Abstract
Interspecific hybridization is a primary cause of extensive morphological and chromosomal variation and plays an important role in plant species diversification. However, the role of interploidal hybridization in the formation of hybrid swarms is less clear. Epidendrum encompasses wide variation in chromosome number and lacks strong premating barriers, making the genus a good model for clarifying the role of chromosomes in postzygotic barriers in interploidal hybrids. In this sense, hybrids from the interploidal sympatric zone between E. fulgens (2n = 2x = 24) and E. puniceoluteum (2n = 4x = 56) were analyzed using cytogenetic techniques to elucidate the formation and establishment of interploidal hybrids. Hybrids were not a uniform group: two chromosome numbers were observed, with the variation being a consequence of severe hybrid meiotic abnormalities and backcrossing with E. puniceoluteum. The hybrids were triploids (2n = 3x = 38 and 40) and despite the occurrence of enormous meiotic problems associated with triploidy, the hybrids were able to backcross, producing successful hybrid individuals with broad ecological distributions. In spite of the nonpolyploidization of the hybrid, its formation is a long-term evolutionary process rather than a product of a recent disturbance, and considering other sympatric zones in Epidendrum, these events could be recurrent.
Highlights
Interspecific hybridization is frequently cited as a primary cause of the extensive morphological and chromosomal variation observed in plant genera and species complexes (Petit et al 1999; Chapman and Abbott 2010; Souza et al 2012; Presgraves 2013), especially in sympatric areas
The chromosome number could be determined in both species: n = 12 in E. fulgens (Fig. 2A and B) and n = 28 in E. puniceoluteum (Fig. 2C)
A few abnormalities were observed in the parental slides, including unpaired chromosomes at prophase I/metaphase I and/or early disjunction at metaphase I in E. fulgens (0.37% and 0.31%, respectively) and unpaired chromosomes at prophase I/metaphase I and anaphase I bridge in E. puniceoluteum (0.58% and 0.48%, respectively; Fig. 2D and E; Table S1)
Summary
Interspecific hybridization is frequently cited as a primary cause of the extensive morphological and chromosomal variation observed in plant genera and species complexes (Petit et al 1999; Chapman and Abbott 2010; Souza et al 2012; Presgraves 2013), especially in sympatric areas. The merging of two divergent genomes into a unique nucleus, caused by hybridization, can set the stage for dynamic changes in the genome, transcriptome, and phenotype of the new hybrids, what could have consequences on parental species after hybrid backcrossing species (Leitch and Leitch 2008; Soltis et al 2009; Paun et al 2010, 2011a; Jiao et al 2011; Buggs et al 2012) This event is responsible for increasing the genetic diversity within species, transferring genetic adaptations between species, breaking down or reinforcing reproductive barriers between closely related groups, which can lead to the emergence of new ecotypes or species, and playing a role in the adaptive radiation of plant species (Soltis et al 2003; Slotte et al 2008; Jorgensen et al 2011).
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