Threatened populations of the Australian squirrel glider (Petaurus norfolcensis) show evidence of evolutionary distinctiveness on a Late Pleistocene timescale

The squirrel glider Petaurus norfolcensis occurs across a broad Australian latitudinal range that includes gaps in distribution and potential biogeographic barriers, creating the potential for evolution of distinct entities within this species. Because of the species’ threatened status in the southern part of its range, we tested for the presence of geographically based independent evolutionary units among gliders sampled from southern, and northern coastal populations, using sequences of mitochondrial cytochrome b DNA (mtDNA) and a set of five nuclear microsatellites in 258 individuals. Our analyses suggest that an initial northward colonisation in the early- to mid-Pleistocene was followed by isolation by distance and, eventually, divergence between the sampled coastal and southern populations in the mid- to late-Pleistocene. We propose that the previously large and diverse southern populations have declined coincidentally with the replacement of wet forests by open sclerophyll woodlands during the preceding few million years. By contrast coastal populations further north appear to have been expanding and at present have an effective population size several times greater than southern populations. These results suggest that the two forms are on different evolutionary trajectories and should be treated separately for conservation purposes. It is highly desirable that loss of southern populations be prevented to maintain the unique genetic diversity accumulated over a considerable evolutionary timescale.     

New species in <Emphasis Type="Italic">Barleria</Emphasis> sect. <Emphasis Type="Italic">Stellatohirta</Emphasis> (<Emphasis Type="Italic">Acanthaceae</Emphasis>) from Africa

Summary  Three new species are described in Barleria L. sect. Stellatohirta M. Balkwill from tropical Africa: B. aristata from south-central Tanzania, B. aenea from south-western Tanzania and northeast Zambia, and B. purpureotincta from south-western Zambia. Their affinities and conservation status are discussed.     

Phylogeographic evidence for the postglacial colonization of the North and Baltic Sea coasts from inland glacial refugia by Triglochin maritima L.

We investigated the geographical distribution of genetic variation in 67 individuals of Triglochin maritima from 38 localities across Europe using AFLP markers. Analysis of genetic variation resulted in the recognition of two major genetic groups. Apart from few geographical outliers, these are distributed (1) along the Atlantic coasts of Portugal, Spain and France and (2) in the North Sea area, the Baltic Sea area, at central European inland localities, the northern Adriatic Sea coast and the Mediterranean coast of southwest France. Considering possible range shifts of T. maritima in reaction to Quaternary climatic changes as deduced from the present-day northern temperature limit of the species, Quaternary changes of coastline in the North Sea area and the very recent origin of the Baltic Sea, we conclude that the coastal populations of T. maritima in the North Sea and Baltic Sea areas originated from inland populations.     

Coastal forests of eastern Africa: status, endemism patterns and their potential causes

Eastern African coastal forests are located within the Swahili regional centre of endemism and Swahili-Maputaland regional transition zone in eastern Africa, between 1d? North and 25d? South, and 34—41d? East. Approximately 3167 km² coastal forest remains: 2 km² in Somalia, 660 km² in Kenya, 697 km² in Tanzania, 16 km² in Malawi, 3 km² in Zimbabwe and perhaps 1790 km² in Mozambique. Most forests are small (≤ 20 km²), and all but 19 are under 30 km² in area. Over 80% of coastal forest is located on government land, principally Forest Reserves; only 8.3 km² is found in National Parks (6.2 km² in Kenya (Arabuko-Sokoke), 2 km² in Tanzania (Mafia Island) and tiny patches in Zimbabwe). Coastal forests are an important and highly threatened centre of endemism for plants (c 550 endemic species), mammals (6 species), birds (9 species), reptiles (26 species), frogs (2 species), butterflies (79 species), snails (>86 species) and millipedes (>20 species). Endemic species are concentrated in the forests of the Tana River, between Malindi in Kenya to Tanga in northern Tanzania, and in southern Tanzania. Forests with highest numbers of endemics are: lower Tana River, Arabuko-Sokoke, Shimba Hills (Kenya); lowland East Usambara, Pugu Hills, Matumbi Hills, Rondo and Litipo and other plateaux near Lindi (Tanzania); the Tanzanian offshore island of Pemba; Bazaruto archipelago (Mozambique), and tiny forest remnants of southern Malawi, eastern Zimbabwe and Mozambique. Most coastal forest endemics have a narrow distributional range, often exhibiting single-site endemism or with scattered or disjunct distributional patterns. They are best interpreted as relicts and not the result of recent evolution. Relictualization probably started with the separation of the ancient Pan African rainforest into two parts during the Miocene. The coastal forests are interpreted as a ‘vanishing refuge’ with the endemic species gradually becoming more and more relict (and presumably extinct) due historically to climatic desiccation and more recently to human destruction.     

