Distribution, shape and clonal growth of the rare endemic tree Olea europaea subsp. laperrinei (Oleaceae) in the Saharan mountains of Niger

The populations of the Laperrine’s olive (Olea europaea subsp. laperrinei) are located in three main areas corresponding to the mountains of northern Niger (Aïr), southern Algeria (Hoggar), and north-western Sudan (western Darfur). The populations native of Niger were found to occur in very fragmented patches from 1550 to 1850 m in five isolated mountains with population sizes not exceeding 100 trees each, except in the Tamgak. Samples in the Tamgak and the Bagzane mountains were studied by combining field observations with identification of genets (using highly variable DNA marker analyzes). Trees were relatively small and multi-stemmed like those in the Hoggar, and were associated with some tropical species as in the western Darfur. They were found on borders of “wadis”, i.e., temporary water courses, in ravines and on hillsides. They were unable to rely on sexual reproduction, which was found to be ineffective. In contrast, 28% of the genetic profiles found (n _genet = 98) were represented with two or more trees without aboveground connections. Molecular and morphological data both demonstrated that the populations used clonal growth (CG) to survive in the current unfavorable period of hyper-aridity, and thus are likely to be remnant populations. Signs of human-related disturbances, recorded on 43% of the sampled trees, should be a determining factor of distribution as well. In the Bagzane mountains especially, where human activities are more intense than in the Tamgak mountains, trees developed preferentially on hillsides and ravines with low access rather than on wadi borders with better edaphic conditions but easier access for livestock/people. CG may be therefore, a survival strategy both against aridity and human-related disturbances. Sexual reproduction may be triggered during a less arid period, following the model of multiple demographic strategies, widespread in arid environments. However, survival would be affected by browsing and cuttings. Lastly, the absence of an efficient sexual strategy coupled with the high fragmentation of very small populations and a narrow altitudinal range of distribution indicates that today the populations of O. e. laperrinei in the Aïr mountain range are more endangered than those from southern Algeria and north-western Sudan.     

On chloroplast DNA variations in the olive ( Olea europaea L.) complex: comparison of RFLP and PCR polymorphisms

Previous papers have dealt with olive chloroplastic DNA (cpDNA) variation revealed using several methods (RFLPs, PCR-RFLPs and microsatellites) and have led to different conclusions. This paper aims to reconsider these divergences. A Southern approach was applied to reveal polymorphism. We used chloroplast DNA of Phillyrea media as a probe. Based on these data, only four chlorotypes were identified in the olive complex. The number of detected lineages was lower than reported in the literature using a direct cpDNA RFLP approach, and was insufficient to distinguish the North African subspecies europaea, maroccana, guanchica and laperrinei. Furthermore, one individual considered belonging to the subspecies laperrinei was questionable. Using other cpDNA and mitochondrial DNA (mtDNA) polymorphisms - based on PCR and RFLP methods, respectively - we showed that this individual displays the cytoplasmic lineage CE1-ME1 characteristic of most Eastern mediterranean cultivars and of Olea europaea subsp. laperrinei from Hoggar. However, based on RAPDs, this individual appeared as mislabelled and probably corresponded to a Mediterranean cultivar or a feral form. In addition, we checked O. e. subsp. laperrinei herbarium samples using two cpDNA microsatellites, which revealed polymorphisms. These also supported that both populations from Niger and Algeria displayed a chlorotype related to CE1. Consequently, based on cpDNA, the relationships of O. e. subsp. laperrinei from Hoggar with a Mediterranean lineage appeared well supported, whereas the South West Moroccan and Macaronesian olives appeared in a different clade using both mtDNA and cpDNA polymorphisms. We conclude that methods based on PCR reveal more polymorphisms in the cpDNA and lead to more-reliable results that the classical RFLP method.     

