Patterns of genetic divergence among populations of the pseudometallophyte Biscutella laevigata from southern Poland

Background and aims

Pseudometallophytes are model organisms for adaptation and population differentiation because they persist in contrasting edaphic conditions of metalliferous and non-metalliferous habitats. We examine patterns of genetic divergence and local adaptation of Biscutella laevigata to assess historical and evolutionary processes shaping its genetic structure.

Methods

We sampled all known populations of B. laevigata in Poland and analyzed respective soil metal concentrations. For genotyping we used nine nuclear microsatellite loci. Population genetic pools were identified (Bayesian clustering) and we estimated genetic parameters and demographic divergence between metallicolous and non-metallicolous populations (ABC-approach).

Results

Populations clustered into two groups which corresponded to their edaphic origin and diverged 1,200 generations ago. We detected a significant decrease in genetic diversity and evidence for a recent bottleneck in metallicolous populations. Genetic structure was unrelated to site distribution but is rather influenced by environmental conditions (i.e. soil metal concentration).

Conclusions

The intriguing disjunctive distribution of B. laevigata in Poland results from a fragmentation of the species range during the Holocene, rather than recent long-distance-dispersal events. The genetic structure of populations, however, continues to be modified by microevolutionary processes at anthropogenic sites. These clear divergence patterns promote B. laevigata as a model species for plant adaptation to polluted environments.     

Genetic diversity and genetic relationships of Chukrasia spp. (Meliaceae) as revealed by inter simple sequence repeat (ISSR) markers

Key message

ISSR characterization of Chukrasia populations from the natural range revealed two distinct groups of populations consonant with morphological differentiation. Results suggest the current taxonomic classification of the genus should be reviewed.

Abstract

There are different views as to whether the genus Chukrasia (Meliaceae) consists of one species, C. tabularis, or two species C. tabularis and C. velutina. Despite a clear pattern of variation in many morphological characteristics such as leaves and bark, some authors regard the latter merely an ecotype of the former in seasonal forest. In the present study, we used ISSR markers to determine the genetic diversity and population structure among 23 Chukrasia subpopulations from across the natural range in Asia. Molecular analysis clearly differentiated two distinct groups of subpopulations, corresponding to the putative species, as well as well-defined subpopulations corresponding to geographic regions within the two groups. The molecular results are in concordance with morphological differentiation and corresponded to the two recognized taxa. The present study suggests that current taxonomic classification of the genus Chukrasia should be reviewed.     

Molecular characterization of Nicaraguan Pinus tecunumanii Schw. ex Eguiluz et Perry populations for in situ conservation

Key message

We conducted molecular characterization of Nicaraguan Pinus tecunumanii populations using microsatellite markers. Populations possess considerable genetic variation but there are risks associated with inbreeding and population fragmentation.

Abstract

We carried out a molecular characterization of three natural populations of Pinus tecunumanii using nine microsatellite markers. All studied populations occur in Nicaragua, where the species has declined primarily due to human-influenced factors. The results showed that there is a high amount of genetic variation in populations (expected heterozygosities 0.775–0.841), populations do not show significant differentiation (mean F _ST 0.0073), apparently due to frequent gene flow or a more continuous distribution and homogenous genetic composition in the past, and inbreeding is common in all populations (F _IS 0.705–0.780). The Structure analysis revealed that there is no evident clustering pattern among P. tecunumanii individuals. Although all studied populations possess a considerable amount of genetic variation, risks associated with inbreeding and population fragmentation should be acknowledged and a conservation strategy developed to safeguard the genetic resources of P. tecunumanii.     

Serpentine ecotypic differentiation in a polyploid plant complex: shared tolerance to Mg and Ni stress among di- and tetraploid serpentine populations of <Emphasis Type="Italic">Knautia arvensis</Emphasis> (Dipsacaceae)

Background and aims

Serpentine soils impose limits on plant growth and survival and thus provide an ideal model for studying plant adaptation under environmental stress. Despite the increasing amount of data on serpentine ecotypic differentiation, no study has assessed the potential role of polyploidy. We tested for links between polyploidy and the response to serpentine stress in Knautia arvensis, a diploid-tetraploid, edaphically differentiated complex.

Methods

Variation in growth, biomass yield and tissue Mg and Ni accumulation in response to high Mg and Ni concentrations were experimentally tested using hydroponic cultivation of seedlings from eight populations of different ploidy and edaphic origin.

