the emerged tips of a continuous volcanic ridge running parallel to the northeastern African coast, originated by episodic volcanic eruptions that can be traced back to the Miocene and that, following a major period of quiescence and erosion, continued from the Pliocene to the present day. The islands have been periodically connected by eustatic sea-level changes resulting from Pleistocene glacial cycles. The ground-dwelling spider Dysdera lancerotensis Simon, 1907 occurs along the entire ridge, except on recent barren lavas and sand dunes, and is therefore an ideal model for studying the effect of episodic geological processes on terrestrial organisms. Nested clade and population genetic analyses using 39 haplotypes from 605 base pairs of mitochondrial DNA cytochrome c oxidase I sequence data, along with phylogenetic analyses including two additional mitochondrial genes, uncover complex phylogeographical and demographic patterns. Our results indicate that D. lancerotensis colonized the ridge from north to south, in contrast to what had been expected given the SSW-NNE trend of volcanism and to what had been reported for other terrestrial arthropods. The occurrence of several episodes of extinction, recolonization and expansion are hypothesized for this species, and areas that act as refugia during volcanic cycles are identified. Relaxed molecular clock methods reveal divergence times between main haplotype lineages that suggest an older origin of the northern islets than anticipated based on geological evidence. This study supports the key role of volcanism in shaping the distribution of terrestrial organisms on oceanic islands and generates phylogeographical predictions that warrant further research into other terrestrial endemisms of this fascinating region.     

Alpine biogeography of Parnassian butterflies during Quaternary climate cycles in North America

Growth of alpine glaciers during the Pleistocene had profound effects on montane landscapes in North America and the organisms now inhabiting alpine ecosystems. Biogeography of this region has often been viewed as a system of sky islands despite the fact that species richness patterns deviate from a strict island biogeographic model. One explanation is that alpine species are not in equilibrium because of late Quaternary geographic range shifts. Genetic data can provide evidence of nonequilibrium dynamics and the distributional shifts that occur during glaciation events in alpine landscapes. Using mitochondrial and nuclear sequence data, we examine the evolutionary history of butterflies in the Parnassius phoebus complex. We test explicit, alternative models of the biogeographic history of Parnassius smintheus and Parnassius behrii , including an equilibrium island model, ancestral radiation and fragmentation, an expanding alpine archipelago and an alpine archipelago refuge model. Our results support the alpine archipelago refuge model, in which alpine butterflies undergo population contraction during glacial climates followed by population expansion during interglacial phases. While butterflies can disperse between distant mountain ranges during glacial periods, gene flow is rare. We find evidence of recent connectivity between California and Colorado, population expansion events following deglaciation ∼20 000 years B.P., and small population sizes during the last glacial period. An analysis of lineage splitting suggests that morphological differences in P. smintheus and P. behrii are the result of late Pleistocene divergence (∼48 000 years B.P.) with limited gene flow. Our results demonstrate that spatially complex and nonequilibrium population dynamics influence alpine diversity patterns.     

Sailing through the Late Pleistocene: unusual historical demography of an East Asian endemic, the Chinese Hwamei (Leucodioptron canorum canorum), during the last glacial period

Pleistocene climate fluctuations shaped the patterns of genetic diversity observed in extant species. In contrast to Europe and North America where the effects of recent glacial cycles on genetic diversity have been well studied, the genetic legacy of the Late Pleistocene for East Asia, a region of great topographical complexity and presumably milder historical climate, remains poorly understood. We analysed 3.86 kb of the mitochondrial genome of 186 Chinese Hwamei birds, Leucodioptron canorum canorum , and found that contrary to the conventional expectation of population decline during cold periods (stadials), the demographic history of this species shows continuous population growth since the penultimate glacial period (about 170 000 years ago). Refugia were identified in the south, coastal regions, and northern inland areas, implying that topographic complexity played a substantial role in providing suitable habitats for the Chinese Hwamei during cold periods. Intermittent gene flow between these refugia during the warmer periods (interstadials) might have resulted in a large effective population of this bird through the last glacial period.     

