RESUMEN
BACKGROUND AND AIMS: The balance between stochastic forces and frequency-dependent mating largely governs style morph frequencies in heterostylous populations. In clonal species, deviations from equal morph ratios often result from founder events and unfavourable conditions for sexual reproduction. The aim of this study was to investigate whether different flooding regimes, because of their influence on sexual vs. clonal reproduction, are associated with regional variation in morph frequencies and floral trait differentiation in populations of the clonal, tristylous, aquatic Eichhornia azurea (Pontederiaceae) in the Pantanal wetlands of Brazil. METHODS: Style morph frequencies were sampled from 73 populations distributed across four flooding regimes differing in depth and duration. Measurements of flower size, sex-organ dimension, pollen size and pollen production were made in selected populations, and pollinator assemblages and their functional traits were recorded. KEY RESULTS: Most populations of E. azurea were tristylous (78 %), but the majority exhibited uneven morph ratios. The frequency of the mid-styled morph was significantly lower than that of the long- and short-styled morphs. Morph evenness was positively associated with population size but not with flooding regime. There were significant phenotypic differences among flooding regimes for all floral traits, including populations with reduced flower size, sex-organ length and smaller pollen. Pollinator assemblages varied with flood duration. CONCLUSIONS: The similar morph structure and evenness of populations, regardless of flooding regime, suggest that sexual reproduction and clonal dispersal are sufficiently common to prevent the signature of founder events from dominating in a region. However, the pervasive occurrence of biased morph ratios in most populations suggests that many are in a non-equilibrium state. The reduced frequency of the mid-styled morph in trimorphic and dimorphic populations may be associated with the weak self-incompatibility of this morph resulting in selfing and inbreeding depression. Clonality in E. azurea and the weak self-incompatibility of the mid-styled morph may make it more vulnerable to geitonogamous selfing.
Asunto(s)
Organismos Acuáticos/fisiología , Eichhornia/anatomía & histología , Ambiente , Flores/anatomía & histología , Humedales , Animales , Brasil , Inundaciones , Geografía , Tamaño de los Órganos , Polen/anatomía & histología , Polinización , Densidad de Población , Carácter Cuantitativo HeredableRESUMEN
BACKGROUND: The glacial and interglacial cycles that characterized the Quaternary greatly affected the distribution and genetic diversity of plants. In the Neotropics, few phylogeographic studies have focused on coastal species outside of the Atlantic Rainforest. Climatic and sea level changes during the Quaternary played an important role in the evolutionary history of many organisms found in coastal regions. To contribute to a better understanding of plant evolution in this environment in Southern South America, we focused on Calibrachoa heterophylla (Solanaceae), an endemic and vulnerable wild petunia species from the South Atlantic Coastal Plain (SACP). RESULTS: We assessed DNA sequences from two cpDNA intergenic spacers and analyzed them using a phylogeographic approach. The present phylogeographic study reveals the influence of complex geologic and climatic events on patterns of genetic diversification. The results indicate that C. heterophylla originated inland and subsequently colonized the SACP; the data show that the inland haplogroup is more ancient than the coastal one and that the inland was not affected by sea level changes in the Quaternary. The major diversification of C. heterophylla that occurred after 0.4 Myr was linked to sea level oscillations in the Quaternary, and any diversification that occurred before this time was obscured by marine transgressions that occurred before the coastal sand barrier's formation. Results of the Bayesian skyline plot showed a recent population expansion detected in C. heterophylla seems to be related to an increase in temperature and humidity that occurred at the beginning of the Holocene. CONCLUSIONS: The geographic clades have been formed when the coastal plain was deeply dissected by paleochannels and these correlate very well with the distributional limits of the clades. The four major sea transgressions formed a series of four sand barriers parallel to the coast that progressively increased the availability of coastal areas after the regressions and that may have promoted the geographic structuring of genetic diversity observed today. The recent population expansion for the entire species may be linked with the event of marine regression after the most recent sea transgression at ~5 kya.
Asunto(s)
Petunia/genética , Filogeografía , Teorema de Bayes , Evolución Biológica , Brasil , Clima , Conservación de los Recursos Naturales , ADN de Cloroplastos/genética , ADN de Plantas/genética , Variación Genética , Fenómenos Geológicos , Océanos y Mares , UruguayRESUMEN
In the Southern and Southeastern Brazilian highlands, a clade of seven species of Petunia that are endemic to the region (P. altiplana, P. bonjardinensis, P. guarapuavensis, P. mantiqueirensis, P. reitzii, P. saxicola and P. scheideana) exists in association with grassland formations. These formations are isolated in high-altitude regions, being surrounded by forested areas, and experienced contraction-expansion cycles associated with the glacial cycles of the Pleistocene. To understand the evolutionary history of this group, the divergence of which is probably linked to these past shifts in habitat, we analysed the sequences of the plastidial intergenic spacers trnH-psbA and trnS-trnG from populations throughout the known distributions of all seven species. The common ancestor of this highland clade started to differentiate â¼0.9 million years (Myr) ago, which corresponds to a high diversification rate of 2.06 species per Myr in the intervening period. The high level of haplotype sharing among several species in the clade and the absence of reciprocal monophyly suggest the persistence of ancestral polymorphisms during speciation events and/or past hybridization, because no hybrid was found. Four of the five species displayed very low genetic diversity and possessed either one or two haplotypes, which is consistent with long-term isolation in restricted areas. The three more diverse species displayed significant population structure, and P. altiplana showed a clear signs of population growth during the last glacial period. These results suggest that diversification occurred as a result of expansion of the ancestral species of the clade during glacial periods followed by fragmentation and isolation during retraction in interglacial periods.