Revisiting genetic structuring in spotted gums (genus Corymbia section Maculatae) focusing on C. maculata, an early diverged, insular lineage

Species delineation in the spotted gum complex was revisited focusing on Corymbia maculata. This study expands the range of C. maculata analysed with microsatellite markers to include populations from the north of the species range. It supported earlier findings that it is a cohesive genetic entity, well resolved from northern spotted gum taxa, Corymbia citriodora and Corymbia henryi; and inferences that its insularity is due to early lineage divergence and historical isolation. The northern extent of C. maculata sampled, as defined by chloroplast and nuclear genomes predominantly of C. maculata character, was the location of Kiwarrak, south of the Manning River near Taree in New South Wales. Trees from a recognised intergrade zone at the Yarratt locality, around 26 km north of Kiwarrak, also possessed a uniquely C. maculata chloroplast haplotype, but their nuclear genomes were predominantly of northern taxa ancestry. Range expansion of northern taxa leading to southerly gene movement into populations formerly C. maculata, would account for this apparent instance of chloroplast capture. Two subpopulations were identified in C. maculata, a northern population of which the Ourimbah locality was the most southerly studied, and a southern population of which Wingello was the most northerly locality studied. Diminished levels of northern taxa ancestry, i.e. C. citriodora or C. henryi, in individuals from the southern, relative to the northern subpopulation of C. maculata, suggested that secondary contact with northern taxa contributes to its substructure.     

Phylogeography and genetic differentiation along the distributional range of the orchid Epidendrum fulgens: a Neotropical coastal species not restricted to glacial refugia

Aim Phylogeographical studies in the Brazilian Atlantic Forest (BAF) have mostly included species associated with forest habitats, whereas taxa associated with grassland and sand‐dune plant communities have so far been largely overlooked. This study examines the phylogeography of the orchid Epidendrum fulgens, which occurs on coastal sand dunes and granitic outcrops, in order to identify major genetic divergences or disjunctions across the range of the species and to investigate the genetic signatures of past range contractions and expansions. Location Southern and south‐eastern seashore vegetation along the BAF biome, and granitic and arenitic outcrops that occur in the subtropical grassland plant communities located south of the BAF. Methods Nine nuclear and four plastid microsatellite loci were used to genotype 424 individuals from 16 populations across the distributional range of E. fulgens. For both sets of markers, we estimated genetic diversity and population differentiation, testing for a north–south gradient of genetic diversity. The plastid haplotype network and a Bayesian assignment analysis of nuclear markers were used to infer population structure. Past demographic changes were investigated using a coalescence approach. Results A deep disjunction was found between northern populations within the BAF and southern populations outside the BAF that occur on granitic and arenitic outcrops. Recent demographic reductions were detected in northern populations on coastal sands. Such demographic changes were not expected for those populations, as previous studies with forest species had found evidence of population expansion in the same areas. Higher genetic diversity was found in southern populations on granite, in contrast to patterns observed in previous studies of forest species. Main conclusions The results are consistent with the long‐term persistence of E. fulgens. Bottlenecks were detected in populations from areas where population expansion events have been detected in other plant (and animal) species, suggesting that forest expansion after the Last Glacial Maximum played a role in the population fragmentation and decrease in genetic diversity in E. fulgens. A substantial genetic division in E. fulgens corresponds to the ‘Portal de Torres’, a region that demarcates the northern limits of subtropical grassland plant communities and the southern limits of the BAF.     