High genetic diversity and clonal growth in relict populations of Olea europaea subsp. laperrinei (Oleaceae) from Hoggar, Algeria

BACKGROUND AND AIMS: The Laperrine's olive (Olea europaea subsp. laperrinei) is an endemic tree from Saharan massifs. Its populations have substantially regressed since the Pleistocene and are presently distributed in a fragmented habitat. Long-term persistence of this taxon is uncertain and programmes of preservation have to be urgently implemented. To define a conservation strategy, the genetic diversity and breeding system of this tree have to be investigated. METHODS: One hundred and eleven ramets were prospected in the laperrinei populations from the Tamanrasset region, southern Algeria. Genetic polymorphism was revealed at nuclear and chloroplast DNA (cpDNA) microsatellite loci allowing a comparative assessment of the genetic diversity of laperrinei and Mediterranean populations based on bi-parental and maternal markers. Additionally, nuclear microsatellite markers enabled the genotypes to be identified unambiguously. KEY RESULTS: Based on nuclear microsatellite data, the total diversity was high (Ht=0.61) in laperrinei populations and similar to that observed in western Mediterranean populations. A substantial cpDNA diversity (Ht=0.19) was also observed. Genetically identical ramets originated from the same stump (which can cover >80 m2) were identified in each population. Sixteen per cent of genets exhibited more than one ramet. In addition, several cases of somatic mutations were unambiguously revealed in distinct ramets stemming from the same stump. CONCLUSIONS: These data show that highly isolated and small laperrinei populations are able to maintain a high genetic diversity. This supports the existence of relict trees persisting for a very long time (probably since the last humid transition, 3000 years ago). It is proposed that the very long persistence associated with an asexual multiplication of highly adapted trees could be a strategy of survival in extreme conditions avoiding a mutational meltdown due to reproduction in reduced populations.     

Relative importance of pollen and seed dispersal across a Neotropical mountain landscape for an epiphytic orchid

Populations of many species are isolated within narrow elevation bands of Neotropical mountain habitat, and how well dispersal maintains genetic connectivity is unknown. We asked whether genetic structure of an epiphytic orchid, Epidendrum firmum, corresponds to gaps between Costa Rican mountain ranges, and how these gaps influence pollen and seed flow. We predicted that significant genetic structure exists among mountain ranges due to different colonization histories and limited gene flow. Furthermore, we predicted that pollen movement contributes more to gene flow than seeds because seeds are released into strong winds perpendicular to the narrow northwest–southeast species distribution, while the likely pollinators are strong fliers. Individuals from 12 populations and three mountain ranges were genotyped with nuclear microsatellites (nDNA) and chloroplast sequences (cpDNA). Genetic diversity was high for both markers, while nDNA genetic structure was low (F_STn = 0.020) and cpDNA structure was moderate (F_STc = 0.443). Significant cpDNA barriers occurred within and among mountain ranges, but nDNA barriers were not significant after accounting for geographic distance. Consistent with these contrasting patterns of genetic structure, pollen contributes substantially more to gene flow among populations than seed (m_p/m_s = 46). Pollinators mediated extensive gene flow, eroding nDNA colonization footprints, while seed flow was comparatively limited, possibly due to directional prevailing winds across linearly distributed populations. Dispersal traits alone may not accurately inform predictions about gene flow or genetic structure, supporting the need for research into the potentially crucial role of pollinators and landscape context in gene flow among isolated populations.     

The role of geography and ecology in shaping repeated patterns of morphological and genetic differentiation between European minnows (Phoxinus phoxinus) from the Pyrenees and the Alps

Neutral and selective processes can drive repeated patterns of evolution in different groups of populations experiencing similar ecological gradients. In this paper, we used a combination of nuclear and mitochondrial DNA markers, as well as geometric morphometrics, to investigate repeated patterns of morphological and genetic divergence of European minnows in two mountain ranges: the Pyrenees and the Alps. European minnows (Phoxinus phoxinus) are cyprinid fish inhabiting most freshwater bodies in Europe, including those in different mountain ranges that could act as major geographical barriers to gene flow. We explored patterns of P. phoxinus phenotypic and genetic diversification along a gradient of altitude common to the two mountain ranges, and tested for isolation by distance (IBD), isolation by environment (IBE) and isolation by adaptation (IBA). The results indicated that populations from the Pyrenees and the Alps belong to two well differentiated, reciprocally monophyletic mtDNA lineages. Substantial genetic differentiation due to geographical isolation within and between populations from the Pyrenees and the Alps was also found using rapidly evolving AFLPs markers (isolation by distance or IBD), as well as morphological differences between mountain ranges. Also, morphology varied strongly with elevation and so did genetic differentiation to a lower extent. Despite moderate evidence for IBE and IBA, and therefore of repeated evolution, substantial population heterogeneity was found at the genetic level, suggesting that selection and population specific genetic drift act in concert to affect genetic divergence.     