Results

Regardless of ploidy level, serpentine populations exhibited higher tolerance to both Mg and Ni stress than their non-serpentine counterparts, suggesting an adaptive character of these traits in K. arvensis. The effect of ploidy was rather weak and confined to a slightly better response of serpentine tetraploids to Mg stress and to higher biomass yields in tetraploids from both soil types.

Conclusions

The similar response of diploid and tetraploid serpentine populations to edaphic stress corresponded with their previously described genetic proximity. This suggests that serpentine tolerance might have been transmitted during the local autopolyploid origin of serpentine tetraploids.

     

Genetic variation in wild Prunus L. subgen. Cerasus germplasm from Iran characterized by nuclear and chloroplast SSR markers

Key message

The selected material of Cerasus subgen. will be useful for conservation and management and important for Prunus breeding programs.

Abstract

Knowledge of relationships among the cultivated and wild species of Cerasus is important for recognizing gene pools in germplasm and developing effective conservation and management strategies. In this study, genetic and phylogenetic relationships of wild Cerasus subgenus species naturally growing in Iran, including P. avium (mazzard), P. mahaleb, P. brachypetala, P. incana, P. yazdiana, P. microcarpa subsp. microcarpa, P. microcarpa subsp. diffusa and P. pseudoprostrata and three commercial species, sweet cherry (P. avium), sour cherry (P. cerasus) and duke cherry (P. x gondouinii) was investigated based on 16 nuclear SSR and five chloroplast SSR. Very high level of polymorphism was detected among the studied species based these molecular markers, indicating high inter and intraspecific genetic variation. Inter and intraspecific genetic similarity coefficients varied from 0.00 to 1.00, indicating high genetic variation in studied germplasm. These two molecular markers types could distinguish differences between all species so that accessions of each species were placed into a single group. Based on molecular markers, a close correlation was observed between intraspecific variation and geographical distribution. Furthermore, based on nuSSR primers, most wild species showed 2–4 alleles and may be tetraploid. In conclusion, the conservation of these highly diverse native populations of Iranian wild Cerasus germplasm is recommended for future breeding activity.     

Variation of trace metal accumulation,major nutrient uptake and growth parameters and their correlations in 22 populations of Noccaea caerulescens

Background and aims

Noccaea caerulescens is a model plant for the understanding of trace metal accumulation and a source of cultivars for phytoextraction. The aim of this study was to investigate natural variation for trace metal accumulation, major nutrient uptake and growth parameters in 22 populations. The correlations among these traits were particularly examined to better understand the eco-physiology and the phytoextraction potential of the species.

Methods

Populations from three edaphic groups, i.e. calamine (CAL), serpentine (SERP) and non metalliferous (NMET) sites were grown in hydroponics for seven weeks at moderate trace metal exposure. Growth indicators, element contents and correlations between these variables were compared.

Results

All the phenotypic characteristics showed a wide variability among groups and populations. The SERP populations showed a smaller plant size, higher cation contents and strong correlations between all element concentrations. NMET populations did not differ in plant size from the CAL ones, but had higher Zn and Ni contents. The CAL populations showed higher Cd and Mn accumulations and lower Ca contents. The trade-off between biomass production and Cd, Ni and Zn accumulation was high in SERP populations and low in the CAL and NMET ones.

Conclusions

N. caerulescens is a genetically diverse species, showing specific features depending on the group and the population. These features may reflect the wide adaptive capacities of the species, and also reveal promising potential for phytoextraction of Cd, Ni and Zn.     

Primate seed dispersal leaves spatial genetic imprint throughout subsequent life stages of the Neotropical tree Parkia panurensis

Key message

The Neotropical tree Parkia panurensis shows a spatial genetic structure from the seed to the adult stage that is most likely the outcome of the seed dispersal provided by primates.

Abstract

Seed dispersal and pollination determine the gene flow within plant populations. In addition, seed dispersal creates the template for subsequent stages of plant recruitment. Therefore, the question arises whether and how seed dispersal affects the spatial genetic structure (SGS) of plant populations. In this study, we used microsatellites to analyse the SGS of the Neotropical tree Parkia panurensis (Fabaceae). This plant species is a major food resource for primates and its seeds are mainly dispersed by primates. Seeds were collected during behavioural observations of a tamarin mixed-species troop in north-eastern Peru. Additionally, leaf samples of juveniles and of adults trees of this species were collected throughout the home range of the tamarin troop. A significant SGS for embryos (located within the dispersed seeds) and for non-reproductive plants are found up to a distance of 300 m. This matches the distance within which most seeds are dispersed. In the adult stage, the scale of a significant SGS is reduced to 100 m. While we cannot explain this scale reduction, our study provides the first evidence that primate seed dispersal does influence the SGS of a tropical tree species.     

