Torbjörn Tyler

Allozyme diversity in relation to geographic distribution and population size in Lathyrus vernus (L.) Bernh. (Fabaceae).

Lathyrus vernus (L.) Bernh. is a diploid, long-lived perennial and insect-pollinated herb with no special adaptation to long-distance dispersal. It occurs on neutral soil in deciduous forests throughout western Eurasia. Due to specific habitat preferences,L. vernus has a fragmented distribution with isolated populations. We investigated allozyme variation at eleven loci in 20 populations ofL. vernus from one geographically central region (the Czech Republic and the Slovak Republic) and two geographically marginal regions (southern and central Sweden) in the species present-day distribution. There was a clear differentiation between the three regions and the genetic distance between the populations was highly correlated with geographic distance. The total genetic diversity (HT) was 0.354. The proportion of genetic diversity due to differentiation between regions, and to differentiation between populations within regions, accounted for 10% each. There was no difference in level of genetic diversity between the three regions. No significant difference in level of genetic diversity was found between small and large populations. The genetic diversity inL. vernus may either be a result of the long generation-time of the species or peculiarities in the post-glacial migration species, e.g. survival only in refugia far east of the sampled populations and/or migration as a continuous process not involving founder-events.

Geographic variation and dispersal history in Fennoscandian populations of two forest herbs

Abstract. Carex digitata and Melica nutans are forest understorey herbs with wide European distributions and their northern range margins in Fennoscandia. The species have closely similar habitat requirements, occur in small populations in old forest stands on base-rich to neutral soils and have restricted dispersal abilities at the present day. This study investigates the structure of allozyme variation (12 and 8 loci, respectively) in material of both species (38 and 37 populations, respectively) from throughout southern Sweden and southern Finland. Both species show a relatively low overall genetic diversity (HT excluding monomorphic loci=0.17 and 0.18, respectively). The hierarchic structuring of allelic diversity in the species is similar, with a relatively high between-population component of diversity (GST=0.36 and 0.37, respectively). Neither of the species shows a clear intraspecific pattern of geographic differentiation. The lack of large-scale patterns of geographic differentiation is not consistent with a simple scenario of discrete and independent waves of immigration into Fennoscandia. However, particularly in M. nutans, a group of populations from a lowland belt across southwestern Finland and southern central Sweden is somewhat differentiated from populations to the north and south. A number of rare alleles in both species are widely, but patchily distributed in low frequencies. Hybridization may account for the scattered occurence of some of the rare alleles in Carex digitata, but cannot explain the distribution of rare alleles in Melica nutans.

Patterns of morphometric variation and a new supraspecific classification of apomictic taxa of Hieracium (Asteraceae) from Denmark and southern Sweden

Patterns of variation among all micro-species of Hieracium sect. Hieracium and H. sect. Vulgata known from Denmark and southern Sweden are investigated. Forty-three, possibly independent morphological characters are used. Significant correlations were revealed among the majority of the characters. Multivariate analyses did not reveal any discontinuities in the variation or any discrete groups of species. However, there were obvious correlations between previous taxonomic classifications and the result of the multivariate analyses. Based on the statistical analyses, three sections and 38 informal species aggregates are recognized. H. sect. Bifidum T. Tyler is described anew. The characters that turned out to be most influential in the multivariate analyses, and thus most important for the classification, were the distribution of stellate tomentum on the phyllaries, the amount of glandular hairs and the amount and pigmentation of simple hairs on the phyllaries, the shape of the leaf-base and the regularity of the leaf dentation. The evolution of the group and the taxonomic treatment is thoroughly discussed in the light of the results.

An allozyme study of sexual and vegetative regeneration in Hieracium pilosella L.

Allozyme markers were used to fingerprint clones of the grassland plant Hieracium pilosella and, by inference, to estimate the relative importance of sexual and vegetative reproduction in a population. Field studies in populations of clonal plant species have often reported negligible or absent recruitment from seed. In contrast, studies of genetic markers have found substantial clonal diversity in populations, suggesting recruitment of new genets into established populations. Our results showed that H. pilosella regenerates from seed both within and between dense clonal patches. Two sites differing in environmental conditions were sampled in order to investigate how the balance between seed-derived and stolon-derived recruitment changes with biotic and abiotic stress. In a relatively drought-prone site on a south-facing slope, the balance was shifted towards recruitment from seed, compared to a mesic site in which vegetative regeneration was more important.