Phylogeography of the montane caddisfly Drusus discolor: evidence for multiple refugia and periglacial survival

We studied the genetic population structure and phylogeography of the montane caddisfly Drusus discolor across its entire range in central and southern Europe. The species is restricted to mountain regions and exhibits an insular distribution across the major mountain ranges. Mitochondrial sequence data (COI) of 254 individuals from the entire species range is analysed to reveal population genetic structure. The data show little molecular variation within populations and regions, but distinct genetic differentiation between mountain ranges. Most populations are significantly differentiated based on F(ST) and exact tests of population differentiation and most haplotypes are unique to a single mountain range. Phylogenetic analyses reveal deep divergence between geographically isolated lineages. Combined, these results suggest that past fragmentation is the prominent process structuring the populations across Europe. We use tests of selective neutrality and mismatch distributions, to study the demographic population history of regions with haplotype overlap. The high level of genetic differentiation between mountain ranges and estimates of demographic history provide evidence for the existence of multiple glacial refugia, including several in central Europe. The study shows that these aquatic organisms reacted differently to Pleistocene cooling than many terrestrial species. They persisted in numerous refugia over multiple glacial cycles, allowing many local endemic clades to form.     

Lack of sex-biased dispersal promotes fine-scale genetic structure in alpine ungulates

Identifying patterns of fine-scale genetic structure in natural populations can advance understanding of critical ecological processes such as dispersal and gene flow across heterogeneous landscapes. Alpine ungulates generally exhibit high levels of genetic structure due to female philopatry and patchy configuration of mountain habitats. We assessed the spatial scale of genetic structure and the amount of gene flow in 301 Dall’s sheep (Ovis dalli dalli) at the landscape level using 15 nuclear microsatellites and 473 base pairs of the mitochondrial (mtDNA) control region. Dall’s sheep exhibited significant genetic structure within contiguous mountain ranges, but mtDNA structure occurred at a broader geographic scale than nuclear DNA within the study area, and mtDNA structure for other North American mountain sheep populations. No evidence of male-mediated gene flow or greater philopatry of females was observed; there was little difference between markers with different modes of inheritance (pairwise nuclear DNA F _ST = 0.004–0.325; mtDNA F _ST = 0.009–0.544), and males were no more likely than females to be recent immigrants. Historical patterns based on mtDNA indicate separate northern and southern lineages and a pattern of expansion following regional glacial retreat. Boundaries of genetic clusters aligned geographically with prominent mountain ranges, icefields, and major river valleys based on Bayesian and hierarchical modeling of microsatellite and mtDNA data. Our results suggest that fine-scale genetic structure in Dall’s sheep is influenced by limited dispersal, and structure may be weaker in populations occurring near ancestral levels of density and distribution in continuous habitats compared to other alpine ungulates that have experienced declines and marked habitat fragmentation.     

Predicted range shifts in North American boreal forest birds and the effect of climate change on genetic diversity in blackpoll warblers (Setophaga striata)

As North American species’ ranges shift northward in response to climate change, populations isolated in high-elevation habitat “islands” at the southern edge of distributions are predicted to decrease in size or be extirpated. Levels of genetic structure and gene flow and the number of private alleles held within these peripheral populations can be used as a measure of the potential loss of genetic diversity due to climate change. We use GIS-based climate niche models to project geographic distributions of 15 boreal forest bird species for the year 2080 under two carbon emissions scenarios to predict the extent to which ranges will shift, leading to the extirpation of isolated populations at the southern periphery of the boreal forest. Breeding distributions of nearly all boreal bird species are predicted to expand as they shift northward, but will dramatically decrease or be completely lost from mountain populations in New York, Vermont, and New Hampshire by 2080. To examine the effect of these shifts on gene pools of migratory bird species we genotyped 178 blackpoll warblers (Setophaga striata) at nine microsatellite loci, sampling four imperiled high-elevation populations and four northern populations. In S. striata 10.4 % of microsatellite alleles were confined to populations expected to be lost due to climate change. However, these accounted for a nonsignificant percent of the genetic structure, and loss of these alleles would not significantly erode species heterozygosity or allelic richness. Our results indicate that isolated southern populations of S. striata, and possibly other migratory species with high gene flow, do not represent genetically isolated, independently evolving units. Efforts to mitigate the effect of climate change on boreal forest birds should focus on species in which peripheral populations harbor significant genetic diversity.     