Genetic and morphological diversity in <Emphasis Type="Italic">Tragopogon graminifolius</Emphasis> DC. (Asteraceae) in Iran

Tragopogon graminifolius DC. is a medicinal plant species of the genus Tragopogon L. (Asteraceae) that grows in different regions of Iran and is extensively used by locals. There is no report on genetic variability and population structure of this important plant species. Therefore, we studied the genetic diversity, population structure and morphological variability of 14 geographical populations of Tragopogon graminifolius in Iran. AMOVA and Gst analyses revealed significant molecular differences among the studied populations. Mantel test showed significant correlation between genetic distance and geographical distance of the studied populations and indicated that the neighboring populations had a higher degree of gene flow. STRUCTURE plot identified three main gene pools for Tragopogon graminifolius in Iran and population assignment test revealed that gene flow occurred mostly among populations of the same gene flow. The studied populations differed significantly in their morphological and genetic features. These results may be of use for future conservation of this important plant species.     

Population genetic diversity and geographical differentiation of MHC class II DAB genes in the vulnerable Chinese egret (<Emphasis Type="Italic">Egretta eulophotes</Emphasis>)

Major histocompatibility complex (MHC) genes are excellent markers for the study of adaptive genetic variation occurring over different geographical scales. The Chinese egret (Egretta eulophotes) is a vulnerable ardeid species with an estimated global population of 2600–3400 individuals. In this study, we sampled 172 individuals of this egret (approximately 6 % of the global population) from five natural populations that span the entire distribution range of this species in China. We examined their population genetic diversity and geographical differentiation at three MHC class II DAB genes by identifying eight exon 2 alleles at Egeu-DAB1, eight at Egeu-DAB2 and four at Egeu-DAB3. Allelic distributions at each of these three Egeu-DAB loci varied substantially within the five populations, while levels of genetic diversity varied slightly among the populations. Analysis of molecular variance showed low but significant genetic differentiation among five populations at all three Egeu-DAB loci (haplotype-based ?_ST: 0.029, 0.020 and 0.042; and distance-based ?_ST: 0.036, 0.027 and 0.043, respectively; all P < 0.01). The Mantel test suggested that this significant population genetic differentiation was likely due to an isolation-by-distance pattern of MHC evolution. However, the phylogenetic analyses and the Bayesian clustering analysis based on the three Egeu-DAB loci indicated that there was little geographical structuring of the genetic differentiation among five populations. These results provide fundamental population information for the conservation genetics of the vulnerable Chinese egret.     

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

Background

Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity.

Results

Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability.

Conclusions

In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.     

Progeny-testing of full-sibs IBD in a SSC2 QTL region highlights epistatic interactions for fatness traits in pigs

Background

Tetraena mongolica (Zygophyllaceae), an endangered endemic species in western Inner Mongolia, China. For endemic species with a limited geographical range and declining populations, historical patterns of demography and hierarchical genetic structure are important for determining population structure, and also provide information for developing effective and sustainable management plans. In this study, we assess genetic variation, population structure, and phylogeography of T. mongolica from eight populations. Furthermore, we evaluate the conservation and management units to provide the information for conservation.

Results

Sequence variation and spatial apportionment of the atp B- rbc L noncoding spacer region of the chloroplast DNA were used to reconstruct the phylogeography of T. mongolica. A total of 880 bp was sequenced from eight extant populations throughout the whole range of its distribution. At the cpDNA locus, high levels of genetic differentiation among populations and low levels of genetic variation within populations were detected, indicating that most seed dispersal was restricted within populations.

Conclusions

Demographic fluctuations, which led to random losses of genetic polymorphisms from populations, due to frequent flooding of the Yellow River and human disturbance were indicated by the analysis of BEAST skyline plot. Nested clade analysis revealed that restricted gene flow with isolation by distance plus occasional long distance dispersal is the main evolutionary factor affecting the phylogeography and population structure of T. mongolica. For setting a conservation management plan, each population of T. mongolica should be recognized as a conservation unit.     

