Human-Assisted Invasions of Pacific Islands by Litoria Frogs: A Case Study of the Bleating Tree Frog on Lord Howe Island

There are substantial differences among taxonomic groups in their capacity to reach remote oceanic islands via long-distance overwater dispersal from mainland regions. Due to their permeable skin and intolerance of saltwater, amphibians generally require human-assisted dispersal to reach oceanic islands. Several Litoria frog species have been introduced to remote islands throughout the Pacific Ocean region. Lord Howe Island (LHI) is an oceanic island that lies approximately 600 km east of the Australian mainland and has a diverse, endemic biota. The bleating tree frog (Litoria dentata) is native to mainland eastern Australia, but was accidentally introduced to LHI in the 1990s, yet its ecology and potential impact on LHI has remained unstudied. We used a mitochondrial phylogeographical approach to determine that L. dentata was introduced from the Ballina region in northeastern New South Wales. The founding population was likely accidentally introduced with cargo shipped from the mainland. We also completed the first detailed investigation of the distribution, ecology and habitat use of L. dentata on LHI. The species is widespread on LHI and is prevalent in human habitat, cattle pasture and undisturbed forest. We discuss the potential impact of introduced Litoria species on Pacific islands and outline what biosecurity protocols could be implemented to prevent the introduction of further amphibian species to the ecologically sensitive oceanic area.     

Limited phylogeographic and genetic connectivity in Acacia species of low stature in an arid landscape

Widespread plant species are expected to maintain genetic diversity and gene flow via pollen and seed dispersal. Stature is a key life history trait that affects seed and potentially pollen dispersal, with limited stature associated with limited dispersal and greater genetic differentiation. We sampled Hill’s tabletop wattle (Acacia hilliana) and curry wattle (Acacia spondylophylla), two co‐distributed, widespread, Acacia shrubs of low stature, across the arid Pilbara region of north‐western Australia. Using chloroplast sequence and nuclear microsatellite data we evaluated patterns of population genetic and phylogeographic diversity and structure, demographic signals, ratios of pollen to seed dispersal, evidence for historical refugia, and association between elevation and diversity. Results showed strong phylogeographic (chloroplast, G _ST = 0.831 and 0.898 for A. hilliana and A. spondylophylla, respectively) and contemporary (nuclear, F _ST = 0.260 and 0.349 for A. hilliana and A. spondylophylla, respectively) genetic structure in both species. This indicates limited genetic connectivity via seed and pollen dispersal associated with Acacia species of small stature compared to taller tree and shrub acacias across the Pilbara bioregion. This effect of stature on genetic structure is superimposed on moderate levels of genetic diversity that were expected based on widespread ranges (haplotype diversity h = 25 and 12; nuclear diversity He = 0.60 and 0.47 for A. hilliana and A. spondylophylla, respectively). Contemporary genetic structure was congruent at the greater landscape scale, especially in terms of strong genetic differentiation among geographically disjunct populations in less elevated areas. Measures of diversity and connectivity were associated with traits of greater geographic population proximity, population density, population size, and greater individual longevity, and some evidence for range expansion in A. hilliana. Results illustrate that low stature is associated with limited dispersal and greater patterns of genetic differentiation for congenerics in a common landscape and highlight the complex influence of taxon‐specific life history and ecological traits to seed and pollen dispersal.     

Multiple introductions and no loss of genetic diversity: invasion history of Japanese Rose, Rosa rugosa, in Europe

The shrub Rosa rugosa (Japanese Rose), native to East Asia, is considered one of the most troublesome invasive plant species in natural or semi-natural habitats of northern Europe and has proven very difficult to control. We aimed at disentangling the species’ invasion history in Europe, including determining the number of introductions and their geographic origin, and at investigating whether populations in the introduced and native ranges differ in genetic diversity, structure and degree of differentiation. We found that introduced (n = 16) and native (n = 16) populations had similar levels of genetic diversity at seven nuclear SSR (microsatellite) loci. European populations lack isolation by distance and are less genetically differentiated than are populations in East Asia. Multiple and at least three independent colonization events, one of which was particularly successful, gave rise to current R. rugosa populations in Europe. The geographic distribution patterns of these three genetic clusters could not be explained by natural dispersal alone, indicating that human mediated secondary dispersal is driving the expansion in Europe. One cluster representing three of the European populations was most likely derived from NW Japan, whereas the origin of the remaining thirteen populations could not clearly be resolved. The introduction and expansion in Europe occurred with no significant loss of genetic diversity. We conclude that high propagule pressure at the primary establishment phase is the most parsimonious explanation for this pattern. A potential for long distance seed dispersal, coastal habitat connectivity and an outcrossing breeding system are factors likely to have enabled populations of R. rugosa to avoid detrimental effects of genetic bottlenecks and will further increase the species’ range size and abundance in Europe. We recommend that human-mediated dispersal should be prevented in order to halt the continued expansion.     

