Abstract
The subfamily Bromelioideae is one of the most diverse groups among the neotropical Bromeliaceae. Previously, key innovations have been identified which account for the extraordinary radiation and species richness of this subfamily, especially in the so-called core Bromelioideae. However, in order to extend our understanding of the evolutionary mechanisms, the genomic mechanisms (e.g. polyploidy, dysploidy) that potentially underlie this accelerated speciation also need to be tested. Here, using PI and DAPI staining and flow cytometry we estimated genome size and GC content of 231 plants covering 30 genera and 165 species and combined it with published data. The evolutionary and ecological significance of all three genomic characters was tested within a previously generated dated phylogenetic framework using ancestral state reconstructions, comparative phylogenetic methods, and multiple regressions with climatic variables. The absolute genome size (2C) of Bromelioideae varied between 0.59 and 4.11 pg, and the GC content ranged between 36.73 and 41.43%. The monoploid genome sizes (Cx) differed significantly between core and early diverging lineages. The occurrence of dysploidy and polyploidy was, with few exceptions, limited to the phylogenetically isolated early diverging tank-less lineages. For Cx and GC content Ornstein–Uhlenbeck models outperformed the Brownian motion models suggesting adaptive potential linked to the temperature conditions. 2C-values revealed different rates of evolution in core and early diverging lineages also related to climatic conditions. Our results suggest that polyploidy is not associated with higher net diversification and fast radiation in core bromelioids. On the other hand, although coupled with higher extinction rates, dysploidy, polyploidy, and resulting genomic reorganizations might have played a role in the survival of the early diverging bromelioids in hot and arid environments.
Highlights
Bromelioideae is the second most species-rich Bromeliaceae subfamily comprising 986 species as well as the most diverse subfamily concerning the number of genera (Gouda et al, 2020)
The tank-less lineages are terrestrial or lithophytic usually characterized by succulent leaves with considerable water storage tissue and CAM photosynthesis, except the earliest diverging Greigia, Ochagavia, Fascicularia, as well as several other species from the Cryptanthoid complex and the genus Fernseea, which are C3 (Horres and Zizka, 1995; Silvestro et al, 2014; Crayn et al, 2015; Leme et al, 2017)
Polyploidy and genomic reorganizations are not associated with higher net diversification and speciation in core bromelioids
Summary
Bromelioideae is the second most species-rich Bromeliaceae subfamily comprising 986 species as well as the most diverse subfamily concerning the number of genera (Gouda et al, 2020) The members of this subfamily occupy terrestrial, lithophytic, and epiphytic habitats in subtropical and tropical biomes in the Neotropics (Smith and Downs, 1979). The tank-less lineages are terrestrial or lithophytic usually characterized by succulent leaves with considerable water storage tissue and CAM photosynthesis, except the earliest diverging Greigia, Ochagavia, Fascicularia, as well as several other species from the Cryptanthoid complex and the genus Fernseea, which are C3 (Horres and Zizka, 1995; Silvestro et al, 2014; Crayn et al, 2015; Leme et al, 2017). Very few species among the core Bromelioideae lack the tank or have a rudimentary one (e.g. Acanthostachys strobilacea, Araeococcus flagellifolius), and only a few have been reported to have C3 instead of CAM photosynthesis (especially from genera Nidularium and Ronnbergia; Crayn et al, 2015)
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