Hybridization and introgression across different ploidy levels in the Neotropical orchidsEpidendrum fulgensandE. puniceoluteum(Orchidaceae)

Abstract

The hypothesis of gene flow between species with large differences in chromosome numbers has rarely been tested in the wild, mainly because species of different ploidy are commonly assumed to be reproductively isolated from each other because of instantaneous and strong postzygotic barriers. In this study, a broad-scale survey of molecular variation was carried out between two orchid species with different ploidy levels: Epidendrum fulgens (2n = 2x = 24 chromosomes) and Epidendrum puniceoluteum (2n = 4x = 52 chromosomes). To test the strength of their reproductive barriers, we investigated the distribution of genetic variation in sympatric and allopatric populations of these two species and conducted crossing experiments. Nuclear and plastid microsatellite loci were used to genotype 463 individuals from eight populations across the geographical range of both species along the Brazilian coastal plain. All six sympatric populations analysed presented hybrid zones, indicating that hybridization between E. fulgens and E. puniceoluteum is a common phenomenon. Bayesian assignment analysis detected the presence of F 1 and F 2 individuals and also signs of introgression, demonstrating a high potential for interspecific gene flow. Introgression occurs preferentially from E. fulgens to E. puniceoluteum. Pure parental individuals of both species display strong genotype-habitat associations, indicating that environment-dependent selection could be acting in all hybrid zones. This study suggests that hybridization and introgression are evolutionary processes playing a role in the diversification of Epidendrum and indicates the importance of investigations of hybrid zones in understanding reproductive barriers and speciation processes in Neotropical orchid species.

The Origin of Diversity in Begonia: Genome Dynamism, Population Processes and Phylogenetic Patterns

“…However, estimating the frequency of hybrid speciation is difficult, as evidence that hybridisation has let to speciation is hard to obtain, particularly in homoploid hybrids (hybrids without a change in ploidy level) (Mallet, 2007). The role that hybridisation has played in contributing new lineages in diverse tropical biomes has yet to be addressed in detail (with some exceptions such as neotropical orchids, eg Pinheiro et al, 2010), however hybrid speciation may be one of the factors contributing to species diversity in large genera such as Begonia. Support for hybridisation and introgression being a mechanism for the generation of diversity would require an understanding of the strength of reproductive isolation between parental species, including factors such as the fertility of hybrids, and few studies have focused on this in Begonia.…”

Next-generation hybridization and introgression

“…The typical population genetic approach is to analyse the patterns of markers in hybrid zones, which are dynamic sites where species interact and cross-hybridize (Barton and Hewitt, 1985;Arnold, 1992;Buggs, 2007), and compare them to reference populations of individuals away from these zones (Rieseberg and Carney, 1998;Pinheiro et al, 2010). The genomic contribution of the parental lineages in each hybrid individual can then be estimated (the 'hybrid index' or 'admixture proportion'; maximum likelihood implementation in HINDEX; Buerkle, 2005) as well as the hybrid class (for example, F1, F1 backcross, model-based Bayesian implementation in NEWHYBRIDS; Anderson and Thompson, 2002).…”

Filogeografia de <i>Cattleya loddigesii</i> Lindl. e <i>Cattleya harrisoniana</i> (ex Lindl.) Bateman (Orchidaceae)

“…Os eventos de introgressão, como observados por van den , podem ser explicados como a ocorrência de intensas trocas gênicas interespecíficas que resultam em grande mistura de genes provenientes do retrocruzamento do híbrido com seus parentais (RIDLEY, 2006). Além disso, se o evento de introgressão é contínuo os genes podem se mover além das fronteiras das espécies utilizando indivíduos, ou até mesmo populações híbridas, como pontes de fluxo gênico e, assim, manterem a conectividade entre elas, colonizar novas áreas antes não habitadas e favorecer o surgimento de novas espécies PINHEIRO et al, 2010PINHEIRO et al, , 2013. Apesar da complexidade gênica que ocorre entre as populações nos eventos de introgressão, muitos dos genes específicos de cada espécie podem ser mantidos sem sofrer qualquer tipo de perda.…”

“…Estudos voltados para a investigação da detecção de zonas híbridas e eventos de introgressão são importantes para a evolução das espécies uma vez que podem desencadear modificações nas paisagens biogeográficas, mudar a conexão das populações, afetar barreiras genéticas, alterar a diversidade genética e permitir a ocorrência de eventos de especiação (PINHEIRO et al, 2010(PINHEIRO et al, , 2013BIERNE et al, 2011;DOMINGUES et al 2012;GAGNAIRE et al, 2013 Pode-se sugerir, portanto, a ocorrência de populações simpátricas das duas espécies, como já descrito por van den Berg e Martins (1998). Além disso, os dados para a análise de atribuição de indivíduos somados com o nível de estruturação em algumas populações suporta a hipótese de que existe maior número de populações híbridas.…”