Genetic structure of disjunct Argentinean populations of the subtropical tree Anadenanthera colubrina var. cebil (Fabaceae)

Anadenanthera colubrina var. cebil is a native South American tree species inhabiting seasonally dry tropical forests (SDTFs). Its current disjunct distribution presumably represents fragments of a historical much larger area of this forest type, which has also been highly impacted by human activities. In this way the hypothesis of this study is that the natural populations of A. colubrina var. cebil from Northern Argentina represent vestiges of ancient fragmentation, but they are additionally influenced by a certain degree of gene flow among them. We aimed to analyze the genetic structure of both nuclear and chloroplast DNA to evaluate the relative role of ancient and recent fragmentation on intraspecific diversity patterns. Sixty-nine individuals of four natural populations were analyzed using eight nuclear microsatellites (ncSSR) and four chloroplast microsatellite loci (cpSSR). The level and distribution of genetic variation were estimated by standard population genetic parameters and Neighbor Joining as well as Bayesian analyses. The eight ncSSR loci were highly polymorphic, while genetic diversity of cpSSRs was low. Nuclear SSRs displayed lower genetic differentiation among populations than cpSSR haplotypes (F _ST 0.11 and 0.95, respectively). However, high differentiation between phytogeographic provinces was observed in both genomes. The high genetic differentiation detected emphasizes the role of ancient fragmentation. However, the Paranaense province also shows the effects of recent fragmentation on genetic structure, whereas gene flow by pollen preserves the effects of genetic drift in the Yungas province.     

Development of microsatellite markers for Anadenanthera colubrina var. cebil (Fabaceae), a native tree from South America

? Premise of the study: Microsatellite primers were developed in the native legume tree Anadenanthera colubrina var. cebil to study the genetic diversity and genetic structure in natural populations in Argentina. ? Methods and Results: Nine microsatellite markers were identified using a genomic library enriched for tandemly repeated motifs, eight of which markers were polymorphic. The polymorphism of these markers was assessed by investigating 20 individuals for fragment polymorphism; three to 13 alleles were observed for each locus. Observed and expected heterozygosities ranged from 0.300 to 1.000 and from 0.463 to 0.900, respectively. ? Conclusions: These results confirm that these primers will be useful for investigating the genetic diversity and genetic structure of natural populations of A. colubrina var. cebil in future studies.     

Hallucinogenic snuff from Northwestern Argentina: Microscopical identification of anadenanthera colubrina var. cebil (fabaceae) in powdered archaeological material

Two mummified bodies have been recovered from the Alero I or La Matanza site (15 km from Cusi-Cusi, Dpto. Santa Catalina, Puna of Jujuy, Argentina) in association with characteristic snuffing paraphernalia. The purpose of this work is to identify the powdered material contained in one of the tubes in order to confirm the hypothesis generated from ethnographical sources, that the rape (snuff) complex was associated with the consumption of Anadenanthera colubrina var. cebil, Fabaceae, the cebil, or, if not, which materials were inhaled. Following analysis with a light microscope, petrographic microscope and scanning electron microscope the unknown material was identified as cebil by comparison with reference material and specialized literature.

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Rapé AlucinóGeno del Noroeste de Argentina: identificación microscópica de Anadenanthera colubrina VAR. cEBIL (fABACEAE) en material arqueológico pulverizado

Resumen  CEBIL (FABACEAE) EN MATERIAL ARQUEOLóGICO PULVERIZADO. En 1991 se recuperaron dos cuerpos momificados en el Alero I La Matanza (distante 15 km de Cusi-Cusi, Dpto. Santa Catalina, en la Puna de Jujuy, Argentina) en asociación con el ajuar caracter#x00ED;istico del complejo del rap#x00E9; o complejo alucinógeno. Uno de los tubos de hueso hallados contenta material pulverizado. El objeto de este trabajo es identificar esta muestra con el objeto de contrastar la hipótesis generada a partir de estudios etnogr#x00E1;fico que asocia el complejo del rapé con el consuma de Anadenanthera colubrina var. cebil, Fabaceae, el cebil, o en caso negativo, identificar el material empleado. Mediante análisis con microscopio fotónico, microscopio petrogr#x00E1;fico y microscopio electrónico de barrido se identific#x20F3; la muestra como cebil por comparación con material de referenda y bibliograf#x00ED;a especializada.

