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Title: Reproductive barriers and fertility of two neotropical orchid species and their natural hybrid
Author: Segalla, Rosane; Pinheiro, Fábio; Morellato, Leonor Patrícia Cerdeira
Year: 2021
Is part of: PLANT SPECIES BIOLOGY, v. 36, p. 348 - 360

Citation: Segalla, Rosane; Pinheiro, Fábio; Morellato, Leonor Patrícia Cerdeira; Reproductive barriers and fertility of two neotropical orchid species and their natural hybrid. PLANT SPECIES BIOLOGY, v.36, p. 348-360, 2021

Abstract: Different pre- and postzygotic isolating mechanisms may prevent interspecific gene exchange in secondary contact zones. Due to the different nature of each isolating barrier, which may act in different life history stages, multidisciplinary approaches are crucial to investigate the evolution of reproductive isolation (RI) in contact zones. In this study, we analysed seven different pre- and postzygotic RI mechanisms and reproductive success of two neotropical orchid species with contrasting pollination strategies, the nectarless food-deceptive Epidendrum denticulatum and the nectar rewarding E. orchidiflorum. The two species occur sympatrically in the coastal vegetation of Southeastern Brazil and share habitats with their natural hybrid E. x purpureum. Our aim was to test the contribution of pre and postzygotic reproductive barriers to species cohesion, examining potential asymmetries among RI mechanisms. Our results indicate habitat isolation as an important prezygotic barrier, strongly influenced by the contrasting habitat preferences found between the parental species. Hybrid sterility was also important, though incomplete, to prevent species collapse in this hybrid zone. This latter barrier was likely shaped by strong differences in chromosome numbers found between parental species (E. denticulatum 2n = 52, E. orchidiflorum 2n = 156). Indeed, hybrids showed lower levels of fertility when compared to parental species, probably due to meiotic abnormalities found in hybrid plants. However, contrary to our expectations, hybrid plants are still able to attract flower visitors during the day and night, and natural pollination success was comparable to one of the parental species, suggesting sexual reproduction of hybrid plants may contribute to the persistence of this hybrid zone. This study highlights the importance of studying hybrid zones between species diverging in several morphological and ecological traits, where the balance of hybridization is still unpredictable and almost unknown.

Funding: Funding for this study was provided by fellowships from CNPq - PIBIC to BLA and FAEPEX (FUNCAMP) to FP. This study was also financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001.
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