Phylogenetics,delimitation and historical biogeography of the pantropical tree genus Thespesia (Malvaceae,Gossypieae)

Thespesia consists of 16 species of trees and shrubs from Southeast Asia–Oceania, Africa and America, the most well known being T. populnea, a small tree of tropical coastal areas around the world. Phylogenetic relationships in the genus and among its allies in tribe Gossypieae were inferred using three plastid and two nuclear regions to ascertain its generic delimitation and explore its biogeographical history. Maximum‐likelihood and Bayesian analyses confirmed that Thespesia is not monophyletic and, based on these results, Azanza is reinstated to accommodate the two species previously placed in Thespesia section Lampas. Dating analyses and ancestral range estimation indicated that Thespesia s.s. most likely originated in Southeast Asia–Oceania c. 30 Mya, but extant species did not begin to differentiate until the late Miocene. Two dispersal events, one into Africa c. 11 Mya and another into America (Antilles) c. 9 Mya, gave rise to the African and the Greater Antillean endemics, respectively. The two most widespread hydrochorous species, T. populnea and T. populneoides, originated in Southeast Asia–Oceania from where they spread to other parts of the world. Our analysis also indicated a much earlier origin than previously reported for the eumalvoid clade and its tribes Gossypieae, Malveae and Hibisceae suggesting that vicariance might have had an important role early in the history of these groups.     

Vicariance or long‐distance dispersal: historical biogeography of the pantropical subfamily Chrysophylloideae (Sapotaceae)

Aim Continental disjunctions in pantropical taxa have been explained by vicariance or long‐distance dispersal. The relative importance of these explanations in shaping current distributions may vary, depending on historical backgrounds or biological characteristics of particular taxa. We aimed to determine the geographical origin of the pantropical subfamily Chrysophylloideae (Sapotaceae) and the roles vicariance and dispersal have played in shaping its modern distribution. Location Tropical areas of Africa, Australasia and South America. Methods We utilized a recently published, comprehensive data set including 66 species and nine molecular markers. Bayesian phylogenetic trees were generated and dated using five fossils and the penalized likelihood approach. Distributional ranges of nodes were estimated using maximum likelihood and parsimony analyses. In both biogeographical and molecular dating analyses, phylogenetic and branch length uncertainty was taken into account by averaging the results over 2000 trees extracted from the Bayesian stationary sample. Results Our results indicate that the earliest diversification of Chrysophylloideae was in the Campanian of Africa c. 73–83 Ma. A narrow time interval for colonization from Africa to the Neotropics (one to three dispersals) and Australasia (a single migration) indicates a relatively rapid radiation of this subfamily in the latest Cretaceous to the earliest Palaeocene (c. 62–72 Ma). A single dispersal event from the Neotropics back to Africa during the Neogene was inferred. Long‐distance dispersal between Australia and New Caledonia occurred at least four times, and between Africa and Madagascar on multiple occasions. Main conclusions Long‐distance dispersal has been the dominant mechanism for range expansion in the subfamily Chrysophylloideae. Vicariance could explain South American–Australian disjunction via Antarctica, but not the exchanges between Africa and South America and between New Caledonia and Australia, or the presence of the subfamily in Madagascar. We find low support for the hypothesis that the North Atlantic land bridge facilitated range expansions at the Palaeocene/Eocene boundary.     

Hydrodynamics and seed dispersal in the lower Amazon

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Northern Hemisphere origin,transoceanic dispersal,and diversification of Ranunculeae DC. (Ranunculaceae) in the Cenozoic

Aim The role of dispersal versus vicariance for plant distribution patterns has long been disputed. We study the temporal and spatial diversification of Ranunculeae, an almost cosmopolitan tribe comprising 19 genera, to understand the processes that have resulted in the present inter‐continental disjunctions. Location All continents (except Antarctica). Methods Based on phylogenetic analyses of nuclear and chloroplast DNA sequences for 18 genera and 89 species, we develop a temporal–spatial framework for the reconstruction of the biogeographical history of Ranunculeae. To estimate divergence dates, Bayesian uncorrelated rates analyses and four calibration points derived from geological, fossil and external molecular information were applied. Parsimony‐based methods for dispersal–vicariance analysis (diva and Mesquite ) and a maximum likelihood‐based method (Lagrange ) were used for reconstructing ancestral areas. Six areas corresponding to continents were delimited. Results The reconstruction of ancestral areas is congruent in the diva and maximum likelihood‐based analyses for most nodes, but Mesquite reveals equivocal results at deep nodes. Our study suggests a Northern Hemisphere origin for the Ranunculeae in the Eocene and a weakly supported vicariance event between North America and Eurasia. The Eurasian clade diversified between the early Oligocene and the late Miocene, with at least three independent migrations to the Southern Hemisphere. The North American clade diversified in the Miocene and dispersed later to Eurasia, South America and Africa. Main conclusions Ranunculeae diversified between the late Eocene and the late Miocene. During this time period, the main oceanic barriers already existed between continents and thus dispersal is the most likely explanation for the current distribution of the tribe. In the Southern Hemisphere, a vicariance model related to the break‐up of Gondwana is clearly rejected. Dispersals between continents could have occurred via migration over land bridges, such as the Bering Land Bridge, or via long‐distance dispersal.     

Genetic variation in an ephemeral mudflat species: The role of the soil seed bank and dispersal in river and secondary anthropogenic habitats

Many ephemeral mudflat species, which rely on a soil seed bank to build up the next generation, are endangered in their natural habitat due to the widespread regulation of rivers. The aim of the present study was to elucidate the role of the soil seed bank and dispersal for the maintenance of genetic diversity in populations of near‐natural river habitats and anthropogenic habitats created by traditional fish farming practices using Cyperus fuscus as a model. Using microsatellite markers, we found no difference in genetic diversity levels between soil seed bank and above‐ground population and only moderate differentiation between the two fractions. One possible interpretation is the difference in short‐term selection during germination under specific conditions (glasshouse versus field) resulting in an ecological filtering of genotypes out of the reservoir in the soil. River populations harbored significantly more genetic diversity than populations from the anthropogenic pond types. We suggest that altered levels and patterns of dispersal together with stronger selection pressures and historical bottlenecks in anthropogenic habitats are responsible for the observed reduction in genetic diversity. Dispersal is also supposed to largely prohibit genetic structure across Europe, although there is a gradient in private allelic richness from southern Europe (high values) to northern, especially north‐western, Europe (low values), which probably relates to postglacial expansion out of southern and/or eastern refugia.