Variation in the chloroplast DNA of Swiss stone pine (Pinus cembra L.) reflects contrasting post-glacial history of populations from the Carpathians and the Alps

Aim To characterize the genetic structure and diversity of Pinus cembra L. populations native to two disjunct geographical areas, the Alps and the Carpathians, and to evaluate the rate of genetic differentiation among populations. Location The Swiss Alps and the Carpathians. Methods We screened 28 populations at three paternally inherited chloroplast simple sequence repeats (cpSSRs) for length variation in their mononucleotide repeats. Statistical analysis assessed haplotypic variation and fixation indices. Hierarchical analysis of molecular variance (AMOVA), Mantel test, spatial analysis of molecular variance (SAMOVA) and barrier analyses were applied to evaluate the geographical partitioning of genetic diversity across the species’ range. Results Haplotypic diversity was generally high throughout the natural range of P. cembra, with the mean value substantially higher in the Carpathians (H = 0.53) than in the Alps (H = 0.35). The isolated Carpathian populations showed the highest haplotype diversity among the populations originating from the High Tatras (Velka Studena Dolina) and South Carpathians (Retezat Mountains). AMOVA revealed that only 3% of the total genetic variation derived from genetic differentiation between the two mountain ranges. Differentiation among Carpathian populations was higher (F_ST = 0.19) than among Alpine populations (F_ST = 0.04). Low, but significant, correlation was found between the geographical and genetic distances among pairs of populations (r = 0.286, P < 0.001). SAMOVA results revealed no evident geographical structure of populations. barrier analysis showed the strongest differentiation in the eastern part of the species’ range, i.e. in the Carpathians. Main conclusions The populations of P. cembra within the two parts of the species’ range still share many cpDNA haplotypes, suggesting a common gene pool conserved from a previously large, continuous distribution range. Carpathian populations have maintained high haplotypic variation, even higher than Alpine populations, despite their small population sizes and spatial isolation. Based on our results, we emphasize the importance of the Carpathian populations of Swiss stone pine for conservation. These populations comprise private haplotypes and they may represent a particular legacy of the species’ evolutionary history.     

Estimating genetic erosion using the example of Picea chihuahuana Martínez

Genetic erosion can be defined as a permanent reduction in richness or evenness of common local alleles or the loss of combination of alleles over time in a defined area. This process can be detrimental to the short-term viability of individuals and populations, the evolutionary potential of populations and species, and the direct use of genetic resources. Various international and intergovernmental organizations and networks have therefore recognized the need to assess and monitor plant genetic erosion in order to prevent such effects. The rare tree species Picea chihuahuana Martínez, which is endemic to Mexico, is an excellent model for estimating potential genetic erosion. The species occurs in about 40 often isolated relict populations in the Sierra Madre Occidental. In this study, the degree of genetic erosion was evaluated in five populations of P. chihuahuana M. in the State of Durango (Mexico), by comparing the genetic diversity in diameter classes (as a surrogate variable for age classes). The results of the study demonstrate a moderate loss of genetic diversity at some amplified fragment length polymorphism (AFLP) loci from the older trees to saplings and to young seedlings in the two largest populations. Significant genetic erosion was only detected in a very small population, named San José de las Causas (SJ). Hence, if genetic diversity at AFLP loci reflects diversity in the genome on the whole, genetic erosion per se does not explain the relict status of Chihuahua spruce, except in very small populations, such as SJ, which comprised of ca. 120 individuals.     

Refugia within refugia: the case study of a canopy tree (Eurycorymbus cavaleriei) in subtropical China

