Hybridization boosters diversification in a Neotropical Bulbophyllum (Orchidaceae) group.

Genetic data shows that cryptic hybrids are more common than previously thought and that hybridization and introgression are widespread processes. Regardless, studies on hybridization are scarce for the highly speciose Bulbophyllum. The genus presents more than 2,200 species and many examples of recent radiations, in which hybridization is expected to be frequent. Currently, only four natural Bulbophyllum hybrids are recognized, all of them recently described based on morphological evidence. Here we test whether genomic evidence supports the hybrid status of two Neotropical Bulbophyllum species, while also evaluating the impact of this phenomenon on the genomes of the putative parental species. We also assess if there is evidence of hybridization among B. involutum and B. exaltatum, sister species that diverged recently. We leverage the power of next-generation sequence data, associated with model-based analysis for three systems putatively constituted by two parental species and one hybrid. All taxa belong to the Neotropical B. sect. Didactyle clade. We found evidence of hybridization in all studied systems. Despite the occurrence of hybridization, there are no signs of backcrossing. Because of the high propensity of hybridization across many taxa, the common occurrence of hybridization during the evolutionary history of B. sect. Didactyle means it is time to account for and examine its evolutionary role in these orchids.

Geographic isolation alone does not explain divergence of a group of orchid species across Brazil's campos rupestres sky-islandsIsolamento geográfico por si só não explica a divergência de um grupo de espécies de orquídeas nos campos rupestres do Brasil.

Mountains play a crucial role in the origin and maintenance of Neotropical biodiversity, but there are still unanswered questions about the diversification of the campos rupestres (CR), an herbaceous-shrubby sky-island vegetation in eastern South America. For orchids distributed across this disjunct rock habitat, difficulties with distinguishing morphological taxa add an additional challenge to disentangling the history of divergence. Here, we combined the power of ddRAD genomic data with broad sampling of Bulbophyllum sect. Didactyle (Orchidaceae), across the CR and other Neotropical outcrops, to estimate evolutionary relationships and evaluate the biogeography of the group's diversification. Although genetic lineages generally align with geographic disjunctions, we also observe distantly related lineages within some previously recognized species. For such taxa, their lack of monophyly and a shared regional divergence pattern suggests a complex history that may include unrecognized diversity. When viewed through the lens of morphological variability, our study raises intriguing questions about the persistence and permeability of species barriers among orchid populations. These results, in addition to the recency of the divergence history of B. sect. Didactyle, provide insights about hypothesized community level vs. species-specific paths of diversification across the Neotropical sky-islands of the CR.

Geographical genetic structuring and phenotypic variation in the Vellozia hirsuta (Velloziaceae) ochlospecies complex.

PREMISE OF THE STUDY: Vellozia hirsuta forms a complex presenting wide morphological and anatomical variation, resulting in five specific names and 14 morpho-anatomical patterns occurring in disjunct populations. We carried out a phylogeographical study to investigate the existence of correlation among the genetic and morphological patterns within this complex, and to determine whether it is composed of various species or should be treated as an ochlospecies, a species having widely polymorphic and weakly polytypic complex variation, with morphological characteristics varying independently. METHODS: We carried out phylogeographical analyses using cpDNA rpl32F-trnL intergenic region. KEY RESULTS: We found 20 haplotypes in 23 populations sampled. The populations are genetically structured (Φ(ST) = 0.818) into four phylogeographical groups demonstrating geographical structuring but with no correlation with morpho-anatomical patterns. Our analyses do not support recognizing any of the species now synonymized under Vellozia hirsuta. The northern populations were the most genetically differentiated and could be considered a distinct taxon, as they are also morphologically different. CONCLUSIONS: It is recommended that Vellozia hirsuta be considered a single enormously variable species. The patterns of variation within V. hirsuta probably are related to climatic changes that occurred during the Pleistocene Epoch in tropical Brazil when reductions in forest cover favored the expansion of V. hirsuta populations into extensive lowland areas. The expansion of forest cover at the end of the glaciations would have again restricted the occurrence of campos rupestres vegetation to high elevations, which constitute the current centers of diversity of this species.