Decadal change in macrobenthic soft-bottom community structure in a high Arctic fjord (Kongsfjorden, Svalbard)

Marine benthic macrofauna communities are considered a good indicator of subtle environmental long-term changes in an ecosystem. In 1997/1998 and 2006, soft-bottom fauna of an Arctic glacial fjord Kongsfjorden was extensively sampled and major communities were identified along the fjord axis, which were related to the diminishing influence of glacial activity. Spatial patterns in community structure and species diversity were significantly different in the central basin of Kongsfjorden between periods while there was no change in the inner part of the fjord. In 1997/98, three faunal associations were distinguished with significant differences in species richness and diversity (H′) while in 2006 only two faunal associations were identified and there were no differences any more between the two formerly distinct associations in the central fjord. The increased input of Atlantic water due to a stronger West Spitsbergen Current may be the reason for unification of previous clear faunal division. The faunal association in the inner, well separated glacial part of the fjord, characterized by strong glacier influence, was protected from Atlantic water inflow and, hence, the macrobenthic fauna essentially remained unaffected. Reduced abundance of species typical for glacial bays in the central part of the fjord in 2006 may result from the decreasing effect of Blomstrandbreen glacier, strong increase of input of Atlantic water into the fjord and increased temperature of West Spitsbergen Current. Higher values of POC in 2006 than in 1998 are likely the effect of increased primary production resulting from warmer water temperatures.     

Pathways of spread of the introduced ascidian Styela clava (Tunicata) in Northern Europe, as revealed by microsatellite markers

Styela clava, a solitary ascidian native to the NW Pacific, has become a conspicuous member of fouling communities in NW European waters. As its natural dispersal appears to be limited, the wide distribution of S. clava along coasts within its introduced range may be attributed to secondary spread assisted by human activities. Here, we used six microsatellite loci to examine the genetic diversity and extent of gene flow among S. clava populations in its European introduced range. Samples were collected from 21 populations within Europe (N = 808), 4 populations within the USA and two populations within the native range (Japan). Large variation in genetic diversity was observed among the European populations but were not explained either by the geographic distance from the first introduction area (i.e. Plymouth, UK) nor by the time elapsed since the introduction. No founder effect was observed in the introduced populations, except possibly in Puget Sound (USA). At least two different introductions occurred in Europe, identified as distinct genetic clusters: northern Danish populations (resembling one Japanese population), and the rest of Europe; a sample from Shoreham (England) possibly represents a third introduction. In North America, the population from the Atlantic was genetically similar to the majority of European populations, suggesting a European origin for populations on this seaboard, while populations from the Pacific coast were genetically similar to the same Japanese population as the Danish populations.     

污损性海鞘的生态特点研究展望

海鞘生长快,繁殖迅速,能产生大量在短时间内附着的幼虫,是海洋污损生物群落中的重要成员,对海上人工设施会产生严重危害。污损性海鞘主要由悉尼海鞘(Ascidia sydneiensis)、史氏菊海鞘(Botryllus schlosseri)、米氏小叶鞘(Diplosoma listerianum)、柄瘤海鞘(Styela clava)、红贺海鞘(Herdmania momus)等9科29属103种组成,其中在太平洋海域64种、印度洋23种、大西洋44种,而北冰洋海域仅3种;另外,其附着污损具有明显的地域性和季节特点,并与深度有关。今后应加强污损性海鞘的生态调查和分类研究,阐明深海及两极海域附着污损特点,揭示幼虫附着变态过程的分子调控机理,完善幼虫采集培养技术,以期更好地掌握海鞘生物学特性与生态特点,丰富和发展海洋生态学内容,并为海洋污损生物的防除奠定基础,促进海洋经济产业的发展。     

Effect of excretory-secretory products of some fouling organisms on settling and metamorphosis of the larvae of <Emphasis Type="Italic">Styela rustica</Emphasis> (Ascidiae)

The effect of the excretory-secretory products of some fouling animals on the settling and metamorphosis of larvae of the solitary ascidian Styela rustica was assessed. The substances secreted by the sponge Halichondria panicea stimulated settling of larvae, but concurrently blocked their metamorphosis. The excretory-secretory products of the mussel Mytilus edulis and the ascidian Molgula citrine did not affect settling of the S. rustica larvae but impeded their subsequent development. Water conditioned by the bivalve Hiatella arctica, stimulated settling and, apparently, metamorphosis of the larvae of S. rustica. The chemical substances produced by adult individuals of S. rustica facilitated settling of conspecific larvae but slightly delayed their metamorphosis.     