     

Landscape genetic structure of natural populations of Acacia caven in Argentina

Acacia caven is a South American species which shows remarkable climate tolerance and ecological adaptability; as such, this species is suitable for colonizing anthropogenically degraded sites. This species is widely distributed, and six varieties have been described based on both morphological traits and molecular markers. Moreover, Aronson (1992) suggests that, for this species, geographical separation could be associated with ecological differentiation. In this study, amplified fragment length polymorphisms were used to study genetic variation within and among 15 populations of A. caven from five eco-regions of Argentina and to investigate (1) whether the varieties are genetically coherent, (2) whether the varieties correspond consistently to a single eco-region, (3) the proportion of the species diversity explained within and among varieties and eco-regions. Eight of the 225 bands appear to be under positive selection. The remaining 217 neutral loci showed a high percentage of polymorphism (99.1%). The estimates of genetic diversity H _j were generally high. The F _ST (0.315) was highly significant, providing evidence for genetic structure among populations. Hierarchical analysis of molecular variance indicated that variation among eco-regions was 8.2% and highly significant. The higher component of variance was found within populations (67.5%). STRUCTURE analysis suggested that the optimal number of K?=?11. The results showed that, in most cases, geographic separation is associated with ecological differentiation. Since differentiation of A. caven populations studied here in eco-regions was highly significant, sampling should include a large number of trees within populations as well as covering the wide ecological diversity of the species.     

Phenotypic and genetic variability of three natural populations of Atriplex halimus

Three natural populations of Atriplex halimus, located in three different climatic contexts, were studied using leaf characteristics (leaf area, leaf length-to-maximum-width ratio, average width of the leaves and leave-to-branch ratio) and isoenzymatic markers. The study showed the existence of a highly significant phenotypical variability. This variability is all the more significant, as populations are geographically distant and located in different climates. The gradual character of this morphological variability, along a climatic gradient, indicates that it is almost a clinical differentiation. Clones obtained from semi-woody cuttings taken on the level of each population and placed in a common parcel have maintained the same leaf characteristics as the population sources, suggesting the genetic origin of this variability. The study of four isoenzymatic systems confirms the existence of this variability. Thus, the percentage of polymorphic loci (P), the expected heterozygosity (He) and the mean number of alleles per locus (A) are of 77.52%, 0.319, and 1.99, respectively. The genetic diversity index (Fst) obtained is 0.089.     

The molecular basis of quantitative genetic variation in natural populations

DNA markers allow us to study quantitative trait loci (QTL) - the genes that control adaptation and quantitative variation. Experiments can map the genes responsible for quantitative variation and address the evolutionary and ecological significance of this variation. Recent studies suggest that major genes segregate within and among natural populations. It is now feasible to study the genes that cause morphological variation, life history trade-offs, heterosis and speciation. These methods can determine the role of epistasis and genotype-by-environment interaction in maintaining genetic variation. QTL mapping is an important tool used to address evolutionary and ecological questions of long-standing interest.     

A preliminary study of genetic variation in populations of Monstera adansonii var. klotzschiana (Araceae) from North-East Brazil, estimated with AFLP molecular markers

