Zeitschrift für Phylogenetik und Evolutionsbiologie

The Neotropics host the most diverse ichthyofauna in the world, with catfish species forming one of the most diverse groups in the region. Nuclear (RAG1) and mitochondrial (ATPase and Cytb) markers were analyzed to identify genetic variability in populations of Pseudoplatystoma reticulatum and Pseudoplatystoma corruscans from the La Plata and Sao Francisco Basins. Bayesian topology identified the division of P. corruscansinto two main clades. One of these clades was formed of samples from the Sao Francisco Basin and the other was formed of samples from the Parana+Paraguay Basins. P. reticulatum was grouped together without any clear geographic or taxonomic patterns in Bayesian topology. While only a few common nuclear haplotypes were widely identified in both species, there was great variability in the mitochondrial sequences. The genetic and geographical distance correlations were tested using the Mantel permutation, which detected no significant relationships.The results of the present study suggest a panmitic population for both species (excluding P. corruscansin the Sao Francisco Basin, which is suggested as a new species), with the greatest diversity concentrated in the region covered by the Pantanal biome, and the lowest diversity in Mogi Guacu, in the Parana Basin. These findings support the establishment of public conservation policies and provide information regarding genetic diversity and population differentiation patterns for these ecological and economically important species.

Identifying regions of a genome that evolve by natural selection, particularly as species diverge, has been a matter of considerable interest. The genomes of 12 species in the eubacterial order Mycoplasmatales were compared to test the hypothesis that natural selection targets genes by function and/or at given moments in the phylogenetic history of the species. These species possess some of the smallest genomes known, and analyses on the set of protein-coding genes common to all species in the study will shed light on the evolution of some of the most critical genes to living organisms. Genes that control cellular processes showed greater evidence of natural selection than genes of unknown function or genes associated with information processing and storage or metabolism. Moreover evidence of natural selection was only detected in the deepest branches of the Mycoplasmatales phylogeny, including one node where a host shift from land plants to insects likely occurred and another node where a host shift from land plants/insects to land vertebrates likely occurred. Many of the genes that showed the strongest evidence of natural selection (e.g. secA, secY, ftsH, ftsY, yidC, lepA, dnaK) encode proteins that are components of the Sec-dependent secretory pathway, which regulates the extracellular translocation of proteins. The Sec-dependent secretory pathway is proposed to play a role in speciation of Mycoplasmatales by altering the type and amount of secreted proteins, thereby affecting virulence of Mycoplasma sp. in response to infection of novel hosts.