Intervarietal and intravarietal genetic structure in Douglas‐fir: nuclear SSRs bring novel insights into past population demographic processes,phylogeography, and intervarietal hybridization

Douglas‐fir (Pseudotsuga menziesii) is one of numerous wide‐range forest tree species represented by subspecies/varieties, which hybridize in contact zones. This study examined the genetic structure of this North American conifer and its two hybridizing varieties, coastal and Rocky Mountain, at intervarietal and intravarietal level. The genetic structure was subsequently associated with the Pleistocene refugial history, postglacial migration and intervarietal hybridization/introgression. Thirty‐eight populations from the USA and Canada were genotyped for 13 nuclear SSRs and analyzed with simulations and traditional population genetic structuring methods. Eight genetic clusters were identified. The coastal clusters embodied five refugial populations originating from five distinct refugia. Four coastal refugial populations, three from California and one from western Canada, diverged during the Pleistocene (56.9–40.1 ka). The three Rocky Mountain clusters reflected distinct refugial populations of three glacial refugia. For Canada, ice covered during the Last Glacial Maximum, we present the following three findings. (1) One refugial population of each variety was revealed in the north of the distribution range. Additional research including paleodata is required to support and determine whether both northern populations originated from cryptic refugia situated south or north of the ice‐covered area. (2) An interplay between intravarietal gene flow of different refugial populations and intervarietal gene flow by hybridization and introgression was identified. (3) The Canadian hybrid zone displayed predominantly introgressants of the Rocky Mountain into the coastal variety. This study provides new insights into the complex Quaternary dynamics of this conifer essential for understanding its evolution (outside and inside the native range), adaptation to future climates and for forest management.     

Genetic structure, habitat fragmentation and bottlenecks in Danish bank voles (Clethrionomys glareolus)

Tissue-samples from 161 bank voles (Clethrionomys glareolus) collected in three forests (five sampling localities) situated in eastern Jutland (Denmark) were analysed by nine microsatellite loci. The genetic diversity found within the populations was high (H_e=0.753–0.806).Bank voles have specific habitat requirements favouring woodlots, hedgerows and deciduous forests as their prime living area. Hence, a natural or human-induced fragmentation of the forest may cause a sub-structuring of the populations and thereby a restriction of dispersal among populations. The sub-structuring indicated by the observed significant genetic differentiation among the five geographically distinct localities (F_st =0.033, P<0.05) could either result from habitat fragmentation or a combination of home range behaviour and different tree composition in the forests. A road situated between two adjacent forests was not found to exert any barrier effect to the gene flow of bank voles. In one out of five localities investigated, genetic evidence for a recent bottleneck-like situation was found. Bank voles are known to exhibit sometimes huge density fluctuations not only from year to year but also from season to season. The bottleneck-like situation found could therefore be due to the low number of individuals during the low-density phase.     

Phylogeny, biogeography, and species boundaries within the Alexandrium minutum group

