Rivers of Indochina as potential drivers of lineage diversification in the spotted flying lizard (Draco maculatus) species complex.

Southeast Asia hosts a rich concentration of biodiversity within multiple biodiversity hotspots. Indochina, a region with remarkably high levels of in situ diversification, possesses five major rivers (Ayeyarwady, Chiang Mai, Mekong, Red, and Salween), several of which coincide with phylogenetic breaks of terrestrial taxa. Draco maculatus possesses a range that stretches across Indochina, which widespread geographic distribution along with potential discrete variation within subspecies alludes to the possibility of this taxon constituting multiple divergent lineages. Using sequence data from three mitochondrial (12S, 16S, and ND2) and three nuclear (BDNF, CMOS, and PNN) genes, we provide the first estimated phylogeny of this hypothesized species complex and examine its phylogeographic architecture with maximum likelihood and Bayes factor delimitation (BFD) approaches. Our results support multiple divergent lineages with phylogenetic breaks coincident with rivers, indicating that river barriers may be contributing to the elevated levels of in situ diversification of Indochina.

Molecular systematics, species delimitation and diversification patterns of the Phyllodactylus lanei complex (Gekkota: Phyllodactylidae) in Mexico.

The description of cryptic gecko species worldwide has revealed both that many putative species are, in fact, conformed by a complex of morphologically conserved species that are genetically distinct and highly divergent, and that gecko species diversity could be underestimated. The taxonomy and species delimitation of geckos belonging to the genus Phyllodactylus is still controversial, 16 of which are distributed in Mexico and 13 are endemic. Although the large morphological variation shown by the Phyllodactylus species from Mexico has been amply documented, little is known about their genetic diversity and evolutionary relationships, and much less regarding cryptic speciation. Here, we included the most comprehensive sampling of populations and species of the Phyllodactylus lanei complex distributed in Mexico, and applied an analytical approach that included probabilistic phylogenetic analyses, jointly with species delimitation methods and Bayesian putative species validation analysis. Our results suggest the existence of 10 lineages within the complex, supporting the existence of cryptic species, and in great contrast with the current taxonomic proposal that includes only four subspecies. The most recent common ancestor (MRCA) for the P. lanei clade originated on the Early Eocene (∼54Mya), along the southern coasts of Mexico, followed by the highest diversification of the complex MRCA during the Eocene (34-56Mya). Lineages subsequently dispersed and diversified towards the northwest, and the diversification process ended with the most recent lineages inhabiting two islands on the coasts of Nayarit (Miocene; 5.5-23Mya). Our results highlight three vicariant events associated with the evolution of the lineages, two of them intimately related to the formation of the Sierra Madre del Sur and the Transmexican Volcanic Belt mountain ranges, main geographic barriers that isolated and facilitated the divergence and speciation in this group of geckos. Finally, we propose that there are 10 species in the P. lanei complex, from which four represent taxonomic changes and six are new species and require a formal description. We acknowledge that more analyses, including a detailed evaluation of morphological characters and use of more unlinked nuclear loci with enough variability, are needed to further support their taxonomic description.

Phylogenetic position, origin and biogeography of Palearctic and Socotran blind-snakes (Serpentes: Typhlopidae).

The majority of the family Typhlopidae occurs in the Neotropic, Australasian, Indo-Malayan and Afrotropic ecoregions. They show a restricted distribution in the western Palearctic, where they include few native species, i.e. Rhinotyphlops simoni, R. episcopus and Typhlops vermicularis. A unique species among typhlopids is T. socotranus, found in Socotra, one of the most endemic-rich archipelagoes. In this study we determine the phylogenetic position of the above mentioned species and discuss their systematics, origin and biogeography. For this purpose we use three protein-coding nuclear markers (AMEL-amelogenin, BDNF-brain-derived neurotrophic factor and NT3-neurotrophin 3) to construct a time-calibrated phylogeny of the family Typhlopidae. Our results show that T. socotranus is a sister-species to T. vermicularis, while R. simoni and R. episcopus are sister-species to each other and are found within the African clade of the family, although they are geographically distributed in west Asia. Additionally we discuss several hypotheses on their origin, as well as the occurence of typhlopids in Eurasia.

Phylogenesis of brain-derived neurotrophic factor (BDNF) in vertebrates.