The impact of waterborne cues from conspecifics and other species on the larvae of Halichondria panacea Pallas, 1766 (Porifera: Demospongiae)

The impacts of different concentrations of the excretory-secretory products (ESPs) of the solitary ascidian Styela rustica (Linnaeus, 1767) and the sponge Halichondria panacea (Pallas, 1766) on the settlement, metamorphosis, and mortality rates of H. panacea larvae were studied in a laboratory experiment. At high concentrations, substances released into the environment by the ascidian S. rustica exerted a negative impact on the metamorphosis rate of sponge larvae. The exposure to moderate or high concentrations of ESPs from conspecific adults led to high mortality of larval sponges; however, low conspecific ESP concentrations markedly stimulated metamorphosis; larval mortality was low. Apparently, different concentrations of the same ESPs can have effects with a different strength and focus. This should be taken into account in the study of chemically mediated interactions between aquatic organisms.     

Frequency of local, regional, and long-distance dispersal of diploid and tetraploid Saxifraga oppositifolia (Saxifragaceae) to Arctic glacier forelands

? Premise of the Study: Climate change forces many species to migrate. Empirical small-scale data on migration and colonization in the Arctic are scarce. Retreating glaciers provide new territory for cold-adapted plant species, but the genetic consequences depend on dispersal distances and frequencies. We estimated local, regional, and long-distance dispersal frequencies, as well as their effect on levels of genetic diversity, in diploid and tetraploid individuals of Saxifraga oppositifolia. ? Methods: Samples were collected in four aged moraines in each of three glacier forelands, in surrounding areas and reference populations in the Arctic archipelago Svalbard. These samples were analyzed for neutral amplified fragment length polymorphisms (AFLPs, n = 707) and ploidy levels (n = 30). ? Key Results: Genetic clustering and ploidy analyses revealed two distinct genetic groups representing diploids and tetraploids, with few intermediate triploids. The groups were intermixed in most sampled populations. No differences in genetic diversity were found between tetraploids and diploids, or between established and glacier foreland populations. Seeds were dispersed over local, regional, and long distances, with the highest proportions of seeds originating from close sources. A minimum of 4-15 founding individuals from several source populations had initially established in each glacier foreland. ? Conclusions: Our data suggest that S. oppositifolia can rapidly colonize new deglaciated areas without losing genetic diversity. Thus, glacier forelands can be alternative habitats for cold-adapted vascular plants tracking their climatic niche. Our data show no difference in colonization success between diploid and tetraploid individuals.     

Trans-Arctic dispersals and the evolution of a circumpolar marine fish species complex, the capelin (Mallotus villosus)

Trans-Arctic dispersals and population and range expansions during the Pleistocene enhanced opportunities for evolutionary diversification and contributed to the process of speciation within the capelin, a northern marine-fish complex exhibiting a circumpolar distribution. Capelin is composed of four highly divergent and geographically discrete mitochondrial DNA (mtDNA) clades (609 bp; cytochrome b). Two clades occur in the North Atlantic, one associated with Canadian Atlantic waters, including Hudson Bay, and the second distributed from West Greenland to the Barents Sea. Two additional clades occur in the Arctic and northeast Pacific Oceans, representing the most recent divergence within the capelin phylogenetic tree. Judged from mtDNA diversity, capelin populations comprising all clades experienced at least one demographic and spatial reduction-expansion episode during recent Pleistocene glaciations that imprinted their molecular architecture. The large contemporary populations in the northeast Pacific and Arctic Oceans exhibited significant genetic structure whereas no such structure was detected in the equally extensive North Atlantic clades. All clades are characterized by one or two prevalent mtDNA haplotypes distributed over the entire range of the clade. Assuming a Pacific ancestor for capelin, we infer that capelin dispersed on two separate occasions to the North Atlantic. A more recent event resulted in the isolation of eastern Pacific and Arctic clades, with the Arctic clade positioned for a potential third Atlantic invasion, as revealed by the presence of this clade in the Labrador Sea. The Labrador Sea is a potential contact zone for three of the four capelin clades.     