Edaphic influences of ophiolitic substrates on vegetation in the Western Italian Alps

Background and aims

Soils derived from serpentinite (serpentine soils) often have low macronutrient concentrations, exceedingly low Ca:Mg molar ratios and high heavy metal concentrations, typically resulting in sparse vegetative cover. This combined suite of edaphic stresses is referred to as the “serpentine syndrome.” Although several plant community-level studies have been conducted to identify the most important edaphic factor limiting plant growth on serpentine, the primary factor identified has often varied by plant community and local climate. Few studies to date have been conducted in serpentine plant communities of alpine or boreal climates. The goal of our study was to determine the primary limiting edaphic factors on plant community species composition and productivity (cover) in the alpine and boreal climate of the Western Alps, Italy.

Methods

Soil properties and vegetation composition were analyzed for several sites underlain by serpentinite, gabbro, and calc-schist substrates and correlated using direct and indirect statistical methods.

Results

Boreal forest soils were well-developed and tended to have low pH throughout the soil profile resulting in high Ni availability. Alpine soils, in comparison, were less developed. The distinct serpentine plant communities of the Western Alps are most strongly correlated with high levels of bioavailable Ni associated with low soil pH. Other factors such as macronutrient deficiency, low Ca:Mg molar ratio and drought appear to be less important.

Conclusions

The strong ecological influence of Ni is caused by environmental conditions which increase metal mobilization.     

Morphometric and ISSR-Analysis of Local Populations of <Emphasis Type="Italic">Geranium molle</Emphasis> L. from the Southern Coast of the Caspian Sea

Geranium molle is known as Dovefoot Geranium or Awnless Geranium. Dovefoot Geranium is a low-growing herb with pink flowers and sharply toothed leaves. Dovefoot Geranium is native to Eurasia and has been introduced to many habitats of the world. This species is very similar to G. robertianum but its palmate-like leaves and bilobed petals show differences. This plant is considered to be anodyne, astringent and vulnerary. We have no information on its population genetic structure, genetic diversity, and morphological variability in Iran. Therefore, due to the importance of these plant species, we performed a combination of morphological and molecular data for this species. For this study, we used 132 randomly collected plants from 18 geographical populations in 4 provinces. Genetic diversity parameters were determined in these populations. STRUCTURE analysis and K-Means clustering identified 14 gene pools in the country and revealed isolation by distance among the studied populations. The Mantel test showed correlation between genetic and geographical distance. AMOVA revealed a significant genetic difference among populations and showed that 40% of total genetic variation was due to within-population diversity. The consensus tree of both molecular and morphological data identified divergent populations. These data may be used in future breeding and conservation of this important medicinal plant in the country.     

Pollen-mediated gene flow promotes low nuclear genetic differentiation among populations of <Emphasis Type="Italic">Cycas debaoensis</Emphasis> (Cycadaceae)

Cycas debaoensis is a critically endangered cycad species endemic to China. This species is found on two kinds of habitats according to the edaphic differences, sand and karst. A previous chloroplast DNA (cpDNA) study indicated that C. debaoensis had low genetic variation within populations and high genetic differentiation among populations. Because maternally inherited cpDNA does not fully characterize genetic structure of the species, we screened seven low-copy nuclear genes and 17 nuclear microsatellite loci to detect the nuclear genetic diversity, differentiation, and the population structure of C. debaoensis. The nuclear genes revealed higher level of genetic diversity. There were both the same and region-specific haplotypes or alleles between the karst and sand regions. Nuclear gene flow among all the populations was much greater than that of cpDNA, which indicated that pollen-mediated gene flow was much greater than seed-mediated gene flow. This promoted low nuclear genetic differentiation among populations of C. debaoensis. The study suggests that both genetic and anthropogenic disturbances have resulted in the critically endangered status of C. debaoensis.     

Parametric and non-parametric masking of randomness in sequence alignments can be improved and leads to better resolved trees

Background

Ants typically distinguish nestmates from non-nestmates based on the perception of colony-specific chemicals, particularly cuticular hydrocarbons present on the surface of the ants' exoskeleton. These recognition cues are believed to play an important role in the formation of vast so-called supercolonies that have been described for some invasive ant species, but general conclusions about the role of these cues are hampered by only few species being studied. Here we use data on cuticular hydrocarbons, aggression and microsatellite genetic markers to investigate the interdependence of chemical recognition cues, genetic distance and nestmate discrimination in the pharaoh ant (Monomorium pharaonis), a widespread pest species, and ask whether introduced populations of this species are genetically differentiated and exhibit intraspecific aggression.

