Mitogenomic investigation reveals a cryptic lineage of Crocodylus in Cuba

Abstract

The American crocodile, Crocodylus acutus (Cuvier, 1807), is the most widely distributed crocodylian in the Americas, and coexists with the endemic and critically endangered Cuban crocodile, Crocodylus rhombifer Cuvier, 1807. Although these species are morphologically distinguishable, previous studies have shown that they are more genetically related to each other than either of them are to continental C. acutus. Here, we characterize the mitochondrial genome of Cuban C. acutus and analyze the resulting data relative to previously published whole mitochondrial genomes to reconstruct patterns of variation and phylogenetic placement within Crocodylus. We sequenced 13,776 basepairs, representing 82% of the entire genome including five (COI, COII, ATP8, ND3, ND4L) of the 13 protein-coding genes and 16 of the 22 tRNAs. Independent gene analysis of nucleotide diversity and genetic distance of Tamura-Nei demonstrated that the 16S rRNA, 12S rRNA, and COI genes are the most conserved in Crocodylus, while ND6 was the most variable (approximately 9%). Phylogenetic analysis confirmed that Cuban C. acutus forms a well-supported sister relationship with C. rhombifer, in contrast to continental C. acutus that clusters with Crocodylus intermedius Graves, 1819. The results are consistent with the hypothesis that Antillean C. acutus represents a cryptic lineage with genetic divergence at the species level. The ability to fully evaluate the taxonomic status of the Caribbean lineage of C. acutus still requires more comprehensive population samplings across the range as well as nuclear DNA sequence data. Of more immediate consequence, our results provide important information to be integrated into current Crocodylus conservation strategies in Cuba.