Viviana G. Solís Neffa

Combined effects of environment and grazing on vegetation structure in Argentine granite grasslands

Abstract Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence-lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing-related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long-term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long-term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation-environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.

Diversification in the South American Pampas: the genetic and morphological variation of the widespread Petunia axillaris complex (Solanaceae)

Understanding the spatiotemporal distribution of genetic variation and the ways in which this distribution is connected to the ecological context of natural populations is fundamental for understanding the nature and mode of intraspecific and, ultimately, interspecific differentiation. The Petunia axillaris complex is endemic to the grasslands of southern South America and includes three subspecies: P. a. axillaris, P. a. parodii and P. a. subandina. These subspecies are traditionally delimited based on both geography and floral morphology, although the latter is highly variable. Here, we determined the patterns of genetic (nuclear and cpDNA), morphological and ecological (bioclimatic) variation of a large number of P. axillaris populations and found that they are mostly coincident with subspecies delimitation. The nuclear data suggest that the subspecies are likely independent evolutionary units, and their morphological differences may be associated with local adaptations to diverse climatic and/or edaphic conditions and population isolation. The demographic dynamics over time estimated by skyline plot analyses showed different patterns for each subspecies in the last 100 000 years, which is compatible with a divergence time between 35 000 and 107 000 years ago between P. a. axillaris and P. a. parodii, as estimated with the IMa program. Coalescent simulation tests using Approximate Bayesian Computation do not support previous suggestions of extensive gene flow between P. a. axillaris and P. a. parodii in their contact zone.

Geographic patterns of morphological variation in Turnera sidoides subsp. pinnatifida (Turneraceae).

With the objective of contributing to understanding the patterns of variation within the Turnera sidoides complex, a detailed evaluation of morphological variation along the range of T. sidoides subsp. pinnatifida was performed. A multivariate analysis based on leaf traits and flower colour data enabled differentiation of five morphotypes. Common-garden experiments demonstrated that the morphological variants have a strong genetic basis. It was also found that the morphotypes are geographically structured along the subspecies range, display different habitat preferences, and occur in regions with different climatic regimes. Although these results are suggestive of adaptive differentiation of T. sidoides subsp. pinnatifida, comparisons between morphological and bioclimatic ordinations showed that the patterns observed cannot be fully explained by current climatic conditions. It is proposed that Miocene–Pleistocene events may explain the origin of the five morphotypes and that current climatic and ecological factors may be contributing to the maintenance of the extent and patterns of morphological differentiation in T. sidoides subsp. pinnatifida.With the objective of contributing to understanding the patterns of variation within the Turnera sidoides complex, a detailed evaluation of morphological variation along the range of T. sidoides subsp. pinnatifida was performed. A multivariate analysis based on leaf traits and flower colour data enabled differentiation of five morphotypes. Common-garden experiments demonstrated that the morphological variants have a strong genetic basis. It was also found that the morphotypes are geographically structured along the subspecies range, display different habitat preferences, and occur in regions with different climatic regimes. Although these results are suggestive of adaptive differentiation of T. sidoides subsp. pinnatifida, comparisons between morphological and bioclimatic ordinations showed that the patterns observed cannot be fully explained by current climatic conditions. It is proposed that Miocene–Pleistocene events may explain the origin of the five morphotypes and that current climatic and ecological factors may be contributing to the maintenance of the extent and patterns of morphological differentiation in T. sidoides subsp. pinnatifida.

Karyotypic studies in Turnera sidoides complex (Turneraceae, Leiocarpae).

Turnera sidoides, with the most southerly distribution of all Turnera species in America, is a complex of obligately outcrossing perennial herbs. Karyotypes of the five subspecies of T. sidoides (x = 7) are described for the first time utilizing root-tip mitotic metaphases. Different ploidy levels were found for all of the subspecies, ranging from diploid to octoploid. The results obtained, coupled with available meiotic and preliminary biosystematic data, support the hypothesis of autopolyploidy within this species complex. Although detailed karyotype analysis shows a high degree of intraspecific uniformity, subspecies may be differentiated by the number, type, and position of satellites, suggesting that chromosome rearrangements may also be involved in the karyotypic evolution of T. sidoides. Karyotype data, coupled with morphological and anatomical features, suggest the removal of T. sidoides from series Leiocarpae.