BACKGROUND AND AIMS: This study sought genetic evidence of long-term isolation in populations of Monstera adansonii var. klotzschiana (Araceae), a herbaceous, probably outbreeding, humid forest hemi-epiphyte, in the brejo forests of Ceará (north-east Brazil), and clarification of their relationships with populations in Amazonia and the Atlantic forest of Brazil. METHODS: Within-population genetic diversity and between-population dissimilarity were estimated using AFLP molecular markers in 75 individuals from eight populations located in Ceará, the Brazilian Atlantic Forest and Amazonia. KEY RESULTS: The populations showed a clinal pattern of weak genetic differentiation over a large geographical region (F(ST) = 0.1896). A strong correlation between genetic and geographical distance (Mantel test: r = 0.6903, P = 0.002) suggests a historical pattern of isolation by distance. Genetic structure analysis revealed at least two distinct gene pools in the data. The two isolated Ceará populations are significantly different from each other (pairwise Phi(PT) = 0.137, P = 0.003) and as diverse (Nei's gene diversity, average H(e) = 0.1832, 0.1706) as those in the Atlantic and Amazon forest regions. The population in southern Brazil is less diverse (Nei's gene diversity, average H(e) = 0.127) than the rest. The Ceará populations are related to those of the Atlantic forest rather than those from Amazonia (AMOVA, among-groups variation = 11.95 %, P = 0.037). CONCLUSIONS: The gene pools detected within an overall pattern of clinal variation suggest distinct episodes of gene flow, possibly correlated with past humid forest expansions. The Ceará populations show no evidence of erosion of genetic diversity, although this was expected because of their isolation. Their genetic differentiation and relatively high diversity reinforce the importance of conserving the endangered brejo forests.     

A molecular genetic study of natural strains of Saccharomyces isolated from Asturian cider fermentations

AIMS: To analyse the genetic diversity and the dynamics of Saccharomyces strains in spontaneous fermentation in ciders. The effect of the cellar, harvest and cider-making technology were evaluated. METHODS AND RESULTS: The ecology of spontaneous cider fermentations in the same cellar (Asturias) was studied for two consecutive harvests (2000 and 2001) by using mtDNA restriction analysis. Our results showed that there was a succession of genetically different strains of Saccharomyces during cider production. In general, strains of Saccharomyces bayanus species predominated at the early fermentation steps (begining and/or tumultuous fermentations), while Saccharomyces cerevisiae yeasts were the most abundant at the end of the fermentation. Five S. bayanus strains (patterns III, VII, VIII, XV and XVII) were present at significant frequencies in all the experimental tanks during the two consecutive years. The results of the cluster analysis (unweighted pair group method using average linkage) showed higher similarities for the patterns III, XV, VII and VIII. Therefore, these strains should be considered associated with the microbiota of this cellar. CONCLUSIONS: A high polymorphism within populations of Saccharomyces was found throughout the different stages of Asturian production of cider. In all the cider fermentations, a variable number of S. bayanus and S. cerevisiae strains was always present. Our results indicate, over the period of time studied, the existence of the natural microbiota in the cellar. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has allowed us to gain a better understanding of the role of wild Saccharomyces yeast in Asturian cider fermentations.     

Reproductive ecology and genetic variability in natural populations of the wild potato,Solanum kurtzianum

The cultivated potato (Solanum tuberosum ssp. tuberosum) has more than 200 related wild species distributed along the Andes, adapted to a wide range of geographical and ecological areas. Since the last century, several collection expeditions were carried out to incorporate genetic variability into the potato germplasm around the world. However, little is known about the reproductive ecology and genetic population structure of natural potato population from field studies. The aim of this work is to study, in the field, the genetic variability and reproductive strategies of populations of one of the most widely distributed potato species in Argentina, Solanum kurtzianum, growing in Mendoza province. AFLP markers showed that the genetic variability is mainly present among plants within populations, indicating that in the sampled populations, sexual reproduction is more relevant than clonal multiplication (by tubers). Additional evidence was obtained evaluating the genetic diversity in populations with a distribution in patches, where several genotypes were always detected. From a field study performed in the Villavicencio Natural Reserve, we found that the average number of plump seeds per fruit was 94.3, identified and calculated the foraging distance of four insect pollinators, and demonstrated the seed dispersal by storm water channels. We argue that the breeding system, the two modes of reproduction and the ecological interaction described here may have a prominent role in determining the genetic structure of S. kurtzianum populations, and discuss the importance of field studies on population genetics, reproductive biology and ecology to design collections and conservation strategies.     