Patterns of allozyme variation in Nordic Pilosella

Abstract.Patterns of allozyme variation have been investigated in 101 clones representing most of the morphological variation (and taxa) found in the amphi-apomictic genus Pilosella Hill. in the Nordic countries. Levels of variation were very high, both within narrowly defined taxa and within the whole data-set, but the correlation between a morphology-based taxonomy and patterns of allozyme variation was very weak. Almost all enzyme bands were found in more than one taxon and the differences between broadly defined species in terms of the frequency of bands were generally small. Cluster analyses did not perfectly recover any taxon but there were some tendencies for samples of some broadly defined taxa (e.g. P. officinarum s. l., and P. cymosa ssp. cymosa) to cluster together. It is concluded that there is considerable gene-flow among virtually all Nordic morpho-types of Pilosella and this is considered an argument for applying a very broad species concept in this genus.

Studies in the Melica ciliata-complex: 1. Distribution of allozyme variation within and among individuals, populations and geographic regions

Abstract.Allozyme variation in 83 European populations of the Melica ciliata/ transsilvanica species complex has been investigated. In spite of a diploid chromosome number, most loci were duplicated and patterns of within-population variation were not explainable unless apomixis or uncommon patterns of chromosomal segregation were assumed. Allelic richness and genetic diversity were very high but most of the variation (55-98%) was due to population differentiation. Geographic patterns were analysed both using phenetic, based on allele frequencies within populations, and cladistic, based on multi-locus genotypes, methods. Both methods congruently recognised three large groups of populations with discrete geographic distributions, in addition to a number of smaller groups. Of the three main groups, one was distributed in eastern and central Europe, one was restricted to western Europe north of the Alps and one was distributed in Iberia, Brittany and along the western shores of the Mediterranean. These groups are likely to have had separate histories but there appears to have been significant gene-flow among them. Among the less distinct groups, it was suggestive that some, e.g. the group containing all populations from the disjunct distribution in the Baltic basin, have been formed by introgression between the three major groups, whereas other deviating populations may represent additional distinct entities.

Patterns of plastid and nuclear variation among apomictic polyploids of Hieracium: evolutionary processes and taxonomic implications

BACKGROUND AND AIMS Apomictic species (with asexual seed production) make up for 20-50 % of all taxonomically recognized species in northern Europe, but the phylogenetic relationships of apomictic species and the mode of evolution and speciation remain largely unknown and their taxonomy is consequently disputed. METHODS In the present study, plastid psbD-trnT sequences (349 accessions) and 12 nuclear microsatellite loci (478 accessions) were used to create an overview of the molecular variation in (mainly) northern European members of the most species-rich of all plant genera, Hieracium s.s. The results are discussed and interpreted in the context of morphological and cytological data on the same species. KEY RESULTS AND CONCLUSIONS The complete psbD-trnT alignment was 1243 bp and 50 polymorphisms defined 40 haplotypes. All haplotypes found in the sections of the genus distributed in the northern European lowlands fell into one of two main groups, group H and group V, mutually separated by seven or eight polymorphisms. All accessions belonging to H. sects. Foliosa, Hieracioides (viz. H. umbellatum) and Tridentata and all but one accession of triploid species of H. sects. Oradea and Vulgata showed haplotypes of group V. Haplotypes of group H were found in all accessions of H. sects. Bifida and Hieracium and in all tetraploid representatives of H. sects. Oreadea and Vulgata. Additional haplotypes were found in accessions of the genus Pilosella and in southern European and Alpine sections of Hieracium. In contrast, the distribution of individual haplotypes in the two major groups appeared uncorrelated with morphology and current taxonomy, but polymorphisms within species were only rarely encountered. In total, 160 microsatellite alleles were identified. Levels of variation were generally high with only nine pairs of accessions being identical at all loci (in all cases representing accessions of the same species). In the neighbor-joining analysis based on the microsatellite data, accessions of the same species generally clustered together and some smaller groups of species congruent with morphology and/or current taxonomy were recovered but, except for H. sect. Oreadea, most larger groups were not correlated with morphology. Although the plastid DNA sequences show too little variation and the nuclear microsatellites are too variable to resolve relationships successfully among species or to fully understand processes of evolution, it is concluded that both species and sections as defined by morphology are largely congruent with the molecular data, that gene flow between the sections is rare or non-existent and that the tetraploid species may constitute the key to understanding evolution and speciation in this genus.