The geographic range and bloom frequency of the toxic dinoflagellate Alexandrium minutum and other members of the A. minutum group have been increasing over the past few decades. Some of these species are responsible for paralytic shellfish poisoning (PSP) outbreaks throughout the world. The origins of new toxic populations found in previously unaffected areas are typically not known due to a lack of reliable plankton records with sound species identifications and to the lack of a global genetic database. This paper provides the first comprehensive study of minutum-group morphology and phylogeny on a global scale, including 45 isolates from northern Europe, the Mediterranean, Asia, Australia and New Zealand.Neither the morphospecies Alexandrium lusitanicum nor A. angustitabulatum was recoverable morphologically, due to large variation within and among all minutum-group clonal strains in characters previously used to distinguish these species: the length:width of the anterior sulcal plate, shape of the 1′ plate, connection between the 1′ plate and the apical pore complex, and the presence of a ventral pore. DNA sequence data from the D1 to D2 region of the LSU rDNA also fail to recognize these species. Therefore, we recommend that all isolates previously designated as A. lusitanicum or A. angustitabulatum be redesignated as A. minutum. A. tamutum, A. insuetum, and A. andersonii are clearly different from A. minutum on the basis of both genetic and morphological data.A. minutum strains from Europe and Australia are closely related to one another, which may indicate an introduction from Europe to Australia given the long history of PSP in Europe and its recent occurrence in Australia. A minutum from New Zealand and Taiwan form a separate phylogenetic group. Most strains of A. minutum fit into one of these two groups, although there are a few outlying strains that merit further study and may represent new species. The results of this paper have greatly improved our ability to track the spread of A. minutum species and to understand the evolutionary relationships within the A. minutum group by correcting inaccurate taxonomy and providing a global genetic database.     

Glacial refugia and postglacial expansion of the alpine–prealpine plant species Polygala chamaebuxus

The shrubby milkwort (Polygala chamaebuxus L.) is widely distributed in the Alps, but occurs also in the lower mountain ranges of Central Europe such as the Franconian Jura or the Bohemian uplands. Populations in these regions may either originate from glacial survival or from postglacial recolonization. In this study, we analyzed 30 populations of P. chamaebuxus from the whole distribution range using AFLP (Amplified Fragment Length Polymorphism) analysis to identify glacial refugia and to illuminate the origin of P. chamaebuxus in the lower mountain ranges of Central Europe. Genetic variation and the number of rare fragments within populations were highest in populations from the central part of the distribution range, especially in the Southern Alps (from the Tessin Alps and the Prealps of Lugano to the Triglav Massiv) and in the middle part of the northern Alps. These regions may have served, in accordance with previous studies, as long‐term refugia for the glacial survival of the species. The geographic pattern of genetic variation, as revealed by analysis of molecular variance, Bayesian cluster analysis and a PopGraph genetic network was, however, only weak. Instead of postglacial recolonization from only few long‐term refugia, which would have resulted in deeper genetic splits within the data set, broad waves of postglacial expansion from several short‐term isolated populations in the center to the actual periphery of the distribution range seem to be the scenario explaining the observed pattern of genetic variation most likely. The populations from the lower mountain ranges in Central Europe were more closely related to the populations from the southwestern and northern than from the nearby eastern Alps. Although glacial survival in the Bohemian uplands cannot fully be excluded, P. chamaebuxus seems to have immigrated postglacially from the southwestern or central‐northern parts of the Alps into these regions during the expansion of the pine forests in the early Holocene.     

Genetic structure and demographic history of the endangered tree species Dysoxylum malabaricum (Meliaceae) in Western Ghats,India: implications for conservation in a biodiversity hotspot

The impact of fragmentation by human activities on genetic diversity of forest trees is an important concern in forest conservation, especially in tropical forests. Dysoxylum malabaricum (white cedar) is an economically important tree species, endemic to the Western Ghats, India, one of the world's eight most important biodiversity hotspots. As D. malabaricum is under pressure of disturbance and fragmentation together with overharvesting, conservation efforts are required in this species. In this study, range‐wide genetic structure of twelve D. malabaricum populations was evaluated to assess the impact of human activities on genetic diversity and infer the species’ evolutionary history, using both nuclear and chloroplast (cp) DNA simple sequence repeats (SSR). As genetic diversity and population structure did not differ among seedling, juvenile and adult age classes, reproductive success among the old‐growth trees and long distance seed dispersal by hornbills were suggested to contribute to maintain genetic diversity. The fixation index (F_IS) was significantly correlated with latitude, with a higher level of inbreeding in the northern populations, possibly reflecting a more severe ecosystem disturbance in those populations. Both nuclear and cpSSRs revealed northern and southern genetic groups with some discordance of their distributions; however, they did not correlate with any of the two geographic gaps known as genetic barriers to animals. Approximate Bayesian computation‐based inference from nuclear SSRs suggested that population divergence occurred before the last glacial maximum. Finally we discussed the implications of these results, in particular the presence of a clear pattern of historical genetic subdivision, on conservation policies.     