Brain-derived neurotrophic factor (BDNF) belongs to neurotrophin family, a class of molecules playing key roles in neuronal development, survival and regeneration, neurite growth and plasticity: memory processes are mainly affected, and mutations of the human BDNF gene are associated to cognitive and behavioural disturbances. All neurotrophins contain a highly conserved C-terminal domain and bind to the same receptor family. Both correct folding and post-translational processing of the entire preproprotein are pivotal for sorting to the extracellular space, dimerization and receptor binding. Evolutionary studies conducted so far demonstrate that a single ancestor gene underwent two independent duplication events at an early stage of vertebrate evolution, leading to the formation of the current neurotrophins. However, works focusing on BDNF evolution are scarce and fragmentary, mainly in lower vertebrates. In this work, we report cloning of eight DNA sequences from amphibians and teleosts, and analysis of the entire coding regions (cDNA sequences) of BDNF from 35 organisms, from teleosts to mammals. A phylogenetic tree was constructed and the analysis of non-synonymous-synonymous substitution rates performed for the different branches. Our results suggest that natural selection is acting on mammals, separating them from other classes. Since preproprotein cleavage and 3D structure of mature protein are important for functional activity of BDNF, we also propose a de novo prediction of the 3D structure of translates in at least one species for each class, in order to get hints about the functional constraints of the protein.

Stimulatory effects of a melatonin receptor agonist, ramelteon, on BDNF in mouse cerebellar granule cells.

Melatonin receptor activation has been linked to the regulation of neurotrophic factors, including the brain-derived neurotrophic factor (BDNF). To further characterize the effects of melatonin receptor stimulation on neuronal BDNF, we used a clinically available novel agonist for MT1 and MT2 melatonin receptors, ramelteon. Primary cultures of cerebellar granule cells (CGC) have been established as an in vitro model for studying neuronal BDNF. We took advantage of the availability of MT1- and MT2-deficient (knockout; KO) mice to employ primary CGC prepared from wild type (WT), MT1 KO, and MT2 KO mice. We investigated the effects of ramelteon on BDNF protein and mRNA content. Administered in a low nanomolar range, ramelteon increased BDNF protein content in all three types of mouse CGC. This ramelteon-triggered BDNF protein elevation was not preceded by a BDNF mRNA increase. However, it was prevented by treatment of cultures with a protein synthesis inhibitor cycloheximide. These results demonstrated that the MT1/MT2 melatonin receptor agonist ramelteon is capable of increasing BDNF protein in neurons expressing either of the two melatonin receptor types and that this action of ramelteon involves translational mechanisms. Further research is needed to explore the putative influence of ramelteon on BDNF-associated neuroplasticity.

Differential regulation of multiple brain-derived neurotrophic factor transcripts in the postnatal and adult rat hippocampus during development, and in response to kainate administration.

Brain-derived neurotrophic factor (BDNF) is expressed at high levels in the hippocampus, where it has been implicated in physiological functions such as the modulation of synaptic strength as well as in the pathophysiology of epileptic seizures. BDNF expression is highly regulated and the BDNF gene can generate multiple transcript isoforms by alternate splicing of four 5' exons (exons I-IV) to one 3' exon (exon V). To gain insight into the regulation of different BDNF transcripts in specific hippocampal subfields during postnatal development, exon-specific riboprobes were used. Our data shows that BDNF exon I and exon II mRNAs are regulated in hippocampal subfields during postnatal development, in contrast to BDNF exon III and exon IV mRNA, which remain relatively stable through this period. Further, exons I and II show distinct temporal patterns of expression in the hippocampus: BDNF I mRNA peaks in adulthood in contrast to BDNF II mRNA which peaks at postnatal day 14 (P14). Finally, we have addressed whether kainate treatment in postnatal pups and adults regulates BDNF through the recruitment of the same, or distinct, BDNF promoters. Our data indicates that kainate-induced seizures induce strikingly different expression of distinct BDNF transcripts, both in magnitude as well as spatial patterns in the hippocampal subfields, of pups as compared to adults. These results suggest that kainate-mediated seizures differentially recruit BDNF promoters in the developing postnatal hippocampus in contrast to the adult hippocampus to achieve a hippocampal subfield specific regulation of exon-specific BDNF mRNAs.