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Tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), is an important component of mixed-evergreen forests and woodlands in coastal California and Oregon, with incursions into the Sierra Nevada and the Klamath Ranges. Sudden Oak Death (SOD) is causing severe dieback and mortality in tanoak and could transform these ecosystems in areas where the pathogen Phytophthora ramorum S. Werres, A.W.A.M. de Cock can become established. Knowledge of genetic diversity within the species is important for both disease resistance screening, conservation and replanting in sites with high mortality. Here we review what has been learned about the genetic structure within tanoak since SOD has caused disease epidemics in the species. We review published work on genetic structure at the species level and provide some re-analyses of these data that show divergence across the geographic range. We also review recently published data on genetic structure at a fine spatial scale that provides some guidelines for the selection of trees as seed sources. Finally, we interpret a range of seed provenancing strategies in the light of our knowledge of tanoak genetic diversity.

Knowledge of population genetic structure of tanoak (Lithocarpus densiflorus) is of interest to pathologists seeking natural variation in resistance to sudden oak death disease, to resource managers who need indications of conservation priorities in this species now threatened by the introduced pathogen (Phytophthora ramorum), and to biologists with interests in demographic processes that have shaped plant populations. We investigated population genetic structure using nuclear and chloroplast DNA (cpDNA) and inferred the effects of past population demographic processes and contemporary gene flow. Our cpDNA results revealed a strong pattern of differentiation of four regional groups (coastal California, southern Oregon, Klamath mountains, and Sierra Nevada). The chloroplast haplotype phylogeny suggests relatively deep divergence of Sierra Nevada and Klamath populations from those of coastal California and southern Oregon. A widespread coastal California haplotype may have resulted from multiple refugial sites during the Last Glacial Maximum or from rapid recolonization from few refugia. Analysis of nuclear microsatellites suggests two major groups: (1) central coastal California and (2) Sierra Nevada/Klamath/southern Oregon and an area of admixture in north coastal California. The low level of nuclear differentiation is likely to be due to pollen gene flow among populations during postglacial range expansion.

Regional distribution of genetic diversity in widespread species may be influenced by hybridization with locally restricted, closely related species. Previous studies have shown that Central American East Pacific populations of the wide-ranged Avicennia germinans, the black mangrove, harbour higher genetic diversity than the rest of its range. Genetic diversity in this region might be enhanced by introgression with the locally restricted Avicennia bicolor. We tested the hypotheses of ancient hybridization using phylogenetic analysis of the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA and intergenic chloroplast DNA; we also tested for current hybridization by population level analysis of nuclear microsatellites. Our results unveiled ancient ITS introgression between a northern Pacific Central American A. germinans lineage and A. bicolor. However, microsatellite data revealed contemporary isolation between the two species. Polymorphic ITS sequences from Costa Rica and Panama are consistent with a zone of admixture between the introgressant ITS A. germinans lineage and a southern Central American lineage of A. germinans. Interspecific introgression influenced lineage diversity and divergence at the nuclear ribosomal DNA; intraspecific population differentiation and secondary contact are more likely to have enhanced regional genetic diversity in Pacific Central American populations of the widespread A. germinans.

European black pine (Pinus nigra Arn.) is a widely distributed Mediterranean conifer. To test the hypothesis that fragmented populations in western Europe survived in situ during the last glacial rather than having been re-colonized in the postglacial period, genetic variation was assessed using a suite of 10 chloroplast DNA microsatellites. Among 311 individuals analysed, 235 haplotypes were detected revealing high levels of chloroplast haplotype diversity in most populations. Bayesian analysis using a model of linked loci, with no prior assumption of population structure, assigned individuals to 10 clusters that corresponded well with the six predefined sampling regions, while an analysis carried out at the population level and assuming unlinked loci, recovered the original six sampling regions. This regional structure was supported by a biogeographical analysis that detected five barriers, with the two most significant separating Alps from Corsica and southern Italy, and southern Spain from the Pyrenees. No signals of demographic expansion were detected, and comparisons of R(ST) with pR(ST) suggested that a stepwise mutational model was important in regional differentiation, but not in population-within-region differentiation. These tests support long-term persistence of the species within the six regions. The temporal depth estimate, assuming a high mutation rate in coalescent modelling, placed the deepest split between the Alps and the other regions at about 150 000 years ago, and the most recent split of Pyrenees from southern France at about 30 000 years ago. Taken together, the data suggest that chloroplast DNA is structured in black pine and disjunct populations in western Europe are likely to have been present during the Last Glacial Maximum.

