Environmental response of Galium palustre s. lat. in a coastal area in Central Sweden

Galium palustre s. lat. is a polymorphic taxon. The differences in morphology are correlated with the level of ploidy, but there is also a certain amount of phenotypic plasticity. The plasticity probably contributes to this taxon's successful colonization of a wide variety of habitats. The amount of plasticity was studied for plants from different kinds of habitats in Sweden, both for diploids (G. palustre s. str.) and octoploids (G. elongatum ), which were cloned. This cloned material was then transplanted to three different localities in Sweden: a sunny exposed sea-shore, a ditch, and a shady alder swamp. The general pattern of morphology was similar for all material, independent of its origin and level of ploidy, with smaller plants (smaller in several vegetative characters) and a more abundant flowering on the exposed seashore than in the ditch, and the largest plants with a fairly sparse flowering in the alder swamp. The octoploid plants originating from the wooded wetland are the least plastic ones but are very variable within the localities. G. palustre var. balneum shows a similar variation pattern as the others, but there are also genetically fixed differences in some characters between it and G. palustre var. palustre . The changes in morphology of the plants in the different localities occur fairly rapidly (in one month), although the differences are more spectacular one year later.     

Serpentine and polyploid differentiation withinGalium pumilum agg. (Rubiaceae) in Eastern C. Europe

The local differentiation of a model group,Galium pumilum agg., was studied in serpentine versus non-serpentine habitats in the Czech Republic and adjacent regions in Austria, Germany and Poland. Serpentine habitats form ecologically distinct islands within the landscape; local micro-evolutionary processes may be important there, both because of small population sizes and the strong selection effects of the metal-rich soils. TheGalium pumilum agg. is a group of taxa showing typical karyological and ecological differentiation; the following species and cytotypes were studied:Galium pumilum Murray (2n=8x=88),G. valdepilosum Heinr. Braun (2n=2x=22, 2n=4x=44),G. sudeticum Tausch (2n=4x=44) andG. austriacum Jacq. (2n=4x=44). The karyological and taxonomic investigation showed that serpentine versus non-serpentine habitats do not play an important role in the differentiation of the species studied. (1) The examined populations ofG. pumilum Murray were homogeneous in chromosome numbers, belonging to the octoploid (2n=88) cytotype only. (2)G. valdepilosum consists of two cytotypes. Both of them occur on and off serpentine sites, but they show pronounced East-West distributional difference. (3)G. sudeticum occupies special localities on serpentine in western Bohemia, which are geographically isolated from its nearest localities in the Krkono?e Mts. The plants coming from both localities belong to the tetraploid cytotype. (4) A highly polyploid plant (2n=12x=ca. 132) from theG. pumilum group was found on serpentine. From the methodological point of view, pollen size turned out to be reliable only for distinguishing octoploids from diploids and tetraploids, but it is less suitable for separating the latter two ploidy levels. The occurrence ofG. austriacum is reported for the Czech Republic for the first time with certainty. This record extends the known distribution area ofG. austriacum in the NW direction.     

Morphological and environmental differentiation as prezygotic reproductive barriers between parapatric and allopatric Campanula rotundifolia agg. cytotypes