The whereabouts of an ancient wanderer: global phylogeography of the solitary ascidian Styela plicata

Genetic tools have greatly aided in tracing the sources and colonization history of introduced species. However, recurrent introductions and repeated shuffling of populations may have blurred some of the genetic signals left by ancient introductions. Styela plicata is a solitary ascidian distributed worldwide. Although its origin remains unclear, this species is believed to have spread worldwide by travelling on ship's hulls. The goals of this study were to infer the genetic structure and global phylogeography of S. plicata and to look for present-day and historical genetic patterns. Two genetic markers were used: a fragment of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and a fragment of the nuclear gene Adenine Nucleotide Transporter/ADP-ATP Translocase (ANT). A total of 368 individuals for COI and 315 for ANT were sequenced from 17 locations worldwide. The levels of gene diversity were moderate for COI to high for ANT. The Mediterranean populations showed the least diversity and allelic richness for both markers, while the Indian, Atlantic and Pacific Oceans had the highest gene and nucleotide diversities. Network and phylogenetic analyses with COI and ANT revealed two groups of alleles separated by 15 and 4 mutational steps, respectively. The existence of different lineages suggested an ancient population split. However, the geographic distributions of these groups did not show any consistent pattern, indicating different phylogeographic histories for each gene. Genetic divergence was significant for many population-pairs irrespective of the geographic distance among them. Stochastic introduction events are reflected in the uneven distribution of COI and ANT allele frequencies and groups among many populations. Our results confirmed that S. plicata has been present in all studied oceans for a long time, and that recurrent colonization events and occasional shuffling among populations have determined the actual genetic structure of this species.     

Population genomic evidence for plant glacial survival in Scandinavia

Quaternary glaciations have played a major role in shaping the genetic diversity and distribution of plant species. Strong palaeoecological and genetic evidence supports a postglacial recolonization of most plant species to northern Europe from southern, eastern and even western glacial refugia. Although highly controversial, the existence of small in situ glacial refugia in northern Europe has recently gained molecular support. We used genomic analyses to examine the phylogeography of a species that is critical in this debate. Carex scirpoidea Michx subsp. scirpoidea is a dioecious, amphi‐Atlantic arctic–alpine sedge that is widely distributed in North America, but absent from most of Eurasia, apart from three extremely disjunct populations in Norway, all well within the limits of the Weichselian ice sheet. Range‐wide population sampling and variation at 5,307 single nucleotide polymorphisms show that the three Norwegian populations comprise unique evolutionary lineages divergent from Greenland with high between‐population divergence. The Norwegian populations have low within‐population genetic diversity consistent with having experienced genetic bottlenecks in glacial refugia, and host private alleles that probably accumulated in long‐term isolated populations. Demographic analyses support a single, pre‐Weichselian colonization into Norway from East Greenland, and subsequent divergence of the three populations in separate refugia. Other refugial areas are identified in North‐east Greenland, Minnesota/Michigan, Colorado and Alaska. Admixed populations in British Columbia and West Greenland indicate postglacial contact. Taken together, evidence from this study strongly indicates in situ glacial survival in Scandinavia.     

Tri-oceanic connectivity of the supposedly cosmopolitan polychaete,Harmothoe imbricata (Annelida: Polynoidae): insights from the COI marker

ABSTRACT

In this study, we investigated the global population genetic structure of the polychaete, Harmothoe imbricata, to determine connectivity patterns within the species. We sequenced the mtDNA marker, cytochrome c oxidase I (COI) from 29 specimens sampled across three sites from the New England coast of the United States. These were supplemented with 145 archived sequences from GenBank and the Barcode of Life Database, representing 16 global populations, which encompassed three broadly defined marine biogeographic regions: the Atlantic, Pacific and Arctic. The resulting haplotype network and pairwise AMOVA results showed marked structure across all the major biogeographic regions and also provides evidence for cryptic diversity in the species. Haplotypes from Arctic populations were more closely related to each other than those from the northwestern and northeastern Atlantic. Two evolutionary divergent lineages were recovered from Los Angeles, California and Manitoba, Canada. The highest genetic diversity was observed in the Arctic populations, providing evidence for an Arctic origin for H. imbricata. While human-mediated introductions may have likely contributed to some of the genetic patterns observed in this study, future work should incorporate a nuclear DNA component which could shed more light on contemporary movement of this species across large spatial scales.     

