The role of hybridization and introgression in maintaining species integrity and cohesion in naturally isolated inselberg bromeliad populations

Abstract

Hybridization is a widespread phenomenon present in numerous lineages across the tree of life. Its evolutionary consequences range from effects on the origin and maintenance, to the loss of biodiversity. We studied genetic diversity and intra- and interspecific gene flow between two sympatric populations of closely-related species, Pitcairnia flammea and P. corcovadensis (Bromeliaceae), which are adapted to naturally fragmented Neotropical inselbergs, based on nuclear and plastidial DNA. Our main results indicate a strong reproductive isolation barrier, although low levels of interspecific gene flow were observed in both sympatric populations. The low rates of intraspecific gene flow observed for both P. corcovadensis and P. flammea populations corroborate the increasing body of evidence that inselberg bromeliad species are maintained as discrete evolutionary units despite the presence of low genetic connectivity. Nuclear patterns of genetic diversity and gene flow revealed that hybridization and introgression might not cause species extinction via genetic assimilation of the rare P. corcovadensis. In the face of reduced intraspecific gene exchange, hybridization and introgression may be important aspects of the Pitcairnia diversification process, with a positive evolutionary impact at the bromeliad community level, and thus contribute to increasing and maintaining genetic diversity in local isolated inselberg populations.

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

“…Here, as in other species (i.e., Mota et al, 2019), P. exserta is kept as a unique evolutionary unit, independently from P. axillaris, but contrarily to those Bromeliads, the gene exchange is not low between Petunia species in Serra do Sudeste (see Turchetto et al, 2019b). P. exserta can be considered narrowly endemic compared to P. axillaris and, in general, has lower diversity indices than its sister species even accounting only sympatric populations (Lorenz-Lemke et al, 2006;Segatto et al, 2014).…”

Systematics of Vriesea (Bromeliaceae): phylogenetic relationships based on nuclear gene and partial plastome sequences

“…Indeed, species complexes and non-monophyletic species are common in plants (Naciri & Linder, 2015;Pinheiro, Dantas-Queiroz & Palma-Silva, 2018) and are thought to be the result of hybridization or incomplete lineage sorting. Assuming that post-zygotic barriers for reproduction of bromeliads are potentially weak (Palma-Silva et al, 2011;Wagner et al, 2015) and that the individuals often grow in mixed aggregates of species sharing the same pollinator, interspecific gene flow may occur and lead to the formation of natural hybrids (Palma-Silva et al, 2011;Lexer et al, 2016;Zanella et al, 2016;Neri, Wendt & Palma-Silva, 2017;Mota et al, 2019). Furthermore, natural hybrids of closely related Vriesea spp.…”

Genome Skimming Reveals Widespread Hybridization in a Neotropical Flowering Plant Radiation

“…Hybridization is also thought to have promoted bromeliad diversity (Palma-Silva et al, 2016) but although both artificial (Vervaeke et al, 2004;Wagner et al, 2015;de Souza et al, 2017) and natural hybrids have been reported (e.g., Palma-Silva et al, 2011), the frequency and exact contribution of this phenomenon to bromeliad diversity are still to be determined. While some studies suggest that hybridization generates intraspecific genetic diversity in isolated populations (Lexer et al, 2016;Neri et al, 2018;Mota et al, 2019), it may also prevent genetic differentiation and blur species boundaries (Goetze et al, 2017). To date, most of the research on hybridization in bromeliads focuses on the population level and studies with a macroevolutionary perspective are lacking.…”