Implications of Anthropogenic Landscape Change on Inter-Population Movements of the Desert Tortoise (Gopherus agassizii)

In the Sonoran Desert of North America, populations of the desert tortoise (Gopherus agassizii) occur in rocky foothills throughout southwestern Arizona and northwestern Mexico. Although tortoise populations appear to be isolated from each other by low desert valleys, individuals occasionally move long distances between populations. Increasingly, these movements are hindered by habitat fragmentation due to anthropogenic landscape changes. We used molecular techniques and radiotelemetry to examine movement patterns of desert tortoises in southern Arizona. We collected blood samples from 170 individuals in nine mountain ranges and analyzed variability in seven microsatellite loci to determine genetic differentiation among populations. Gene flow estimates between populations indicate that populations exchanged individuals historically at a rate greater than one migrant per generation, and positive correlation between genetic and geographic distance of population pairs suggests that the limiting factor for gene flow among populations is isolation by distance. Life history traits of the desert tortoise, a long-lived species with delayed sexual maturity, may severely constrain the ability of small populations to respond to disturbances that increase adult mortality. Historic gene flow estimates among populations suggests that recovery of declining populations may rely heavily on the immigration of new individuals from adjacent mountain ranges. Management strategies compatible with the evolutionary history of gene flow among disjunct populations will help ensure the long-term persistence of Sonoran desert tortoise populations.     

Population genetic structure of the oriental fruit fly, <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> (Hendel) (Diptera: Tephritidae) from Yunnan province (China) and nearby sites across the border

Bactrocera dorsalis (Diptera: Tephritidae) is an important pest for many tropical and subtropical fruits. The fly is probably introduced in Yunnan, a southwestern province of China that shares borders with Vietnam, Laos and Myanmar. Depending on local environmental conditions, this species occurs either only in the most favorable seasons or year-round. To infer the genetic diversity and structure of the fly in the region, and to understand the relationships between the flies of year-round and seasonal areas, we analyzed 304 individuals from 14 populations using the mitochondrial cytochrome oxidase I gene (COI). The sampled populations were structured into four groups, probably isolated by the main natural barriers in Yunnan such as mountain ranges and rivers. Our data suggest either that B. dorsalis in Yunnan originated from multiple introductions events, even if the source populations still need to be identified; or that Yunnan is a natural origin of this species (i.e., that it is not invasive there). Finally, we found some evidences that the seasonal populations were colonized from nearby year-round populations.     

江西主要山脉春兰野生居群遗传结构与分化

利用ISSR分子标记对江西省主要山脉的21个春兰(Cymbidium goeringii(Rchb.f.)Rchb.f.)居群进行居群遗传结构研究。结果显示,利用14个筛选的引物共扩增出139条条带,其中多态性条带118条,多态性条带百分率(PPL)为84.89%。21个居群的Nei s基因多样性(He)为0.2292,Shannon指数(I)为0.3613。AMOVA分析表明,春兰居群间变异占50.79%,居群内变异占49.21%,居群间的遗传分化大于居群内的分化。STRUCTURE群体遗传结构和UPGMA聚类分析均表明,江西主要山脉的春兰居群存在地理隔离和生境片断化。推测江西春兰曾广泛分布于罗霄山脉和武夷山脉,受第四纪冰期影响,春兰群体因气候剧烈变化而骤减,仅在山脉间适宜的环境中得以保存并繁衍至今,罗霄山脉和武夷山脉是春兰最主要的两个冰期避难所。综合遗传多样性与居群遗传结构特点,建议在遗传多样性较高的石城(SC)、宜丰(YF)、贵溪(GX)居群设点进行就地保护;对资源破坏严重的大余(DY)和井冈山(JGS)居群实行迁地保护。     

Genetic population structure of the net-winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south-western Cape, South Africa: implications for dispersal

SUMMARY 1. The net‐winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net‐winged midge should exhibit a high degree of population sub‐structuring. 2. Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south‐western Cape of South Africa. 3. Twenty‐five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour‐joining tree revealed two highly divergent clades (～5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units. 4. The distribution of genetic variation was examined using analysis of molecular variance (amova ). This showed most of the variation to be distributed among the two ranges (～80%), with a small percentage (～15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001). 5. Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra‐generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna. 6. The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi.     