Asunto(s)
Evolución Molecular , Genética de Población , Petunia/genética , Filogeografía , Brasil , ADN de Cloroplastos/genética , ADN de Plantas/genética , ADN Espaciador Ribosómico/genética , Ecosistema , Variación Genética , Haplotipos , Filogenia , Análisis de Secuencia de ADNRESUMEN
Intrinsic reproductive barriers among the species of Petunia are weak and genetic isolation is obtained mainly by geographical separation and ecological diversification. The Serra do Sudeste region in the extreme south of Brazil is one of the centres of diversity of this genus and is characterized by the presence of species with different pollination syndromes. Petunia exserta is known only from four sandstone towers in a restricted area of this region (about 500 km(2)) and is characterized by its differentiated habitat (shelters in the sandstone towers) and by its floral characteristics adapted to ornithophily. In towers where this species is sympatric with the sphingophilous Petunia axillaris, phylogenetically close to P. exserta, we found plants with intermediate floral morphology, suggesting hybridization between them. To test this hypothesis and to better understand its consequences we analysed the sequences of the plastid trnH-psbA, trnS-trnG and psbB-psbH intergenic spacers in 121 individuals sampled all over the P. exserta distribution. The joint analysis of the three markers revealed 13 haplotypes and the network showed two main genetic clades, which probably represent the original gene pool of the two species in the region. In general, individuals of a given population presented the same haplotype, independently of phenotype, corroborating the hybridization hypothesis. Field observations suggest that hummingbirds are responsible for the interspecific gene flow. Analysis of molecular variance revealed high interpopulational diversity among the towers. The low gene flow between populations is possibly related to the autochoric seed dispersion system.
Asunto(s)
Ecología , Variación Genética , Hibridación Genética , Petunia/genética , Geografía , Haplotipos/genética , Dinámica PoblacionalRESUMEN
Four chloroplast (cp), one mitochondrial (mt), and one ribosomal nuclear (ITS) DNA regions were studied in four artificial and one natural interspecific Passiflora hybrids. The ITS results confirmed their hybrid origin and all mtDNAs were maternally inherited. The same, however, was not true for cpDNA. The four hybrids (three artificial and one natural) derived from species of the Passiflora subgenus showed a cpDNA paternal inheritance, while the one involving taxa of the Decaloba subgenus gave evidence of maternal transmission. These results are of significance for the ongoing studies which are being performed on the molecular evolution of this genus and furnish important background for investigations aimed at clarifying the factors which determine cpDNA inheritance.
Asunto(s)
ADN de Plantas/genética , Passiflora/genética , Secuencia de Bases , Cruzamientos Genéticos , ADN de Cloroplastos/genética , ADN Mitocondrial/genética , ADN Espaciador Ribosómico/genética , Evolución Molecular , Datos de Secuencia Molecular , Orgánulos/genética , Passiflora/clasificación , Homología de Secuencia de Ácido NucleicoRESUMEN
Representatives from 11 Petunia Jussieu species in south and southeast Brazil were compared with two Calibrachoa La Llave & Lex., one Bouchetia Dunal, and two Nierembergia Ruiz & Pav. taxa in relation to DNA molecular variability. A total of 4532 base pairs related to one nuclear, five plastidial and one mitochondrial systems was investigated. Petunia and Calibrachoa, although separated among themselves, clearly differentiate from the two other genera. Despite the fact that the Petunia species do not show marked molecular differences, they can be separated in two complexes, in good agreement with altitude data. Petunia + Calibrachoa should have diverged from other clades at about 25 million years before present.
Asunto(s)
Evolución Molecular , Genoma de Planta , Petunia/genética , Filogenia , Marcadores GenéticosRESUMEN
BACKGROUND AND AIMS: Passiflora actinia and P. elegans, two markedly parapatric species, have their southern and northern distribution limits, respectively, in the most southern part of the Brazilian Atlantic Rain Forest. Despite the fact that they are classified in different taxonomic series, previous phylogenetic studies of this genus revealed a high genetic similarity between them. The aim of the present work was to analyse in more detail their geographical range in this region of overlap, to investigate intraspecific genetic variability and phylogeographic structure, and to search for possible hybrids. METHODS: Eighty-two localities were searched for these species, and nuclear internal transcribed spacer (ITS) sequences were investigated for 32 individuals of P. actinia, 20 of P. elegans and one putative interspecific hybrid. Plastid trnL-trnF and psbA-trnH were examined for 12 plants of each species and the putative hybrid. KEY RESULTS: Both species showed a high level of intraspecific and intra-individual ITS variability. Network analysis revealed a north-south geographic gradient in their intra and interspecific relationships. Mismatch analyses suggested a recent population expansion of P. elegans. The plastid markers showed restricted variability but, together with the nuclear data, they contributed to the identification of an interspecific hybrid of intermediate morphology at the border of the distribution of these two species. Both genetic and morphological data indicate the absence of an extensive hybridization zone between these species. CONCLUSIONS: Gene flow between lineages is the possible cause for the presence of different ITS sequences within a given plant, the absence of homogenization being due to the high degree of vegetative reproduction in the two species. Differentiation of P. actinia into geographic groups and the origin of P. elegans may have been influenced by the Atlantic Forest migration towards southern Brazil. The genetic pattern of the interspecific hybrid indicates that plastid inheritance in these species is at least sometimes paternal.