Life in the desert: The impact of geographic and environmental gradients on genetic diversity and population structure of Ivesia webberi

For range‐restricted species with disjunct populations, it is critical to characterize population genetic structure, gene flow, and factors that influence functional connectivity among populations in order to design effective conservation programs. In this study, we genotyped 314 individuals from 16 extant populations of Ivesia webberi, a United States federally threatened Great Basin Desert using six microsatellite loci. We assessed the effects of Euclidean distance, landscape features, and ecological dissimilarity on the pairwise genetic distance of the sampled populations, while also testing for a potential relationship between I. webberi genetic diversity and diversity in the vegetative communities. The results show low levels of genetic diversity overall (H _e = 0.200–0.441; H _o = 0.192–0.605) and high genetic differentiation among populations. Genetic diversity was structured along a geographic gradient, congruent with patterns of isolation by distance. Populations near the species’ range core have relatively high genetic diversity, supporting in part a central‐marginal pattern, while also showing some evidence for a metapopulation dynamic. Peripheral populations have lower genetic diversity, significantly higher genetic distances, and higher relatedness. Genotype cluster admixture results suggest a complex dispersal pattern among populations with dispersal direction and distance varying on the landscape. Pairwise genetic distance strongly correlates with elevation, actual evapotranspiration, and summer seasonal precipitation, indicating a role for isolation by environment, which the observed phenological mismatches among the populations also support. The significant correlation between pairwise genetic distance and floristic dissimilarity in the germinated soil seed bank suggests that annual regeneration in the plant communities contribute to the maintenance of genetic diversity in I. webberi.     

Genetic Diversity and Population Structure of Sitodiplosis mosellana in Northern China

The wheat midge, Sitodiplosis mosellana, is an important pest in Northern China. We tested the hypothesis that the population structure of this species arises during a range expansion over the past 30 years. This study used microsatellite and mitochondrial loci to conduct population genetic analysis of S. mosellana across its distribution range in China. We found strong genetic structure among the 16 studied populations, including two genetically distinct groups (the eastern and western groups), broadly consistent with the geography and habitat fragmentation. These results underline the importance of natural barriers in impeding dispersal and gene flow of S. mosellana populations. Low to moderate genetic diversity among the populations and moderate genetic differentiation (F _ST = 0.117) between the two groups were also found. The populations in the western group had lower genetic diversity, higher genetic differentiation and lower gene flow (F _ST = 0.116, Nm = 1.89) than those in the eastern group (F _ST = 0.049, Nm = 4.91). Genetic distance between populations was positively and significantly correlated with geographic distance (r = 0.56, P<0.001). The population history of this species provided no evidence for population expansion or bottlenecks in any of these populations. Our data suggest that the distribution of genetic diversity, genetic differentiation and population structure of S. mosellana have resulted from a historical event, reflecting its adaptation to diverse habitats and forming two different gene pools. These results may be the outcome of a combination of restricted gene flow due to geographical and environmental factors, population history, random processes of genetic drift and individual dispersal patterns. Given the current risk status of this species in China, this study can offer useful information for forecasting outbreaks and designing effective pest management programs.     

Molecular phylogeny and phylogeography of the Cuban cave-fishes of the genus Lucifuga: evidence for cryptic allopatric diversity

