The explosive radiation of the NeotropicalTillandsiasubgenusTillandsia(Bromeliaceae) has been facilitated by pervasive hybridization

Abstract

AbstractThe recent rapid radiation ofTillandsiasubgenusTillandsia(Bromeliaceae) provides an attractive system to study the drivers and limits of species diversification. This species-rich Neotropical monocot clade includes predominantly epiphytic species displaying vast phenotypic diversity. Recent in-depth phylogenomic work revealed that the subgenus originated within the last 7 MY while expanding through one major event from South into Central America within the last 5 MY. However, disagreements between phylogenies and lack of resolution at shallow nodes suggested that hybridization occurred throughout the radiation, together with frequent incomplete lineage sorting and/or considerable gene family evolution. We used whole-genome resequencing data and a newly available reference genome to explore the evolutionary history of 34 representative ingroup species employing both a tree-based and a network approach. Our results indicate that lineage co-occurrence does not predict relatedness and confirm significant deviations from a tree-like structure, coupled with pervasive gene tree discordance. Focusing on hybridization, ABBA-BABA and related statistics were used to infer the rates and relative timing of introgression, while topology weighting uncovered high heterogeneity of the phylogenetic signal along the genome. High rates of hybridization within and among clades suggest that, in contrast to previous hypotheses, the expansion of subgenusTillandsiainto Central America proceeded in several dispersal events, punctuated by episodes of diversification and gene flow. Network analysis revealed reticulation as a prominent propeller during radiation and establishment in different ecological niches. This work contributes a plant example of prevalent hybridization during rapid species diversification, supporting the hypothesis that interspecific gene flow facilitates explosive diversification.