Results

Microsatellite analyses of a total of 35 colonies from four continents revealed extremely high levels of genetic differentiation between almost all colonies (F _ST = 0.751 ± 0.006 SE) and very low within-colony diversity. This implies that at least 34 and likely hundreds more independent lineages of this ant have spread worldwide. Aggression tests involving workers from 14 different colonies showed only low levels of aggression, even between colonies that were geographically and/or genetically very distant. Chemical analyses of groups of worker ants showed that all colonies had the same cuticular compounds, which varied only quantitatively among colonies. There was a positive correlation between geographical and genetic distance, but no other significant relationships were detected between aggression, chemical profile, genetic distance and geographical distance.

Conclusions

The pharaoh ant has a global invasion history of numerous independent introductions resulting in genetically highly differentiated colonies typically displaying surprisingly low levels of intraspecific aggression, a behaviour that may have evolved in the native range or by lineage selection in the introduced range.     

Specialized edaphic niches of threatened copper endemic plant species in the D.R. Congo: implications for ex situ conservation

Background and aims

Copper (Cu) rich soils derived from rocks of the Katangan Copperbelt in the south-eastern Democratic Republic of Congo (DRC) support a rich diversity of metallophytes including 550 heavy metal tolerant; 24 broad Cu soil endemic; and 33 strict Cu soil endemic plant species. The majority of the plant species occur on prominent Cu hills scattered along the copperbelt. Heavy metal mining on the Katangan Copperbelt has resulted in extensive degradation and destruction of the Cu hill ecosystems. As a result, approximately 80 % of the strict Cu endemic plant species are classified as threatened according to IUCN criteria and represent a conservation priority. Little is known about the soil Cu tolerance optimum of the Cu endemic plant species. The purpose of this study was to quantify the soil Cu concentration (Cu edaphic niche) of four Cu endemic plant species to inform soil propagation conditions and microhabitat site selection for planting of the species in Cu hill ecosystem restoration.

Methods

The soil Cu concentration tolerance of Cu endemic plant species was studied including Crotalaria cobalticola (CRCO); Gladiolus ledoctei (GLLE); Diplolophium marthozianum (DIMA); and Triumfetta welwitschii var. rogersii (TRWE-RO). The in situ natural habitat distributions of the Cu endemic plant species with respect to soil Cu concentration (Cu edaphic niche) was calculated by means of a generalised additive model. Additionally, the seedling emergence and growth of the four Cu endemic plant species in three soil Cu concentrations was tested ex situ and the results were compared to that of the natural habitat soil Cu concentration optimum (Cu edaphic niche).

Results

CRCO exhibited greater performance on the highest soil Cu concentration, consistent with its calculated Cu edaphic niche occurring at the highest soil Cu concentrations. In contrast, both DIMA and TRWE-RO exhibited greatest performance at the lowest soil Cu concentration, despite the calculated Cu edaphic niche occurring at moderate soil Cu concentrations. GLLE exhibited equal performances in the entire range of soil Cu concentrations.

Conclusions

These results suggest that CRCO evolved via the edaphic specialization model where it is most competitive in Cu hill habitat with the highest soil Cu concentration. In comparison, DIMA and TRWE-RO appear to have evolved via the endemism refuge model, which indicates that the species were excluded into (i.e., took refuge in) the lower plant competition Cu hill habitat due to their inability to effectively compete with higher plant competition on normal soils. The soil Cu edaphic niche determined for the four species will be useful in conservation activities including informing soil propagation conditions and microhabitat site selection for planting of the species in Cu hill ecosystem restoration.

     

Nitrogen or phosphorus limitation in rich fens? - Edaphic differences explain contrasting results in vegetation development after fertilization

Background and aims

Many rich fens are threatened by high nutrient inputs, but the literature is inconsistent with respect to the type of nutrient limitation and the influence of edaphic characteristics.

Methods

We performed experiments with N- and P-fertilization in three endangered rich fen types: floating fen with Scorpidium scorpioides, non-floating fen with Scorpidium cossonii, floodplain fen with Hamatocaulis vernicosus. In addition, K-fertilization was carried out in the floodplain fen.