Underground environments are increasingly recognized as reservoirs of faunal diversity. Extreme environmental conditions and limited dispersal ability of underground organisms have been acknowledged as important factors promoting divergence between species and conspecific populations. However, in many instances, there is no correlation between genetic divergence and morphological differentiation. Lucifuga Poey is a stygobiotic fish genus that lives in Cuban and Bahamian caves. In Cuba, it offers a unique opportunity to study the influence of habitat fragmentation on the genetic divergence of stygobiotic species and populations. The genus includes four species and one morphological variant that have contrasting geographical distributions. In this study, we first performed a molecular phylogenetic analysis of the Lucifuga Cuban species using mitochondrial and nuclear markers. The mitochondrial phylogeny revealed three deeply divergent clades that were supported by nuclear and morphological characters. Within two of these main clades, we identified five lineages that are candidate cryptic species and a taxonomical synonymy between Lucifuga subterranea and Lucifuga teresinarum. Secondly, phylogeographic analysis using a fragment of the cytochrome b gene was performed for Lucifuga dentata, the most widely distributed species. We found strong geographical organization of the haplotype clades at different geographic scales that can be explained by episodes of dispersal and population expansion followed by population fragmentation and restricted gene flow. At a larger temporal scale, these processes could also explain the diversification and the distribution of the different species.     

Distribution of Lutzomyia longipalpis Chemotype Populations in S?o Paulo State,Brazil

BackgroundAmerican visceral leishmaniasis (AVL) is an emerging disease in the state of São Paulo, Brazil. Its geographical expansion and the increase in the number of human cases has been linked to dispersion of Lutzomyia longipalpis into urban areas. To produce more accurate risk maps we investigated the geographic distribution and routes of expansion of the disease as well as chemotype populations of the vector.Conclusion/SignificanceThe maps in the present study show that there are two distinct epidemiological patterns of AVL in São Paulo State and that the expansion of human and canine AVL cases through the Western region has followed the same dispersion route of only one of the two species of the L. longipalpis complex, (S)-9-methylgermacrene-B. Entomological vigilance based on the routes of dispersion and identification of the chemotype population could be used to identify at-risk areas and consequently define the priorities for control measures.     

Isolated populations of a rare alpine plant show high genetic diversity and considerable population differentiation

Background and Aims

Gene flow and genetic variability within and among alpine plant populations can be greatly influenced by the steep environmental gradients and heterogeneous topography of alpine landscapes. In this study, the effects are examined of natural isolation of alpine habitats on genetic diversity and geographic structure in populations of C. thyrsoides, a rare and isolated European Alpine monocarpic perennial with limited seed dispersal capacity.

Methods

Molecular diversity was analysed for 736 individuals from 32 populations in the Swiss Alps and adjacent Jura mountains using five polymorphic microsatellite loci. Pollen flow was estimated using pollen grain-sized fluorescent powder. In addition, individual-based Bayesian approaches were applied to examine population structure.

Key Results

High within-population genetic diversity (H_E = 0·76) and a relatively low inbreeding coefficient (F_IS = 0·022) were found. Genetic differentiation among populations measured with a standardized measure was considerable (G′_ST = 0·53). A significant isolation-by-distance relationship was found (r = 0·62, P < 0·001) and a significant geographic sub-structure, coinciding with proposed postglacial migration patterns. Altitudinal location and size of populations did not influence molecular variation. Direct measures of pollen flow revealed that insect-mediated pollen dispersal was restricted to short distances within a population.

Conclusions

The natural isolation of suitable habitats for C. thyrsoides restricts gene flow among the populations as expected for a monocarpic species with very limited seed dispersal capacities. The observed high within-population genetic diversity in this rare monocarpic perennial is best explained by its outcrossing behaviour, long-lived individuals and overlapping generations. Despite the high within-population genetic diversity, the considerable genetic differentiation and the clear western–eastern differentiation in this species merits consideration in future conservation efforts.Key words: Alpine plant, Campanula thyrsoides, genetic diversity, gene flow, genetic differentiation, glacial history, G′_ST, habitat isolation, microsatellites, monocarpy, SSR     

Genetic studies of various Prosopis species (Leguminosae,Section Algarobia) co‐occurring in oases of the Atacama Desert (northern Chile)