Genomic Relationships between Turnera krapovickasii (2x, 4x) and T. ulmifolia (6x) (Turneraceae, Turnera)

Abstract Interspecific crosses between two species of the Turnera ulmifolia complex with yellow flowers have been carried out. As a result, two hybrids were obtained: T. krapovickasii (K4) x T. ulmifolia (U), 2n = 4x=20 and T. ulmifolia (U) x T. krapovickasii (K5), 2n = 5x=25. The hybrids were cytologically studied in order to determine their genomic relationships. The chromosome pairing data of hybrids indicates that T. ulmifolia is a segmental allopolyploid and, on the basis of the results obtained, the genomic constitution AuAuBaBaBuBu is proposed for this species. The cytological analysis of the tetraploid hybrid has also revealed the presence of PMCs with 2n = 40 that should have been formed by pre-meiotic chromosome doublings and would give rise to the formation of fertile 2n gametes. From this finding, it is suggested that, in the genus Turnera, unreduced gametes may result from at least two mechanisms: (1) premeiotic doubling and (2) meiotic nuclear restitution.

Evolutionary Relationships between the Diploid Turners grandiflora and the Octoploid T. fernandezii (Turneraceae)

Aiming to analyze the evolutionary relationships between the diploid species Turnera grandiflora (2n = 2x = 10) and the octoploid T. fernandezii (2n = 8x = 40), inter-specific hybrids were recovered by in vitro embryo rescue methods. The full-grown plants obtained were all pentaploids (2n = 5x = 25) confirming their hybrid nature. The chromosome associations observed in the hybrids during meiosis were indicative for an autopentaploid, suggesting that T. fernandezii carries the genome of T. grandiflora (CgCg) but at the octoploid level (CgCg CgCg CgCg CgCg). This fact confirms a close evolutionary relationship between the species and supports the hypothesis that T. grandiflora is the progenitor of T. fernandezii. A tentative hypothesis regarding the autopolyploid origin of T. fernandezii is finally formulated.

Morphometric analysis of Schizachyrium condensatum (Poaceae) and related species

Our aim was to assess the degree of morphological differentiation of a group of taxa of Schizachyrium Nees, which presents similar inflorescences and shares habitat and geographic areas: Schizachyrium bimucronatum, S. condensatum, S. lactiflorum, S. microstachyum subsp. microstachyum, S. microstachyum subsp. elongatum, and S. plumigerum. To accomplish this purpose, 22 exomorphological traits were analyzed using multivariate methods. The results obtained support the identity of Schizachyrium condensatum and related species as independent taxa. In addition, the analysis evidences the reliability of several inflorescence characters, which had not been previously considered in the identification of the different taxa. Based upon the information obtained, a new identification key for these taxa was constructed.

Karyotype analysis of some Paullinieae species (Sapindaceae)

Abstract The karyotypes of four species of South American Paullinieae-Sapindaceae are analized for the first time: Paullinia coriacea, 2n= 24= 16m + 6sm + 2st; Serjania cissoides, 2n= 24= 18m + 2sm + 4st ; S. suborbicularis, 2n= 24= 12m + 8sm + 4st and the diploid cytotype of U. ulmacea 2n= 2x= 22= 16m + 6sm. The significance of the results are discussed in relation to previous information for these genera and also in regard to the systematics treatment of this tribe.

Identity of Schizachyrium sulcatum and S. brevifolium (Poaceae: Andropogoneae)

Schizachyrium sulcatum, distributed in Brazil, Bolivia and Colombia, is described, illustrated, and reported for the first time from Peru and Venezuela. Synonymy, geographical distribution, ecology, and a list of representative specimens examined are provided. Characters of taxonomic value are established in order to differentiate this species fromS. brevifolium. A comparative study based on morphology, leaf anatomy, and micromorphological features of the spikelets and leaf blade are included. The multivariate analysis based on morphological variables allowsS. sulcatum to be distinguished clearly fromS. brevifolium.

Variabilidad genética en poblaciones de Elionurus muticus (Poaceae) de Corrientes, Argentina, a partir de marcadores moleculares de ADN nuclear y cloroplástico.

Genetic variability in populations of Elionurus muticus (Poaceae) from Corrientes, Argentina, based on molecular markers of nuclear and chloroplastic DNA. Elionurus muticus constitutes a valuable renewable resource; it is used as forage, soil fixer, clothing flavoring, to drive away moths, as antiseptic, against gonorrhea and urinary problems, for bronchitis, to cure leprosy, among other uses. In addition, due to its citral content, it has been proposed as a surrogate for essential oils, such as citronella. Despite its potential, there are few works of genetic characterization of this species. In this work, we genetically characterize populations of E. muticus from Corrientes (Argentina), using molecular markers RAPD and cpDNA. Results show genetic variability in populations, which would be the results of genetic drift, a history of population reduction and the reproduction types of the species. Since, in previous works in Argentinian populations, it was found morphological variability and in the ability to produce oils, a joint analysis of morphological, chemical and genetic variability, in a bigger number of populations, representative of the entire area of distribution of the species, will enrich the knowledge about the state of the current genetic resources of E. muticus, and will contribute to the enhancement of the species as a natural resource and as a potential crop for sustainable commercial use.