The four western North American red oak species (Quercus wislizeni, Q. parvula, Q. agrifolia, and Q. kelloggii) are known to produce hybrid products in all interspecific combinations. However, it is unknown whether hybrids are transitory resulting from interspecific gene flow or whether they are maintained through extrinsic selection. Here, we examine cryptic hybrid structure in Q. wislizeni through a broad region including contact and isolation from three other western North American red oaks using amplified fragment length polymorphism molecular markers. All four species were simultaneously detected in the genetic background of individuals morphologically assigned to Q. wislizeni, although the contribution of Q. kelloggii was minor. In some cases, introgression was detected well outside the region of sympatry with one of the parental species. Molecular structure at the individual level indicated this was due to long-distance pollen dispersal and not to local extinction of parental species. Species admixture proportions were correlated with climatic variables and greater proportions of Q. agrifolia and Q. parvula were present in the genetic background of Q. wislizeni in sites with cooler and more humid summers, corresponding with habitat preferences of the parental species. Partial Mantel tests indicated that climate was more important than distance from pollen source in this association. Despite high levels of introgression, species integrity was maintained in some populations in close proximity to the other species, providing further support to environmental selection in determining population genetic structure. Thus, the contribution of species mixtures to population genetic structure varies across the landscape according to availability of pollen, but more importantly to varying environmental selection pressures that produce a complex pattern of hybrid and pure gene pools.

The combination of sprouting and reproduction by seed can have important consequences on fine-scale spatial distribution of genetic structure (SGS). SGS is an important consideration for species’ restoration because it determines the minimum distance among seed trees to maximize genetic diversity while not prejudicing locally adapted genotypes. Local environmental conditions can be expected to influence levels of clonal spread and SGS, particularly in the case of disturbance regimes such as fire. Here, we characterize fine-scale genetic structure and clonal spread in tanoak from drier upland sites and more mesic lowland woodlands. Clonal spread was a significant mode of stand development, but spread was limited on average to about 5–6 m. Gene dispersal was decomposed into clonal and sexual components. The latter varied according to whether it was estimated from all ramets with the clonal component removed or for a single ramet per genet. We used the difference in these 2 estimates of gene dispersal as a measure of the effect of clonality on effective population size in this species. Although upland sites had a greater number of ramets per genet, most of the other indices computed were not significantly different. However, they tended to show greater heterozygote excess and shorter gene dispersal distances than the lowland sites. The average distance among inferred sibships on upland sites was approximately at the scale of maximum clonal range. This was not the case on lowland sites, where sibs were more dispersed. We recommend minimum distances among seed trees to avoid selecting clones and to maximize genetic diversity for restoration. An overall goal of habitat restoration following severe disturbances is to maximize genetic diversity through appropriate management of recruitment from natural or artificial seeding. The choice of seed is critically important to avoid practices that would reduce evolutionary potential of the rehabilitated habitat and should be based on

Biometrical variability of foliage, cones, and seeds were analyzed in 8 native populations (throughout the range) of a relictual species,Cupressus bakeriJeps. (Cupressaceae) from California and Oregon. The partition of variation within and among populations for this rare plant was investigated and the justification for subspecies status was reviewed. Morphological characters varied significantly, with more of the variation among populations than at the population level. Multivariate analyses indicated close affinities among populations on serpentine sites suggesting the presence of a serpentine race. However, the high degree of variation among populations did not permit their clear separation into the two subspecies described byWolf (1948). We conclude thatC. bakeri should be treated as a monotypic species.

Acorns of mediterranean evergreen oak were collected from eight ecogeographically contrasting localities in Italy and Spain. Biometrical analysis of acorns and their cupules showed much greater variation among Spanish populations, encompassing the variation in Italy. The Spanish population at El Pardo, considered the type locality for Quercus rotundifolia, separated from all others. Multivariate analyses of the chemical data indicated, on the one hand, separation of Spain from Italy, and on the other hand, a separation of interior Spanish populations from coastal populations. The importance of lipid composition in the former separation may reflect genetic differentiation between these two origins. Coastal populations were closer to Italian and we suggest were a zone of introgression and hybridization between Quercus ilex and Q. rotundifolia and probably also Quercus coccifera at Bonete Albacete. Key words: Quercus ilex, Quercus rotundifolia, biometry, diversity, chemistry, ecogeography.