In the Atacama Desert from northern Chile (19–24°S), Prosopis (Leguminosae) individuals are restricted to oases that are unevenly distributed and isolated from each other by large stretches of barren landscape constituting an interesting study model as the degree of connectivity between natural populations depends on their dispersal capacity and the barriers imposed by the landscape. Our goal was to assess the genetic diversity and the degree of differentiation among groups of Prosopis individuals of different species from Section Algarobia and putative hybrids (hereafter populations) co‐occurring in these isolated oases from the Atacama Desert and determine whether genetic patterns are associated with dispersal barriers. Thirteen populations were sampled from oases located on three hydrographic basins (Pampa del Tamarugal, Rio Loa, and Salar de Atacama; northern, central, and southern basins, respectively). Individuals genotyped by eight SSRs show high levels of genetic diversity (H _O = 0.61, A _r = 3.5) and low but significant genetic differentiation among populations (F _ST = 0.128, F _ST‐ENA = 0.129, D _JOST = 0.238). The AMOVA indicates that most of the variation occurs within individuals (79%) and from the variance among individuals (21%); almost, the same variation can be found between basins and between populations within basins. Differentiation and structure results were not associated with the basins, retrieving up to four genetic clusters and certain admixture in the central populations. Pairwise differentiation comparisons among populations showed inconsistencies considering their distribution throughout the basins. Genetic and geographic distances were significantly correlated at global and within the basins considered (p < .02), but low correlation indices were obtained (r < .37). These results are discussed in relation to the fragmented landscape, considering both natural and non‐natural (humans) dispersal agents that may be moving Prosopis in the Atacama Desert.     

Evolutionary Origin and Phylogeography of the Diploid Obligate Parthenogen Artemia parthenogenetica (Branchiopoda: Anostraca)

Background

Understanding the evolutionary origin and the phylogeographic patterns of asexual taxa can shed light on the origin and maintenance of sexual reproduction. We assessed the geographic origin, genetic diversity, and phylogeographic history of obligate parthenogen diploid Artemia parthenogenetica populations, a widespread halophilic crustacean.

Methodology/Principal Findings

We analysed a partial sequence of the Cytochrome c Oxidase Subunit I mitochondrial gene from an extensive set of localities (including Eurasia, Africa, and Australia), and examined their phylogeographic patterns and the phylogenetic relationships of diploid A. parthenogenetica and its closest sexual relatives. Populations displayed an extremely low level of mitochondrial genetic diversity, with one widespread haplotype shared by over 79% of individuals analysed. Phylogenetic and phylogeographic analyses indicated a multiple and recent evolutionary origin of diploid A. parthenogenetica, and strongly suggested that the geographic origin of parthenogenesis in Artemia was in Central Asia. Our results indicate that the maternal sexual ancestors of diploid A. parthenogenetica were an undescribed species from Kazakhstan and A. urmiana.

Conclusions/Significance

We found evidence for multiple origin of parthenogenesis in Central Asia. Our results indicated that, shortly after its origin, diploid A. parthenogenetica populations underwent a rapid range expansion from Central Asia towards the Mediterranean region, and probably to the rest of its current geographic distribution. This contrasts with the restricted geographic distribution, strong genetic structure, and regional endemism of sexual Artemia lineages and other passively dispersed sexual continental aquatic invertebrates. We hypothesize that diploid parthenogens might have reached their current distribution in historical times, with a range expansion possibly facilitated by an increased availability of suitable habitat provided by anthropogenic activities, such as the spread of solar saltworks, aided by their natural dispersal vectors (i.e., waterbirds).     

High Levels of Genetic Connectivity among Populations of Yellowtail Snapper,Ocyurus chrysurus (Lutjanidae – Perciformes), in the Western South Atlantic Revealed through Multilocus Analysis

In the present study, five loci (mitochondrial and nuclear) were sequenced to determine the genetic diversity, population structure, and demographic history of populations of the yellowtail snapper, Ocyurus chrysurus, found along the coast of the western South Atlantic. O. chrysurus is a lutjanid species that is commonly associated with coral reefs and exhibits an ample geographic distribution, and it can therefore be considered a good model for the investigation of phylogeographic patterns and genetic connectivity in marine environments. The results reflected a marked congruence between the mitochondrial and nuclear markers as well as intense gene flow among the analyzed populations, which represent a single genetic stock along the entire coast of Brazil between the states of Pará and Espírito Santo. Our data also showed high levels of genetic diversity in the species (mainly mtDNA), as well a major historic population expansion, which most likely coincided with the sea level oscillations at the end of the Pleistocene. In addition, this species is intensively exploited by commercial fisheries, and data on the genetic structure of its populations will be essential for the development of effective conservation and management plans.     