Fine- and regional-scale genetic structure of the exotic ascidian Styela clava (Tunicata) in southwest England, 50 years after its introduction

Styela clava , an ascidian native to the northwest Pacific, was first recorded in the Atlantic at Plymouth, southwest England, in 1953. It now ranges in the northeast Atlantic from Portugal to northern Denmark, and has colonized the east coast of North America. Within the region of first introduction, we aimed to characterize current genetic diversity in the species, elucidate the respective roles of human-aided vs. natural dispersal, and assess the extent of larval dispersal by looking for genetic differentiation at very small scales. Eight sites, mostly marinas, were studied along c . 200 km of coast in southwest England encompassing Plymouth. Five microsatellite loci were genotyped in 303 individuals to analyse gene flow at regional (among sites) and fine (within sites) scales. F -statistics and assignment tests were used to investigate regional genetic structure. At the fine scale, deviation from mutation–drift equilibrium was tested, and isolation by distance and genetic clustering analyses were undertaken. Significant genetic differentiation existed between sites, unrelated to geographical separation; migration between geographically distant marinas was inferred, highlighting the likely importance of human-mediated dispersal in range expansion and occupancy by S. clava . Fine-scale population structure was present within at least four sites, which may be explained by the limited dispersal ability of this ascidian and recruitment from differentiated pools of larvae. Populations in enclosed marinas had higher self-recruitment rates than those in open sites. Some marinas might therefore function as reservoirs of propagules for subsequent spread, whereas others might be sinks for migrants.     

Phylogeographic mitogenomics of Atlantic cod Gadus morhua: Variation in and among trans‐Atlantic,trans‐Laurentian,Northern cod,and landlocked fjord populations

The historical phylogeography, biogeography, and ecology of Atlantic cod (Gadus morhua) have been impacted by cyclic Pleistocene glaciations, where drops in sea temperatures led to sequestering of water in ice sheets, emergence of continental shelves, and changes to ocean currents. High‐resolution, whole‐genome mitogenomic phylogeography can help to elucidate this history. We identified eight major haplogroups among 153 fish from 14 populations by Bayesian, parsimony, and distance methods, including one that extends the species coalescent back to ca. 330 kya. Fish from the Barents and Baltic Seas tend to occur in basal haplogroups versus more recent distribution of fish in the Northwest Atlantic. There was significant differentiation in the majority of trans‐Atlantic comparisons (Φ_ST = .029–.180), but little or none in pairwise comparisons within the Northwest Atlantic of individual populations (Φ_ST = .000–.060) or defined management stocks (Φ_ST = .000–.023). Monte Carlo randomization tests of population phylogeography showed significantly nonrandom trans‐Atlantic phylogeography versus absence of such structure within various partitions of trans‐Laurentian, Northern cod (NAFO 2J3KL) and other management stocks, and Flemish Cap populations. A landlocked meromictic fjord on Baffin Island comprised multiple identical or near‐identical mitogenomes in two major polyphyletic clades, and was significantly differentiated from all other populations (Φ_ST = .153–.340). The phylogeography supports a hypothesis of an eastern origin of genetic diversity ca. 200–250 kya, rapid expansion of a western superhaplogroup comprising four haplogroups ca. 150 kya, and recent postglacial founder populations.     

Clumping behavior and byssus production as strategies for substrate competition in Mytilus edulis

Laboratory experiments showed that the mussel Mytilus edulis aggregated more intensely around living organisms (the bivalve Hiatella arctica and the solitary ascidian Styela rustica, which commonly co‐occur with mussels in fouling communities) than around inanimate objects. When exposed to an inanimate object, mussels attached their byssal threads primarily to the substrate, close to the object, but when exposed to a living organism, they attached their byssal threads directly to the organism. The ascidian was more intensely covered with byssal threads than was the bivalve. Mussel attachment to the ascidians was apparently determined by the physical characteristics of the tunic and to a lesser extent by the excretion‐secretion products released by S. rustica. This study indicates that mussels can use byssus threads as a means of entrapment of potential competitors for space. It remains unclear why mussels preferentially attached to ascidians compared to the bivalve. This can be explained either by competitive interactions, or by attractiveness of the ascidian tunic as an attachment substratum.     

