Introgressive hybridization between Plantago major L. taxa

Occurrence and direction of introgressive hybridization between Plantago major taxa were tested. Plantago major plants were collected from 10 Egyptian locations. Four populations of two European taxa were used for comparison. These are ecologically and geographically separated and were identified as the subspecies Plantago major ssp. major and Plantago major ssp. intermedia. In the Egyptian populations, most individuals fall within the variation range of P. major ssp. intermedia. Only one population, from Burg El-Arab, morphologically resembled clearly P. major ssp. major and showed some ISSR fragments that characterize pure populations of this taxon. All individuals of population 2 (Alexandria) and some individuals of populations 1, 3, 5, 6 and 10 (Alexandria, Aswan) morphologically corresponded to P. major ssp. intermedia. All individuals collected from Egypt had ISSR fragments characterizing both pure P. major ssp. major and pure P. major ssp. intermedia. Most of these individuals had a higher percentage of intermedia-type fragments than major-type fragments, suggesting that P. major ssp. intermedia in Egypt shows some introgression towards P. major ssp. major. The pure populations were distinct from each other, while the Egyptian populations were intermediate according to principal coordinate analysis (PCoA) of ISSR data. In the populations collected from Egypt, major and intermedia cannot be seen as separate species. The study suggests that the dominant taxa introgressed to the minority population(s). Taxon frequency may be a key component in determining the direction of introgression.     

Lipid Composition of the Roots of Plantago Species: Response to Alteration of the Level of Mineral Nutrition and Ecological Significance

In a study of the adaptation of Plantago species to their specific environment the lipid composition of the roots of several species: Plantago major L. ssp. major, Plantago major L. ssp. pleiosperma Pilger, Plantago lanceolata L., Plantago media L., Plantago maritima L., Plantago coronopus L. was studied as well as the effect of the nutritional regime. Upon exposure to low-salt conditions Plantago major L. ssp. major L. and Plantago maritima L. maintained the level of free sterols in the roots, despite a depressed level of total sterols, and the root lipids were more saturated than under high-salt conditions. Both factors may reduce nutrient leakage from the roots to the low-salt condition. Upon exposure to low-salt conditions, all Plantago species showed a decreased level of galactolipid (exception: Plantago coronopus) and a decreased level of sitosterol (exception: Plantago maritima); the latter being compensated by an elevated level of cholesterol + tocopherol in Plantago major ssp. pleiosperma, Plantago lanceolata and Plantago media. Plantago coronopus was the only species which under low-salt conditions showed an increased level of free sterols, among which cholesterol was the most important; thus indicating a high degree of regulation of membrane permeability under alternating nutritional conditions. The level of sulfolipid was kept constant in all Plantago species, with the highest level observed in Plantago maritima. The role which various lipids may play in maintenance of membrane integrity under alternating nutritional conditions is discussed.     

Genetic variability in Plantago species in relation to their ecology

Summary Twelve Plantago major plants, good representatives of their populations, appeared to be genetically different for several characters which are important for adaptation to the respective habitat conditions. These characters are: juvenile growth, leaf morphology, production of secondary rosettes, flowering time, seed production, seed size and adult leaf production. The adaptive value of some of these characters was investigated by transplantation experiments in the field and by intraspecific competition experiments. The roadside type of ssp. major was adapted to trampling by being erect and elastic. The lawn type of ssp. major was adapted to a short, frequently cut, vegetation by being prostrate and by producing leaves with short petioles throughout the growth season. In the natural situations in which ssp. pleiosperma occurs, growth rate and first-year seed production of this subspecies were considerably higher than that of ssp. major. In a number of experiments, F₁s and F₂s were included, derived from crosses between the original plants. The F₁s were generally rather well adapted to both parental habitats, whereas the F₂s appeared to be less fit. The various alternatives in spending resources relevant for fitness optimization in different habitats are discussed.Grassland Species Research Group Publication No. 93     