Aim Eurycorymbus cavaleriei (Lévl.) Rehd. et Hand.‐Mazz. (Sapindaceae) is a Tertiary relict tree endemic to subtropical China. This area is a centre for speciation and evolution within the East Asia biome and one of its most important refugial locations. In this study we aim to elucidate the phylogeographical patterning in E. cavaleriei, in order to identify the locations of the species’ main refugia and the predominant patterns of migration that have led to the contemporary spatial genetic structure of chloroplast variation. Location Subtropical China. Methods We sampled 18 populations of E. cavaleriei throughout its geographical range. Chloroplast DNA (cpDNA) sequence data from two non‐coding regions ((trnS/trnG and pl20/5′‐rps12) were obtained from 170 individuals for phylogeographical analyses. Relationships among cpDNA haplotypes were determined using median‐joining networks. Genetic structure was examined by spatial analysis of molecular variance (SAMOVA). Population differentiation was estimated by G_ST and N_ST statistics. Results Ten distinct haplotypes were identified. The level of differentiation among populations was relatively high (G_ST = 0.817), and N_ST was significantly higher than G_ST (P < 0.05), indicating that strong phylogeographical structure is exhibited by this species. The SAMOVA revealed five diverging groups of related haplotypes, which coincide with major landscape features in this region. Main conclusions The high differentiation among populations of E. cavaleriei may be a combined effect of historical and contemporary processes, such as the low effective population size for the chloroplast genome of a dioecious species, long‐term range fragmentation and limited seed dispersal for the species. Clear‐cut geographical distributions of ancestral haplotypes of the species suggest multiple potential refugia across subtropical China. The identified refugial regions have long been recognized as centres of plant diversity and endemism for China and have also been suggested as glacial refugia for many other plant species. The combination of these factors means that these locations should be considered as the highest priority for inclusion in conservation policies and sustainable forest management strategies for subtropical China.     

Phylogeographic differentiation in the mitochondrial control region in the koala, Phascolarctos cinereus (Goldfuss 1817)

The koala, Phascolarctos cinereus, is a geographically widespread species endemic to Australia, with three currently recognized subspecies: P.c. adustus, P.c. cinereus, and P.c. victor. Intraspecific variation in the mitochondrial DNA (mtDNA) control region was examined in over 200 animals from 16 representative populations throughout the species’ range. Eighteen different haplotypes were defined in the ≈ 860 bp mtDNA control region, as determined by heteroduplex analysis/temperature gradient gel electrophoresis (HDA/TGGE). Any single population typically possessed only one or two haplotypes yielding an average within-population haplotypic diversity of 0.180 ± 0.003, and nucleotide diversity of 0.16%. Overall, mtDNA control region sequence diversity between populations averaged 0.67%, and ranged from 0% to 1.56%. Nucleotide divergence between populations averaged 0.51%, and ranged from 0% to 1.53%. Neighbour-joining methods revealed limited phylogenetic distinction between geographically distant populations of koalas, and tentative support for a single evolutionarily significant unit (ESU). This is consistent with previous suggestions that the morphological differences formalized by subspecific taxonomy may be interpreted as clinal variation. Significant differentiation in mtDNA-haplotype frequencies between localities suggested that little gene flow currently exists among populations. When combined with microsatellite analysis, which has revealed substantial differentiation among koala populations, we conclude that the appropriate short-term management unit (MU) for koalas is the local population.     

Genetic variation and geographical structure of five mouse-sized opossums (Marsupialia, Didelphidae) throughout the Guiana Region

