Explaining the differences in African and Neotropical species richness by comparing diversification rates in Renealmia L.f. (Zingiberaceae).
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Valderrama Escallon, Eugenio
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The well-known high species richness of the tropical forests is not uniform through its different regions; Africa is species-poor when compared to Southeast Asia and the Neotropical region. One of the hypotheses for differences between the richness in the Neotropics and Africa points to the importance of recent speciation in the Neotropics. This is considered in particular in Andean-centred taxa that probably diversified in response to the opportunities for speciation offered by the final uplift of the tropical Andes (during the past c. 25 million years [Ma] to the present, with higher rates on the past 10 Ma to the present). The aim of this thesis is to test this hypothesis in the genus Renealmia L.f. (Zingiberaceae), an Andean centred lineage (c. 64 Neotropical spp.) that also occurs in Africa (c. 17 spp.). A taxonomic account of the Colombian species (c. 32; the country with the most species) is presented, and three species new to science were discovered and are described in an updated revision. I designed a new approach for obtaining nuclear phylogenetic markers for estimating species-level phylogenies using transcriptomes for recent diversification that could be applied to samples from herbarium specimens. I generated de-novo transcriptomes for two Renealmia species and a relative in the subfamily Alpinioideae that were combined with data available in repositories to target low copy number and potentially orthologous genes with short introns. I obtained sequence data for eight introns (ranging from 219 to 924 bp) and an rRNA (ITS1 & ITS2) marker for 40 species and at least one marker for 64 species, comprising a total of 137 accessions of which 67.9%(93) were sampled from herbarium specimens. Gene and species-trees were estimated for the genus. I found that most of the subgroups based on morphological characters are supported by the molecular data but a possible combination of incomplete lineage sorting (related to recent radiations or large population sizes) and/or introgression through hybridisation makes difficult to solve the relationships among these subgroups. Finally I estimated and compared diversification rates of the Neotropical and African lineages using dated phylogenies based on the trees estimated. I used available and customized methods that take into account incomplete taxon sampling, the uncertainty in the phylogenetic relationships and the stochasticity inherent to diversifications processes. Differences in diversification rates between Africa and the Neotropics indicate increased speciation attributable to the Andean orogeny in the Neotropical lineages of Renealmia.