Results

The floodplain fen showed no response to P-addition, but N- and K-addition led to grass encroachment and decline of moss cover and species richness. In contrast, in the P-limited floating fen with S. scorpioides, P-addition led to increased vascular plant production at the expense of moss cover. Scorpidium scorpioides, however, also declined after N-addition, presumably due to ammonium toxicity. The fen with S. cossonii took an intermediate position, with NP co-limitation. These striking contrasts corresponded with edaphic differences. The N-limited fen showed low Ca:Fe ratios and labile N-concentrations, and high concentrations of plant-available P and Fe-bound P. The P-limited fen showed an opposite pattern with high Ca:Fe ratios and labile N-concentrations, and low P-concentrations.

Conclusions

This implies that edaphic characteristics dictate the nature of nutrient limitation, and explain contrasting effects of N- and P-eutrophication in different fens.     

Genetic diversity and population structure of the secondary symbiont of tsetse flies, Sodalis glossinidius, in sleeping sickness foci in Cameroon

Background

Previous studies have shown substantial differences in Sodalis glossinidius and trypanosome infection rates between Glossina palpalis palpalis populations from two Cameroonian foci of human African trypanosomiasis (HAT), Bipindi and Campo. We hypothesized that the geographical isolation of the two foci may have induced independent evolution in the two areas, resulting in the diversification of symbiont genotypes.

Methodology/Principal Findings

To test this hypothesis, we investigated the symbiont genetic structure using the allelic size variation at four specific microsatellite loci. Classical analysis of molecular variance (AMOVA) and differentiation statistics revealed that most of the genetic diversity was observed among individuals within populations and frequent haplotypes were shared between populations. The structure of genetic diversity varied at different geographical scales, with almost no differentiation within the Campo HAT focus and a low but significant differentiation between the Campo and Bipindi HAT foci.

Conclusions/Significance

The data provided new information on the genetic diversity of the secondary symbiont population revealing mild structuring. Possible interactions between S. glossinidius subpopulations and Glossina species that could favor tsetse fly infections by a given trypanosome species should be further investigated.     

Inter- and intraspecific genetic and morphological variation in a sibling pair of carabid species

Background

Pogonus littoralis and Pogonus chalceus are very close related species with quite different ecological preferences within salt marshes. We study the evolutionary processes in and between these presumably young species. Therefore, we compare the variation in ecologically relevant characters and the genetic variation within one of the species (intraspecific differentiation) with the variation of the two types of characters between the two species (interspecific variation). Data are compared between two independent sets of populations, one set at a small geographical scale (the ecologically diverse Guérande area in France) and the other set at a Atlantic-Mediterranean scale.

Results

Body and relative wing size and IDH1 allozyme data show that the intraspecific variation in P. chalceus is high and in the same range as the interspecific variation (P. chalceus versus P. littoralis). Based on neutral markers (other allozymes and mitochondrial DNA) on the other hand, the intraspecific variation in P. chalceus is much lower in comparison to the interspecific variation.

Conclusion

The different ecotypes in the highly polytypic species P. chalceus are as highly differentiated in ecological characters as true species, but are not recognised as such by screening neutral DNA polymorphisms. This can be interpreted as a case of ongoing speciation driven by natural selection adapting each ecotype to its respective ecological niche. The same ecological process can be recognised in the differentiation between the two sister species, where en plus reproductive isolation between the two gene pools occurred, allowing independent drift and mutation accumulation in neutral genetic characters.     

Historical changes in population structure during rice breeding programs in the northern limits of rice cultivation

Key message

The rice local population was clearly differentiated into six groups over the 100-year history of rice breeding programs in the northern limit of rice cultivation over the world.

Abstract

Genetic improvements in plant breeding programs in local regions have led to the development of new cultivars with specific agronomic traits under environmental conditions and generated the unique genetic structures of local populations. Understanding historical changes in genome structures and phenotypic characteristics within local populations may be useful for identifying profitable genes and/or genetic resources and the creation of new gene combinations in plant breeding programs. In the present study, historical changes were elucidated in genome structures and phenotypic characteristics during 100-year rice breeding programs in Hokkaido, the northern limit of rice cultivation in the world. We selected 63 rice cultivars to represent the historical diversity of this local population from landraces to the current breeding lines. The results of the phylogenetic analysis demonstrated that these cultivars clearly differentiated into six groups over the history of rice breeding programs. Significant differences among these groups were detected in five of the seven traits, indicating that the differentiation of the Hokkaido rice population into these groups was correlated with these phenotypic changes. These results demonstrated that breeding practices in Hokkaido have created new genetic structures for adaptability to specific environmental conditions and breeding objectives. They also provide a new strategy for rice breeding programs in which such unique genes in local populations in the world can explore the genetic potentials of the local populations.