Extreme levels of intra-specific divergence among Cape Peninsula populations of the Cape galaxias,Galaxias zebratus Castelnau 1861, reveals a possible species complex

The Cape galaxias, Galaxias zebratus, is part of the paleao-endemic fauna characteristic of the south-western Cape, South Africa, and is the only galaxiid found in continental Africa. A 284-bp fragment of the cytochrome b region of the mtDNA was sequenced from 48 individual galaxiids, representing 10 populations from the Cape Peninsula. Five sequences, for four additional populations sampled at the extremes of the species range, were obtained from the literature. Analysis of cyt b mtDNA from these 14 populations of G. zebratus revealed five distinct and highly divergent lineages with low levels of intra-population mtDNA haplotype diversity. A new and distinct genetic lineage is described from the southern part of the Cape Peninsula. Estimates of genetic divergence between populations ranged from <1% to >17%. The observed level of sequence divergence represents the largest yet reported for any single fish species. The distribution of these lineages and their degree of sequence divergence refutes a model of isolation by distance. Results suggest that periods of low sea level may have been important in creating opportunities and alternative routes for dispersal and migration for Cape Peninsula populations.     

肋果沙棘北缘居群的遗传多样性与遗传结构

该研究利用SSR分子标记,对肋果沙棘(Hippophae neurocarpa)分布区北缘青海祁连地区5个自然居群进行分析,旨在了解小地理尺度下肋果沙棘北缘居群的遗传多样性和片段化分布居群的遗传结构,为肋果沙棘居群的资源保护提供了依据。采用6对微卫星引物对107个样本DNA进行扩增,共检测到27个等位变异,变幅为2~9个,平均每个位点有4.67个,平均观测杂合度(Ho)和期望杂合度(He)分别为0.142和0.230,Shannon信息指数(I)的变幅介于0.280~0.567之间,平均值为0.374,说明肋果沙棘北缘居群的遗传多样性较为丰富。遗传分化系数Fst=0.483,分子方差分析(AMOVA)表明肋果沙棘有48.33%的变异存在于居群间,51.67%存在于居群内。对5个居群之间的遗传距离与地理距离做Mental检验,结果表明遗传距离与地理距离相关性不显著,对基因流检测发现居群间的Nm为0.328,推测遗传漂变是居群分化的关键因素之一。Structure分析把5个居群分为2组。UPGMA聚类分析表明5个居群聚为2个分支,其中居群ARX为单独的一支,与主坐标分析的结果一致。基于分布区北缘青海祁连肋果沙棘自然居群的遗传结构分析,建议应尽可能多地保护不同的地方居群。     

青藏高原濒危植物唐古特大黄的遗传多样性

唐古特大黄(Rheum tanguticum)是中国传统的中藏药材,近几年由于生境的严重破坏,已濒临灭绝,并被列入濒危植物名单。为了探索唐古特大黄物种濒危的原因并保护其野生资源,本研究采集了9个居群87个个体的唐古特大黄样本,基于该物种的叶绿体基因trn S-G序列对其进行了遗传多样性研究。结果表明,唐古特大黄物种具有较高的遗传多样性水平(Ht=0.694),其中95.97%的遗传分化来自于居群间(G_(ST)=0.960),4.03%的遗传分化来自于居群内(Hs=0.028)。AMOVA分析也显示唐古特大黄居群间基因流较小(N_m=0.01),存在较高的遗传分化(F_(ST)=0.9631)。唐古特大黄较高的遗传多样性水平可能与该物种较长的进化史和生活史有关,居群间较高的遗传分化可能与高山地区特殊的地理环境和人类活动有关。根据研究结果,建议对唐古特大黄所有野生居群进行就地保护,同时收集种质资源开展异地繁殖工作,以保护物种的遗传多样性,维持其进化潜力。     