Recent population expansion and connectivity in the hydrothermal shrimp Rimicaris exoculata along the Mid‐Atlantic Ridge

Aim Deep‐sea hydrothermal vents are unstable habitats that are both spatially and temporally fragmented. In vent species, a ‘short‐term insurance’ hypothesis would lead us to expect mostly self‐recruitment, limiting the loss of larvae in the deep ocean or water column and increasing genetic differentiation over the time elapsed since colonization. Alternatively, a ‘long‐term insurance’ hypothesis would support the prediction of selection for large‐scale dispersal, to ensure long‐term persistence in these ephemeral habitats. The main goal of this study was to infer the spatial and temporal distribution of genetic diversity of the shrimp Rimicaris exoculata, which forms high‐density local populations on hydrothermal vents along the Mid‐Atlantic ridge. Location Deep‐sea hydrothermal vents along the Mid‐Atlantic Ridge. Methods We used sequences of mitochondrial cytochrome c oxidase subunit I (COI, 710 bp) to assess the spatio‐temporal distribution of genetic diversity across five hydrothermal fields from 36° N to 4° S. Results In contrast to previous results from pioneer studies, very high haplotype diversity was observed in vents across the entire region (i.e. 0.69–0.82), indicating current large effective population size and low drift. The star‐like shape of the network of haplotypes, the lack of spatial genetic structure and the significance of tests reflecting demographic effects, together with the fitting of a population expansion model, all support a recent population expansion. Main conclusions Our results suggest a very recent common history of R. exoculata populations/demes along the Mid‐Atlantic Ridge, derived after a common bottleneck or founder event and followed by a concomitant demographic expansion. This study therefore suggests a large effective population size and/or high dispersal capacity, as well as a possible recent (re)colonization of Mid‐Atlantic hydrothermal vents by R. exoculata.     

PHYLOGEOGRAPHIC PATTERNS INDICATE TRANSATLANTIC MIGRATION FROM EUROPE TO NORTH AMERICA IN THE RED SEAWEED CHONDRUS CRISPUS (GIGARTINALES,RHODOPHYTA)1

Inferring how the Pleistocene climate oscillations have repopulated the extant population structure of Chondrus crispus Stackh. in the North Atlantic Ocean is important both for our understanding of the glacial episode promoting diversification and for the conservation and development of marine organisms. C. crispus is an ecologically and commercially important red seaweed with broad distributions in the North Atlantic. Here, we employed both partial mtDNA Cox1 and nrDNA internal transcribed spacer region 2 (ITS2) sequences to explore the genetic structure of 17 C. crispus populations from this area. Twenty‐eight and 30 haplotypes were inferred from these two markers, respectively. Analysis of molecular variance (AMOVA) and of the population statistic Φ_ST not only revealed significant genetic structure within C. crispus populations but also detected significant levels of genetic subdivision among and within populations in the North Atlantic. On the basis of high haplotype diversity and the presence of endemic haplotypes, we postulate that C. crispus had survived in Pleistocene glacial refugia in the northeast Atlantic, such as the English Channel and the northwestern Iberian Peninsula. We also hypothesize that C. crispus from the English Channel refugium repopulated most of northeastern Europe and recolonized northeastern North America in the Late Pleistocene. The observed phylogeographic pattern of C. crispus populations is in agreement with a scenario in which severe Quaternary glaciations influenced the genetic structure of North Atlantic marine organisms with contiguous population expansion and locally restricted gene flow coupled with a transatlantic dispersal in the Late Pleistocene.     

