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

Abstract

The 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.

Closely related facultative and constitutive CAM phenotypes show little transcriptomic overlap in the subgenusTillandsia

“…T. vanhyningii and T. leiboldiana are closely related members of a recent radiation with an estimated maximum divergence time of 3.22 Mya (Barfuss et al ., 2016; Mendoza et al ., 2017; Yardeni et al ., 2023). Despite the relatively short time in which these species have diverged, our analyses demonstrate clear differentiation on the physiological and transcriptomic level, resulting in distinct photosynthetic phenotypes.…”

“…It is, in other words, still unclear whether CAM is in fact a complex trait that can be The subgenus Tillandsia (genus Tillandsia, Bromeliaceae) is an emerging model to study repeated evolution of ecological traits within a plant adaptive radiation. As part of one of the fastest diversifying lineages in the plant kingdom (Givnish et al, 2014), the subgenus is considered an adaptive radiation that generated more than 250 species over the last 7 million years (Barfuss et al, 2016;Mendoza et al, 2017;Yardeni et al, 2023). Numerous key innovation traits characterise this radiation, including CAM, which occurs in a broad range of phenotypes ranging from C3-like to constitutive CAM (Crayn, Winter and Smith, 2004;De La Harpe et al, 2020).…”