Genetic diversity and sex‐biased dispersal in the brown spotted pitviper (Protobothrops mucrosquamatus): Evidence from microsatellite markers

Dispersal plays a vital role in the geographical distribution, population genetic structure, quantity dynamics, and evolution of a species. Sex‐biased dispersal is common among vertebrates and many studies have documented a tendency toward male‐biased dispersal in mammals and female‐biased dispersal in birds. However, dispersal patterns in reptiles remain poorly understood. In this study, we explored the genetic diversity and dispersal patterns of the widely distributed Asian pitviper Protobothrops mucrosquamatus. In total, 16 polymorphic microsatellite loci were screened in 150 snakes (48 males, 44 females, 58 samples without sex information) covering most of their distribution. Microsatellite analysis revealed high genetic diversity in P. mucrosquamatus. Bayesian clustering of population assignment identified two major clusters for all populations, somewhat inconsistent with the mitochondrial DNA phylogeny of P. mucrosquamatus reported in previous research. Analyses based on 92 sex‐determined and 37 samples of P. mucrosquamatus from three small sites in Sichuan, China (Mingshan, Yibin, and Zizhong) consistently suggested female‐biased dispersal in P. mucrosquamatus, which is the first example of this pattern in snakes. The female‐biased dispersal patterns in P. mucrosquamatus may be explained by local resource competition.     

Genetic Diversity and Spatial Genetic Structure of Chamaedaphne calyculata (Ericaceae) at the Western Periphery in Relation to its Main Continuous Range in Eurasia

A previous phylogeography and genetic diversity study of Chamaedaphne calyculata (Ericaceae) showed that populations over its geographic range were strongly separated into two groups: a Eurasian/NW North American group and a NE North American one corresponding with the disjunct distribution of Sphagnum-dominated peatlands in north-western and central-eastern North America. Here, I have extended the survey and focused on the species’ detailed postglacial origin and the effect of isolation on genetic diversity patterns, particularly within island-like populations at the western periphery of its range in Europe. Using AFLP markers, estimates of genetic diversity within 16 C. calyculata populations in the Eurasian group were low (percentage of polymorphic loci P _PL=14.9–24.8 %, Nei’s gene diversity H=0.060–0.119). Genetic diversity patterns within this species did not support the hypothesis that genetic diversity decreases towards the periphery of the range. Bayesian clustering analysis showed that population-level admixture was present in almost all studied 16 populations, suggesting multi-directional gene flow. On the other hand, the majority of assigned individuals (ca. 98 % of individuals) were offspring of the original residents, confirming that C. calyculata populations in the present day acted as discrete genetic units both in its continuous range and at its western periphery, and that gene flow was historic rather than contemporary in Eurasia. There was no correlation between genetic and geographic distance in the Eurasian group (r=0.02, P>0.05, Mantel test) nor at the western periphery (r=0.15, P>0.05, Mantel test). The isolation-by-distance (IBD) scatterplot matched Hutchinson and Templeton’s interpretation (case III), and geographic distance between populations was not a reliable predictor of the degree of genetic differentiation between populations. It is suggested that the lack of IBD might be a result of random genetic drift in rather disconnected populations that have become increasingly fragmented relatively recently. Positive and significant relationships between genetic and geographic distance on a small population scale was the result of biparental inbreeding of C. calyculata and restricted seed rain. Despite sporadic generative reproduction and limited dispersal, the fine-scale genetic structure within populations has been maintained, even though population sizes have been reduced to small fragments in recent years.     

The influence of contemporary and historic landscape features on the genetic structure of the sand dune endemic,Cirsium pitcheri (Asteraceae)

Narrow endemics are at risk from climate change because of their restricted habitat preferences, lower colonization ability and dispersal distances. Landscape genetics combines new tools and analyses that allow us to test how both past and present landscape features have facilitated or hindered previous range expansion and local migration patterns, and thereby identifying potential limitations to future range shifts. We have compared current and historic habitat corridors in Cirsium pitcheri, an endemic of the linear dune ecosystem of the Great Lakes, to determine the relative contributions of contemporary migration and post-glacial range expansion on genetic structure. We used seven microsatellite loci to characterize the genetic structure for 24 populations of Cirsium pitcheri, spanning the center to periphery of the range. We tested genetic distance against different measures of geographic distance and landscape permeability, based on contemporary and historic landscape features. We found moderate genetic structure (Fst=0.14), and a north–south pattern to the distribution of genetic diversity and inbreeding, with northern populations having the highest diversity and lowest levels of inbreeding. High allelic diversity, small average pairwise distances and mixed genetic clusters identified in Structure suggest that populations in the center of the range represent the point of entry to the Lake Michigan and a refugium of diversity for this species. A strong association between genetic distances and lake-level changes suggests that historic lake fluctuations best explain the broad geographic patterns, and sandy habitat best explains local patterns of movement.     