Aim and location To study the patterns of genetic variation and geographical structure of five forest‐dwelling didelphid species distributed throughout the Guiana Region (Marmosops parvidens, M. pinheiroi, Monodelphis brevicaudata, Marmosa murina, Micoureus demerarae) and place the results for wide‐ranging species (M. murina, M. demerarae) in the broader geographical context of the rest of the taxon ranges based on published data. Methods Variation in the mitochondrial cytochrome b gene were analysed in order to assess intra‐specific sequence divergence as well as haplotypic and nucleotide diversity among populations. Relationships between haplotypes were inferred by cladistic (maximum parsimony) and probabilistic (maximum likelihood) approaches, allowing comparisons between tree topologies and patterns of populations geographical distribution. Results Phylogenetic analysis of the Guiana Region populations suggest the lack of common patterns of geographical structure among mouse‐sized opossums except for both Marmosops species. Marmosops parvidens and M. pinheiroi showed individuals from Surinam strongly related with those from Guyana, and haplotypes from French Guiana having a basal position. Concerning Micoureus demerarae, haplotypes from Venezuela were positioned as ancestral, in contrast with Monodelphis brevicaudata, whose French Guiana haplotypes were clustered in a basal position. No evidence of geographical structure was observed for Marmosa murina. Genetic variation within Guiana Region populations fluctuated between 1% for M. murina and 7% in the case of M. brevicaudata. Regarding the widely distributed species, phylogeographical structure at the scale of the Amazon Basin suggests that Guiana Region populations are the sister group of south‐eastern Amazonian and Atlantic Forest populations, thus resulting in an eastern clade well separated from the western Amazonian regions. Main conclusions Monophyly of mouse‐sized opossums haplotypes over the Guiana Region confirms the presence of a well‐differentiated zoogeographical area relative to other Amazonia bioregions. Low genetic diversity among Guiana Region samples suggests a relatively recent origin of populations dating from later Miocene and Pleistocene periods. Moreover, nucleotide and haplotypic diversity values suggest an evolutionary scenario of rapid population growth and dispersal over the Guiana territory, from an ancestral population with small effective size. Dispersal events – rather than vicariance – seem to be responsible for the present genetic and phylogeographical patterns observed in the Guiana Region.     

Stem anatomy of Rhipsalis (Cactaceae) and its relevance for taxonomy

We used paternally inherited chloroplast microsatellites (cpSSR) to study population genetic structure in the endemic and highly restricted Serbian spruce Picea omorika. Fragment size polymorphism at the five cpSSR regions that could be amplified out of the nine tested combined into only four different haplotypes in the seven populations studied. Mean total haplotypic diversity was H _T = 0.395, and mean within-population diversity was H _s = 0.279. Haplotypic variation was lower than in most conifers described so far and partitioned into two geographical groups. All northern P. omorika populations were fixed or nearly fixed for the common haplotype, while southern populations exhibited two to three haplotypes. We suggest that current P. omorika populations are shaped by extreme demographic bottleneck and random genetic drift linked to Quaternary glacial cycles. P. omorika thus belongs to the small group of genetically depauperate tree species.     

Phylogeography of Podocarpus matudae (Podocarpaceae): pre‐Quaternary relicts in northern Mesoamerican cloud forests

Aim Cloud forests of northern Mesoamerica represent the northern and southern limit of the contact zone between species otherwise characteristic of North or South America. Several phylogeographic studies featuring temperate conifer species have improved our understanding of species responses to environmental changes. In contrast, conifer species that presumably colonized northern Mesoamerica from South America are far less studied. A phylogeographic study of Podocarpus matudae (Podocarpaceae) was conducted to identify any major evolutionary divergences or disjunctions across its range and to determine if its current distribution is associated with pre‐Quaternary climatic and/or long‐distance dispersal events. Location Northern Mesoamerica (Mexico and Guatemala). Methods Sixteen populations (157 individuals) of P. matudae were screened for variation at two plastid DNA markers. The intra‐specific phylogenetic relationships among haplotypes were reconstructed using Bayesian inference. Population genetic analyses were undertaken to gain insight into the evolutionary history of these populations. To test whether genetic divergence among populations occurred at different time‐scales plastid DNA sequence data and fossil‐ and coalescent‐based calibrations were integrated. Results The combination of plastid markers yielded 11 haplotypes. Differentiation among populations based on DNA variation (G_ST) (0.707, SE 0.0807) indicated a clear population structure in P. matudae. Differentiation for ordered alleles (N_ST) (0.811, SE 0.0732) was higher than that for G_ST, indicating phylogeographical structure in P. matudae. Most of the total variation (81.3%, P < 0.0001) was explained by differences among populations. The estimated divergence time between the unique haplotypes from a Guatemalan population and the two most common haplotypes from the Sierra Madre Oriental in Mexico was between 10 and 20 Ma, and further haplotype divergence in the poorly resolved clade of the Sierra Madre Oriental occurred between 3 and 0.5 Ma. Main conclusions Divergence estimations support the hypothesis that extant Podocarpus matudae populations are pre‐Quaternary relicts. This finding is consistent with fossil and pollen data that support a Miocene age for temperate floristic elements in Mesoamerican cloud forests, whereas further haplotype divergence within the Sierra Madre Oriental, Chiapas and Guatemala occurred more recently, coinciding with Pleistocene cloud forest refugia.     