Unicoloniality, recognition and genetic differentiation in a native Formica ant

Some ants have an extraordinary form of social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This mode of social organization has been primarily studied in introduced and invasive ant species, so that the recognition ability and genetic structure of ants forming unicolonial populations in their native range remain poorly known. We investigated the pattern of aggression and the genetic structure of six unicolonial populations of the ant Formica paralugubris at four hierarchical levels: within nests, among nests within the same population, among nests of populations within the Alps or Jura Mountains and among nests of the two mountain ranges. Ants within populations showed no aggressive behaviour, but recognized nonnestmates as shown by longer antennation bouts. Overall, the level of aggression increased with geographic and genetic distance but was always considerably lower than between species. No distinct behavioural supercolony boundaries were found. Our study provides evidence that unicoloniality can be maintained in noninvasive ants despite significant genetic differentiation and the ability to discriminate between nestmates and nonnestmates.     

The influence of a competitor on the geographic mosaic of coevolution between crossbills and lodgepole pine

The geographic mosaic theory of coevolution posits that the form of selection between interacting species varies across a landscape with coevolution important and active in some locations (i.e., coevolutionary hotspots) but not in others (i.e., coevolutionary coldspots). We tested the hypothesis that the presence of red squirrels (Tamiasciurus hudsonicus) affects the occurrence of coevolution between red crossbills (Loxia curvirostra complex) and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) and thereby provides a mechanism giving rise to a geographic mosaic of selection. Red squirrels are the predominant predispersal seed predator and selective agent on lodgepole pine cones. However, in four isolated mountain ranges east and west of the Rocky Mountains, red squirrels are absent and red crossbills are the main predispersal seed predator. These isolated populations of pine have apparently evolved without Tamiasciurus for about 10,000 to 12,000 years. Based on published morphological, genetic, and paleobotanical studies, we infer that cone traits in these isolated populations that show parallel differences from cones in the Rocky Mountains have changed in parallel. We used data on crossbill and conifer cone morphology and feeding preferences and efficiency to detect whether red crossbills and lodgepole pine exhibit reciprocal adaptations, which would imply coevolution. Cone traits that act to deter Tamiasciurus and result in high ratios of cone mass to seed mass were less developed in the isolated populations. Cone traits that act to deter crossbills include larger and thicker scales and perhaps increased overlap between successive scales and were enhanced in the isolated populations. In the larger, isolated mountain ranges crossbills have evolved deeper, shorter, and therefore more decurved bills to exploit these cones. This provides crossbills with higher feeding rates, and the change in bill shape has improved efficiency by reducing the concomitant increases in body mass and daily energy expenditures that would have resulted if only bill size had increased. These parallel adaptations and counter adaptations in red crossbills and lodgepole pine are interpreted as reciprocal adaptations and imply that these crossbills and pine are in coevolutionary arms races where red squirrels are absent (i.e., coevolutionary hotspots) but not where red squirrels are present (i.e., coevolutionary cold-spots).     

Nuclear DNA microsatellites reveal genetic variation but a lack of phylogeographical structure in an endangered species, Fraxinus mandshurica, across North-east China

Background and Aims

The widely accepted paradigm that the modern genetic structure of plant species in the northern hemisphere has been largely determined by recolonization from refugia after the last glacial maximum fails to explain the presence of cold-tolerant species at intermediate latitudes. Another generally accepted paradigm is that mountain ridges act as important barriers causing genetic isolation of species, but this too has been challenged in recent studies. The aims of the work reported here were to determine the genetic diversity and distribution patterns of extant natural populations of an endangered cool temperate species, Faxinus mandshurica, and to examine whether these two paradigms are appropriate when applied to this species over a wide geographical scale.