GENETIC POLYMORPHISM IN THE MORPHOLOGICALLY REDUCED DWARF MISTLETOES (ARCEUTHOBIUM,VISCACEAE): AN ELECTROPHORETIC STUDY

Arceuthobium is a well defined genus of obligate parasites of conifers. Assessment of taxonomic and phylogenetic relationships in this group is difficult owing to morphological reductions and complex host relationships. In the present study, genetic relationships within and among 19 taxa were examined using starch gel electrophoresis of triploid seed endosperm tissue. Allelic frequency data for eleven polymorphic loci were derived from analysis of 40 natural populations collected from the U.S. and Mexico. The genus showed remarkably high levels of genetic diversity: averaged across the 19 taxa, 66.7% of the loci were polymorphic with an average of 2.23 alleles per locus. This level of polymorphism is approximately double the average value reported for many dicotyledons and stands in contrast to the overall uniform morphology of these parasites. Unweighted pair group cluster analysis (UPGMA) of genetic similarity measures was conducted for all sampled populations and the results compared to a phenetic system of classification for the genus. Similarities between the two studies include the recognition of two subgenera based upon the segregation of the verticillately branched Arceuthobium americanum from the remainder of the taxa examined. Analysis of isozyme data supported a grouping of six taxa: A. vaginatum ssp. cryptopodum, A. vaginatum ssp. durangense, A. gillii, A. rubrum, A. divaricatum, and A. douglasii. The placement of the latter three taxa in other groups by phenetic criteria provides evidence for molecular divergence not seen using morphological features. The Campylopodum group of taxa comprised eleven members that were linked at similarity values of 80% or greater. Populations were not unambiguously grouped according to species as defined by the phenetic study or at similarity levels comparable to other well defined species in this study. This group is either not reproductively isolated or molecular differentiation is cryptic due to rapid adaptive radiation onto numerous host tree species.     

Isolation of polymorphic microsatellite loci in Plantago major and P. intermedia

Plantago major and P. intermedia are two closely related inbreeding species. The isolation of polymorphic codominant microsatellite markers will provide valuable tools to investigate the reproductive isolation and the evolution of the two species. The isolation of microsatellite loci was achieved using a membrane enrichment method. Primers were designed to microsatellite flanking sequences and were analysed using fluorescent labels. Results indicated that nine out of the 10 loci amplified in both species, and that all the loci were polymorphic. The amplification of the loci was tested in a variety of Plantago species and was shown to be limited.     

Efflux of Potassium from Wheat Roots Induced by Changes in the Water Potential of the Root Medium

Growth of Plantago major L., ssp. major L. and ssp. pleiosperma Pilger and P. maritime L. was followed at two levels of mineral nutrition (low-salt and high-salt). In addition the response of transfer of plants from low-salt conditions to high-salt conditions and vice versa was studied. Growth of the studied Plantago species was strongly stimulated by high-salt conditions. The Ca²⁺- and Mg²⁺-stimulated ATPase activity of microsomal preparations of the roots was also studied. In P. major ssp. major and P. maritime a major pH optimum was observed at pH 6.5, and in addition a second pH optimum was found at pH 8.0. High-salt plants of these two species were characterized by biphasic stimulation curves for Ca²⁺ and Mg²⁺, whereas P. major ssp. pleiosperma showed a monophasic pattern. The ATPase activity per g dry weight of P. major and P. maritima was highest in high-salt plants. The species investigated here are adapted to relatively nutrient-rich conditions, and the properties of ATPases (K_m, K_max, protein content) and the growth responses are discussed in relation to this ecological property.     

A genetic investigation of the esters of caffeic acid with rhamnose or glucose in leaves of Plantago major

The genetic relationship between two sugar esters of caffeic acid in the leaves of Plantago major has been investigated. The difference is shown to be due to a single gene. Glucose accounts for the sugar part in the dominant phenotype while in the recessive type the sugar is rhamnose. This difference is only partly correlated with the division of the species into subspecies. The rhamnose type is found only in P. major ssp. pleiosperma Pilger, although only in less than half of the plants investigated.     

