Triploids can play an important role in polyploid evolution. However, their frequent sterility is an obstacle for the origin and establishment of neotetraploids. Here we analyzed the microsporogenesis of triploids (x = 7) and the crossability among cytotypes of Turnera sidoides, aiming to test the impact of triploids on the origin and demographic establishment of tetraploids in natural populations. Triploids of T. sidoides exhibit irregular meiotic behavior. The high frequency of monovalents and of trivalents with non-convergent orientations results in unbalanced and/or non-viable male gametes. In spite of abnormalities in chromosome pairing and unbalanced chromosome segregation, triploids are not completely sterile and yielded up to 67% of viable pollen. Triploids that originated by the fusion of 2n × n gametes of the same taxon showed more regular meiotic behavior and higher fertility than triploids from the contact zone of diploids and tetraploids or triploids of hybrid origin. The reproductive isolation of T. sidoides cytotypes of different ploidy level is not strict and the 'triploid block' may be overcome occasionally. Triploids of T. sidoides produce diploid and triploid progeny suggesting that new generations of polyploids could originate from crosses between triploids or from backcrosses with diploids. The capability of T. sidoides to multiply asexually by rhizomes, would enhance the likelihood that a low frequency of neopolyploids can be originated and maintained in natural populations of T. sidoides.
Turnera sidoides is a complex of outcrossing, perennial, rhizomatous herbs that is widely distributed in southern South America. Five subspecies are recognized taxonomically based on morphological features and geographical distribution. In certain regions, the areas of distribution of the subspecies overlap partially. In such contact zones, the extent of reproductive barriers among subspecies is still largely unknown, but morphologically intermediate individuals have been found in the field, indicating that hybridization may actually occur between subspecies. Crossability among subspecies of T. sidoides has been shown by experimental studies with cultivated plants, but the mechanisms involved in natural populations are still unknown. To investigate the mechanisms that underlie gene flow within the T. sidoides complex, in this paper we analyze the morphological and genetic variation, as well as the crossability among taxa in a contact zone between subspecies pinnatifida and sidoides, in southeastern Uruguay. Our results constitute the first evidences of ongoing natural hybridization between subspecies of T. sidoides and suggest that, although hybridization may not have been of significance in the early phase of the species differentiation, reticulate evolution is ongoing enhancing the current morphological and genetic variability of the complex.
The evolutionary processes that shape the unique biodiversity of the Neotropical Chaquean Domain are still poorly understood, and choosing an appropriate model to address evolutionary questions is essential for understanding the current patterns of Chaquean diversity. We used the Turnera sidoides autopolyploid complex as a model to assess current and past environmental factors and the processes that shaped and maintain its intraspecific variation in the Chaquean Domain. Based on current and past niche modelling, cytogeographical and genetic divergence analyses, we provide strong evidence that the T. sidoides complex has been in an active process of intraspecific allopatric diversification at the diploid level since the early Pleistocene. Further diversification of the complex involved the emergence of independent polyploid series in each morphologically divergent lineage. Cytotypes in each series do not differ in diagnostic morphological traits, but are reproductively isolated and have different ecological requirements. Currently, each subspecies/morphotype and cytotype are true species according to the biological, evolutionary and ecological concepts; however, they are still considered to be the same morphological species. Our study has clarified the effect of the complex processes of diversification occurring in the Chaquean Domain on T. sidoides and that much diversity is overlooked when only the morphological species concept is considered when estimating the diversity of Neotropical ecoregions.
The lowlands of mid-latitude South America comprise complex temperate ecoregions characterized by a unique biodiversity. However, the processes responsible for shaping its species diversity are still largely unknown. Turnera sidoides subsp. carnea is a variable subspecies occurring in the lowlands of northeastern Argentina and Uruguay, extending to southern Paraguay and Brazil. It constitutes a good model to perform evolutionary studies. Here we used an integrative approach to understand the process of diversifi cation within this subspecies and to increase the knowledge concerning patterns and processes responsible for shaping the species diversity in the temperate lowlands of South America. The results provided strong evidences that this subspecies is an autopolyploid complex per se, being in an active process of intrasubspecifi c diversifi cation. Morphological and genetic data show that the diversity of T. sidoides subsp. carnea is in congruence with the great past and present abiotic and biotic variability of the mid-latitude South American lowlands. The evolutionary history of this subspecies is consistent with past fragmentation and allopatric differentiation at diploid level. Geographic isolation and local adaptation would have promoted strong morphological, ecological, and genetic differentiation, resulting in two morphotypes and different genetic groups indicative of incipient speciation.
