Abstract
Hybridization has the potential to generate or homogenize biodiversity and is a particularly common phenomenon in plants, with an estimated 25% of plant species undergoing interspecific gene flow. However, hybridization in Amazonia's megadiverse tree flora was assumed to be extremely rare despite extensive sympatry between closely related species, and its role in diversification remains enigmatic because it has not yet been examined empirically. Using members of a dominant Amazonian tree family (Brownea, Fabaceae) as a model to address this knowledge gap, our study recovered extensive evidence of hybridization among multiple lineages across phylogenetic scales. More specifically, using targeted sequence capture our results uncovered several historical introgression events between Brownea lineages and indicated that gene tree incongruence in Brownea is best explained by reticulation, rather than solely by incomplete lineage sorting. Furthermore, investigation of recent hybridization using ~19,000 ddRAD loci recovered a high degree of shared variation between two Brownea species that co-occur in the Ecuadorian Amazon. Our analyses also showed that these sympatric lineages exhibit homogeneous rates of introgression among loci relative to the genome-wide average, implying a lack of selection against hybrid genotypes and persistent hybridization. Our results demonstrate that gene flow between multiple Amazonian tree species has occurred across temporal scales, and contrasts with the prevailing view of hybridization's rarity in Amazonia. Overall, our results provide novel evidence that reticulate evolution influenced diversification in part of the Amazonian tree flora, which is the most diverse on Earth.
Highlights
Reproductive isolation is often seen as a prerequisite for speciation and as a defining feature of species (Barraclough, 2019; Mayr, 1942)
Since Amazonia is the largest expanse of rainforest in the world, containing at least 6,800 tree species (Cardoso et al, 2017) and given that hybridization is widely acknowledged as a powerful creative force in plant evolution, being known to generate morphological and genetic novelty (Rieseberg et al, 2007), the paucity of studies examining it as an aspect of evolution in the hyperdiverse rainforests of Amazonia is surprising
This contrasts with previous work, which suggested that hybridization is an extremely rare phenomenon in Amazonian trees (Ashton, 1969; Ehrendorfer, 1970; Gentry, 1982)
Summary
Reproductive isolation is often seen as a prerequisite for speciation and as a defining feature of species (Barraclough, 2019; Mayr, 1942). Regions under divergent selection may remain distinct due to reduced fitness of hybrid genotypes at such loci, resulting in a low rate of introgression, as demonstrated in temperate-zone tree species, where divergence between hybridizing lineages is maintained through selection (Hamilton & Aitken, 2013; Sullivan, Owusu, Weber, Hipp, & Gailing, 2016). This explains why species that hybridize can remain as biologically distinct (and taxonomically identifiable) groups despite undergoing genetic exchange with other species (Abbott et al, 2013; Seehausen et al, 2014). We test whether recent gene flow between Brownea species occurs at the landscape scale and if so, whether it occurs evenly across the genome or differentially for subsets of loci
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
