''Chelonoidis niger donfaustoi'', known as the eastern Santa Cruz tortoise, is a subspecies of

Galápagos tortoise The Galápagos tortoise or Galápagos giant tortoise (''Chelonoidis niger'') is a species of very large tortoise in the genus ''Chelonoidis'' (which also contains three smaller species from mainland South America). It comprises 15 subspecies ( ...

living on

Santa Cruz Island Santa Cruz Island ( Spanish: ''Isla Santa Cruz'', Chumash: ''Limuw'') is located off the southwestern coast of Ventura, California, United States. It is the largest island in California and largest of the eight islands in the Channel Islands ...

, within the Galápagos. Until 2015, ''C. n. donfaustoi'' was considered conspecific with the western Santa Cruz tortoise, ''C. n. porteri''.

Tortoise populations on Santa Cruz Island

Earlier mitochondrial DNA studies of tortoises on Santa Cruz showed up to three genetically distinct lineages found in nonoverlapping population distributions around the regions of Cerro Monturra in the northwest, Cerro Fatal in the east, and La Reserva (or La Caseta) in the southwest. Although traditionally classified together, the lineages were all shown to be more closely related to tortoises on other islands than to each other, and thus are thought to be the result of three separate colonizations of the island. Cerro Monturra tortoises are most closely related to ''duncanensis'' tortoises from Pinzón, Cerro Fatal to ''chathamensis'' from San Cristóbal, while Reserva tortoises are closer to the four southern races of Isabela. Tortoises are aided in

oceanic dispersal Oceanic dispersal is a type of biological dispersal that occurs when terrestrial organisms transfer from one land mass to another by way of a sea crossing. Island hopping is the crossing of an ocean by a series of shorter journeys between isla ...

by their ability to float with their heads up, and to survive up to six months without food or water.

Classification

In 2015, ''Chelonoidis niger donfaustoi'' was reclassified as a new subspecies on the basis of genetic and morphological data. ''C. n. donfaustoi'' is the sister lineage to ''C. n. chathamensis'' on San Cristóbal, and is part of a clade that also includes ''C. n. hoodensis'' of Española and ''C. n. abingdoni'' of Pinta. Genetically, ''C. n. donfaustoi'' differs from other tortoises by

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

frequency at 12 microsatellite loci, which allowed assignment to the genetically distinct cluster. ''C. n. donfaustoi'' also shares a set of

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecule ...

s distinct from that of ''C. porteri'' on the same Santa Cruz Island and from ''C. n. chathamensis''. The reclassification reduced the

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

of ''C. porteri'' to the western and southwestern parts of Santa Cruz Island. At the same time it confined ''C. n. donfaustoi'' to the eastern part of Santa Cruz Island, with a population size estimated at 250 individuals. ''C. porteri'' was shown to be part of a clade that includes the Floreana and southern Isabela tortoises, as well as specimens reputedly representing Rábida and Fernandina. The subspecies received the scientific epithet ''donfaustoi'' in honor of Fausto Llerena Sánchez, who devoted 43 years to giant tortoise conservation as a park ranger within the Galapagos National Park Directorate. “Don Fausto” was the primary caretaker of endangered tortoises in captivity. ''C. n. donfaustoi'' is the 15th known tortoise subspecies to be discovered on the islands, with four of those subspecies being extinct. The classification of a new tortoise subspecies was the first in over a century.

Appearance

While similar to other Galápagos tortoises, ''C. n. donfaustoi'' can be distinguished from them by means of

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

size and shape. Some Galápagos tortoises are larger than ''C. n. donfaustoi'', with higher anterior opening of the shell.

References

{{Taxonbar, from=Q21179602 Chelonoidis Subspecies Turtles of South America Endemic reptiles of the Galápagos Islands Reptiles of Ecuador Reptiles described in 2015