Quinua and Relatives (Chenopodium sect.Chenopodium subsect.Celluloid)

Traditionally viewed as an Andean grain crop,Chenopodium quinoa Willd. includes domesticated populations that are not Andean, and Andean populations that are not domesticated. Comparative analysis of leaf morphology and allozyme frequencies have demonstrated that Andean populations, both domesticated(quinua) and free-living(ajara), represent an exceptionally homogeneous unit that is well differentiated from allied domesticates of coastal Chile(quingua) and freeliving populations of the Argentine lowlands(C. hircinum). This pattern of relationships indicates that Andean populations represent a monophyletic crop/weed system that has possibly developed through cyclic differentiation (natural vs. human selection) and introgressive hybridization. Relative levels of variation suggest that this complex originated in the southern Andes, possibly from wild types allied withC. hircinum, with subsequent dispersal north to Colombia and south to the Chilean coast. Coastal populations were apparently isolated from post-dispersal differentiation and homogenization that occurred in the Andes. Other data point toward a center of origin in the northern Andes with secondary centers of genetic diversity subsequently developing in the southern Andes and the plains of Argentina. Comparative linkage of South American taxa, all tetraploid, with North American tetraploids of the subsection will eventually clarify this problem. While the possibility of a direct phyletic connection betweenC. quinoa and the Mexican domesticate(C. berlandieri subsp. nuttalliae,) cannot be excluded, available evidence indicates that the latter represents an autonomous lineage that is associated with the basal tetraploid, C. b. subsp.berlandieri, through var.sinuatum, whereas South American taxa show possible affinities to either var. zschackei or var.berlandieri. An extinct domesticate of eastern North America,C. b. subsp.jonesianum, represents either another instance of independent domestication, possibly from subsp. b. var.zschackei, or a northeastern outlier of subsp.nuttalliae.     

Late Quaternary climatic vegetational shifts in an ecological transition zone of northern Madagascar: insights from genetic analyses of two endemic rodent species

The Loky‐Manambato region, located in northern Madagascar, is a biotically rich contact zone between different forest biomes. Local current forest cover is composed of both humid and dry formations, which show elevational stratification. A recent phylogeographical study of a regional dry forest rodent, Eliurus carletoni (subfamily Nesomyinae), found genetic evidence of forest contractions between 18 750 and 7500 years BP, which based on extrapolation of the pollen subfossil record, was thought to be associated with an expansion of local humid forests. Herein, we conduct a genetic test of this hypothesis and focused on populations on two neighbouring massifs of forest‐dependent rodent species, one associated with low‐elevation dry forests (E. carletoni) and the other with higher elevation humid forests (Eliurus tanala). Using mitochondrial markers and a combination of traditional and coalescent‐based phylogeographical, historical demographic and population genetic methods, we found evidence of historical connections between populations of E. tanala. Adjacent populations of E. carletoni and E. tanala exhibit opposite historical demographic patterns, and for both, evidence suggests that historical demographic events occurred within the last 25 000 years BP. These findings strongly support the proposed late Quaternary shifts in the floristic composition of the Loky‐Manambato region.     

