DIFFERENTIAL RESPONSES TO MAGNESIUM AND CALCIUM BY NATIVE POPULATIONS OF AGROPYRON SPICATUM

Plants of Agropyron spicatum (Pursh) Scribn. and Smith. from populations native to serpentine and nonserpentine soils were grown at varying levels of magnesium and calcium in culture solutions. The yields of plants from the two populations were different. At high Mg levels (low Ca) the yield of the serpentine population was significantly higher than that of the nonserpentine population. At low Mg the yield of the serpentine population leveled off at a Mg: Ca ratio of 1:2, while the yield of the nonserpentine population increased up to a Mg:Ca ratio of 1:8 and showed no leveling off. Chemical analyses of tissue showed that the Ca uptake of plants from the serpentine population was significantly higher than that of the nonserpentine population. In addition, the serpentine population maintained a lower Mg concentration in the shoots than the nonserpentine population at comparable Mg substrate levels. The two populations showed differences in Ca and Mg uptake efficiency and Mg/Ca, Ca + Mg/K + Na, and Ca + Mg + K + Na in the shoots. The ecotypic differentiation with respect to Mg and Ca between native populations of serpentine and nonserpentine A. spicatum does not appear to be due to any single mechanism but, rather, a combination of several possible mechanisms, i.e., differences in root morphology, uptake mechanisms, translocation of nutrients, and interactions between cations.     

ECOLOGICAL GENETICS OF SERPENTINE TOLERANCE IN THE MOSS,FUNARIA FLAVICANS: VARIATION WITHIN AND AMONG HAPLOID SIB FAMILIES

Many mosses occur both on and off serpentine soils, but experiments designed to test whether serpentine populations of widespread species display genetic adaptations for growth on serpentines have not been reported. Toward that end, two populations of the moss, Funaria flavicans, were grown on nutrient media varying in nickel and chromium concentration and in the ratio of magnesium to calcium. Three haploid siblings from each of five sporophytic families from the two populations were grown on five experimental media. There was no evidence that serpentine plants were more tolerant of nickel, chromium, high magnesium/calcium, or high nickel combined with high magnesium/calcium. In fact, plants from the nonserpentine population produced more protonemal growth than the serpentine plants on every medium except the control, on which plants from the two populations were indistinguishable. Large differences in nickel tolerance among haploid sib families (families of meiotic progeny derived from the same sporophyte) from the nonserpentine site provided evidence of genetic polymorphism in that population.     

Genetic structure of kestrel populations and colonization of the Cape Verde archipelago

Genetic diversity and population structure were studied in eight populations of the kestrel Falco tinnunculus to identify the genetic consequences of spatial distribution and to infer the colonization patterns of the Cape Verde archipelago. We studied genetic differentiation and gene flow among seven island populations and one mainland population using nine microsatellite loci. Within the archipelago, differentiation was strong and genetic diversity and heterozygosity were low but variable among populations. Two subspecies F. tinnunculus neglectus on the northwestern islands and F. tinnunculus alexandri on all the other islands were identified as genetically distinct units. F. t. alexandri could be further separated into two groups on eastern and southern islands. Populations are probably founded by birds originating from the mainland. Immigration is more likely to the eastern and southern populations, whereas the northwestern islands with the lowest genetic diversity and highest differentiation are likely to exhibit fewer founding events by immigrants. The number of founding events on each island may depend not only on geographical distance to neighbouring populations, but also on directional immigration due to the northeastern trade winds. This may explain differences in genetic differentiation and diversity between populations and subspecies and may enable allopatric speciation.     