Methods

1435 adult individuals were sampled from 30 natural populations across the main and central range of the species, covering major mountain ranges across North-east China (NEC). Genetic variation was estimated based on nine polymorphic nuclear microsatellite loci. Phylogeographical analyses were employed using various approaches, including Bayesian clustering, spatial analysis of molecular variance, Monmonier''s algorithm, neighbor-joining trees, principal co-ordinate analysis and isolation by distance.

Key Results

Genetic diversity within populations was relatively high, and no significant recent bottlenecks were detected in any of the populations. A significant negative correlation between intra-population genetic diversity and latitude was identified. In contrast, genetic differentiation among all the populations examined was extremely low and no clear geographic genetic structure was identified, with the exception of one distinct population.

Conclusions

The modern genetic structure in this species can be explained by extensive gene flow, an absence of mountains acting as barriers, and the presence of a wide refuge across NEC rather than multiple small refugia. Intra-population genetic variation along latitudes is probably associated with the systematically northward shifts of forest biomes in eastern China during the mid-Holocene. To determine important genetic patterns and identify resources for conservation, however, it will be necessary to examine differentially inherited genetic markers exposed to selection pressures (e.g. chloroplast DNA) and to investigate different generations.Key words: Fraxinus mandshurica, nuclear microsatellites, latitude variation, historical migration, fossil pollen, spatial genetic structure, genetic barriers     

Genetic structure in Pinus cembra from the Carpathian Mountains inferred from nuclear and chloroplast microsatellites confirms post-glacial range contraction and identifies introduced individuals

Genetic differentiation of scattered populations at neutral loci is characterized by genetic drift counteracted by the remaining gene flow. Populations of Pinus cembra in the Carpathian Mountains are isolated and restricted to island-like stands at high-elevation mountain ranges. In contrast, paleobotanical data suggest an extended early Holocene distribution of P. cembra in the Carpathians and its surrounding areas, which has contracted to the currently disjunct occurrences. We analyzed the genetic variation of 11 Carpathian populations of P. cembra at chloroplast and, in part newly developed, nuclear microsatellites. Both marker types revealed low levels of genetic differentiation and a lack of isolation by distance, reflecting the post-glacial retraction of the species to its current distribution. Stronger effects of genetic drift were implied by the higher genetic differentiation found for haploid chloroplast than for diploid nuclear markers. Moreover, we found no association between the values of population genetic differentiation for the two marker types. Several populations indicated recent genetic bottlenecks and inbreeding as a consequence of decline in population sizes. Moreover, we found individuals in two populations from the Rodnei Mountains that strikingly differed in assignment probabilities from the remaining specimens, suggesting that they had been introduced from a provenance outside the studied populations. Comparison with Eastern Alpine P. cembra and individuals of the closely related Pinus sibirica suggests that these individuals presumably are P. sibirica. Our study highlights the importance of the maintenance of sufficiently large local population sizes for conservation due to low connectivity between local occurrences.     

Isozyme polymorphisms provide evidence of clinal variation with elevation in Nothofagus pumilio

Variable physical conditions along elevational gradients strongly influence patterns of genetic differentiation in tree species. Here, the hypothesis is tested that different growth forms of Nothofagus pumilio, which characterizes the subalpine forests in the southern Andes, will display continuous genetic variation with elevation. At each of four elevational strips in three different mountain ranges, fresh leaf tissue was sampled from 30 randomly selected individuals to be analyzed by protein electrophoresis. Allelic frequencies were used to test for heterogeneity across populations and to classify populations into different elevational strips by discriminant analysis. The degree of population divergence was estimated by F(ST). Clinical variation on within-population genetic characteristics was analyzed by linear regressions against elevation. Seven enzyme systems coded for 14 putative isozyme loci, 57% of which were polymorphic in at least one population. Allele frequencies significantly varied with elevation and discriminant analysis separated populations at different elevational strips. Among-population divergence within any mountain range was small, but greater than among different mountain ranges. Overall, low-elevation populations were more variable than high-elevation populations, and regression analyses suggested continuous variation in populations of N. pumilio 100 m apart. Marked stepwise phenological differences on mountain slopes are most probably responsible for the isolation of nearby populations.     

