Phylogenetic relationships and DNA sequence evolution among species of pitvipers

Pitvipers of the genus Bothrops comprise a complex and speciose group of snakes whose systematic and evolutionary relationships are poorly understood. To date very few studies have investigated the evolutionary genetics of these organisms from the perspective of DNA sequence variation. We employ here the maximum likelihood formalism to study phylogenetic relationships and sequence evolution among eight species of pitvipers, based on the first 310 base pairs of the mitochondrial cytochrome b gene. Sequence evolution is studied with models of nucleotide substitution that follow a time-homogeneous Poisson process. Likelihood ratio statistics are employed to test the significance of competing hypotheses regarding the mutational process, such as equal base frequencies, equal rates of transitions and transversions, homogeneity of rates among sites and a molecular clock.