Population demographic history of a temperate shrub,Rhododendron weyrichii (Ericaceae), on continental islands of Japan and South Korea

Continental islands provide opportunities for testing the effects of isolation and migration on genetic variation in plant populations. In characteristic of continental islands is that the geographic connections between these islands, which are currently distinguished by seaways, have experienced fluctuations caused by sea‐level changes due to climate oscillations during the Quaternary. Plant populations on the islands have migrated between these islands via the exposed seafloors or been isolated. Here, we examined the demographic history of a temperate shrub, Rhododendron weyrichii, which is distributed in the southwestern parts of the Japanese archipelago and on an island of South Korea, using statistical phylogeographic approaches based on the DNA sequences of two chloroplast and eight nuclear loci in samples analyzed from 18 populations on eight continental islands, and palaeodistribution modeling. Time estimates for four island populations indicate that the durations of vicariance history are different between these populations, and these events have continued since the last glacial or may have predated the last glacial. The constancy or expansion of population sizes on the Japanese islands, and in contrast a bottleneck in population size on the Korean island Jeju, suggests that these islands may have provided different conditions for sustaining populations. The result of palaeodistribution modeling indicates that the longitudinal range of the species as a whole has not changed greatly since the last glacial maximum. These results indicate that exposed seafloors during the glacial period formed both effective and ineffective migration corridors. These findings may shed light on the effects of seafloor exposure on the migration of plants distributed across continental islands.     

Response of a southern temperate marsupial, the Tasmanian pademelon (Thylogale billardierii), to historical and contemporary forest fragmentation

Despite only limited Pleistocene glacial activity in the southern hemisphere, temperate forest species experienced complex distributional changes resulting from the combined effects of glaciation, sea level change and increased aridity. The effects of these historical processes on population genetic structure are now overlain by the effects of contemporary habitat modification. In this study, 10 microsatellites and 629 bp of the mitochondrial control region were used to assess the effects of historical forest fragmentation and recent anthropogenic habitat change on the broad-scale population genetic structuring of a southern temperate marsupial, the Tasmanian pademelon. A total of 200 individuals were sampled from seven sites across Tasmania and two islands in Bass Strait. High mitochondrial and nuclear genetic diversity indicated the maintenance of large historical population sizes. There was weak phylogeographical structuring of haplotypes, although all King Island haplotypes and three Tasmanian haplotypes formed a divergent clade implying the mid-Pleistocene isolation of a far northwestern population. Both the mitochondrial and nuclear data indicated a division of Tasmanian populations into eastern and western regions. This was consistent with a historical barrier resulting from increased aridity in the lowland 'midlands' region during glacial periods, and with a contemporary barrier resulting from recent habitat modification in that region. In Tasmania, gene flow appears to have been relatively unrestricted during glacial maxima in the west, while in the east there was evidence for historical expansion from at least one large glacial refuge and recolonization of Flinders Island.     

Population genetic structure of the point-head flounder, <Emphasis Type="Italic">Cleisthenes herzensteini</Emphasis>, in the Northwestern Pacific

Intraspecific phylogenies can provide useful insights into how populations have been shaped by historical and contemporary processes. To determine the population genetic structure and the demographic and colonization history of Cleisthenes herzensteini in the Northwestern Pacific, one hundred and twenty-one individuals were sampled from six localities along the coastal regions of Japan and the Yellow Sea of China. Mitochondrial DNA variation was analyzed using DNA sequence data from the 5′ end of control region. High levels of haplotype diversity (>0.96) were found for all populations, indicating a high level of genetic diversity. No pattern of isolation by distance was detected among the population differentiation throughout the examined range. Analyses of molecular variance (AMOVA) and the conventional population statistic Fst revealed no significant population genetic structure among populations. According to the exact test of differentiation among populations, the null hypothesis that C. herzensteini within the examined range constituted a non-differential mtDNA gene pool was accepted. The demographic history of C. herzensteini was examined using neutrality test and mismatch distribution analyses and results indicated Pleistocene population expansion (about 94–376 kya) in the species, which was consistent with the inference result of nested clade phylogeographical analysis (NCPA) showing contiguous range expansion for C. herzensteini. The lack of phylogeographical structure for the species may reflect a recent range expansion after the glacial maximum and insufficient time to attain migration-drift equilibrium.     