Genetic differentiation in Plantago major L. in growth and P uptake under conditions of P limitation

To study possible adaptive mechanisms inbred lines from three populations of Plantago major from sites that were found to differ in P availability were compared. In a pot experiment the growth and P uptake either in the presence or absence of Glomus fasciculatum was determined. Under these P-limited conditions it was shown by partitioning the relative growth rate (RGR, in mg g^-1 day^-1) in the components root weight ratio (RWR, in g_roots g_plant ^-1), specific P uptake rate (SPUR, in mol P g_roots ^-1 day^-1), and P-efficiency (PEFF, in mg mol P^-1), that the increase in RGR of mycorrhizal infected plants was related to an increase in SPUR, and a decrease in RWR and PEFF. P. major ssp. major had a lower RGR (related to a lower PEFF and SPUR) and a higher RWR than P. major ssp. pleiosperma. In a second experiment three inbred lines were compared upon P depletion in a nutrient solution. The P. major ssp. major line had a lower RGR and higher RWR, and a higher accumulation of P in the roots than the P. major ssp. pleiosperma lines under optimal growing conditions. There were no differences among the inbred lines in the relative contribution of inorganic P to the total P concentration in the shoot. The results are discussed in relation to the characteristics of the habitats of the investigated P. major populations.     

Recurrent origin of peripheral,coastal (sub)species in Mediterranean Senecio (Asteraceae)

Background: It is argued that coastal endemic taxa may evolve in parallel at the periphery of the distributional range of a widespread species.

Aims: We tested this hypothesis for the origins of three peripheral, coastal isolates of Senecio, S. glaucus ssp. glaucus (Israel), S. g. ssp. coronopifolius p.p. (Sicily), and S. hesperidium (Morocco), from widespread S. glaucus ssp. coronopifolius. We also determined the relative roles of selection vs. genetic drift in shaping phenotypic divergence in ssp. glaucus and S. hesperidium, using Lande’s test of neutral morphological change.

Methods: We surveyed morphological and/or allozyme variation in the three peripheral isolates and mainly inland populations of S. g. ssp. coronopifolius.

Results: Genetic data supported independent origins of the coastal taxa from nearby populations of ssp. coronopifolius. These descendant and ancestral populations showed pronounced morphological but weak genetic differentiation. Phenotypic similarities between ssp. glaucus (Israel) and S. hesperidium (Morocco) in plant height and floral traits may have resulted from parallel divergent selection from ssp. coronopifolius, though drift remains an alternative cause in S. hesperidium.

Conclusions: Our results indicate parallel ecotype formation and (sub)speciation in Senecio in which primarily selective vs. neutral determinants promoted the recurrent origin of coastal types in, respectively, Israel and Morocco.     

Establishment of Plantago lanceolata L. and Plantago major L. among grass

Summary Establishment of Plantago lanceolata and P. major ssp major among grass was studied in a field experiment in which survival and selection on date of seedling emergence and plant size was investigated in relation to the vegetation structure. P. major — in contrast to P. lanceolata — was not able to establish itself in grass because of its lower competitive ability caused by later germination, smaller seedling size, and shorter leaves. In both species there was selection for early germination. For P. lanceolata a significant correlation was found between the strength of selection and the light climate, determined by the structure of the grass sward. Plants that germinated early were at an advantage because they were larger, especially the leaves, when compared with plants that germinated late. It seems likely that selection was mainly by competition for light. Contrary to expectation P. major-seedlings had a higher shade tolerance than those of P. lanceolata. The performance of both species is discussed in relation to their different life strategies.Grassland species research group publication no 142     