Sensitivity of the woodland herb Anemone hepatica to changing environmental conditions

Abstract The decline of deciduous woodland populations of Anemone hepatica L. in southern Sweden is documented and possible causes are discussed. The study was based on (1) re-investigations of 6.25 km2 grid-squares first studied in 1938–1970, (2) distribution of A. hepatica in woodland sites with well-known soil chemical properties and (3) a detailed study over 12 consecutive years into the relationships between biological characteristics of the species (number of individuals, vegetative development, flowering frequency) and environmental variables (temperature, precipitation), soil chemistry and time. There was a close relationship between soil acidity (pH, solubility of Al3+) and both distribution and biological characteristics. The biological variables declined significantly over time but were not related to climatic variability. Increasing soil acidity and Al3+ solubility are concluded to be the main factors responsible for the decline of A. hepatica in S. Swedish deciduous woodlands. Abbreviations: CEC = Cation exchange capacity. Nomenclature: Karlsson (1998).

Allozyme variation in Carex sect. Digitatae - Evidence of introgression, genetic distinctiveness and evolution of taxa

Abstract. A subset of populations of the European taxa of Carex sect. Digitatae, including Carex digitata, C. pallens, C. ornithopoda, C. pediformis ssp. rhizodes and C. humilis have been investigated for allozyme variation. The (presumably) distantly related C. pendula was used as a reference taxon. Carex digitata, C. pallens and C. ornithopoda on the one hand, and C. humilis and C. pediformis on the other, shared the majority of the alleles. Cluster analyses based on genetic distances grouped populations of C. digitata and C. ornithopoda in a mixed subcluster whereas all populations of C. pallens formed a subcluster distinct from the digitata/ornithopoda cluster. This in spite of the fact that C. ornithopoda is morphologically clearly distinct from C. digitata whereas C. pallens is barely distinguishable from the latter. Carex pediformis and C. humilis appeared not more genetically similar to C. digitata than to the reference taxon. It is concluded that 1) C. digitata, C. pallens and C. ornithopoda are closely related and most probably forms a monophyletic group, 2) C. pallens is a genetically distinct species, 3) C. pediformis and C. humilis are not closely related to the rest of C. sect. Digitatae, 4) C. pediformis and C. humilis are relatively closely related, 5) introgression do occur between the investigated species but not to such an extent that it can explain major geographic patterns of variation in C. digitata.

Critical notes on species of Hieracium (Asteraceae) reported as common to Sweden and Britain

Abstract All species of Hieracium sectt. Hieracium, Vulgata (incl. Bifida) and Oreadea originally described from the Nordic countries, but reported in recent accounts as occuring in the British Isles, have been scrutinised based on specimens and published descriptions. Out of 29 species stated as occurring in Britain and native to Fennoscandia, only four are confirmed (H. caesiomurorum, H. oistophyllum, H. pellucidum and H. triviale). These are all species with wide distributions in Fennoscandia and northern Europe and their occurence in Britain is thus not surprising. In addition, the first British occurrence of the widespread European species H. neopinnatifidum is reported. Apart from the above four, H. caesitium, H. diaphanoides and H. austrinum (H. scanicum) are possibly also native to both areas, although the material examined is not fully conclusive. In addition, at least a few species occur as aliens in both Sweden and Britain, but a further twelve need to be critically compared. Most of the Nordic names used for British plants are found to be based on misidentifications and the species concerned will have to be described and named anew. It is concluded that it is not good practice to borrow names of Hieracium species from distant areas without critically comparing types, authentic specimens and relevant literature. Only a very few species of this genus have distributions that stretch into several countries or across major water bodies.