Serpentine soils promote ectomycorrhizal fungal diversity

Serpentine soils impose physiological stresses that limit plant establishment and diversity. The degree to which serpentine soils entail constraints on other organisms is, however, poorly understood. Here, I investigate the effect of serpentine soils on ectomycorrhizal (ECM) fungi by conducting a reciprocal transplant experiment, where serpentine and nonserpentine ECM fungal communities were cultured in both their native and non-native soils. Contrary to expectation, serpentine soils hosted higher fungal richness compared to nonserpentine, and most species were recovered from serpentine soil, suggesting ECM fungi are not overall specialized or strongly affected by serpentine edaphic constraints.     

Ectomycorrhizal communities of Quercus garryana are similar on serpentine and nonserpentine soils

Serpentine soils, rich in iron, magnesium, and heavy metals, select for unique plant communities and for endemic species. Because mycorrhizal fungi mediate the interaction between plants and soil, we hypothesized that distinct ectomycorrhizal fungi would colonize Quercus garryana roots on serpentine and nonserpentine soils. We sampled roots of Q. garryana on serpentine soils at two locations in the Klamath-Siskiyou Mountains of southwestern Oregon and identified ectomycorrhizas by morphological and molecular methods. The same six most abundant and most frequent mycorrhizal species, Cenococcum geophilum, Tuber candidum, Genea harknessii, Tomentella sp., Sebacina sp., and Inocybe sp., were found on serpentine and nonserpentine soils. Based on similarities calculated using the Sørensen index in Non-metric Multidimensional Scaling, mycorrhizal communities on serpentine and nonserpentine soils were not significantly different. This study showed that ectomycorrhizal species associated with Q. garryana exhibit edaphic tolerance and were neither reduced nor excluded by serpentinite or peridotite parent materials.     

Collinsia sparsiflora in serpentine and nonserpentine habitats: using F2 hybrids to detect the potential role of selection in ecotypic differentiation

Here we document phenotypic differences between serpentine and nonserpentine ecotypes of Collinsia sparsiflora, as well as patterns of selection in these contrasting soil habitats. We transplanted the two parental ecotypes and experimental F2 hybrids into six field sites, and collected morphological, phenological and fitness data on emergent plants. To focus on edaphically mediated selection, rather than on pollinator-mediated selection, we used pollinator-exclusion cages. Transplanted parentals of the two ecotypes showed genetic differentiation for floral traits, but not for phenological traits or cotyledon size. For the F2 hybrids growing on serpentine soils, there was significant directional selection on cotyledon size, flower size and flower shape. However, the pattern of selection did not differ significantly between serpentine and nonserpentine sites. Overall, we did not see evidence for divergent selection on the two soil types. We conclude that differences in floral traits between the ecotypes do not reflect adaptation to physical conditions associated with soil type, and that there are unmeasured traits that must be contributing to ecotypic differentiation.     

The evolution of the Streptanthus glandulosus complex (Cruciferae): genetic divergence and gene flow in serpentine endemics

An analysis of the levels and distribution of allozyme variation in the Streptanthus glandulosus species complex was undertaken to test paradigms of speciation processes in the context of serpentine endemism. Electrophoretic analysis of 21 putative enzyme loci in 1,224 individuals representing 56 populations revealed extensive intrapopulational variation and interpopulational divergence. Estimates of gene flow among populations within taxa are typically lower than is theoretically needed to counteract the effects of genetic drift (i.e., Nm values are below 0.5), suggesting that drift may play a significant role in the evolution of the complex. A cluster analysis of genetic identities between populations using UPGMA demonstrates geographically structured groupings, some of which include neighboring populations of different taxa. Moreover, the genetic identity between two populations is correlated with the distance by which they are separated. The results are consistent with a hypothesis of a paleoendemic origin of the complex. The ancestor of the complex (perhaps S. glandulosus ssp. glandulosus) probably was formerly distributed more continuously across serpentine and nonserpentine habitat throughout its range. Elimination of the nonserpentine populations allowed regional and population-level divergence, following a model of geographic speciation.     