Genetic variability in Plantago species in relation to their ecology

Summary A survey of enzyme variability in several populations of Plantago major in the Netherlands has been made. Nine of 36 loci were found to be polymorphic. The most extensively studies population showed 7 polymorphic loci (19%). The average heterozygosity was 0.005, a low value since P. major is predominantly inbreeding; a first estimate of the outcrossing rate is only 10%. All nine variable loci show simple Mendelian inheritance, seven of them could be placed into four different linkage groups. Marked differences in allele frequencies were found between two subspecies: ssp. major and ssp. pleiosperma. Two enzyme loci possess subspecies-specific alleles, Pgm-1 and Got-1. The most likely explanation of this phenomenon is the existence of fitness differences, caused either by the enzyme loci themselves or by linked loci.Grassland Species Research Group Publication no. 14     

Inbreeding and soil conditions affect dispersal and components of performance of two plant species in fragmented landscapes

During habitat fragmentation, plant populations become smaller and more isolated from each other, resulting in increasing inbreeding rates within populations. Furthermore, fragmentation is often accompanied by a progressive deterioration of soil conditions. Overall, high inbreeding rates and poor soil conditions decrease plant performance and so increase the probability of extinction of fragmented plant populations. The goal of this study was to investigate the effects of inbreeding and soil acidification on seed and offspring traits of Succisa pratensis and Hypochaeris radicata, two plant species differing in mating system, lifespan and dispersal ability. For each species, plants from four populations of different sizes were hand-pollinated. The selfed and outcrossed progeny were grown at two soil pH levels. Overall, results showed that the dispersal potential of H. radicata was reduced by selfing, indicating that dispersal capacity is not independent from the genetic erosion process. Variation among seed families and its interactions with pollination treatments indicate that dispersal capacity may have a genetic basis. The performance of both species decreased sharply as soil conditions became more acidic, but inbreeding did not aggravate the process. These results suggest that S. pratensis and H. radicata populations may decline in the long term; however, family level variation suggests a potential for adaptation to new conditions.     

Genetic Variation in Hippophae rhamnoides ssp. sinensis (Elaeagnaceae) Revealed by RAPD Markers

Hippophae rhamnoides ssp. sinensis is endemic to China, and it is a dioecious, outcrossing plant. Although many studies have been undertaken mainly on its agricultural, nutritional, medical, and ornamental value, little is known about its population genetics. This study uses random amplified polymorphic DNA to investigate the genetic diversity and population genetic structure of 13 natural populations of the subspecies sinensis. Fifteen primers amplified 107 reproducible bands, with 95 (88.79%) being polymorphic. The gene diversity within population was 0.168, considerably lower than that of tree species and most perennial, outcrossing species, but higher than that of annual or short-lived, selfing species. The Gst value showed that 18.3% of the total genetic variation resided among populations, a little lower than that of outcrossing species. The present results are quite similar to those previously reported in another subspecies, H ssp. . rhamnoides rhamnoides. The low genetic differentiation among populations in ssp. sinensis may be attributed to the long-distance dispersal of seeds facilitated by birds, in addition to its characteristics of outcrossing, wind pollination, and widespread distribution. No association between genetic distance and geographical distribution was found. The population relationships revealed by the UPGMA dendrogram parallel this result, in that genetic distance did not increase with geographic separation. This pattern of population differentiation may imply the adaptation of ssp. s populations to the local environment, given that its habitats vary greatly across its distribution.     

Partial self-incompatibility and inbreeding depression in a native tree species of La Réunion (Indian Ocean)

We investigated the reproductive system of the threatened taxon Dombeya acutangula ssp. acutangula Cav. (Sterculiaceae), an endemic tree of the Mascarene archipelago (Indian Ocean). A controlled crossing experiment was performed in two natural populations located in the remnants of the low-elevation dry forest on the island of La Réunion. Active pollination, probably mainly by insects, was necessary for reproduction in this species. Individuals varied in their degree of self-sterility from 0 to 100%. Outcrossing between nearby individuals produced lower seed set than did crosses between more distant individuals within one of the two tested populations. The variation in reproductive success on selfing and in the different types of crosses could result from inbreeding depression causing embryo death, and we provide evidence that progenies from selfing have lower seed size and quality. However, for inbreeding depression to account for the dramatic variation in seed set found in our crossing experiment, the distribution of genetic load and number of lethal factors required appear unrealistic. We favour an alternative interpretation, that D. acutangula possesses an incompatibility system similar to that found in other Sterculiaceae species such as Theobroma cacao L. Such an incompatibility system allows a certain amount of selfing, and different individuals vary in their degree of self-incompatibility. The low success of crosses among close neighbours in one population suggests that there was spatial structure for incompatibility alleles in that population. This could partly explain the decline of the species in fragmented and disturbed habitats, since relatedness at incompatibility loci may increase in small or isolated population and thus reduce mate availability. Received: 2 March 1998 / Accepted: 3 August 1998     