Conservation genetics of three flightless beetle species in southern California

Regional scale conservation decisions can be aided by information on the distribution of intraspecific diversity, especially the extent to which patterns are common to multiple species. We compare patterns of intraspecific mitochondrial cytochrome oxidase I (COI) variation among three flightless beetles (Coleoptera: Tenebrionidae: Nyctoporis carinata LeConte; Staphylinidae: Sepedophilus castaneus (Horn); Carabidae: Calathus ruficollis Dejean) in the southern part of the California Floristic Province biodiversity hotspot. All species exhibit moderate to high levels of total variation, ranging from 2% to 10% (maximum uncorrected distance). Most populations of all species exhibit unique haplotypes, but few populations’ haplotypes constitute exclusive clades. Many adjacent pairs of populations show indications of some, though limited, genetic connectedness, due either to gene flow or ancestral polymorphism. However, in most cases this diminishes sharply over greater distances. By both statistical and phylogenetic measures, Sierra Nevadan populations are highly distinct from those in the coast and transverse ranges. Among the latter, the eastern transverse ranges are generally most unique and isolated, with diversity in the western parts of these ranges showing fewer barriers. Otherwise, few measures agree on areas of highest conservation value, and overall patterns tend to be species-specific.     

Phylogeography of the bark beetle Dendroctonus mexicanus Hopkins (Coleoptera: Curculionidae: Scolytinae)

Dendroctonus mexicanus is polyphagous within the Pinus genus and has a wide geographical distribution in Mexico and Guatemala. We examined the pattern of genetic variation across the range of this species to explore its demographic history and its phylogeographic pattern. Analysis of the mtDNA sequences of 173 individuals from 25 Mexican populations allowed to us identify 53 geographically structured haplotypes. High haplotype and low nucleotide diversities and Tajima’s D indicate that D. mexicanus experienced rapid population expansion during its dispersal across mountain systems within its current range. The nested clade phylogeographic analysis indicates that the phylogeographic pattern of D. mexicanus is explained by continuous dispersion among lineages from the Sierra Madre Occidental, the Sierra Madre Oriental and the Trans-Mexican Volcanic Belt. However, we also observed isolation events among haplotypes from the Cofre de Perote/Trans-Mexican Volcanic Belt/Sierra Madre Oriental and the Trans-Mexican Volcanic Belt/Sierra Madre del Sur, which is consistent with the present conformation of mountain systems in Mexico and the emergence of geographical barriers during the Pleistocene.     

Indications for a recent Holarctic expansion of pike based on a preliminary study of mtDNA variation

An extremely limited haplotypic diversity within populations and a strikingly low divergence between European and Canadian haplotypes were found in pike Esox lucius . Certain haplotypes were associated with a particular geographical region in Europe: a widespread European and a restricted Hungarian–Norwegian type. The low haplotypic intraspecific divergence suggests a late Pleistocene expansion from an ancestral population.     

Genetic variation of Pinus uncinata (Pinaceae) in the Pyrenees determined with cpSSR markers

The genetic variation within and between 13 populations (385 individuals) of Pinus uncinata was analyzed with ten chloroplast microsatellite markers. Both the infinite allele mutation and stepwise mutation model (SMM) have been applied to the analysis of the genetic structure and the geographical distribution of haplotypic variation. High level of genetic diversity and low but significant differentiation among compared population were found. Three marginal populations, Sierra de Cebollera, Margaride Mountains and Sierra de Gúdar are strongly differentiated from the rest. Mutations following SMM-like process contributed significantly to the regional differentiation. The pattern of genetic structure observed in mountain pine is common in conifers with a wide distribution range. Lack of significant genetic structuring may be a result of a recent fragmentation of a historically larger population and/or interspecific hybridization and introgression. The southernmost populations from the Sierra Cebollera and the Sierra de Gúdar are the most genetically distinct. This suggests a long period of spatial isolation and/or origin from different ancestral populations.     