Evolutionary history of a desert perennial Arnebia szechenyi (Boraginaceae): Intraspecific divergence,regional expansion and asymmetric gene flow

The complex interactions of historical, geological and climatic events on plant evolution have been an important research focus for many years. However, the role of desert formation and expansion in shaping the genetic structures and demographic histories of plants occurring in arid areas has not been well explored. In the present study, we investigated the phylogeography of Arnebia szechenyi, a desert herb showing a near-circular distribution surrounding the Tengger Desert in Northwest China. We measured genetic diversity of populations using three maternally inherited chloroplast DNA (cpDNA) fragments and seven bi-paternally inherited nuclear DNA (nDNA) loci that were sequenced from individuals collected from 16 natural populations across its range and modelled current and historical potential habitats of the species. Our data indicated a considerably high level of genetic variation within A. szechenyi and noteworthy asymmetry in historical migration from the east to the west. Moreover, two nuclear genetic groups of populations were revealed, corresponding to the two geographic regions separated by the Tengger Desert. However, analysis of cpDNA data did not show significant geographic structure. The most plausible explanation for the discrepancy between our findings based on cpDNA and nDNA data is that A. szechenyi populations experienced long periods of geographic isolation followed by range expansion, which would have promoted generalized recombination of the nuclear genome. Our findings further highlight the important role that the Tengger Desert, together with the Helan Mountains, has played in the evolution of desert plants and the preservation of biodiversity in arid Northwest China.     

Phylogeography and genetic diversity of the red squirrel (Sciurus vulgaris) in China: Implications for the species' postglacial expansion history

The geographical distribution of Sciurus vulgaris spans much of the Palearctic from western Europe and the UK eastward to the pacific coast of East Asia. S. vulgaris occurs in China only in the far northwest and the northeast. Understanding of the species’ postglacial expansion history in East Asia has been limited by the paucity of molecular data. In this study, we used partial D-loop and cytochrome b gene sequences to assess mitochondrial DNA variation in S. vulgaris in China. Our objectives were to (1) determine phylogeographical patterns of S. vulgaris in China; (2) understand the species’ postglacial expansion history in this region; and (3) quantify genetic diversity levels within S. vulgaris populations in China. We identified a supported phylogenetic group in S. vulgaris from China, and found no tendency for haplotypes to cluster by geographic region. Our analysis of S. vulgaris from China and other regions supports the hypothesis that the Calabria region of southern Italy is a glacial refugium for the species. We tentatively propose a postglacial expansion pattern for the squirrels: migrating from Calabria via Central and Eastern Europe to Russia and from there to China, and firstly to the northwest and then to northeast in China. We found high levels of genetic diversity in S. vulgaris populations across China as a whole, and discussed its influential factors.     

Molecular Markers Reveal Limited Population Genetic Structure in a North American Corvid,Clark’s Nutcracker (Nucifraga columbiana)

The genetic impact of barriers and Pleistocene glaciations on high latitude resident species has not been widely investigated. The Clark’s nutcracker is an endemic North American corvid closely associated with Pinus-dominated forests. The nutcracker’s encompasses known barriers to dispersal for other species, and glaciated and unglaciated areas. Clark’s nutcrackers also irruptively disperse long distances in search of pine seed crops, creating the potential for gene flow among populations. Using the highly variable mitochondrial DNA control region, seven microsatellite loci, and species distribution modeling, we examined the effects of glaciations and dispersal barriers on population genetic patterns and population structure of nutcrackers. We sequenced 900 bp of mitochondrial control region for 169 individuals from 15 populations and analysed seven polymorphic microsatellite loci for 13 populations across the Clark’s nutcracker range. We used species distribution modeling and a range of phylogeographic analyses to examine evolutionary history. Clark’s nutcracker populations are not highly differentiated throughout their range, suggesting high levels of gene flow among populations, though we did find some evidence of isolation by distance and peripheral isolation. Our analyses suggested expansion from a single refugium after the last glacial maximum, but patterns of genetic diversity and paleodistribution modeling of suitable habitat were inconclusive as to the location of this refugium. Potential barriers to dispersal (e.g. mountain ranges) do not appear to restrict gene flow in Clark’s nutcracker, and postglacial expansion likely occurred quickly from a single refugium located south of the ice sheets.     