Palaeovegetation of China: a pollen data-based synthesis for the mid-Holocene and last glacial maximum

Pollen data from China for 6000 and 18,000 ¹⁴C yr bp were compiled and used to reconstruct palaeovegetation patterns, using complete taxon lists where possible and a biomization procedure that entailed the assignment of 645 pollen taxa to plant functional types. A set of 658 modern pollen samples spanning all biomes and regions provided a comprehensive test for this procedure and showed convincing agreement between reconstructed biomes and present natural vegetation types, both geographically and in terms of the elevation gradients in mountain regions of north‐eastern and south‐western China. The 6000 ¹⁴C yr bp map confirms earlier studies in showing that the forest biomes in eastern China were systematically shifted northwards and extended westwards during the mid‐Holocene. Tropical rain forest occurred on mainland China at sites characterized today by either tropical seasonal or broadleaved evergreen/warm mixed forest. Broadleaved evergreen/warm mixed forest occurred further north than today, and at higher elevation sites within the modern latitudinal range of this biome. The northern limit of temperate deciduous forest was shifted c. 800 km north relative to today. The 18,000 ¹⁴C yr bp map shows that steppe and even desert vegetation extended to the modern coast of eastern China at the last glacial maximum, replacing today’s temperate deciduous forest. Tropical forests were excluded from China and broadleaved evergreen/warm mixed forest had retreated to tropical latitudes, while taiga extended southwards to c. 43°N.     

Phylogeography of Quercus variabilis Based on Chloroplast DNA Sequence in East Asia: Multiple Glacial Refugia and Mainland-Migrated Island Populations

The biogeographical relationships between far-separated populations, in particular, those in the mainland and islands, remain unclear for widespread species in eastern Asia where the current distribution of plants was greatly influenced by the Quaternary climate. Deciduous Oriental oak (Quercus variabilis) is one of the most widely distributed species in eastern Asia. In this study, leaf material of 528 Q. variabilis trees from 50 populations across the whole distribution (Mainland China, Korea Peninsular as well as Japan, Zhoushan and Taiwan Islands) was collected, and three cpDNA intergenic spacer fragments were sequenced using universal primers. A total of 26 haplotypes were detected, and it showed a weak phylogeographical structure in eastern Asia populations at species level, however, in the central-eastern region of Mainland China, the populations had more haplotypes than those in other regions, with a significant phylogeographical structure (N _ST =0.751> G _ST =0.690, P<0.05). Q. variabilis displayed high interpopulation and low intrapopulation genetic diversity across the distribution range. Both unimodal mismatch distribution and significant negative Fu’s F_S indicated a demographic expansion of Q. variabilis populations in East Asia. A fossil calibrated phylogenetic tree showed a rapid speciation during Pleistocene, with a population augment occurred in Middle Pleistocene. Both diversity patterns and ecological niche modelling indicated there could be multiple glacial refugia and possible bottleneck or founder effects occurred in the southern Japan. We dated major spatial expansion of Q. variabilis population in eastern Asia to the last glacial cycle(s), a period with sea-level fluctuations and land bridges in East China Sea as possible dispersal corridors. This study showed that geographical heterogeneity combined with climate and sea-level changes have shaped the genetic structure of this wide-ranging tree species in East Asia.     

The genetic structure of <Emphasis Type="Italic">Quercus crispula</Emphasis> in northeastern Japan as revealed by nuclear simple sequence repeat loci

Previous studies have reached different discussions about the genetic variation and genetic structure of Quercus crispula populations in northeastern Japan. This is a common oak species in Eastern Asia. Some studies have suggested that the populations in northeastern Japan were derived from those remaining in the southwest after the last glacial maximum (LGM), whilst other studies have found evidence that populations persisted in northeastern Japan during the LGM. Using seven highly polymorphic nuclear simple sequence repeat loci, we investigated the genetic structure of 16 Q. crispula populations along a latitudinal gradient in northeastern Japan (northern Honshu and Hokkaido), spanning about half of the species’ biogeographic range in the country. Although the level of population differentiation was low (F _ST = 0.021; G^￠_\textST G^{\prime}_{\text{ST}}  = 0.090), two geographically differentiated clusters were detected by STRUCTURE analysis. The first cluster included most of the populations in Hokkaido, and may indicate continued survival throughout past glacial periods. We found a significant decrease in allelic richness with latitude, so the second cluster may represent an expansion of the lineage from Honshu during the post-glacial period. These results should enhance our understanding of historical north–south migrations of this species in northeastern Japan.     