Cytogenetic variability within and across populations of Cebus apella in Argentina

Two geographically separated populations of Cebus apella are found in Argentina. We have found important differences in the phenotypic characteristics of these populations, despite marked karyotypic similarity. Two well-distinguished phenotypes were established. Individuals from the northwest of Argentina are phenotypically similar to the Paraguayan populations and are recognized as C. apella paraguayanus. This subspecies is also found in the northeast of Argentina. Other specimens from the northeast are more similar phenotypically to the Brazilian subspecies C. apella nigritus and C. apella libidinosus and are designated as C. apella vellerosus. The two subspecies C. apella paraguayanus and C. apella vellerosus share the same diploid number of chromosomes (2n = 54). Cytogenetic comparisons using G-, Q- and R-banding techniques and C-banding methods with the chromosomes carrying large heterochromatic blocks (No. 3, 5, 11, 12, 13, 19) showed differences between the subspecies. The presence of different polymorphisms and even of heteromorphisms in the same chromosomic pair across geographically isolated populations of the same subspecies is illustrated with Argentinian and Paraguayan specimens.     

Intraspecific variability in natural populations of Glossina palpalis gambiensis from West Africa, revealed by genetic and morphometric analyses

Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae) from West Africa (Senegal and Burkina Faso) were analysed for microsatellite DNA polymorphisms and size of the wings. In the overall sample a strong heterozygote deficiency was found at two polymorphic microsatellite loci. It led to a highly significant value of Fis (within-sample heterozygote deficit) in the western zone of Sideradougou area in Burkina Faso. Genetic differentiation was significant on a macrogeographic scale, i.e. between tsetse coming from Senegal and Burkina Faso. Wing measures also differed between these two countries; flies from Senegal appeared to be smaller. Microsatellite loci further allowed differentiation of populations of G. palpalis gambiensis trapped on the same hydrographic network a few kilometres apart. The results are interpreted as indicating that further investigations will allow the study of genetic variability of tsetse flies in relation to the dynamics of transmission of human and animal trypanosomoses.     

Cuticular hydrocarbon composition and phenotypic variability in sympatric populations of Ixodes ricinus ticks from Poland

Gas chromatography of cuticular hydrocarbons was used to assess genetic similarity and heterozygosity between 18 sympatric populations of adult Ixodes ricinus ticks collected from Poland. Sixteen n-alkanes, 45 monomethylalkanes, and 36 dimethylalkanes were identified. Forty-one compounds were detected in 90% of the specimens and nine hydrocarbons were present in all the specimens studied. Visual inspection of chromatograms revealed major differences in the relative abundance of hydrocarbons between populations of I. ricinus. The average proportion of heterozygotic hydrocarbons was 50.68%, while the average genetic similarity among all populations was 0.967. Two other methods were used to measure the intrapopulation variability: the number of isomeric forms for each hydrocarbon and the range of hydrocarbon abundance. It was found that some hydrocarbons manifested an unexpectedly high number of isomeric patterns, such as nonacosane (21 patterns), triacontane (23), pentacosane (26), and hexacosane (28). Our data suggest that I. ricinus ticks from Poland consist of several interbreeding, non-isolated populations, with a high degree of genetic flow between them.     

Genetic variation in natural populations of Anthurium sinuatum and A. pentaphyllum var. pentaphyllum (Araceae) from north‐east Brazil using AFLP molecular markers

Genetic variation was investigated using AFLP markers in 12 populations of Anthurium sinuatum and A. pentaphyllum var. pentaphyllum (Araceae) in north‐east Brazil, Amazonia and the Brazilian Atlantic forest. Two unique genetic patterns characterized the populations of A. sinuatum as a group, but no correlation between genetic and geographical interpopulation distance was found; the Amazonian population was not separated from that in Ceará. The isolated Ceará brejo populations of A. sinuatum were genetically distinct, but genetic diversity levels were similar to populations elsewhere, with no evidence of genetic erosion. Anthurium pentaphyllum populations were significantly different from each other; Bayesian genetic structural analysis found no common genetic pattern, but revealed genetic clusters unique to subgroups and individual populations in the Atlantic forest and French Guiana. Anthurium pentaphyllum and A. sinuatum can be distinguished genetically, but individuals of both species formed intermediate genetic clusters that blurred their distinction. We suggest that genetic mixing of A. sinuatum and A. pentaphyllum has occurred in north‐east Brazil, possibly connected with cycles of humid forest expansion. The weak genetic structure in A. sinuatum is consistent with the natural fragmentation of continuous forest areas, possibly during the Holocene. This study highlights the scientific importance of the highly threatened brejo forests for tropical American biogeography. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 88–105.     