Low genetic diversity and significant structuring of the common hamster populations <Emphasis Type="Italic">Cricetus cricetus</Emphasis> in Poland revealed by the mtDNA control region sequence variation

The genetic diversity of 12 populations in the present range of the common hamster Cricetus cricetus (Linnaeus, 1758) in Poland was established. The 366 bp of the mtDNA control region was sequenced for 195 individuals. As few as seven haplotypes were found and their distribution was geographically structured. The large geographic areas were fixed or almost fixed for a single haplotype and three groups of populations, that do not share any haplotypes, have been defined. Proportions of genetic diversity attributable to variation between groups of populations, between populations within groups and within populations were 93.64, 1.92 and 4.45% (SAMOVA: p < 0.001 for all estimates), respectively. Such pattern of variation is most probably the result of historical, postglacial bottlenecks and present genetic drift after the population decline in the last few decades.     

Genetic evidence for recent range fragmentation and severely restricted dispersal in the critically endangered Sierra Madre Sparrow, Xenospiza baileyi

Assessing patterns of genetic structure and diversity of threatened species has become an essential tool for determining conservation status and designing management strategies. We examine the genetic structure of the Sierra Madre sparrow (Xenospiza baileyi), a species restricted to fragmented patches of subalpine bunchgrass in three small isolated areas of northwestern and central Mexico. Coding and non-coding regions of mtDNA (1,878 bp) from individuals of the only three known populations revealed the existence of a single major lineage, with closely related haplotypes being shared between populations across the range. The sharing of haplotypes between the distant northwest and central populations (~800 km) suggests a recent fragmentation of a formerly contiguous population. Despite a lack of large-scale phylogeographic structure, haplotype frequencies at local scales revealed significant genetic differentiation and high F _ST values between all three remaining populations, even between localities separated by less than 12 km. These results suggest restricted gene flow and limited dispersal, likely due to the species’ inability to cross areas of unsuitable habitat. On the basis of genetic interchange and ecological equivalence criteria, we recommend that the species be managed as a single unit, permitting the strengthening of the small population in the northwest with individuals from central Mexico, and/or the translocation of individuals to new areas of suitable habitat.     

From middens to molecules: phylogeography of the piñon pine,Pinus edulis

Aim Data from packrat middens have established a hypothesized historical biogeography of piñon pine, Pinus edulis, including locations of glacial refugia in the south‐western USA and subsequent migration out of the refugia. In this study, we used molecular techniques to test the glacial refugial hypotheses inferred from packrat (Neotoma) midden data for P. edulis. Location South‐western USA. Methods Two fragments of chloroplast DNA (a portion of the matK gene and a portion of the rbcL gene) for a total of 1045 base pairs were amplified and sequenced for 100 individuals. Thirty‐one populations were sampled throughout the range of P. edulis. Phylogenetic analyses included maximum parsimony and maximum likelihood. Results Very little variation existed among the individuals sampled. Four haplotypes were identified. The inferred ancestral haplotype was the most widespread; it was most common in Texas and New Mexico where, with the exception of one individual, it was the only haplotype found. Arizona and Utah populations were more diverse, with almost half of the populations containing two or more haplotypes. The most derived haplotype was most abundant in Arizona. Main conclusions The distribution of haplotypes is geographically informative. Only one haplotype exists in the south‐eastern portion of the range of P. edulis whereas up to four haplotypes are found in other populations, suggesting one of two hypotheses: either all modern populations are descended from a refugial population in central Arizona, or modern populations are descended from two refugial populations, one in central Arizona and another in Texas–southern New Mexico. Interpreting these data in the light of packrat midden data gives more support for the latter hypothesis.     