云贵高原抚仙湖近13300年的花粉/炭屑记录*

抚仙湖是云贵高原著名的断陷深水湖,其沉积物蕴藏着流域地质历史时期丰富的环境信息。对钻取自该湖的900cm 湖泊沉积物岩芯进行花粉/炭屑分析及花粉数据的主成分分析表明,抚仙湖流域的植被、气候与火灾在过去的13 300年经历了5个阶段的变化：(1)13 300—10 400cal．a BP,植被以松林为主,伴有山地暗针叶林和常绿阔叶林,表明该时期气候较为冷湿,森林火灾多发,在后期随着温度和湿度的降低,森林火灾愈加频繁。(2)10 400—5 700cal．a BP,松林收缩,常绿阔叶林扩张,出现一定数量的落叶阔叶林,显示该时期气候偏暖偏干;此阶段早期随着气候变暖变干森林火灾的发生延续上阶段高发的状态,直到9 500cal．a BP后随着湿度的增加森林火灾明显减少。(3)5 700—1 800cal．a BP,松林变化较小,常绿/落叶阔叶林比重增大,首次出现了暖热性的枫香林,显示该时期暖湿的气候特征,火灾发生频率低。(4)1 800—500cal．a BP,松林扩张,阔叶林收缩,本阶段后期草本植被比重开始增加,显示该时期气候相对冷干,森林火灾发生频率较高。(5)500cal．a BP至今,松林收缩,落叶阔叶树种增多,草本植物花粉明显增多,显示该时期气候温凉偏干,森林火灾发生频率降低。     

Pleistocene isolation in the Northwestern Pacific marginal seas and limited dispersal in a marine fish, Chelon haematocheilus (Temminck & Schlegel, 1845)

The Northwestern Pacific has a unique tectonic and geographical history with several marginal seas separating Asia from the Pacific Ocean. During low sea level periods of Pleistocene glaciations, populations might have been isolated in three marginal seas: the Sea of Japan, East China Sea and South China Sea. Following postglacial sea level rise, we would expect the populations isolated in the three regions to have been homogenized by high dispersal potential. To assess these hypotheses, we explore the intraspecific phylogeographical patterns in redlip mullet, Chelon haematocheilus. Fragments of 435 bp at the 5' end of mitochondrial DNA control region were sequenced for 272 individuals from nine localities over most of the species' range. Three distinct lineages were detected, which might have diverged in the three marginal seas during Pleistocene low sea levels. Contrary to homogenization expectation, there were strong differences in the geographical distribution of the three lineages. Analyses of molecular variance and the population statistic Phi(ST) also revealed significant genetic structure among populations of the three marginal seas. These results indicate that gene flow in Chelon haematocheilus is far more restricted spatially than predicted by the potential dispersal capabilities of this species. The lack of phylogeographical structure in East China Sea may reflect a recent range expansion after the last glacial maximum and insufficient time to attain migration-drift equilibrium.     

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 ¹⁴C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 ¹⁴C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 ¹⁴C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid‐Holocene. At 18,000 ¹⁴C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year‐round cooling.     

Population history and genetic structure of a circumpolar species: the arctic fox

The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to cyclical restriction in glacial refugia during the Ice Ages. We investigated population history and genetic structure through mitochondrial control region variation in 191 arctic foxes from throughout the arctic. Several haplotypes had a Holarctic distribution and no phylogeographical structure was found. Furthermore, there was no difference in haplotype diversity between populations inhabiting previously glaciated and unglaciated regions. This suggests current gene flow among the studied populations, with the exception of those in Iceland, which is surrounded by year-round open water. Arctic foxes have often been separated into two ecotypes: 'lemming' and 'coastal'. An analysis of molecular variance suggested particularly high gene flow among populations of the 'lemming' ecotype. This could be explained by their higher migration rate and reduced fitness in migrants between ecotypes. A mismatch analysis indicated a sudden expansion in population size around 118 000 BP, which coincides with the last interglacial. We propose that glacial cycles affected the arctic fox in a way opposite to their effect on temperate species, with interglacials leading to short-term isolation in northern refugia.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 79–89.