Repeatedly out of Beringia: Cassiope tetragona embraces the Arctic

Aim Eric Hultén hypothesized that most arctic plants initially radiated from Beringia in the Late Tertiary and persisted in this unglaciated area during the Pleistocene glaciations, while their distribution ranges were repeatedly fragmented and reformed elsewhere. Whereas taxonomic and fossil evidence suggest that Cassiope tetragona originated in Beringia and expanded into the circumarctic area before the onset of the glaciations, lack of chloroplast DNA (cpDNA) variation may suggest that colonization was more recent. We address these contradictory scenarios using high‐resolution nuclear markers. Location Circumpolar Arctic. Methods The main analysis was by amplified fragment‐length polymorphism (AFLP), while sequences of chloroplast DNA verified the use of Cassiope mertensiana as an outgroup for C. tetragona. Data were analysed using Bayesian clustering, principal coordinates analyses, parsimony and neighbour‐joining, and measures of diversity and differentiation were calculated. Results The circumpolar C. tetragona ssp. tetragona was well separated from the North American C. tetragona ssp. saximontana. The genetic structure in ssp. tetragona showed a strong east–west trend, with the Beringian populations in an intermediate position. The highest level of diversity was in Beringia, while the strongest differentiation in the data set was found between the populations from the Siberian Arctic west of Beringia and the remainder. Main conclusions The results are consistent with a Beringian origin of the species, but the levels and geographical patterns of differentiation and gene diversity suggest that the latest expansion from Beringia into the circumarctic was recent, possibly during the current interglacial. The results are in accordance with a recent leading‐edge mode of colonization, particularly towards the east throughout Canada/Greenland and across the North Atlantic into Scandinavia and Svalbard. As fossils demonstrate the presence of the species in North Greenland 2.5–2.0 Ma, as well as in the previous interglacial, we conclude that C. tetragona expanded eastwards from Beringia several times and that the earlier emigrants of this woody species became extinct. The last major westward expansion from Beringia seems older, and the data suggest a separate Siberian refugium during at least one glaciation.     

Pleistocene glaciations and contemporary genetic diversity in a Beringian fish,the broad whitefish,Coregonus nasus (Pallas): inferences from microsatellite DNA variation

The contemporary distribution of genetic variation within and among high latitude populations cannot be fully understood without taking into consideration how species responded to the impacts of Pleistocene glaciations. Broad whitefish, Coregonus nasus, a species endemic to northwest North America and the Arctic coast of Russia, was undoubtedly impacted by such events because its geographic distribution suggests that it survived solely within the Beringian refuge from where it dispersed post‐glacially to achieve its current range. We used microsatellite DNA to investigate the role of glaciations in promoting intraspecific genetic variation in broad whitefish (N = 14 localities, 664 fish) throughout their North American range and in one Russian sample. Broad whitefish exhibited relatively high intrapopulation variation (average of 11.7 alleles per locus, average H_E = 0.61) and moderate levels of interpopulation divergence (overall F_ST = 0.10). The main regions assayed in our study (Russia, Alaska, Mackenzie River and Travaillant Lake systems) were genetically differentiated from each other and there were declines in genetic diversity with distance from putative refugia. Additionally, Mackenzie River system populations showed less developed and more variable patterns of isolation‐by‐distance than populations occupying former Alaskan portions of Beringia. Finally, our data suggest that broad whitefish dispersed from Beringia using coastal environments and opportunistically via headwater stream connections that once existed between Yukon and Mackenzie River drainages. Our results illustrate the importance of history (e.g. glaciation) and contemporary dispersal ecology in shaping the current genetic population structure of Arctic faunas.     

Phylogeography of an estuarine mysid, Neomysis integer (Crustacea, Mysida), along the north-east Atlantic coasts

