PhD Student, Memorial University of Newfoundland
This research looks at the origin and evolution of endemic plant genera in the biodiverse Caribbean
The aim of this study was to better understand the historical assembly and evolution of endemic seed plant genera in the Caribbean, by first determining divergence times of endemic genera to test whether the GAARlandia landbridge played a role in the archipelago colonization, and second by testing South America as the main colonization source as expected by the position of landmasses and recent evidence of an asymmetrical biotic interchange. To accomplish this we gathered DNA sequences from four loci for 610 species, including 41 seed plant genera endemic to the Caribbean (out of 180 in total). We reconstructed a dated molecular phylogeny using Bayesian inference and ten calibrations. To estimate the range of the ancestors of endemic genera we performed a model selection between a null and a more complex biogeographical model that included timeframes based on geological information and dispersal probabilities among regions. We present evidences on the role that GAARlandia played in the origin of endemic plant genera and where were the ancestors of these genera most likely distributed.
Abstract: Using the Acalyphoideae, we explore the origin and diversification of the Caribbean flora. This lineage of flowering plants constitutes an important component of the flora of the Caribbean islands with many endemics. Furthermore, because it is also diverse in adjacent Mexico, Mesoamerica and South America, it allows a representative analysis of possible migration routes into the Caribbean.Neotropics, Cuba, Hispaniola and the Caribbean region, Mexico and Mesoamerica.We generated a well-resolved and dated phylogenetic hypothesis based on a dense sampling, in particular of the New World taxa but also representing all remaining Acalyphoideae, and combined datasets of chloroplast spacers and introns. Bayesian divergence-time estimation was applied to determine node ages. Ancestral states of distributional areas were reconstructed in a Bayesian framework to determine the geographical origin of the Caribbean ancestors.A Neotropical clade started to diversify 59.29 [50.41–68.44 95% highest posterior density (HPD)] Ma within the Acalyphoideae. The Caribbean islands then were reached several times independently from the Miocene onwards. The exclusively Caribbean Leucocroton–Lasiocroton–Garciadelia [9.1 (6.3–12.3 95% HPD) Ma] and Acidoton–Platygyna [9.3 (5.2–15.4 95% HPD) Ma] clades exhibit one of the most successful plant radiations in the region, and Caribbean subclades of Acalypha and Bernardia just date back to the Pliocene and Pleistocene, respectively.Our data show that Mexico and Mesoamerica have played a key role as a source for today's Caribbean Acalyphoideae. Their ancestors arrived from the mainland to the Caribbean islands during the Miocene when Caribbean land masses were completely separated and then diversified in situ. We postulate long-distance dispersal to have played a major role for colonizing the Caribbean.
Pub.: 01 Jul '16, Pinned: 20 Jun '17
Abstract: The Caribbean Islands are one of the ten insular biodiversity hotspots that are defined based on endemicity, massive habitat loss and vulnerability to extinction. Asteraceae genera endemic to islands have provided well known examples of plant radiation worldwide and illustrate the importance of these insular systems for evolutionary and conservation studies. A review of known patterns of taxonomic diversity and molecular cladistics is provided for Asteraceae genera and species endemic in the Caribbean Island biodiversity hotspot. We found that when compared with other island systems worldwide the Caribbean Islands have the highest number of endemic genera (41), have endemic genera in the highest number of tribes, and harbor the only Asteraceae tribe endemic to an island system, the Feddeeae which is restricted to Cuba. These unique patterns identify the Caribbean Islands as the most important insular area of endemism for this major plant family. Molecular cladistic studies are limited to only seven species in seven endemic genera and six endemic species in five non-endemic genera. These few studies are however relevant as: (1) they confirm the tribal status of the Feddeeae, (2) suggest colonization events from the highlands of Cuba toward low elevation and geologically recent areas of the Bahamas and South Florida, (3) provide evidence for biogeographical links to remote regions of the Pacific Basin, and (4) identify sister relationships with continental taxa, mostly from North America.