The decay of genetic variability in geographically structured populations. II

The ultimate rate of approach to equilibrium in the infinite stepping-stone model is calculated. The analysis is restricted to a single locus in the absence of selection, and every mutant is assumed to be new to the population. Let f(t, x) be the probability that two homologous genes separated by the vector x in generation t are the same allele. It is supposed that $\text{f(}\text{0, x}\text{) = O(x}{}^{\mathrm{?2?\eta }}\text{), η > 0,}\text{as}\text{x ≡ ¦}\text{x}\text{¦ → ∞}$. In the absence of mutation, f(t, x) tends to unity at the rate $\text{t}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$ in one dimension and (ln t)^?1 in two dimensions. Thus, the loss of genetic variability in two dimensions is so slow that evolutionary forces not considered in this model would supervene long before a two-dimensional natural population became completely homogeneous. If the mutation rate, u, is not zero f(t, x) asymptotically approaches equilibrium at the rate $\text{(1 ? u)}{}^{\mathrm{2t}}\text{t}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ in one dimension and (1 ? u)^2tt^?1(lnt)^?2 in two dimensions. Integral formulas are presented for the spatial dependence of the deviation of f(t, x) from its stationary value as t → ∞, and for large separations this dependence is shown to be (const + x) in one dimension and (const + ln x) in two dimensions. All the results are the same for the Malécot model of a continuously distributed population provided the number of individuals per colony is replaced by the population density. The relatively slow algebraic and logarithmic rates of convergence for the infinite habitat contrast sharply with the exponential one for a finite habitat.     

Factors affecting levels of genetic diversity in natural populations.

Genetic variability is the clay of evolution, providing the base material on which adaptation and speciation depend. It is often assumed that most interspecific differences in variability are due primarily to population size effects, with bottlenecked populations carrying less variability than those of stable size. However, we show that population bottlenecks are unlikely to be the only factor, even in classic case studies such as the northern elephant seal and the cheetah, where genetic polymorphism is virtually absent. Instead, we suggest that the low levels of variability observed in endangered populations are more likely to result from a combination of publication biases, which tend to inflate the level of variability which is considered ''normal'', and inbreeding effects, which may hasten loss of variability due to drift. To account for species with large population sizes but low variability we advance three hypotheses. First, it is known that certain metapopulation structures can result in effective population sizes far below the census size. Second, there is increasing evidence that heterozygous sites mutate more frequently than equivalent homozygous sites, plausibly because mismatch repair between homologous chromosomes during meiosis provides extra opportunities to mutate. Such a mechanism would undermine the simple relationship between heterozygosity and effective population size. Third, the fact that related species that differ greatly in variability implies that large amounts of variability can be gained or lost rapidly. We argue that such cases are best explained by rapid loss through a genome-wide selective sweep, and suggest a mechanism by which this could come about, based on forced changes to a control gene inducing coevolution in the genes it controls. Our model, based on meiotic drive in mammals, but easily extended to other systems, would tend to facilitate population isolation by generating molecular incompatabilities. Circumstances can even be envisioned in which the process could provide intrinsic impetus to speciation.     

Nucella lapillus: A possible model for the study of genetic variation in natural populations

The explanation of the maintenance of the large amount of genetic variation in natural populations is a major problem faced by evolutionary geneticists. It is proposed that Nucella lapillus would make a suitable model for the study of this problem. The presence of visible interpopulation variation in characteristics which can be utilised for such studies, is demonstrated at a particular geographic location. The importance of experimental design in studying genetic variation is emphasised.