Testing Pleistocene refugia theory: phylogeographical analysis of Desmognathus wrighti,a high-elevation salamander in the southern Appalachians

During the colder climates of the Pleistocene, the ranges of high-elevation species in unglaciated areas may have expanded, leading to increased gene flow among previously isolated populations. The phylogeography of the pygmy salamander, Desmognathus wrighti, an endemic species restricted to the highest mountain peaks of the southern Appalachians, was examined to test the hypothesis that the range of D. wrighti expanded along with other codistributed taxa during the Pleistocene. Analyses of genetic variation at 14 allozymic loci and of the 12S rRNA gene in the mtDNA genome was conducted on individuals sampled from 14 population isolates throughout the range of D. wrighti. In contrast to the genetic patterns of many other high-elevation animals and plants, genetic distances derived from both molecular markers showed significant isolation by distance and genetic structuring of populations, suggesting long-term isolation of populations. Phylogeographical analyses revealed four genetically distinct population clusters that probably remained fragmented during the Pleistocene, although there was also evidence supporting recent gene flow among some population groups. Support for isolation by distance is rare among high-elevation species in unglaciated areas of North and Middle America, although not uncommon among Plethodontid Salamanders, and this pattern suggests that populations of D. wrighti did not expand entirely into suitable habitat during the Pleistocene. We propose that intrinsic barriers to dispersal, such as species interactions with other southern Appalachian plethodontid salamanders, persisted during the Pleistocene to maintain the fragmented distribution of D. wrighti and allow for significant genetic divergence of populations by restricting gene flow.     

Impact of urban fragmentation on the genetic structure of the eastern red-backed salamander

Urban development is a major cause of habitat loss and fragmentation. Few studies, however, have dealt with fragmentation in an urban landscape. In this paper, we examine the genetic structure of isolated populations of the eastern red-backed salamander (Plethodon cinereus) in a metropolitan area. We sampled four populations located on a mountain in the heart of Montréal (Québec, Canada), which presents a mosaic of forested patches isolated by roads, graveyards and buildings. We assessed the genetic structure of these populations using microsatellite loci and compared it to the genetic structure of four populations located in a continuous habitat in southern Québec. Our results indicate that allelic richness and heterozygosity are lower in the urban populations. Exact differentiation tests and pairwise F _ST also show that the populations found in the fragmented habitat are genetically differentiated, whereas populations located in the continuous habitat are genetically homogeneous. These results raise conservation concerns for these populations as well as for rare or threatened species inhabiting urban landscapes.     

Range-wide genetic structure in a north-east Asian spruce (Picea jezoensis) determined using nuclear microsatellite markers

Aim We used microsatellite markers to determine the range‐wide genetic structure of Picea jezoensis and to test the hypothesis that the past population history of this widespread cold‐temperate spruce has resulted in a low level of genetic variation and in imprints of inbreeding and bottlenecks in isolated marginal populations. Location The natural range of the three infraspecific taxa of P. jezoensis throughout north‐east Asia, including isolated marginal populations. Methods We analysed a total of 990 individuals across 33 natural populations using four nuclear microsatellite loci. Population genetic structure was assessed by analysing genetic diversity indices for each population, examining clustering (model‐based and distance‐based) among populations, evaluating signals of recent bottlenecks, and testing for isolation by distance (IBD). Results The 33 populations were clustered into five groups. The isolated marginal groups of populations (in Kamchatka, Kii in Japan and South Korea) exhibited low levels of allelic richness and gene diversity and a complete or almost complete loss of rare alleles. A recent bottleneck was detected in the populations in Hokkaido across to mid‐Sakhalin. The IBD analysis revealed that genetic divergence between populations was higher for populations separated by straits. Main conclusions Picea jezoensis showed a higher level of genetic differentiation among populations (F_ST = 0.101) than that observed in the genus Picea in general. This might be attributable to the fact that historically the straits around Japan acted as barriers to the movement of seeds and pollen. The low levels of genetic diversity in the isolated marginal population groups may reflect genetic drift that has occurred after isolation. Evidence of a significant bottleneck between the Hokkaido and mid‐Sakhalin populations implies that the cold, dry climate in the late Pleistocene resulted in the decline and contraction of populations, and that there was a subsequent expansion followed by a founder effect when conditions improved. The high polymorphism observed in P. jezoensis nuclear microsatellites revealed cryptic genetic structure that organellar DNA markers failed to identify in a previous study.