Pub.: 22 Apr '08, Pinned: 20 Jun '17
Abstract: Initial molecular phylogenetic studies established the monophylly of the large genus Croton (Euphorbiaceae s.s.) and suggested that the group originated in the New World. A denser and more targeted sampling of Croton species points to a South American origin for the genus. The nuclear and chloroplast genomes indicate a different rooting for the phylogeny of Croton. Although we favor the rooting indicated by the chloroplast data our conclusions are also consistent with the topology inferred from the nuclear data. The satellite genera Cubacroton and Moacroton are embedded within Croton. These two genera are synonimized into Croton and a new subgenus, Croton subgenus Moacroton, is circumscribed to include them and their allied Croton species. Croton subgenus Moacroton is morphologically characterized by a primarily lepidote indumentum, bifid or simple styles, and pistillate flowers with sepals that are connate at the base. This newly circumscribed subgenus is found from North America to South America, and in contrast to the majority of Croton species most of its members are found in mesic habitats. The group is most diverse in the greater Caribbean basin. A molecular clock was calibrated to the phylogeny using the available Euphorbiaceae fossils. The timing and pattern of diversification of Croton is consistent with both the GAARlandia and Laurasian migration hypotheses. A single species, Croton poecilanthus from Puerto Rico, is placed incongruently by its nuclear and chloroplast genomes. The possibility of this species being of hybrid origin is discussed.
Pub.: 29 Apr '08, Pinned: 20 Jun '17
Abstract: Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree-species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera.DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree-species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted.Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia-Lepidozamia-Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia.A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.
Pub.: 03 Sep '13, Pinned: 20 Jun '17
Abstract: The Western Indian Ocean region (WIOR) is home to a very diverse and largely unique flora that has mainly originated via long-distance dispersals. The aim of this study is to gain insight into the origins of the WIOR biodiversity and to understand the dynamics of colonization events between the islands. We investigate spatial and temporal hypotheses of the routes of dispersal, and compare the dispersal patterns of plants of the Coffeeae alliance (Rubiaceae) and their dispersers. Rubiaceae is the second most species-rich plant family in Madagascar, and includes many endemic genera. The neighbouring archipelagos of the Comoros, Mascarenes and Seychelles also harbour several endemic Rubiaceae.The islands of the Western Indian Ocean.Phylogenetic relationships and divergence times were reconstructed from plastid DNA data of an ingroup sample of 340 species, using Bayesian inference. Ancestral areas and range evolution history were inferred by a maximum likelihood method that takes topological uncertainty into account.At least 15 arrivals to Madagascar were inferred, the majority of which have taken place within the last 10 Myr. Most dispersal events were supported as being from mainland Africa, but Catunaregam may have dispersed from Asia. Although most Coffeeae alliance lineages are zoochorous, the general pattern of dispersals from Africa is incongruent with the biogeographic origins of the extant Malagasy volant frugivores. Several out-of-Madagascar dispersals were inferred to the neighbouring islands, as well as back-colonizations of Africa.The African flora has been of foremost importance as source of dispersal to the islands of the Western Indian Ocean. Following the colonization of Madagascar, rapid radiations appear to have taken place in some clades, and Madagascar has also been an important source area for subsequent dispersal to the Comoros, Mascarenes and Seychelles.
Pub.: 08 Mar '17, Pinned: 20 Jun '17
Abstract: The Bahamas archipelago is formed by young, tectonically stable carbonate banks that harbor direct geological evidence of global ice-volume changes. We sought to detect signatures of major changes on gene flow patterns and reconstruct the phylogeographic history of the monophyletic Zamia pumila complex across the Bahamas.Nuclear molecular markers with both high and low mutation rates were used to capture two different time scale signatures and test several gene flow and demographic hypotheses.Single-copy nuclear genes unveiled apparent ancestral admixture on Andros, suggesting a significant role of this island as main hub of diversity of the archipelago. We detected demographic and spatial expansion of the Zamia pumila complex on both paleo-provinces around the Piacenzian (Pliocene)/Gelasian (Pleistocene). Populations evidenced signatures of different migration models that have occurred at two different times. Populations on Long Island (Z. lucayana) may either represent a secondary colonization of the Bahamas by Zamia or a rapid and early-divergence event of at least one population on the Bahamas.Despite changes in migration patterns with global climate, expected heterozygosity with both marker systems remains within the range reported for cycads, but with significant levels of increased inbreeding detected by the microsatellites. This finding is likely associated with reduced gene flow between and within paleo-provinces, accompanied by genetic drift, as rising seas enforced isolation. Our study highlights the importance of the maintenance of the predominant direction of genetic exchange and the role of overseas dispersion among the islands during climate oscillations.
Pub.: 19 May '17, Pinned: 20 Jun '17
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