Globin-intron Sequences Imply Molecular Relationships Between the Galapagos Giant Tortoise and the Aldabra Giant Tortoise

Abstract

The author previously established a molecular tree based on the cDNA-derived primary structures of globins in two giant tortoises, Geochelone nigra and G. gigantea. The divergence time was estimated to be 15-21 million years ago. In the present study, the author reexamined the divergence time of these two species using another source of genetic information-globin-introns-including those from the Chaco tortoise (G. chilensis), a close relative of G. nigra. The previously determined divergence time was supported by the findings of this intron study. However, the inter-relationships based on the intron nucleotide sequences of the globins from the three Geochelone species remain controversial, because it is difficult to determine which of the three is the ancestral species. In addition, the nucleotide sequences reveal the following interesting characteristics: (1) an abnormal GC dinucleotide sequence located at the 5'-splicing site of the second intron of α D globins instead of a consensus GT-this finding is common to all studied Geochelone species; (2) a repeated sequence 5'-GCCCCGCGCCCCGC-3' found only in the first intron of the G. nigra α A globin gene, is a unique feature distinguishing the Galapagos giant tortoise from the other Geochelone tortoises that have non-repeated GCCCCGC sequences.

Molecular Evolutionary Relationships of Side-Necked Turtle Hemoglobin:cDNA-Derived Primary Structures and Computer-Assisted Tertiary Structuresof α^A, α^D, and β Globin Chains

“…The isolation of corresponding globin chains was also easily conducted by a reversed-phase column. The elution profiles of the hydrophobic column and reversed-phase column are not presented here because they closely resembled those of previous studies 24) . The cDNA-nucleotide sequences (data not shown here) and cDNA-derived primary structures (Fig.…”

“…Thus, the present molecular evolutionary analysis indicates that the tertiary and quaternary structure give relatively little phylogenetic information on the study species. Accordingly, the phylogenetic relationships of the four side-necked turtle species merit further investigation with more genetic information on molecules, as in a previous study conducted on globin-intron sequences to elucidate the molecular phylogeny of two giant tortoises 24) , the Galapagos tortoise and the Aldabra tortoise.…”