Should I Stay or Should I Go? Dispersal and Population Structure in Small,Isolated Desert Populations of West African Crocodiles

The maintenance of both spatial and genetic connectivity is paramount to the long-term persistence of small, isolated populations living in environments with extreme climates. We aim to identify the distribution of genetic diversity and assess population sub-structuring and dispersal across dwarfed desert populations of Crocodylus suchus, which occur in isolated groups, usually less than five individuals, along the mountains of Mauritania (West Africa). We used both invasive and non-invasive sampling methods and a combination of mitochondrial DNA (12 S and ND4) and microsatellite markers (32 loci and a subset of 12 loci). Our results showed high genetic differentiation and geographic structure in Mauritanian populations of C. suchus. We identified a metapopulation system acting within four river sub-basins (high gene flow and absence of genetic structure) and considerable genetic differentiation between sub-basins (F _ST range: 0.12–0.24) with rare dispersal events. Effective population sizes tend to be low within sub-basins while genetic diversity is maintained. Our study suggests that hydrographic networks (temporal connections along seasonal rivers during rainy periods) allow C. suchus to disperse and maintain metapopulation dynamics within sub-basins, which attenuate the loss of genetic diversity and the risk of extinction. We highlight the need of hydrographic conservation to protect vulnerable crocodiles isolated in small water bodies. We propose C. suchus as an umbrella species in Mauritania based on ecological affinities shared with other water-dependent species in desert environments.     

Phylogeographic and demographic effects of Quaternary climate oscillations in Hexinia polydichotoma (Asteraceae) in Tarim Basin and adjacent areas

In order to investigate the genetic diversity and influence of climate oscillations on evolutionary processes of organisms in Northwest China, we selected Hexinia polydichotoma, a species endemic to China, and examined the phylogeographic structure and historical factors that influenced the evolutionary history of this species in its entire cover range, Tarim Basin and adjacent areas. In the study, 17 haplotypes were identified in H. polydichotoma on the basis of two chloroplast DNA sequences (trnH–psbA and ycf6–psbM). Shown in the network, the two common haplotypes, A and D, respectively, mainly distribute along the northern and southern rims of the basin. The analyses of molecular variance analysis suggest that genetic variation primarily occurs among populations, and all populations were subdivided into five groups by SAMOVA. Geographic range expansion along the southern and northern rims of the basin was supported by the significant value for Tajima’s D and by the unimodal mismatch distribution. It is possible that during the interglacial period of the middle Pleistocene, a large amount of snow and glacial ice melted from the mountains surrounding Tarim Basin. This increased water, the expanding desert, and the dispersal ability of H. polydichotoma were important factors driving not only geographic range expansion, but also the current phylogeographic structure of this species. It is possible that during the middle Pleistocene, the climatic fluctuations resulted in expansion and contraction cycles of river systems and oases, and may consequently have caused population fragmentation.     

Comparative chloroplast and nuclear DNA analysis of Castanea species in the southern region of the USA

Boundaries between American Castanea species (Castanea dentata, the American chestnut and C. pumila var. pumila, the Allegheny chinkapin, and var. ozarkensis, the Ozark chinkapin) have been difficult to establish because of intraspecific variation, interspecific similarities and the incidence of chestnut blight, which has prevented trees from maturing. In this study, informative chloroplast (cp) DNA and nuclear sequences from Castanea taxa were analyzed to gain a better understanding of their phylogeography in North America. Our emphasis has been on the most southern Castanea population in the Appalachian region, known for its morphological diversity. This Ruffner Mountain (Alabama) population shows a high number of unique haplotypes, which can be divided into two main groups. One group shares homology with the widespread and evolutionarily recent C. dentata haplotype. The other group shares homology with American chestnuts and Allegheny chinkapin taxa from southern states. This group has been the result of recent and more ancient cp capture and hybridization, indicative of hybrid zone clustering and glacial refugial origin. The range of C. pumila must have been more extensive along the Coastal Plains region, since only a few mutations separate the Ozark chinkapin from the main Allegheny chinkapin haplotype. The geographic origin of the American Castanea species complex appears to be in the Gulf Coast region.