Comparison of ectomycorrhizas of Quercus garryana (Fagaceae) on serpentine and non-serpentine soils in southwestern Oregon

The diversity of ectomycorrhizal communities associated with Quercus garryana on and off serpentine soils was compared and related to landscape-level diversity. Serpentine soils are high in magnesium, iron, and heavy metals and low in fertility. In plant communities on serpentine soils, a high proportion of flowering plant species are endemic. At three sites with paired serpentine and nonserpentine soils in southwestern Oregon, we sampled Q. garryana roots and categorized ectomycorrhizas by morphotyping and by restriction fragment length patterns. Ectomycorrhizas were abundant at all sites; no single fungal species dominated in the ectomycorrhizas. Of 74 fungal species characterized by morphotype and pattern of restriction fragment length polymorphisms, 46 occurred on serpentine soils, and 32 were unique to serpentine soil. These species are potentially endemic to serpentine soil. Similarities in species composition between paired serpentine and nonserpentine soils were not significantly lower than among three serpentine sites or among three nonserpentine sites. We conclude that mycorrhizal communities associated with oaks on serpentine soil do not differ in species richness or species evenness from those on neighboring nonserpentine soil.     

Hybridization between Arctostaphylos viscida and A. canescens in Oregon

Evidence of natural hybridization betweenArctostaphylos viscida andA. canescens in southwestern Oregon was obtained from morphological studies of field populations. Hybridization occurs where populations ofA. viscida andA. canescens meet in areas where serpentine and nonserpentine soils abut. At these contacts,A. viscida forms large populations only on serpentine andA. canescens only on nonserpentine. Most of the indentifiable hybrids survive on either transitional or nonserpentine soils. The small proportion that are found on serpentine are considered to be backcrosses toA. viscida. The hybrid plants are similar to several putative species maintained in the standard floras, and it is suggested that these no longer be given taxonomic recognition.     

Influence of substrate type and microsite availability on the persistence of foxtail pine (Pinus balfouriana, Pinaceae) in the Klamath Mountains, California

The persistence of poor competitors within species-rich assemblages is often tied to habitat heterogeneity. Here, the persistence of foxtail pine (Pinus balfouriana) in the Klamath Mountains of northern California was addressed using a two-step approach. First, the response of foxtail pine to shading from six co-occurring conifers was examined using two morphological indices. Foxtail pine increased the height to the first branch that supported foliage, and this branch was shorter when compared with those on all other sampled conifers, suggesting that foxtail pine is a poor competitor for light. Second, three hypotheses to explain foxtail pine persistence were tested: habitat heterogeneity at large spatial scales (substrate hypothesis), habitat heterogeneity at small spatial scales (microsite hypothesis), and the long lifespan of foxtail pine (successional hypothesis). Habitat heterogeneity at multiple spatial scales favored the persistence of foxtail pine. At large spatial scales, ultramafic substrates affected the importance and competitive abilities of shade-tolerant conifers. At small spatial scales, species richness, species diversity (H'), and stand density were positively correlated with microsite availability. No support was found for the successional hypothesis. Results are subsequently linked with general hypotheses of species coexistence in species-rich assemblages.     

CHARACTERIZING SELECTION ON PHENOTYPIC PLASTICITY IN RESPONSE TO NATURAL ENVIRONMENTAL HETEROGENEITY

Adaptive genetic differentiation and adaptive phenotypic plasticity can increase the fitness of plant lineages in heterogeneous environments. We examine the relative importance of genetic differentiation and plasticity in determining the fitness of the annual plant, Erodium cicutarium, in a serpentine grassland in California. Previous work demonstrated that the serpentine sites within this mosaic display stronger dispersal‐scale heterogeneity than nonserpentine sites. We conducted a reciprocal transplant experiment among six sites to characterize selection on plasticity expressed by 180 full‐sibling families in response to natural environmental heterogeneity across these sites. Multivariate axes of environmental variation were constructed using a principal components analysis of soil chemistry data collected at every experimental block. Simple linear regressions were used to characterize the intercept, and slope (linear and curvilinear) of reaction norms for each full‐sibling family in response to each axis of environmental variation. Multiple linear regression analyses revealed significant selection on trait means and slopes of reaction norms. Multivariate analyses of variance demonstrated genetic differentiation between serpentine and nonserpentine lineages in the expression of plasticity in response to three of the five axes of environmental variation considered. In all but one case, serpentine genotypes expressed a stronger adaptive plastic response than nonserpentine genotypes.     