Cost of reproduction as reduced growth in genotypes of two congeneric species with contrasting life histories

Summary We examined the effect of reproduction on growth in 33 genotypes of Plantago major and 14 genotypes of P. rugelii. These two herbaceous perennials have contrasting life histories; P. major reproduces at a smaller size, and allocates a larger proportion of its biomass to reproduction, than P. rugelii. The effect of reproduction on frowth was determined experimentally using photoperiod manipulations to control level of reproduction. The difference in growth between reproductive treatments was divided by the difference in capsule weight to produce a measure of reproductive cost per g of capsule for genotypes of the two species. In both species there was substantial variation among genotypes in the effect of reproduction on growth. Much of this variation could be correlated with differences among genotypes in the extent of reproductive investment and plant size. Cost in terms of reduction in growth per g of capsule increased with reproductive investment in P. rugelii, and with plant size in P. major. We suggest the differences between species in timing and extent of reproduction are related to the differences between species in effect of reproduction on growth. Plantago rugelii may reproduce to a lesser extent than P. major because cost per g of capsule in terms of reduced vegetative biomass, increases with reproductive output in the former species, but not in the latter. Similarly, P. major may reproduce earlier than P. rugelii because cost per g of capsule increases with plant size in P. major, but not in P. rugelii.     

Scrophularia arguta,a widespread annual plant in the Canary Islands: a single recent colonization event or a more complex phylogeographic pattern?

Many studies have addressed evolution and phylogeography of plant taxa in oceanic islands, but have primarily focused on endemics because of the assumption that in widespread taxa the absence of morphological differentiation between island and mainland populations is due to recent colonization. In this paper, we studied the phylogeography of Scrophularia arguta, a widespread annual species, in an attempt to determine the number and spatiotemporal origins of dispersal events to Canary Islands. Four different regions, ITS and ETS from nDNA and psbA‐trnH and psbJ‐petA from cpDNA, were used to date divergence events within S. arguta lineages and determine the phylogenetic relationships among populations. A haplotype network was obtained to elucidate the phylogenetic relationships among haplotypes. Our results support an ancient origin of S. arguta (Miocene) with expansion and genetic differentiation in the Pliocene coinciding with the aridification of northern Africa and the formation of the Mediterranean climate. Indeed, results indicate for Canary Islands three different events of colonization, including two ancient events that probably happened in the Pliocene and have originated the genetically most divergent populations into this species and, interestingly, a recent third event of colonization of Gran Canaria from mainland instead from the closest islands (Tenerife or Fuerteventura). In spite of the great genetic divergence among populations, it has not implied any morphological variation. Our work highlights the importance of nonendemic species to the genetic richness and conservation of island flora and the significance of the island populations of widespread taxa in the global biodiversity.     

