Complete mitochondrial genome sequences of three Crocodylus species and their comparison within the Order Crocodylia

Crocodylus is the largest genus within the Order Crocodylia consisting of eleven species. This paper reports the complete mitochondrial genome sequences of three Crocodylus species, Crocodylus moreletii, Crocodylus johnstoni and Crocodylus palustris, and compares the newly obtained mitochondrial DNA sequences with other crocodilians, available in the public databases. The mitochondrial genomes of C. moreletii, C. johnstoni and C. palustris are 16,827 bp, 16,851 bp and 16,852 bp in length, respectively. These mitochondrial genomes consist of 13 protein coding genes, two ribosomal RNA genes, 22 transfer RNA genes and a non-coding region. The mitochondrial genomes of all the Crocodylus species, studied herein show identical characteristics in terms of nucleotide composition and codon usage, suggestive of the existence of analogous evolutionary patterns within the genus, Crocodylus. The synonymous and non-synonymous substitution rates for all the protein coding genes of Crocodylus were observed in between 0.001 and 0.275 which reveal the prevalence of purifying selection in these genes. The phylogenetic analyses based on complete mitochondrial DNA data substantiate the previously established crocodilian phylogeny. This study provides a better understanding of the crocodilian mitochondrial genome and the data described herein will prove useful for future studies concerning crocodilian mitochondrial genome evolution.