Effects of historical demography and ecological context on spatial patterns of genetic diversity within foxtail pine (Pinus balfouriana; Pinaceae) stands located in the Klamath Mountains, California

The density and dispersion of individuals, nonequilibrium demographics, and habitat fragmentation all affect the magnitude and extent of spatial genetic structure within forest tree populations. Here, we investigate the link between historical demography and spatial genetic structure within ecologically contrasting stands of foxtail pine (Pinus balfouriana) in the Klamath Mountains of northern California. We defined two stand types a priori, based largely on differences in foxtail pine density and basal area, and for each type we sampled two stands. Population expansions, likely from Pleistocene bottlenecks, were detected in three of the four stands. The magnitude and extent of spatial autocorrelation among genotypes at five nuclear microsatellites differed dramatically among stands, with those having lower foxtail pine density exhibiting strong patterns of isolation by distance. Moran's I statistics were 7-fold higher for the first distance class (<25 m) in these stands relative to those observed in stands with higher foxtail pine density (I(25) = 0.14 vs. 0.02). We conclude that differences in spatial genetic structure between stand types are due to differences in ecological attributes that affected expansion from inferred bottlenecks.     

THE EFFECT OF SERPENTINE ON THE POPULATION STRUCTURE OF SILENE DIOICA (CARYOPHYLLACEAE)

Serpentine soils are rich in heavy metals and have a distinctive flora. Silene dioica is a member of the Scandinavian serpentine plant community but is also widespread outside serpentine soils. To study the population genetic consequences of serpentine stress and the origin and evolution of serpentine populations we analyzed the isozyme genetic structure of S. dioica. Seventeen populations located in the mountains of Västerbotten and Jämtland, central Sweden, were investigated by starch gel enzyme electrophoresis. About one half of the populations grow in serpentine soils and the rest on adjacent non-serpentine sites. Analyses of allele frequencies show that both serpentine and non-serpentine populations in the northern part of the studied area (Västerbotten) are genetically similar. Evidently serpentine does not exert strong selection acting upon isozyme loci. In the south (Jämtland), however, the serpentine populations exhibit genetic differentiation. This allozyme divergence is probably not due to direct selection but rather represents the effects of isolation and genetic drift. The results suggest that S. dioica has colonized serpentine repeatedly and that the tolerant populations have a multiple origin.     

Phylogenetic Comparisons of Bacterial Communities from Serpentine and Nonserpentine Soils

I present the results of a culture-independent survey of soil bacterial communities from serpentine soils and adjacent nonserpentine comparator soils using a variety of newly developed phylogenetically based statistical tools. The study design included site-based replication of the serpentine-to-nonserpentine community comparison over a regional scale (~100 km) in Northern California and Southern Oregon by producing 16S rRNA clone libraries from pairs of samples taken on either side of the serepentine-nonserpentine edaphic boundary at three geographical sites. At the division level, the serpentine and nonserpentine communities were similar to each other and to previous data from forest soils. Comparisons of both richness and Shannon diversity produced no significant differences between any of the libraries, but the vast majority of phylogenetically based tests were significant, even with only 50 sequences per library. These results suggest that most samples were distinct, consisting of a collection of lineages generally not found in other samples. The pattern of results showed that serpentine communities tended to be more similar to each other than they were to nonserpentine communities, and these differences were at a lower taxonomic scale. Comparisons of two nonserpentine communities generally showed differences, and some results suggest that the geographical site may control community composition as well. These results show the power of phylogenetic tests to discern differences between 16S rRNA libraries compared to tests that discard DNA data to bin sequences into operational taxonomic units, and they stress the importance of replication at larger scales for inferences regarding microbial biogeography.     