Turnera sidoides (x=7) is one of the few well-studied South American autopolyploid complexes. Since polyploidy has played a prominent role within this complex, ongoing studies in T. sidoides focus on understanding the mechanisms involved in the origin and the establishment of polyploids using integrative approaches. This paper synthesises the results of more than 20 years of research on this topic. Cytogenetics analysis provided evidences for the production of unreduced male and female gametes, supporting the hypothesis of bilateral sexual polyploidization as the mechanism of origin of polyploids in T. sidoides. The finding of viable triploids suggested that unilateral sexual polyploidization could also be an important mechanism for the origin of tetraploids in T. sidoides. The occurrence of plants continuously forming many unreduced gametes would play a key role in the establishment of neopolyploids in natural populations. Also, the higher number of propagules that tetraploids contribute to subsequent generations, the ability to multiply asexually by rhizomes, and the occurrence of occasional cases of self-compatibility and successful illegitimate crosses in polyploids increase the likelihood that a low frequency of neopolyploids can be maintained in natural populations of T. sidoides. In addition, integration of cytogeographic and genetic divergence data together with past niche modelling provided further insights supporting the hypothesis that historical climatic and geomorphological events provided favourable conditions for the establishment of autopolyploids, with the wider distribution of tetraploids of T. sidoides being the result of their range expansion. Key words: cytogeography, establishment, origin, polyploidy, unreduced gametes
Este trabajo evaluó la tasa de crecimiento micelial (Kr) y la producción de basidiomas de dos cepas comerciales del hongo shiitake Lentinula edodes (B05 y M3790) en formulaciones compuestas de residuos lignocelulósicos procedentes de actividades agrícolas y agroindustriales de la región andina de Patagonia Norte y de materiales leñosos de plantas invasoras. Las formulaciones consistieron de un sustrato base, como chips de madera de sauce (ChS), chips de madera de rosa mosqueta (ChRM), pelusa de rosa mosqueta (PRM) o virutas de lenga (VL), mezclado con un suplemento, como salvado de trigo (ST) o bagazo de cebada cervecera (BC). Las dos cepas evaluadas mostraron mayores Kr con ChRM-ST. La producción de basidiomas tuvo lugar lo largo de 1 a 4 oleadas, durante un máximo de 124 días. Las máximas eficiencias biológicas (EB) se obtuvieron con la cepa M3790, destacándose ChS (118,86%) y VL (88,73%), ambos suplementados con ST. La cepa B05 alcanzó las máximas EB con ChS-ST (54,72%) y con ChRM-BC (50,43%). Los resultados obtenidos especialmente con ChRM y ChS, sumado a su abundancia en Patagonia argentina, sugieren que estos materiales pueden ser aprovechados como sustratos para la producción comercial de shiitake, actividad aún no desarrollada a gran escala en la región.
Twenty-four populations of Turnera sidoides were analysed, using seed storage protein fingerprinting techniques, including 19 populations of Turnera spp. and three of Piriqueta spp. for comparative purposes. The aim was to characterize the T. sidoides complex and to evaluate its profiles as a character to clarify its taxonomic position, as well as its evolutionary relationships within the genus Turnera. The present work is the first comparative study of the seed protein fingerprint in Turneroideae. The results proved that seed proteins are useful characters to discriminate between genus and species, as well as to characterize them. The finding of exclusive bands in Turnera and Piriqueta are evidence for the existence of genetic differences between genera, and support their taxonomic identity. Our results are in agreement with evolutionary tendencies of karyotype proposed for Turnera, and support the close relationships between species belonging to the same series, except T. sidoides, which should be singled out of Leiocarpae, supporting the proposal of its inclusion in an independent series.
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