Abstrac Background and aims: The genus Acacia has a pantropical distribution and currently consists in approximately 1.450 species throughout the world. In Argentina the species belong to two subgenera: Acacia and Aculeiferum. In this work the morphology of two species was studied, one belonging to the first subgenus, Acacia caven var. caven and Acacia bonariensis, corresponding to the second one. The aim of this study was to evalúate the interspecific and ¡ntraspecific variation based on 12 exomorphological traits. The hypothesis was that the selected traits were able to differentiate species and populations. M&M: The study was based on the Kruskal Wallis test and several analyses with multivariate methods. Results: The Kruskal Wallis test found that nine characters were able to differentiate the species and one the populations. From the multivariate analyses the result was that, except for one character, the remaining ones were significant for the interspecific differentiation. Conclusions: This showed a clear separation between species according to the taxonomic classification already established. However, no differences between reserves could be evidenced for either of the species with these methods. In conclusion, these analyses set a precedent for future studies including more natural populations and the genetic study of the differentiation at molecular level.

Abstract In order to elucidate the role of evolutionary forces in shaping the variation of quantitative traits in Senegalia gilliesii we evaluate seven phenotypic traits in three Argentinean populations, two of them sharing environmental and vegetation type conditions, and a third one ecologically differentiated from the former. The phenotypic traits were compared with molecular markers. Here, we search for signatures of selection by means of the comparison PST-FST. We assessed if the averages of the seven phenotypic traits were different among populations by means of ANOVA and we performed discriminant analysis of principal components (DAPC) for both morphological and molecular data. The ANOVA showed significant results only for two traits. For all foliar traits and two spine traits, the PST-FSTcomparison suggested the occurrence of stabilizing selection. The DAPC obtained from AFLP data showed three well defined groups of populations; when the same analysis was conducted with morphological data the scatterplot showed high overlapping among individuals and could not separate the populations. Overall, our findings suggest a prominent role of stabilizing selection in all foliar traits and stipular spine length. These results could be extrapolated to other tropical and subtropical acacias. Further studies are needed to analyse the mechanisms underlying genetic differentiation in natural populations of S. gilliesii, find its relationship with eco-geographical variables.

Bayesian clustering as implemented in STRUCTURE or GENELAND software is widely used to form genetic groups of populations or individuals. On the other hand, in order to satisfy the need for less computer-intensive approaches, multivariate analyses are specifically devoted to extracting information from large datasets. In this paper, we report the use of a dataset of AFLP markers belonging to 15 sampling sites of Acacia caven for studying the genetic structure and comparing the consistency of three methods: STRUCTURE, GENELAND and DAPC. Of these methods, DAPC was the fastest one and showed accuracy in inferring the K number of populations (K = 12 using the find.clusters option and K = 15 with a priori information of populations). GENELAND in turn, provides information on the area of membership probabilities for individuals or populations in the space, when coordinates are specified (K = 12). STRUCTURE also inferred the number of K populations and the membership probabilities of individuals based on ancestry, presenting the result K = 11 without prior information of populations and K = 15 using the LOCPRIOR option. Finally, in this work all three methods showed high consistency in estimating the population structure, inferring similar numbers of populations and the membership probabilities of individuals to each group, with a high correlation between each other.

In the present work, isoenzyme electrophoresis was used to analyze the variability and phenetic relationships among seven American species of genus Prosopis belonging to three different sections: P. argentina (Monilicarpa), P. glandulosa, P. velutina, P. flexuosa, P. ruscifolia, P. kuntzei (Algarobia), and P. reptans (Strombocarpa). The genetic variability in P. argentina, P. reptans, and P. kuntzei was significantly lower than in the rest of the species analyzed. The species belonging to different sections are highly differentiated, but the relationships retrieved among species belonging to the section Algarobia suggested that the series of this section are not natural groups. P. kuntzei is as differentiated from the remaining species of Algarobia as from P. reptans or P. argentina, suggesting that this species might be included in a different section. The series within section Algarobia are not supported by the clusters retrieved in the phenogram based on isoenzymatic data. The results suggest that the two North American species (P. velutina and P. glandulosa) would have originated in different founder events.

Técnicas de análise por alozimas e DNA polimórfico aleatoriamente amplificado (RAPD) foram comparadas quanto a sua utilidade para estudos genéticos e taxonômicos em populações de Prosopis glandulosa e P. velutina. Isozimas e RAPD deram estimativas igualmente elevadas de variabilidade genética. A estrutura genética e a diferenciação foram analisadas pelo índice F DT não hierárquico de Wright (1978). Para todas as populações consideradas, ambos os marcadores produziram estimativas baixas do fluxo de genes (Nm < 1). Quando apenas as populações de P. glandulosa foram analisadas, os dados de isozima deram estimativas do fluxo gênico mais elevadas (Nm > 1), em concordância com o esperado para populações co-específicas. Contudo, com os dados de RAPD a redução esperada em F DT e o aumento em Nm não foram observados. A correlação entre F DT e as matrizes de distância geográfica (teste de Mantel) para todas as populações foi significante (P = 0,02) quando baseada em isozimas, mas não tanto (P = 0,33) quando baseada em RAPD. Não foram observadas associações significantes entre variáveis genéticas e geográficas ou climáticas. Dois sistemas isoenzimáticos (GOT e PRX) possibilitaram a distinção entre P. glandulosa e P. velutina, mas não foram detectadas por RAPD bandas diagnósticas para o reconhecimento de populações ou espécies aqui estudadas. Contudo, os marcadores de RAPD mostraram valores mais elevados para a diferenciação genética entre populações co-específicas de P. glandulosa e um coeficiente de variação menor do que aqueles obtidos a partir de isozimas.