Background and AimsReproductive isolation and local establishment are necessary for plant speciation. Polyploidy, the possession of more than two complete chromosome sets, creates a strong postzygotic reproductive barrier between diploid and tetraploid cytotypes. However, this barrier weakens between polyploids (e.g. tetraploids and hexaploids). Reproductive isolation may be enhanced by cytotype morphological and environmental differentiation. Moreover, morphological adaptations to local conditions contribute to plant establishment. However, the relative contributions of ploidy level and the environment to morphology have generally been neglected. Thus, the extent of morphological variation driven by ploidy level and the environment was modelled for diploid, tetraploid and hexaploid cytotypes of Campanula rotundifolia agg. Cytotype distribution was updated, and morphological and environmental differentiation was tested in the presence and absence of natural contact zones.MethodsCytotype distribution was assessed from 231 localities in Central Europe, including 48 localities with known chromosome counts, using flow cytometry. Differentiation in environmental niche and morphology was tested for cytotype pairs using discriminant analyses. A structural equation model was used to explore the synergies between cytotype, environment and morphology.Key ResultsTremendous discrepancies were revealed between the reported and detected cytotype distribution. Neither mixed-ploidy populations nor interploidy hybrids were detected in the contact zones. Diploids had the broadest environmental niche, while hexaploids had the smallest and specialized niche. Hexaploids and spatially isolated cytotype pairs differed morphologically, including allopatric tetraploids. While leaf and shoot morphology were influenced by environmental conditions and polyploidy, flower morphology depended exclusively on the cytotype.ConclusionsReproductive isolation mechanisms vary between cytotypes. While diploids and polyploids are isolated postzygotically, the environmental niche shift is essential between higher polyploids. The impact of polyploidy and the environment on plant morphology implies the adaptive potential of polyploids, while the exclusive relationship between flower morphology and cytotype highlights the role of polyploidy in reproductive isolation.     

Agrostis mertensii (Poaceae) in hokkaido

Populations of theAgrostis flaccida-mertensii complex in Hokkaido were examined as part of the taxonomic study of this complex, which has a wide range and comprises a polyploid series of 2x–8x (x=7). The principal aim was to clarify the taxonomic status of hexaploids growing in Hokkaido. Field explorations were made in the mountains and on the coasts in Hokkaido, and the materials were gathered from 19 localities. The occurrence of four cytotypes (2x, 4x, 6x, 8x), as well as some triploids and septaploids, of this complex in Hokkaido was confirmed, and the ranges of respective cytotypes were delineated. Morphological examinations showed that diploids, triploids and tetraploids are referable toAgrostis flaccida and octoploids toA. mertensii. The hexaploids of Hokkaido were morphologically different fromA. flaccida and also from the related hexaploid species,A. tateyamensis, distributed in Honshu. The hexaploids were quite similar to octoploidA. mertensii in all the morphological features examined and also in habitat preference. Septaploids were sterile hybrids between hexaploids and octoploids. A conclusion was drawn that the hexaploid plant of Hokkaido should be grouped with the octoploid in one and the same species,Agrostis mertensii Trin.Agrostis mertensii in this amended sense is discussed from a cytogeographical viewpoint.     

Impaired male meiosis, morphology and distribution pattern of different cytotypes of Bupleurum lanceolatum Wall. (Apiaceae) from the Western Himalayas

Detailed male meiosis, critical morphological observations and distribution pattern of diploid as well as tetraploid cytotypes of the Western Himalayan species, Bupleurum lanceolatum have been evaluated at present. A diploid (n = 8) cytotype is reported from Kashmir, whereas, both diploid (n = 8) and tetraploid (n = 16) cytotypes are available from two districts Kangra and Sirmaur of Himachal Pradesh. Out of these, the tetraploid cytotype makes new addition for the species on a worldwide basis. As per behavior, a tetraploid cytotype is characterized by abnormal meiosis leading to high pollen sterility and size variation of the pollen grains. Morphologically, tetraploids are noted to be luxuriant in comparison to the diploids.     

Cytotype distribution inEmpetrum (Ericaceae) at various spatial scales in the Czech Republic

