Ameaçada, rara e diversa : avaliação genômica revela linhagem críptica em espécie dos campos sulinos

A Serra do Sudeste é considerada um centro de diversidade do gênero Petunia, com a distribuição de duas espécies endêmicas e outras duas de ampla distribuição. Petunia secreta é uma espécie com distribuição restrita apenas à localidade denominada Pedra do Segredo. A espécie é classificada como rara, endêmica e em perigo de extinção. Em 2014, uma população numerosa, composta por indivíduos com morfologia similar à P. secreta, foi encontrada em um ambiente antropizado, na beira da rodovia BR-290. A caracterização genética desta população mostrou acentuada diferenciação em relação às populações da área original de descrição da espécie. Aqui realizamos uma investigação sobre a origem dessa população por meio de variações encontradas em nível genômico, comparando-a com populações naturais de outras espécies do gênero de ocorrência próxima à população de interesse. Os resultados sugerem inexistência de fluxo gênico com as espécies P. integrifolia e P. exserta; presença de um componente genético exclusivo à BR-290; compartilhamento parcial de polimorfismos com P. axillaris e P. secreta canônica. A análise da demografia histórica demonstrou que a linhagem BR-290 teria surgido a partir de um ancestral comum com P. secreta, com tempo de divergência estimado em 25 Kya, coincidindo com as mudanças climáticas do Pleistoceno. Desta forma, sugere-se que esta linhagem seja considerada uma forma independente e críptica a P. secreta, devendo ser tida como uma nova espécie no gênero e protegida como tal.Serra do Sudeste is considered a center of diversity of the genus Petunia, with the distribution of two endemic and two widely distributed species. Petunia secreta is narrowly distributed, restricted to the locality called Pedra do Segredo. The species is classified as rare, endemic, and endangered. In 2014, a large population, composed of individuals with a morphology similar to P. secreta, was found in an anthropized environment, on the side of the BR-290 highway. The genetic characterization of this population showed marked differentiation in relation to the populations of the original area of P. secreta description. Here, we carry out an investigation into the origin of this population based on variations at the genomic level, comparing natural populations of other Petunia species occurring close to the BR-290 population. The results suggested that there is no gene flow with P. integrifolia and P. exserta; BR-290 shows an exclusive genetic component; there is partial polymorphism sharing between BR-290 and P. axillaris and canonical P. secreta. The analysis of historical demography showed that the BR-290 lineage would have emerged from a common ancestor with P. secreta, with an estimated divergence time of 25 Kya, coinciding with the Pleistocene climate changes. Thus, it is suggested that this lineage should be considered as an independent and cryptic form of P. secreta, and should be considered as a new species in the genus and protected as such

Estruturação populacional geracional de Petunia axillaris, Petunia exserta e seus híbridos naturais na região de Guaritas, RS

A hibridação interespecífica é um processo evolutivo que ocorre naturalmente e frequentemente em espécies de plantas, sendo um dos principais eventos promotores de diversidade em Angiospermas. Na Serra do Sudeste, Rio Grande do Sul, região central do bioma Pampa, ocorrem duas espécies do gênero Petunia (Solanaceae). Estas são plantas herbáceas, anuais, que apresentam características morfológicas associadas a diferentes polinizadores. Petunia axillaris tem flores brancas e atrai mariposas para sua polinização; Petunia exserta possui flores vermelhas e é polinizada por beija-flores. Enquanto que as plantas da primeira espécie se distribuem por todo o Pampa, a segunda espécie é endêmica da Serra do Sudeste. O microambiente em que se desenvolvem também é diferente, com P. exserta crescendo no interior de cavernas nas torres areníticas que formam a região, enquanto P. axillaris ocorre nos topos e faces das mesmas torres ou em campos abertos no restante do Pampa. Indivíduos híbridos, com coloração da corola intermediária entre as duas espécies são observados em duas torres na Serra do Sudeste. O objetivo deste trabalho foi contribuir para o entendimento do processo de hibridação entre estas espécies na região de simpatria, sua origem e consequências. Para isto foram coletadas populações isoladas das duas espécies, compostas por indivíduos de morfologia típica de cada uma, e as duas populações de coocorrência, estas em duas gerações, 2011 e 2015. Estes indivíduos foram analisados através de sua caracterização morfológica quanto à cor da corola e por seus genótipos baseados em polimorfismos de microssatélites nucleares. Os resultados obtidos indicaram que cada zona de contato apresenta constituições morfológica e genética diferentes e que em ambos eventos de hibridação recente ocorrem a cada ano. Em ambos também foram evidentes eventos de introgressão e não foi observada correlação entre a cor da flor e a composição genética dos indivíduos híbridos.Interspecific hybridization is an evolutionary process occurring naturally and frequently in plant species, being one of the main diversity drivers in Angiosperm. In the Serra do Sudeste, Rio Grande do Sul, central region in the Pampas, two Petunia (Solanaceae) species occur in sympatry. These species are annual and herbaceous plants that display morphological characteristics associated to different pollinators. Petunia axillaris has white flowers and attracts moths, whereas P. exserta has red and hummingbird-pollinated flowers. The plants of P. axillaris are widely distributed throughout the Pampas and P. exserta is endemic to the Serra do Sudeste. The microenvironment in which these species grow is also different, with P. exserta inhabiting inside caves in arenitic towers that form the region, whereas P. axillaris occurs on top and faces of the same towers or in open fields in the rest of the Pampas. Hybrid individuals, with intermediary corolla colour (dark to pale pink), are observed in two towers in the Serra do Sudeste. The main aim of the present work was to understand the hybridization process between these species in the sympatric distribution and the origin and consequences of hybridization. For this, isolated populations of the two species were collected, composed only by typical individuals of each species, and the two co-occurrence populations, during two generations, 2011 and 2015. These individuals were analysed based on the corolla colour and polymorphisms of nuclear microsatellites. The results indicated that each contact zone has different morphological and genetic constitutions and that in both recent hybridization events occur every year. In both, introgression and ancient hybridization were detected and no correlation was observed between flower colour and the genetic composition of hybrid individuals