Hierarchical structure of mitochondrial lineages of Tomicus destruens (Coleoptera,Scolytidae) related to environmental variables

We investigated here the relation of environmental variables with the distribution of mitochondrial lineages using a bark beetle species of Mediterranean distribution as a model. We analysed a total number of 460 DNA sequences of Tomicus destruens provided by intensive and extensive collection and GenBank entries. We combined phylogeography and regression models to study the role of five environmental predictors at fine scale in the distribution of a local genealogy. The analysis revealed a high genetic diversity, with 52 haplotypes present in Sierra Espuña forest (SE Spain) and 21 haplotypes in the other 14 Spanish populations, all included in the western clade of the Mediterranean phylogeography of the species. We found a micro‐distribution of the species related to altitude and putative niche segregation between lineages associated with the micro‐environmental conditions of their host pine trees. We compared the phylogeographic hypothesis obtained here with the phylogeography obtained integrating our data with all data published elsewhere. Here, we demonstrate a relation between the environmental heterogeneity and the haplotypic diversity at Mediterranean Basin scale. This analysis allows us to support the evolutionary scenario where the phylogeography and current molecular diversity of T. destruens is a consequence of the recolonization from two principal refugia at both extremes of the Mediterranean Basin and, according to our data, we propose that the heterogeneity of habitats allows fixation of the mitochondrial lineages.     

High genetic diversity and stable Pleistocene distributional ranges in the widespread Mexican red oak Quercus castanea Née (1801) (Fagaceae)

The Mexican highlands are areas of high biological complexity where taxa of Nearctic and Neotropical origin and different population histories are found. To gain a more detailed view of the evolution of the biota in these regions, it is necessary to evaluate the effects of historical tectonic and climate events on species. Here, we analyzed the phylogeographic structure, historical demographic processes, and the contemporary period, Last Glacial Maximum (LGM) and Last Interglacial (LIG) ecological niche models of Quercus castanea, to infer the historical population dynamics of this oak distributed in the Mexican highlands. A total of 36 populations of Q. castanea were genotyped with seven chloroplast microsatellite loci in four recognized biogeographic provinces of Mexico: the Sierra Madre Occidental (western mountain range), the Central Plateau, the Trans‐Mexican Volcanic Belt (TMVB, mountain range crossing central Mexico from west to east) and the Sierra Madre del Sur (SMS, southern mountain range). We obtained standard statistics of genetic diversity and structure and tested for signals of historical demographic expansions. A total of 90 haplotypes were identified, and 29 of these haplotypes were restricted to single populations. The within‐population genetic diversity was high (mean h_S = 0.72), and among‐population genetic differentiation showed a strong phylogeographic structure (N_ST = 0.630 > G_ST = 0.266; p < .001). Signals of demographic expansion were identified in the TMVB and the SMS. The ecological niche models suggested a considerable percentage of stable distribution area for the species during the LGM and connectivity between the TMVB and the SMS. High genetic diversity, strong phylogeographic structure, and ecological niche models suggest in situ permanence of Q. castanea populations with large effective population sizes. The complex geological and climatic histories of the TMVB help to explain the origin and maintenance of a large proportion of the genetic diversity in this oak species.     

Chloroplast DNA and isozyme evidence on the evolution ofSenecio vulgaris (Asteraceae)

Chloroplast DNA (cpDNA) and isozyme variation were analyzed over a range of populations of two infraspecific taxa of the tetraploidSenecio vulgaris. The isozyme data were supportive of the hypothesis that the weedy and cosmopolitanS. vulgaris var.vulgaris is an evolutionary derivative ofS. vulgaris subsp.denticulatus from the coasts of W Europe and montane altitudes in S Spain and Sicily. The two taxa exhibited a very high genetic identity with subsp.denticulatus containing slightly more isozyme diversity than was found in var.vulgaris. — Three cpDNA haplotypes (A, B, C) already known from other Mediterranean diploid species ofSenecio were resolved in var.vulgaris, and an additional fourth haplotype (E) was found in subsp.denticulatus. Two alternative hypotheses were chosen to account for the origin and maintenance of the observed cpDNA composition ofS. vulgaris. It either reflects (1) the retention of an ancestral polymorphism which stems from the recurrent and polytopic formation of ancestral tetraploid lineages; or (2)S. vulgaris originally was characterized by haplotype E, and haplotypes A, B and C were acquired through repeated introgressive hybridization with related diploid species. The finding that very low levels of nuclear (isozyme) diversity were present in both taxa ofS. vulgaris examined supports the second of these two hypotheses; however, more detailed analysis of nuclear genetic diversity is required before a firm conclusion can be reached on this matter.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