Ploidy levels inEmpetrum (crowberry) from the Czech Republic and from one adjacent locality in Poland were estimated by flow cytometry to examine cytotype distribution patterns at large (within the country), medium (within mountain ranges) and small (within particular localities) spatial scales. Diploid, triploid, and tetraploid individuals were found. Triploids are reported from Central Europe for the first time; they occurred in the Krkono?e Mts. Exclusively diploid plants were observed in three mountain ranges (the Kru?né hory Mts., Labské pískovce Mts., Adr?pa?sko-Teplické skály Mts.), exclusively tetraploids were observed in the Jeseníky Mts., and both cytotypes were observed in the ?umava Mts., Jizerské hory Mts. and Krkono?e Mts. Except for the latter mountain range, diploids and tetraploids were always found in different habitats. Spatial isolation is supposed to be the main barrier preventing cytotype mating. A mosaic-like sympatric occurrence of different cytotypes was demonstrated in the Krkono?e Mts., where peat bogs and rocky places were not spatially separated. Eight of 11 localities studied there were inhabited by diploids and tetraploids (five localities), diploids and triploids (one locality) or all three ploidy levels (two localities). Diploid and triploid plants occasionally intermingled at 0.3 × 0.3 m. Flower sex in crowberries was strongly associated with ploidy level: diploids usually had unisexual flowers, the tetraploids bore exclusively bisexual flowers. However, a few diploid plants with hermaphrodite flowers occurred in one population in the Krkono?e Mts.     

Higher seed size and germination rate may favour autotetraploids of Vicia cracca L. (Fabaceae)

The phenotypic effect of increased cell size in polyploid angiosperms has been repeatedly described; the ecological consequences of the gigas effect are, however, relatively poorly understood. Here, we investigated the effect of cytotype, seed weight, and inter‐population variation on seedling germination and growth in diploid and autotetraploid Vicia cracca L. in a common garden experiment. Seeds used in this study originated in the contact zone of the cytotypes in Central Europe. Tetraploids had heavier seeds than diploids and greater germination rates irrespective of seed size. Both seed weight and germination rate displayed high inter‐population variation. Further, tetraploids seem to germinate earlier and deposit fewer reserves into the seed bank than diploids. Mean above‐ground biomass and seedling height were similar in the two cytotypes of V. cracca. Nonetheless, the tallest tetraploid seedlings were taller than the tallest diploid seedlings, which may be advantageous under strong competition in dense vegetation. This study thus demonstrates that tetraploids of V. cracca may have superior competitive ability to diploids in certain habitats. It also suggests the necessity of studying multiple populations per cytotype when comparing diploids and polyploids, as the effect of population may be of similar or even higher magnitude than the effect of cytotype. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 57–73.     

Competition between cytotypes changes across a longitudinal gradient in Centaurea stoebe (Asteraceae)

? Premise of the Study: Polyploidy resulting from whole genome duplication has contributed to the adaptive evolution of many plant species. However, the conditions necessary for successful polyploid evolution and subsequent establishment and persistence in sympatry with diploid progenitors are often quite limited. One condition thought to be necessary for establishment is a substantial competitive superiority of the polyploid. ? Methods: We conducted a pairwise competition experiment using diploid and tetraploid cytotypes of Centaurea stoebe L. to determine whether (1) tetraploids have greater competitive ability than diploids, (2) cytotypes from mixed-cytotype populations have more balanced competitive abilities than single-cytotype populations, and (3) competitive abilities change along a longitudinal gradient. ? Key Results: Across sampling localities, tetraploids did not produce greater aboveground biomass than diploids but suffered from greater intracytotypic competition. Tetraploids allocated greater biomass belowground than diploids, regardless of competition treatment, and had greater performance for traits associated with long-term persistence (bolted more frequently and produced more accessory rosettes). Competitive ability of tetraploids did not differ between single- and mixed-cytotype populations but varied along a longitudinal gradient. Tetraploids were stronger intercytotypic competitors in Western Europe (Switzerland and Germany) than in Eastern Europe (Hungary and Slovakia), which indicates that cytotype coexistence may be more likely in Eastern Europe, the proposed origin of tetraploids, than in Western Europe. ? Conclusions: Our study addresses the importance of examining competitive interactions between cytotypes across their distributional range, as competitive interactions were not consistent across sampling localities.     