Species boundary and extensive hybridization and introgression in Petunia

Studying the role of hybridization in the speciation of plants is one of the most thrilling areas of evolutionary biology. Hybridization in natural populations can act in opposition to divergence, contribute to adaptation through introgression or foster the emergence of new lineages via hybrid speciation. Species of the plant genus Petunia grow in open areas in southern South America. Some natural interspecific hybrid events have been described for the genus, such as between the endemic P. exserta and the widespread P. axillaris. Both species occur in sympatry in Serra do Sudeste (Brazil), where they occur in diverse habitats and exhibit floral divergence, which has been related to the attraction of different primary pollinators. The present study evaluates the maintenance of the species boundaries front of hybridization and introgression. Direct and indirect methods of estimating gene exchange employed genotyping 720 reproductive plants and 611 progenies of both species with eight microsatellite loci. Gene exchange was found to be frequent and bidirectional between the species, indicating that introgression changes their genetic constitution in areas of sympatry. Limits of the studied species are being maintained because of the high level of inbreeding and backcrosses that are habitat-dependent

What could be the fate of secondary contact zones between closely related plant species?

Interspecific hybridization has been fundamental in plant evolution. Nevertheless, the fate of hybrid zones throughout the generations remains poorly addressed. We analyzed a pair of recently diverged, interfertile, and sympatric Petunia species to ask what fate the interspecific hybrid population has met over time. We analyzed the genetic diversity in two generations from two contact sites and evaluated the effect of introgression. To do this, we collected all adult plants from the contact zones, including canonicals and intermediary colored individuals, and compared them with purebred representatives of both species based on seven highly informative microsatellite loci. We compared the genetic diversity observed in the contact zones with what is seen in isolated populations of each species, considering two generations of these annual species. Our results have confirmed the genetic differentiation between the species and the hybrid origin of the majority of the intermediary colored individuals. We also observed a differentiation related to genetic variability and inbreeding levels among the populations. Over time, there were no significant differences per site related to genetic diversity or phenotype composition. We found two stable populations kept by high inbreeding and backcross rates that influence the genetic diversity of their parental species through introgression

Could the reproductive system explain the stability and long-term persistence in a natural hybrid zone of Petunia (Solanaceae)?

The long-term success of populations is dependent on individual reproductive success, and in general, increased population size and genetic diversity contribute to population maintenance, reducing the risk of local extinction. Interspecific hybridization has consequences that can vary according to the hybrids' fate, which can be strongly influenced by the reproductive capacity of hybrids and canonical individuals from the contact zone. We examined the reproductive biology and morphology of two closely related Petunia (Solanaceae) species and their interspecific hybrids from Serra do Sudeste, Southern Brazil, and we measured their reproductive success under controlled conditions based on seed production and germination from five pollination treatments. We found differences in self-compatibility degree among individuals, lineages, and pollination treatments based on high total seed production (> 204,000 seeds) and germination (630 seedlings evaluated). No correlation was observed between corolla colour and reproductive success or between floral morphological traits and compatibility. High self-compatibility and inter-lineage compatibility can explain the hybrid populations' maintenance and origin, favouring the two analysed species' introgression

Morphological and genetic perspectives of hybridization in two contact zones of closely related species of Petunia (Solanaceae) in southern Brazil

Interspecific hybridization has several consequences for parental species, from blurring species limits to the emergence of new taxa. Petunia axillaris and P. exserta occur in sympatry in southernmost Brazil and naturally hybridize despite their different pollination syndromes and habitat requirements. We employed genetic and morphological analyses to characterize two contact zones between the species with the aim of determining the effect of interspecific hybridization. Microsatellite loci and a morphometric evaluation of the corolla shape were used to classify individuals based on their origin as pure parental or hybrids. Corolla color was used to classify individuals a priori (white, red or intermediate, for P. axillaris, P. exserta or hybrid, respectively). Corolla color was found to be a good indicator of the genetic component of each species and their hybrid, while the shape of the corolla did not always correspond to genetic origin. Hybridization increased the variability, and introgression occurred in both directions in this system