Budding speciation via peripheral isolation: the Psorodonotus venosus (Orthoptera,Tettigoniidae) species group example

The peripatric or budding species model has remained theoretical until recently. The habitat preference and range pattern of the mountainous Psorodonotus venosus species group, distributed in Anatolia and Caucasus, offered potential to test the predictions of the model. The study aimed to confirm the parameters and to provide evidence for peripatric speciation in a terrestrial group. Fourteen populations representing the total range of the group were studied. Sequences of two mitochondrial fragments including four loci (12S rDNA+tDNAval+16S rDNA and COI) and a nuclear fragment including three loci (ITS1+5.8S rDNA+ITS2) were obtained and used in phylogenetic, time estimation, population genetics and demographic analyses. Additionally, phenotypical data were provided for the group. Phylogenetic analyses supported the monophyly of the PVG and suggested similar intralineage relationships, but did not support the monophyly of each of the species in the group. The molecular chronograms indicated radiation of the group throughout the Pleistocene. Demographic analyses suggested constant population sizes for the populations in the centre of the range but a significant departure from constancy in four peripheral populations. Genetic diversity is significantly reduced in peripheral populations, but not in others. We arrived to following conclusions. The data suggest that P. venosus is the ancestral species and P. rugulosus, P. tendurek and P. hakkari are bud species, as their haplotypes are nested within P. venosus. As expected under the budding speciation model, (i) in contrast to ancestral species, genetic diversity is reduced, and there are signs of departure from constant population size in bud species; (ii) bud species have isolated and restricted ranges, while the ancestral species does not, (iii) the relative ages of ancestral and bud species are the most reliable data to confirm the model, and chronograms of PVG well support this prediction, and (iv) the divergence events in the group co‐occurred with major climatic transformations of the Pleistocene.     

Origins and Relationship of Cave Populations of the Blind Mexican Tetra, Astyanax Fasciatus, in the Sierra De El Abra

The blind morph of Astyanax fasciatus (Pisces: Characidae) has been more thoroughly studied than any other cave inhabiting organism. Most studies of A. fasciatus have used individuals from different caves of the Sierra de El Abra, Mexico, and have assumed that each population independently evolved to live in the cave environment. We analyzed the relationships among several cave populations that delineate the Sierra de El Abra using RAPD markers. The results indicate that all cave populations are more closely related to one another than they are to the surface populations. This suggests that present day cave populations derived from a common ancestral stock, most likely due to a single colonization event, or alternatively, that strong gene flow among cave populations has occurred, raising precaution against considering each cave population as independent.     

Colonization of the Tibetan Plateau by the homoploid hybrid pine Pinus densata

Pinus densata is an intriguingly successful homoploid hybrid species that occupies vast areas of the southeastern Tibetan Plateau in which neither of its parental species are present, but the colonization processes involved are poorly understood. To shed light on how this species colonized and became established on the plateau, we surveyed paternally inherited chloroplast (cp) and maternally inherited mitochondrial (mt) DNA variation within and among 54 populations of P. densata and its putative parental species throughout their respective ranges. Strong spatial genetic structure of both cp and mtDNA were detected in P. densata populations. Mitotypes specific to P. densata were likely generated by complex recombination events. A putative ancestral hybrid zone in the northeastern periphery of P. densata was identified, and we propose that the species then colonized the plateau by migrating westwards. Along the colonization route, consecutive bottlenecks and surfing of rare alleles caused a significant reduction in genetic diversity and strong population differentiation. The direction and intensity of introgression from parental species varied among geographic regions. In western parts of its range, the species seems to have been isolated from seed and pollen flow from its parent species for a long time. The observed spatial distribution of genetic diversity in P. densata also appears to reflect the persistence of this species on the plateau during the last glaciation. Our results indicate that both ancient and contemporary population dynamics have contributed to the spatial distribution of genetic diversity in P. densata, which accordingly reflects its evolutionary history.