Aim The brackish water mysid, Neomysis integer, is one of the most common mysid species along the coasts of the north‐east Atlantic. In the present study, the phylogeographical patterns were examined throughout the distribution range of N. integer. In particular, the latitudinal trends in genetic diversity and the distribution of genetic variation were examined in order to elucidate the imprints of the Pleistocene glaciations. Location North‐east Atlantic coasts from the Baltic Sea to the south of Spain. Methods A total of 461 specimens from 11 populations were analysed by means of single‐stranded conformation polymorphism analysis combined with DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase I gene. The genetic structure was examined by using a progression of phylogenetic, demographic and population genetic analyses to elucidate not only the geographical structure, but also the evolutionary history producing that structure. Results The levels of genetic diversity were relatively uniform throughout the distribution range, with the exception of a decline at the northern and southern edges of distribution. A high heterogeneity was observed between the populations analysed (global Φ_ST = 0.787). This is caused by the disparate distribution of the cytochrome oxidase I haplotypes, with several population‐specific haplotypes. A clear genetic break (2.4% sequence divergence) occurred between the southernmost Guadalquivir population and all other populations. Main conclusions The present study corroborates the expectations of the genetic patterns typically observed in an estuarine species. The within‐population variability was low, whereas a significant (moderate to high) divergence was observed between populations. Phylogeographical analysis revealed that northern populations within the English Channel, North Sea and Baltic Sea are characterized by several widespread haplotypes, while the Irish population and all sites south of the Bay of Biscay consist solely of unique haplotypes. This pattern, combined with the relative high levels of genetic diversity, could be indicative for the presence of a glacial refugium in the English Channel region. Under this scenario N. integer must have survived the Last Glacial Maximum in the palaeoriver system present in that region.     

Colonization of vegetation-rich moraines and inference of multiple sources of colonization in the High Arctic for Salix arctica

Vegetation-rich patches in the High Arctic may serve as a significant source for vegetation reconstruction in the climate changes. Diversity and colonization, however, of such potential source populations in the High Arctic has rarely been studied. We examined chloroplast sequence variation in Salix arctica, a key species in the Canadian High Arctic, from four adjacent glacial moraines of differing ages on Ellesmere Island, Canada, as well as two other populations located at the center and southern end of the species’ range. The estimated ages of the moraines varied from 35,000 to 250 years old. The older moraine populations showed higher within-population genetic variation compared with the other moraine populations, which is generally attributed to differences in establishment age associated with plant densities among moraines. The moraines with smaller plant density had lower genetic diversity and had no private haplotypes, indicating the local population size and genetic diversity may not be recovered within a few thousand years. This suggests seed dispersal at a local scale may be limited even in species with high velocity of seed dispersal, and that High Arctic vegetation-rich patches may serve as significant source populations for sustaining local genetic diversity. In addition, the three regions we observed comprised an evolutionarily distinct lineage and significant population differentiation. This implies multiple sources for the colonization during the most recent deglaciation, resulting in the current wide distribution. Local as well as range-wide processes of colonization would be essential to understand vegetation responses in High Arctic to the environmental changes.     

High levels of population subdivision in a morphologically conserved Mediterranean toad (Alytes cisternasii) result from recent,multiple refugia: evidence from mtDNA,microsatellites and nuclear genealogies

Pleistocene glaciations often resulted in differentiation of taxa in southern European peninsulas, producing the high levels of endemism characteristic of these regions (e.g. the Iberian Peninsula). Despite their small ranges, endemic species often exhibit high levels of intraspecific differentiation as a result of a complex evolutionary history dominated by successive cycles of fragmentation, expansion and subsequent admixture of populations. Most evidence so far has come from the study of species with an Atlantic distribution in northwestern Iberia, and taxa restricted to Mediterranean‐type habitats remain poorly studied. The Iberian Midwife toad (Alytes cisternasii) is a morphologically conserved species endemic to southwestern and central Iberia and a typical inhabitant of Mediterranean habitats. Applying highly variable genetic markers from both mitochondrial and nuclear genomes to samples collected across the species’ range, we found evidence of high population subdivision within A. cisternasii. Mitochondrial haplotypes and microsatellites show geographically concordant patterns of genetic diversity, suggesting population fragmentation into several refugia during Pleistocene glaciations followed by subsequent events of geographical and demographic expansions with secondary contact. In addition, the absence of variation at the nuclear β‐fibint7 and Ppp3caint4 gene fragments suggests that populations of A. cisternasii have been recurrently affected by episodes of extinction and recolonization, and that documented patterns of population subdivision are the outcome of recent and multiple refugia. We discuss the evolutionary history of the species with particular interest in the increasing relevance of Mediterranean refugia for the survival of genetically differentiated populations during the Pleistocene glaciations as revealed by studies in co‐distributed taxa.