AUTOPOLYPLOIDY IN HEUCHERA MICRANTHA (SAXIFRAGACEAE)

Heuchera micrantha (Saxifragaceae) is a morphologically variable species comprising five varieties: diversifolia, erubescens, hartwegii, micrantha, and pacifica. Both diploids (2n = 14) and tetraploids (2n = 28) occur within the species. The tetraploid cytotype occupies the central portion of the geographic range of the species, whereas diploids occur primarily in the southern and northern portions of the range. Both diploids and tetraploids have been detected within vars. diversifolia, pacifica, and hartwegii. All counts for vars. erubescens and micrantha are diploid and tetraploid, respectively. Several lines of evidence suggest that tetraploid H. micrantha is of autopolyploid origin. The species is distinct morphologically and is also well separated geographically from other closely related species in subsection Micranthae. The two cytotypes are karyologically identical, possess nearly the same suite of allozymes, and have a very high genetic identity (Ī = 0.971). Significantly, an earlier study documented tetrasomic inheritance in the tetraploid cytotype. Following theoretical expectations, the mean number of alleles per locus, proportion of loci that are polymorphic, and observed heterozygosity are significantly higher for the autotetraploid than for the diploid. The occurrence of both cytotypes in three of the varieties suggests that autopolyploidy may have occurred several times independently in H. micrantha. This was further substantiated by discriminant analysis using morphological characters, which provided evidence for a minimum of two separate origins for the autopolyploid cytotype.     

Four new cytotypes of the onchocerciasis vector blackfly Simulium guianense in Brazil

Abstract. Simulium (Trichodagmia) guianense is an important Amazonian vector of onchocerciasis. Examination of the polytene chromosome banding patterns of larvae from five sites in Brazil revealed the occurrence of four cytotypes, designated A, B, C and D. The chromosomal standard, Simulium guianense A , occurred at two localities in Goias State (on the Rio Tocantins and Rio Mucambao) where it was the only cytotype. The other three sites examined yielded one different cytotype from each: B from Rio Oyapoque in Amapa State, C from Rio Tocantins in Maranhao State, and D from Rio Xingu in Para State. All cytotypes differed by at least two fixed inversions, but a sex determining system was not evident in any cytotype. As the cytotypes have been found allopatrically it is not certain that they represent sibling species; sampling of sympatric populations would resolve this. During certain times of the year, voracious anthropophagy by S.guianense sensu lato occurs at the localities sampled for cytotypes A, C and D (biting data are not available for the cytotype B locality). In some other areas, however, S.guianense s.l. is entirely zoophilic. Further studies are needed, therefore, to elucidate the biting habits, vectorial capacity, geographic distribution and taxonomic status of these four, and perhaps additional, cytotypes comprising the S.guianense complex.     

An experimental test of local adaptation among cytotypes within a polyploid complex

The geographic distributions of polyploids suggest they can have distinct and sometimes broader niches compared to diploids. However, relatively few field experiments have investigated whether range differences are associated with local adaptation or reflect other processes, such as dispersal limitation. In three years of transplants across the elevational ranges of five cytotypes in the Claytonia perfoliata complex, we found evidence for local adaptation. In at least one study year germination was higher within the natural range for each cytotype, and four of the five cytotypes attained larger biomass within their natural range. Fitness within and beyond range varied across years, with two instances of cytotypes showing higher fitness beyond the range, highlighting a potential role of temporal variability in cytotype differentiation. Polyploids as a group did not outperform diploids, but the cytotype with highest fitness across environments was a hexaploid reported to be invasive. Our results suggest that differences in geographic ranges within the C. perfoliata complex reflect local adaptation of cytotypes. Although we did not find a general polyploid advantage, our findings support the idea that occasional polyploid cytotypes exhibit high fitness relative to other cytotypes, and contribute to growing evidence supporting ecological differentiation of cytotypes within polyploid complexes.     

Intraspecific karyotypic polymorphism is highly concordant with allozyme variation in Lysimachia mauritiana (Primulaceae: Myrsinoideae) in Taiwan: implications for the colonization history and dispersal patterns of coastal plants

Background and Aims

Investigating intraspecific karyotypic and genetic variations jointly can provide unique insights into how historical, ecological and cytogenetic factors influence microevolution. A coastal herb, Lysimachia mauritiana, exhibits extensive karyotypic polymorphism and displays a complex cytogeographic pattern across the Ryukyus. To explore whether a similar degree of chromosomal variation exists south of the Ryukyus, and in an attempt to ascertain the mechanisms that may have generated the patterns, comprehensive sampling was conducted in Taiwan.