Variations in synchronicity between colonization rate by the pathogen and host phenology may account for unexplained spatial distribution of canker disease. The hypothesis that synchronous pathogenicity and host development are necessary for incidence of sudden oak death disease was tested by correlating seasonal variations in host cambial phenology and response to inoculation with Phytophthora ramorum. • Response to infection was estimated by inoculating branch cuttings from coast live oak (Quercus agrifolia) trees at nine dates through a full annual cycle in2003-2004 . Host phenology was estimated from measurements of bud burst and cambial activity in spring 2006. • Lesions were largest in the spring soon after the cambium resumed activity. A moderate genetic component to lesion size was detected. Variation among trees in date of largest lesions correlated with variation in timing of bud burst and cambial phenology. • The data support the hypothesis that active host cambial tissue is a necessary requisite for successful infection with the pathogen that causes sudden oak death canker disease. Genetic variation in host phenology will buffer coast live oak against epidemics of this disease

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.

Cuticular permeability is thought to be related to the biophysical properties of cuticular waxes and, in turn, to the chemical composition of this boundary layer. However, thus far evidence for this relationship has been elusive. We investigated possible correlations between habitat and inter- and intraspecific variations in two parameters likeley to affect crystallinity and transition melting temperatures of waxes. Three species from the family Cupressaceae (Austrocedrus chilensis, Fitzroya cupressoides, Pilgerodendron uviferm) were selected as a model system because they are closely related and form a continuum over 20° of latitude in South America that includes important climatic differences. We found major divergence among the three species and more fine-scale population differentiation for A. chilensis and P. uviferum in weighted mean carbon number (N) and dispersion about this mean (d). Broad-sense heritabilities, estimated from ramet-ortet regressions and from analysis of variance among or...

We have examined possible adaptation in cuticular alkane composition in the halophytic mangrove genus Rhizophora. Relative composition of the dominant alkanes varied: 1. among the three sympatric species from the Atlantic-East-Pacific region, 2. with geographic region within species and, 3. among populations within geographic region. For R. mangle, longer chain alkanes were more important in the semi-arid regions of north-west Africa and the Pacific coast of north-central Mexico. Mantel tests showed that inter-population taxonomic distances for the major alkanes were correlated with taxonomic distances for annual rainfall and mean maximum temperature, but not with weighted geographic distance. Since alkane carbon chain length should affect the biophysical properties of waxes, with longer chain lengths increasing crystallinity and impermeability, our data provides support for the hypothesis that observed differentiation is due to natural selection, rather than stochastic processes in this species. The same pattern was not observed for R. racemosa or R. harrisonii. Since these two species occupy less saline conditions and are more restricted in their latitudinal range, selection pressure may be less important than other evolutionary forces such as genetic drift. There was some evidence that alkane composition was more closely correlated with mean minimum temperatures in R. racemosa, that might set the latitudinal limits in this species.

Foliage, cones and seeds of Cupressus bakeri were collected from 5 1 trees in 6 populations from the NE and NW flanks of Goosenest Mountain in the Cascade Ranges of California. Biometrical analyses showed a high degree of differentiation among populations despite their geographic proximity. Population GN2, from the NW side of the mountain, was most distinct from all others. Variation between populations GN1 and GN2 was surprisingly great considering their close proximity, and similar ecological conditions, suggesting genetic differentiation. Morphological differences among populations of the NE side of the mountain (GN4, GN5 and GN6) may have been due to phenotypic plasticity to differing ecological conditions. These latter populations had characteristics similar to those of the Siskiyou Mountains, suggesting that Goosenest Mountain can be considered a region of transition and differentiation in this species., Les feuilles, les cônes et les graines de 51 individus de Cupressus bakeri Jeps. ont été récoltés dans 6 populations naturelles du versant NE et NW du Mont de Goosenest dans la chaîne montagneuse de Cascades en Californie. L’analyse multivariante effectuée sur les caractères biométriques a montré un degré élevé de différenciation entre les diverses populations, même géographiquement très proches. La population GN2 du versant NW est bien distincte des autres. La variation entre les populations GN1 et GN2, très voisines, dans des conditions écologiques similaires, est surprenante et nous suggérons qu’il s’agit d’une différenciation plutôt d’origine génétique. La différence morphologique observée entre les populations du versant NE (GN4, GN5, GN6) est due aux conditions écologiques : c’est une différenciation phénotypique. Ces dernières populations possèdent les caractéristiques de celles du Mont Siskiyou et cela nous a incités à penser que le Mont de Goosenest pourrait être en effet une zone de transition et de différenciation pour cette espèce., Dodd Richard S., Afzal-Rafii Zara, Power Ariel B. Biodiversity within natural populations of Cupressus bakeri (Goosenest Mountain, California). In: Ecologia mediterranea, tome 16,1990. pp. 51-57.