Congeneric Serpentine and Nonserpentine Shrubs Differ More in Leaf Ca:Mg than in Tolerance of Low N, Low P, or Heavy Metals

Serpentine soils limit plant growth by NPK deficiencies, low Ca availability, excess Mg, and high heavy metal levels. In this study, three congeneric serpentine and nonserpentine evergreen shrub species pairs were grown in metalliferous serpentine soil with or without NPKCa fertilizer to test which soil factors most limit biomass production and mineral nutrition responses. Fertilization increased biomass production and allocation to leaves while decreasing allocation to roots in both serpentine and nonserpentine species. Simultaneous increases in biomass and leaf N:P ratios in fertilized plants of all six species suggest that N is more limiting than P in this serpentine soil. Neither N nor P concentrations, however, nor root to shoot translocation of these nutrients, differed significantly between serpentine and nonserpentine congeners. All six species growing in unfertilized serpentine soil translocated proportionately more P to leaves compared to fertilized plants, thus maintaining foliar P. Leaf Ca:Mg molar ratios of the nonserpentine species were generally equal to that of the soil. The serpentine species, however, maintained significantly higher leaf Ca:Mg than both their nonserpentine counterparts and the soil. Elevated leaf Ca:Mg in the serpentine species was achieved by selective Ca transport and/or Mg exclusion operating at the root-to-shoot translocation level, as root Ca and Mg concentrations did not differ between serpentine and nonserpentine congeners. All six species avoided shoot toxicity of heavy metals by root sequestration. The comparative data on nutrient deficiencies, leaf Ca:Mg, and heavy metal sequestration suggest that the ability to maintain high leaf Ca:Mg is a key evolutionary change needed for survival on serpentine soil and represents the physiological feature distinguishing the serpentine shrub species from their nonserpentine congeners. The results also suggest that high leaf Ca:Mg is achieved in these serpentine species by selective translocation of Ca and/or inhibited transport of Mg from roots, rather than by uptake/exclusion at root surfaces.     

Phylogenetic comparisons of bacterial communities from serpentine and nonserpentine soils

I present the results of a culture-independent survey of soil bacterial communities from serpentine soils and adjacent nonserpentine comparator soils using a variety of newly developed phylogenetically based statistical tools. The study design included site-based replication of the serpentine-to-nonserpentine community comparison over a regional scale ( approximately 100 km) in Northern California and Southern Oregon by producing 16S rRNA clone libraries from pairs of samples taken on either side of the serepentine-nonserpentine edaphic boundary at three geographical sites. At the division level, the serpentine and nonserpentine communities were similar to each other and to previous data from forest soils. Comparisons of both richness and Shannon diversity produced no significant differences between any of the libraries, but the vast majority of phylogenetically based tests were significant, even with only 50 sequences per library. These results suggest that most samples were distinct, consisting of a collection of lineages generally not found in other samples. The pattern of results showed that serpentine communities tended to be more similar to each other than they were to nonserpentine communities, and these differences were at a lower taxonomic scale. Comparisons of two nonserpentine communities generally showed differences, and some results suggest that the geographical site may control community composition as well. These results show the power of phylogenetic tests to discern differences between 16S rRNA libraries compared to tests that discard DNA data to bin sequences into operational taxonomic units, and they stress the importance of replication at larger scales for inferences regarding microbial biogeography.     