Methods

Karyotypes were analysed at mitotic metaphase for 550 individuals from 42 populations throughout Taiwan Proper and its adjacent islands. In addition, genetic variation was estimated using 12 allozymes (21 loci) of 314 individuals sampled from 12 localities.

Key Results

Four chromosome numbers and eight cytotypes, including four endemic cytotypes, were detected. Cytotype distributions were highly structured geographically, with single cytotypes present in most populations and four major cytotypes dominating the north, east and south of Taiwan and the Penghu Archipelago. Allozyme variation was very low and F-statistics indicated an extremely high level of population differentiation, implying limited gene flow among populations. Cluster analysis of allozyme variation uncovered four geographic groups, each corresponding perfectly to the four dominant cytotypes. The geographic structure of cytotype distribution and allozyme variation probably resulted from severe genetic drift triggered by genetic bottlenecks, suggesting that Taiwanese populations were likely to be derived from four independent founder events. In the few localities with multiple cytotypes, cytogeographic patterns and inferences of chromosomal evolution revealed a trend of northward dispersal, consistent with the course of the Kuroshio Current that has been influential in shaping the coastal biota of the region.

Conclusions

The data elucidate the patterns of colonization and the effects of the Kuroshio Current on the distribution of L. mauritiana in Taiwan. These inferences are highly relevant to other coastal plant species in the region and will stimulate further studies.     

Diploid and Tetraploid Cytotypes of Centaurea stoebe (Asteraceae) in Central Europe: Morphological Differentiation and Cytotype Distribution Patterns

The taxomically critical species Centaurea stoebe is represented in Central Europe by a diploid (2n?=?18) and a tetraploid (2n?=?36) cytotype. Their morphological differentiation and taxonomic treatment is still controversial. Karyological (chromosome numbers and flow cytometric measurements) and multivariate morphometric analyses were used here to address cytotype distribution patterns and their morphological differentiation. Material from 38 localities (771 individuals) in Slovakia, Hungary and Austria, including type localities of the names traditionally applied to the different cytotypes, was sampled and evaluated using both morphometric and karyological approaches. The morphological tendency towards cytotype differentiation is evident only at a population level, and is blurred at the level of individual plants. Diploid populations prevail in the area studied, as well as throughout Europe; mixed-cytotype populations were also found. The present data, namely the weak morphological distinction, largely sympatric occurrence of the cytotypes, and the existence of mixed-cytotype populations, favour taxonomic treatment as a single species, without recognition of infraspecific units.     

Chloroplast DNA Intraspecific Phylogeography of Prairie Cordgrass (Spartina pectinata Bosc ex Link)

Chloroplast DNA (cpDNA) sequences are appropriate for studying intraspecific phylogeography. Comparing cpDNA phylogeny with different cytotypes provides insights into the origin and establishment of polyploid species. We have previously defined the geographic distribution of cytotypes in prairie cordgrass throughout the different regions of the United States. In this study, chloroplast haplotype variation is explored in 54 populations of prairie cordgrass, using nine noncoding chloroplast regions. These chloroplast analyses were combined with the cytotype surveys of prairie cordgrass to infer the phylogeography and to elucidate the origin of the different cytotypes. In this study, we identified three haplotypes, Prairie Cordgrass Group 1 (PCG1), Prairie Cordgrass Group 2 (PCG2), and Prairie Cordgrass Group 3 (PCG3). In general, related haplotypes were strongly associated with geographic distribution. Useful insertions–deletions (indels) were also found among prairie cordgrass populations. The PCG1 haplotypes collected inthe East North Central to the New England regions of the US, were polyploid (tetraploid, hexaploid, and octoploids), while the PCG2 haplotypes, found in southern South Dakota, Iowa, and Missouri, were primarily octoploids, but also included a small number of tetraploids. The PCG3 haplotypes were octoploids and were collected in North Dakota, South Dakota, and Minnesota.     