Allozyme and random amplified polymorphic DNA (RAPD) techniques have been compared for their usefulness for genetic and taxonomic studies in Prosopis glandulosa and P. velutina populations. Isozymes and RAPDs yielded similarly high estimates of genetic variability. Genetic structure and differentiation were analyzed through non-hierarchical Wright's F DT. For all populations considered, both markers produced low gene flow (Nm < 1) estimates. When only P. glandulosa populations were analyzed, isozyme data yielded higher gene flow estimates (Nm > 1), in agreement with that expected for conspecific populations. However, in RAPD data the expected reduction in F DT and the increase in Nm were not observed. Correlation between F DT and geographical distance matrices (Mantel test) for all populations was significant (P = 0.02) when based on isozymes, but not so (P = 0.33) when based on RAPDs. No significant associations among genetic and geographical or climatic variables were observed. Two isoenzyme systems (GOT and PRX) enabled us to distinguish between P. glandulosa and P. velutina, but no diagnostic band for recognition of populations or species studied here were detected by RAPD. However, RAPD markers showed higher values for genetic differentiation among conspecific populations of P. glandulosa and a lower coefficient of variation than those obtained from isozymes.

The way in which genetic variability is distributed within and among populations depends on different factors, outstanding among these are the reproductive system and the adaptive strategy. Population structure, in turn, imposses restrictions to those evolutionary processes tending to a growing adaptation to the environment and/or specific differentiation. Studies on population structure were made for the Prosopis genus and the genetic differentiation was analyzed for 15 species of Algarobia, Strombocarpa and Monilicarpa Sections using isoenzyme techniques, RAPD, RFLP and DNA sequenciation. The linkage system was analyzed in 7 species of the Algarobia Section from data obtained from isoenzyme electrophoresis, which showed that although these species are mostly exogamous they can reach up to 28% of self-fecundation, with an average of 19%. This behaviour and the limited capacity for pollen and seed dispersal determine an excess of homozygotes in the populations. Except for P. kuntzei, Algarobia species are closely related, independently of their ploidy level and geographical distribution, and are not grouped according to series. Species in the Strombocarpa Section exhibit much lower variability than those in Algarobia. P. argentina (Monilicarpa Section) is the most distinctly differentiated of the species studied to date. Natural hybridation is frequent among species of the Algarobia Section. This phenomenon and the great similarity among these species make their recognition difficult. The results obtained using RFLP techniques in mitocondria and cloroplasts confirm the great affinity among Algarobia species, and provide evidence that they would have a common origin.

La forma en que se distribuye la variabilidad genética dentro y entre poblaciones depende de diferentes factores entre los que se puede mencionar el sistema reproductivo y la estrategia adaptativa. La estructura de las poblaciones, a su vez, establece restricciones a los procesos evolutivos tendientes a la adaptación creciente al ambiente y/o la diferenciación específica. Los marcadores bioquímicos y moleculares constituyen herramientas para evaluar la proporción de la diversidad genética en entidades de complejidad creciente. Esta información permite hacer inferencias acerca de los mecanismos evolutivos que podrían haber conducido al escenario actual. En el género Prosopis se realizaron estudios de estructura poblacional y se analizó la diferenciación genética en 15 especies de la Sección Algarobia, Strombocarpa y Monilicarpa utilizando las técnicas de isoenzimas, RAPD, RFLP y Secuenciación de ADN. En siete especies de la sección Algarobia se analizó, a partir de datos provenientes de electroforesis de isoenzimas, el sistema de apareamiento, pudiendo demostrarse que aunque éstas son mayormente exógamas, pueden presentar hasta un 28% de autofecundación, con un promedio del 19%. La variabilidad genética en especies de Algarobia es alta, pero tiende a ocurrir dentro de las poblaciones. Por esta razón con muestras de pocas poblaciones se cubre la mayor parte de la variación genética detectada por isoenzimas y por la técnica de RAPD. Con excepción de P. kuntzei, las especies de Algarobia son muy afines entre sí independientemente de su nivel de ploidía y distribución geográfica y las mismas no se agrupan de acuerdo con las series. En las especies estudiadas de la sección Strombocarpa la variabilidad es mucho menor que en Algarobia. Estas especies se diferencian mucho entre sí y se separan claramente de las de Algarobia. Finalmente P. argentina (secc. Monilicarpa) es la especie más diferenciada de las estudiadas hasta el presente. La hibridación natural es un hecho frecuente entre especies de la sección Algarobia. La técnica de RAPD ha permitido obtener bandas marcadoras de especie que podrían utilizarse para inferir los progenitores putativos de híbridos naturales. Finalmente los resultados obtenidos por las técnicas de RFLP de mitocondrias y cloroplastos, así como la de secuenciación de un fragmento de este último plástido han permitido estudios cladísticos que confirman la alta afinidad entre especies de Algarobia y brindan evidencias de que las mismas tendrían un origen común.