Molecular phylogenetics of sub-Saharan African natricine snakes, and the biogeographic origins of the Seychelles endemic Lycognathophis seychellensis.

Phylogenetic relationships of sub-Saharan African natricine snakes are understudied and poorly understood, which in turn has precluded analyses of the historical biogeography of the Seychelles endemic Lycognathophis seychellensis. We inferred the phylogenetic relationships of Seychelles and mainland sub-Saharan natricines by analysing a multilocus DNA sequence dataset for three mitochondrial (mt) and four nuclear (nu) genes. The mainland sub-Saharan natricines and L. seychellensis comprise a well-supported clade. Two maximally supported sets of relationships within this clade are (Limnophis,Natriciteres) and (Afronatrix,(Hydraethiops,Helophis)). The relationships of L. seychellensis with respect to these two lineages are not clearly resolved by analysing concatenated mt and nu data. Analysed separately, nu data best support a sister relationship of L. seychellensis with (Afronatrix,(Hydraethiops,Helophis)) and mt data best support a sister relationship with all mainland sub-Saharan natricines. Methods designed to cope with incomplete lineage sorting strongly favour the former hypothesis. Genetic variation among up to 33 L. seychellensis from five Seychelles islands is low. Fossil calibrated divergence time estimates support an overseas dispersal of the L. seychellensis lineage to the Seychelles from mainland Africa ca. 43-25 million years before present (Ma), rather than this taxon being a Gondwanan relic.

Phylogenetic affinity of an enigmatic Rubiaceae from the Seychelles revealing a recent biogeographic link with Central Africa: gen. nov. Seychellea and trib. nov. Seychelleeae.

The granitic islands of the Seychelles harbor about 268 native angiosperm species, with 28% being endemics there. The Seychelles biota contains a mix of ancient taxa with Gondwanan origins and young taxa that arrived there via dispersals. We investigate the phylogenetic position of an enigmatic, critically endangered, Seychellean endemic of the coffee family (Rubiaceae), Psathura/Psychotria sechellarum, and assess whether its presence on the granitic islands of the Seychelles is the result of vicariance or long-distance dispersal. Phylogenetic relationships of the family were reconstructed based on the Bayesian and maximum-likelihood phylogenetic analyses of sequence data from five plastid markers of 107 terminals. Divergence times were estimated using a Bayesian-based method. Psathura/Psychotria sechellarum is distantly related to Psychotria s.l. (including Psathura), and is strongly supported as sister to the Central African genus Colletoecema. Their striking morphological differences, coupled with their geographic separation and genetic distinctness, support the recognition of the new genus Seychellea and new tribe Seychelleeae to accommodate the Seychellean species. The Colletoecema-Seychellea clade constitutes an early-divergent lineage in the subfamily Rubioideae, with an old stem and a young crown ages estimated to be in the Late Cretaceous and late Oligocene-early Pliocene, respectively. Colletoecema diverged from Seychellea in the late Oligocene-early Pliocene and their respective crown ages are inferred to be late Miocene-middle Pleistocene and Pleistocene, respectively. The ancestor of the two genera was likely present in Africa, and reached the Seychelles via avian dispersal. Unlike Colletoecema with three species, Seychellea is monospecific, with very few individuals left in the wild. The species should be a top candidate for conservation priority, as its extinction would cause loss of genetic diversity of this entire lineage.