A new cytotype of Jacobaea vulgaris (Asteraceae): frequency,morphology and origin

Jacobaea vulgaris subsp. vulgaris (syn. Senecio jacobaea subsp. jacobaea) constitutes an intricate polyploid complex distributed in Europe. Four cytotypes have been reported in this species, three with euploid (diploid, tetraploid and octoploid; 2n=20, 40 and 80) and one with aneuploid (2n=32) chromosome numbers. Here we report that the diploid chromosome number (2n=20) reported from Bulgaria is due to misidentification with Jacobaea aquatica. On the other hand, we have discovered a new, hexaploid (2n=6x=60) cytotype within J. vulgaris subsp. vulgaris using flow cytometry. The new cytotype occurs within four sympatric populations of otherwise tetraploid and octoploid plants in Pannonia (one locality in the eastern Czech Republic and two localities in southwestern Slovakia) and in Podillya (one locality in western Ukraine). The frequency of hexaploid individuals within 76 studied populations is very low (only 10 of 693 analysed plants), and hexaploids probably represent hybrids between tetraploid and octoploid plants. Three mixed populations with hexaploid plants were subjected to detailed morphological and pollen fertility analyses. Multivariate morphometric analysis reveals partial separation of tetraploid and octoploid plants, whereas hexaploid individuals are similar in morphology to octoploids. In comparison with tetraploids, octoploids and hexaploids exhibit slightly longer ray florets, involucral bracts and tubular florets and more hairy outer achenes. Hexaploid plants display larger pollen grains and lower pollen fertility compared to tetraploids and octoploids.     

THE EVOLUTIONARY HISTORY OF PARTHENOGENETIC CNEMIDOPHORUS LEMNISCATUS (SAURIA: TEIIDAE). II. MATERNAL ORIGIN AND AGE INFERRED FROM MITOCHONDRIAL DNA ANALYSES

Restriction endonuclease analyses were performed on mitochondrial DNAs (mtDNAs) representing unisexual parthenogenetic (cytotypes A, B, and C) and bisexual (cytotypes D and E) populations of Amazonian lizards presently regarded as Cnemidophorus lemniscatus. The results of mtDNA cleavage map comparisons among these C. lemniscatus indicated that (1) there was no cleavage site variation among the unisexuals, (2) mtDNAs from the bisexual cytotypes D and E differed in sequence from one another by about 13%, and (3) mtDNAs from cytotypes A–C differed from those of cytotype D by about 5% and from those of cytotype E by about 13%. Higher resolution restriction fragment size comparisons confirmed the high degree of similarity among the unisexual mtDNAs, but identified 12 cleavage site variants among the 13 cytotype D mtDNAs examined. Both cladistic and phenetic (UPGMA) analyses of the data indicate that the unisexual and cytotype D mtDNAs form a single clade, suggesting that a female of cytotype D was the maternal progenitor of the unisexuals. The similarity among the unisexual mtDNAs and the variability among those of cytotype D suggest that the three unisexual cytotypes arose recently from a common maternal lineage. The mtDNA variability observed among cytotype D individuals has a strong geographic component, suggesting that the unisexuals arose from one or a few geographically proximal populations. The mtDNA comparisons also support the conclusion, based on allozyme comparisons (Sites et al., 1990, this issue), that cytotypes D and E, although presently allocated to C. lemniscatus, are separate species.     