MATING SYSTEM IN NATURAL POPULATIONS OF JEFFREY PINE

The mating system and allozyme variation at 20 loci in three Klamath Mountains and two Sierra Nevada populations of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) were investigated. On average, multilocus estimates of the proportion of viable progeny due to outcrossing (t_m) were high in all populations (mean t_m = 0.935, range 0.881 to 0.971). Despite differences in stand structure, t_m did not differ (P > 0.05) between the Klamath (mean t_m = 0.933) and Sierra Nevada (mean t_m = 0.937) populations. At all but one locus in one population and at two in another, genotype frequencies fit (P > 0.05) Hardy-Weinberg expectations. Mean estimates of observed heterozygosity in Klamath (0.182) and Sierra Nevada (0.327) populations were comparable to values reported for other conifers.     

Differentiation patterns in the E. MediterraneanScutellaria rubicunda group (Lamiaceae)

Strict sterility barriers where found between theScutellaria populations on Sicily and the Greek populations. The material from Samos is separated by a strict sterility barrier from the other Greek populations. In contrast, the populations on mainland Greece and adjacent islands are all ± interfertile. Three species are recognized,S. rubicunda Hornem., endemic to Sicily, andS. brevibracteata subsp.icarica, endemic to Samos and Ikaria. All other populations are referred toS. rupestris with eight subspecies, most of which are endemic to one island or to one mountain. Three new subspecies are described, viz. subsp.rechingeri and subsp.olympica, endemic to mt Vourinos and mt Olympus in North Greece, respectively, and subsp.caroli-henrici, native to the Malea peninsula of Peloponnisos. The phytogeographical connections and genetic differentiation within and between populations are discussed.Dedicated to Prof. DrK. H. Rechinger on the occasion of his 80th birthday.     

Microallopatry caused strong diversification in Buthus scorpions (Scorpiones: Buthidae) in the Atlas Mountains (NW Africa)

The immense biodiversity of the Atlas Mountains in North Africa might be the result of high rates of microallopatry caused by mountain barriers surpassing 4000 meters leading to patchy habitat distributions. We test the influence of geographic structures on the phylogenetic patterns among Buthus scorpions using mtDNA sequences. We sampled 91 individuals of the genus Buthus from 51 locations scattered around the Atlas Mountains (Antiatlas, High Atlas, Middle Atlas and Jebel Sahro). We sequenced 452 bp of the Cytochrome Oxidase I gene which proved to be highly variable within and among Buthus species. Our phylogenetic analysis yielded 12 distinct genetic groups one of which comprised three subgroups mostly in accordance with the orographic structure of the mountain systems. Main clades overlap with each other, while subclades are distributed parapatrically. Geographic structures likely acted as long-term barriers among populations causing restriction of gene flow and allowing for strong genetic differentiation. Thus, genetic structure and geographical distribution of genetic (sub)clusters follow the classical theory of allopatric differentiation where distinct groups evolve without range overlap until reproductive isolation and ecological differentiation has built up. Philopatry and low dispersal ability of Buthus scorpions are the likely causes for the observed strong genetic differentiation at this small geographic scale.     

Genetic structure among and within populations of the serpentine endemic Heteropappus hispidus ssp. leptocladus (Compositae)

Heteropappus hispidus ssp. leptocladus is an edaphic endemic taxon that is confined to serpentine and limestone-derived soils and is allopatrically distributed in three regions of western Japan. In this study, we attempted to detect genomic signatures of seven H. hispidus ssp. leptocladus populations along with eight other subspecies populations using eight nuclear microsatellite loci. The Mantel test supported an isolation by distance model across all H. hispidus populations, thus implying the possibility of parallel evolution for each subspecies. Results from AMOVA recognized relatively larger differentiations in geographic distribution compared to intraspecific taxonomy. Relationships indicated by neighbor-joining phylogenetic tree analysis and population structure generally did not reflect an intraspecific taxonomy. Populations from limestone-derived soil harbored a homogeneous genetic structure with neighboring populations from serpentine-derived soils. These results suggest that the edaphic ecotype may have derived allopatrically while a lack of edaphic constraint existed between serpentine and limestone soils.