Stepping-stone expansion and habitat loss explain a peculiar genetic structure and distribution of a forest insect

It is challenging to unravel the history of organisms with highly scattered populations. Such species may have fragmented distributions because extant populations are remnants of a previously more continuous range, or because the species has narrow habitat requirements in combination with good dispersal capacity (naturally or vector borne). The northern pine processionary moth Thaumetopoea pinivora has a scattered distribution with fragmented populations in two separate regions, northern and south-western Europe. The aims of this study were to explore the glacial and postglacial history of T. pinivora, and add to the understanding of its current distribution and level of contemporary gene flow. We surveyed published records of its occurrence and analysed individuals from a representative subset of populations across the range. A 633 bp long fragment of the mtDNA COI gene was sequenced and nine polymorphic microsatellite loci were genotyped. Only nine nucleotide sites were polymorphic in the COI gene and 90% of the individuals from across its whole range shared the same haplotype. The microsatellite diversity gradually declined towards the north, and unique alleles were found in only three of the northern and three of southern sites. Genetic structuring did not indicate complete isolation among regions, but an increase of genetic isolation by geographic distance. Approximate Bayesian model choice suggested recent divergence during the postglacial period, but glacial refugia remain unidentified. The progressive reduction of suitable habitats is suggested to explain the genetic structure of the populations and we suggest that T. pinivora is a cold-tolerant relict species, with situation-dependent dispersal.     

The Kuroshio Current influences genetic diversity and population genetic structure of a tropical seagrass,Enhalus acoroides

Information on genetic diversity and differentiation of seagrass populations is essential for the conservation of coastal ecosystems. However, little is known about the seagrasses in the Indo‐West Pacific Ocean, where the world's highest diversity of seagrasses occurs. The influence of sea currents on these populations is also unknown. We estimated the genetic diversity and population genetic structure and identified reproductive features in Enhalus acoroides populations from the Yaeyama Islands, Hainan Island and the Philippines. The Philippines are situated at the centre of the E. acoroides range, Yaeyama and Hainan are peripheral populations, and the Yaeyama population is at the northern limit of the species range. The powerful Kuroshio Current flows from the Philippines to Yaeyama. Genetic analyses using nine microsatellite markers indicated that reproduction of E. acoroides is mostly sexual. Clonal diversity does not decrease in northern populations, although genetic diversity does. However, the genetic diversity of the Yaeyama populations is greater than that of the Hainan populations. Significant genetic differentiation among most populations was evident; however, the Yaeyama and north‐east Philippines populations were genetically similar, despite being separated by ~1100 km. An assignment test suggested that recruitment occurs from the north‐east Philippines to Yaeyama. The strong current in this region is probably responsible for the extant genetic diversity and recruitment patterns.     

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

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

Phylogeography of a stream-dwelling frog (Pseudacris cadaverina) in southern California

Recent phylogeographic studies of animal taxa in California have revealed common geographic patterns of evolutionary divergence and genetic diversity that are generally attributable to landscape influences. However, there remains a paucity of knowledge on the evolution of freshwater taxa in southern California. Here, we investigate phylogeographic patterns in a stream-dwelling frog (Pseudacris cadaverina). Two hundred and twenty-one individuals were collected from 46 populations across the species’ range in southern California. Using 1100 bp of sequence data from cytochrome b and tRNA-Glu, we conducted phylogenetic analyses, analysis of molecular variance, and nested clade phylogeographic analysis to gain insight into the factors contributing to the distribution of genetic diversity in P. cadaverina. We tested for evidence of two putative phylogeographic breaks and tested hypotheses that genetic diversity in this species is partitioned into (1) major watersheds, (2) mountain ranges, and (3) coastal and desert regions. Our results suggest that the eastern Transverse Ranges are the center of origin for extant P. cadaverina lineages and that the observed genetic structure in this species was established during the Pleistocene Epoch. There is strong support for three major haplotype groups and a Transverse Range break in P. cadaverina that is concordant with breaks found in numerous other taxa. The distribution of genetic diversity in P. cadaverina is due in large part to the separation of populations into different major watersheds and mountain ranges. Gene flow appears to be generally limited among disjunct populations throughout the region and some desert populations have been isolated by historical habitat fragmentation.