Studies on the Asian Eupatorias

Analysis of 265 plants derived from 13 sites in the Rokko Mountains shows that the widely distributed eastern AsianEupatorium chinense var.simplicifolium consists of seven cytotypes. These polymorphic karyotypes comprise four levels of ploidy based on X=10 and partial deficiency, occurring either alone or in combination. The polyploid cytotypes exhibit anomalous meiosis and highly variable pollen stainability in contrast to the nearly-normal behaviour of the diploid. The polyploid cytotypes were revealed as being agamospermous. They are readily distinguishable from the diploid cytotypes by several morphological characters and by growth habits closely related to their respective niches. Two or more cytotypes occurred in all sites examined, the most common being the coexistence of triploid and tetraploid cytotypes. The frequencies of occurrence of the pentaploid plants and the cytotypes involving a deficient chromosome were relatively low. While the diploid cytotype is restricted to fragile gravitational slopes and rocky areas which are poor in species and lack tall competitors, the polyploids occur widely in the grasslands, the roadsides or the forest-margins, closely associated with tall grasses and forbs such asMiscanthus sinensis. Based on these data, theE. chinense var.simplicifolium complex is divided into two distinct groups: the diploid cytotype and the polyploid cytotypes.     

Polyploidy and habitat differentiation in Dactylis glomerata L. from Galicia (Spain)

Summary The microdistribution of diploid and tetraploid plants of Dactylis glomerata L. was examined and related to their immediate environment in several sites in central Galicia, where morphologically indistinguishable individuals of both ploidies grow in sympatry. The two related cytotypes differed in habitat preference. Diploids were mainly confined to the low-density forest-floor habitat in woodlands of mostly ancient origin, whereas tetraploids were widespread in varied habitats but clearly predominant in open areas, particularly in disturbed anthropic sites. The in situ comparison of plant performance showed that where plants of each ploidy were more common they produced more tillers, panicles and seeds. This habitat preference closely reflected differences in life-history characteristics. The tetraploids had an early and short flowering time almost always completed before the aestival drought, whereas the diploids began to flower several weeks later and flowered throughout the drought. Comparisons along artificial gradients of soil water availability and light transmittance indicated that the cytotypes had distinct physiological requirements which probably originated in metabolic and more general genetic differentiation and could be directly attributable to ploidy. Habitat differentiation increases the species' colonizing ability. It also amplifies divergence in reproductive strategy between diploids and tetraploids, which reduces ineffective crossing between cytotypes and thereby permits them to coexist in sympatry. The effect of hybridization at the polyploid level on the differentiation between cytotypes was assessed from the recent introduction of a foreign tetraploid entity into the study area. Hybridization between the two distinct tetraploids was found to increase habitat differentiation between the diploids and the tetraploids, but the major part of this differentiation is probably attributable to ploidy itself.     

Geographical distribution of Allium oleraceum cytotypes in Finland and Sweden

Chromosome numbers from a total number of 226 populations of Allium oleraceum were determined in Finland, Sweden and seven other countries. Two different chromosome numbers or cytotypes were found, tetraploids (2n = 32) and pentaploids (2n = 40). In Finland, samples were collected for chromosome counts from a total of 190 populations, which fairly well covers the distribution area of the species in Finland. The majority of the populations of A. oleraceum in Finland contained only one of the two cytotypes. A clear pattern in the geographical distribution of the cytotypes could be distinguished. The pentaploid cytotype predominates in the Åland Islands and in the archipelago of Regio aboënsis. The tetraploid cytotype predominates on the mainland of the Regio aboënsis and along the coast of the Nylandia. In south Häme, all studied native populations were of the tetraploid cytotype. Of all the studied populations in Finland 43.7% were tetraploid and 51.6% pentaploid. A few mixed populations with both tetraploid and pentaploid plants occurring in the same population were also found (4.7%). The chromosome numbers of 19 populations of A. oleraceum from the southern part of Sweden were pentaploids, with the exception of one tetraploid population. It seems that the pentaploid cytotype is predominant in Sweden, but no conclusions about a geographical pattern between the two cytotypes could be drawn. Based on the occurrence of the cytotypes, it is suggested that the pentaploid cytotype might have spread to Finland from the Swedish east coast via the Åland Islands to Kaland on the Finnish west coast and along the coast of Nyland to the archipelagos of Kotka and Hamina in Karelia australis. The tetraploid populations in south Häme are clearly connected to Iron Age activity and to old inland trade routes, and may be of eastern origin.