Genetic diversity and similarity in the Barbarea vulgaris complex (Brassicaceae)

Two subspecies of Barbarea vulgaris are taxonomically recognized as ssp. vulgaris and ssp. arcuata. In addition, two types of Barbarea vulgaris ssp. arcuata occurs in Denmark. The G‐type is resistant to an herbivorous flea beetle (Phyllotreta nemorum) whereas the P‐type is susceptible. A previous study suggested that the P‐type evolved by a loss of resistance from a resistant progenitor. We analyzed the genetic relatedness among eight Barbarea taxa: B. vulgaris spp. vulgaris, B. vulgaris ssp. arcuata G‐ and P‐types, hybrids between the types, B. verna, B. intermedia, B. stricta, B. orthoceras and B. australis, using AFLP and SSR markers. A clear distinction between the G‐ and P‐types was revealed. Both were distinct from B. vulgaris ssp. vulgaris, the G‐type less so than the P‐type. Barbarea verna and B. intermedia formed unambiguous clusters, whereas the remaining taxa produced less discrete groupings. Possible evolutionary scenarios for flea‐beetle resistance and susceptibility are discussed, including lineage sorting from a polymorphic ancestral population, and de novo loss of resistance in the P‐type of B. vulgaris ssp. arcuata.     

Multidisciplinary approaches for species delimitation in Sisyrinchium (Iridaceae)

A remarkable morphological similarity in natural populations of different groups of Sisyrinchium spp. (Iridaceae) makes classification of some species difficult. The present paper focused on two morphological categories of S. sellowianum (MC‐I and MC‐II) with distinct morphological traits. Morphological, cytogenetic, reproductive biology and genetic studies were performed, aiming to elucidate and better characterize such variation. The basic chromosome number established for the species was x = 9 and diploid and tetraploid populations were observed for MC‐I, whereas MC‐II showed only diploid populations. Different pollen morphologies were recognized in each morphological category. Based on pollination experiments, MC‐I is out‐crossing, whereas MC‐II is selfing. The populations were highly differentiated (F_ST = 0.46, θ^B = 0.62). In MC‐I, observed variation was greater within populations (69%) than among populations (31%), whereas in MC‐II, 61% of the variation was among populations and 39% within populations. This study evidenced that the two morphological categories correspond to distinct and reproductively isolated species and that floral traits reflect their breeding system, with allogamous plants in MC‐I and autogamous in MC‐II. Furthermore, MC‐II is unveiled as S. platycaule, a neglected taxon of Sisyrinchium in Brazil. The tools applied in this study were substantially able to check the identity of the two morphological categories as two different species and present the variation encountered in the taxa.     

GENETIC STRUCTURE OF POPULATIONS OF GEOGRAPHICALLY RESTRICTED AND WIDESPREAD SPECIES OF ASTRAGALUS (FABACEAE)

Evolutionary theory predicts that species with small ranges and few individuals will exhibit low levels of genetic polymorphism. We investigated the population genetic structure of two locally endemic and two geographically widespread species of Astragalus. To facilitate direct comparisons among these congeners, three populations of each species were sampled in a consistent manner and scored for allozyme polymorphisms at 12 loci. Genetic polymorphism was lower in restricted A. linifolius and A. osterhouti than in widespread A. pectinatus. However, the restricted species do exhibit a moderate level of isozyme variation, comparable to that of widespread A. pattersoni and higher than has been detected in several other rare plant taxa. As measured by Wright's F statistics, there were no consistent differences between the restricted and widespread taxa with respect to the organization of genetic variation. F_ST values were low in all taxa, indicating little heterogeneity among populations.     

Comparison of Plantago Species from Nutrient-rich and Nutrient-poor Conditions: Growth Response, ATPases and Lipids of the Roots, as Affected by the Level of Mineral Nutrition

Two groups of Plantago species, one of relatively nutrient-rich habitats (Plantago major L., P. major L. ssp. pleiosperma Pilger and P. martrima L.) and the other of relatively nutrient poor habitats (P. lanceolata L., P. media L. and P. coronopus L.), were compared with respect to the response of the plants to alterations of the level of mineral nutrition. The comparison deals with growth response and root cell membrane functions (Ca²⁺ and Mg²⁺ stimulated ATPases and lipids). As far as these parameters are concerned species from relatively nutrientpoor habitats are not much affected by bringing the plants to high-salt conditions, while the reverse was true for species from relatively nutrient-rich habitats when transferred to low salt medium.