Chelonoidis donfaustoi, Nikos Poulakakis, Danielle L. Edwards, Ylenia Chiari, Ryan C. Garrick, Michael A. Russello, Edgar Benavides, Gregory J. Watkins-Colwell & Scott Glaberman, 2015

Nikos Poulakakis, Danielle L. Edwards, Ylenia Chiari, Ryan C. Garrick, Michael A. Russello, Edgar Benavides, Gregory J. Watkins-Colwell & Scott Glaberman, 2015, Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island, PLoS ONE 10 (10), pp. 1-18 : 12-15

Chelonoidis donfaustoi sp. nov. Poulakakis, Edwards, and Caccone

urn:lsid:zoobank.org:act:333D161C-2BA0-43D3-B84E-B0FBC859787D

( Fig 6 A–6E)

Common name: Eastern Santa Cruz Tortoise. To distinguish the two extant lineages now recognized on Santa Cruz Island, we also propose to substitute for the current common name Chelonoidis porteri from “Santa Cruz tortoise,” which inappropriately subsumes both lineages, to the “Western Santa Cruz tortoise” to more clearly distinguish these two, distinct taxa.

Holotype

Below we provide the morphological description of the skull from the designated C. donfaustoi holotype. This morphological description is not intended to diagnose the new species, but to clearly describe the specimen. Anatomical terms follow Gaffney (1979). Specimen UWZS 32700 is a skull ( Fig 6 A–6E) and single carapace marginal scute. The skull is nearly equal in basicranial length and maximum width ( Table 5 ). The quadratojugal broadly contacts the jugal anteriorly and narrowly contacts the postorbital dorsally. Anterior edge of maxilla is rough. Posterior edge of maxilla does not extend past the contact of maxilla to jugal. In lateral view ( Fig 6 E) the squamosal is only narrowly visible dorsal to the quadrate and is not visible posterior to the quadrate. Dorsally the squamosal only narrowly contacts the opisthotic ( Fig 6 A). Contact of the pre-frontals to the frontals is broad and V-shaped, with the pre-frontal extending posteriorly forming the majority of the medial margin of the eye socket. The parietal extends nearly as far dorsally as the pre-frontal extends posteriorly and bisects the frontals. Maxilla contact with pre-frontal extends dorsally and is visible when the skull is viewed dorsally. Preootic is wider than long and does not extend posteriorly much beyond the foramen stepedio-temporale. Supraoccipital extends posteriorly well beyond the squamosal. Contact between basisphenoid and basioccipital is V-shaped with the lateral contact extending posteriorly. Vomer does not contact basisphenoid. Palatine bone much longer than wide. Prefrontal visible ventrally making contact with the palatine and vomer.

Diagnosis. The new species can be diagnosed by a combination of genetic, morphological, and geographic distribution evidence.

Genetic characters. This species can be distinguished from all other Galapagos tortoise species by allele frequency differences at 12 microsatellite loci, which allow assignment of Cerro Fatal tortoises to their own genetically distinct cluster. This cluster is as genetically divergent from the other named species as the genetic clusters grouping them. Furthermore, a set of polymorphisms in the mitochondrial control region sequence (haplotypes) is unique to the Cerro Fatal taxon ( Fig 3 ). In particular, all individuals from Cerro Fatal share a set of nucleotides that separates them from the C. porteri (Reserva) species on the same island and from C. chathamensis (San Cristóbal), the sister taxon to the Cerro Fatal tortoises.

Morphological characters: Although there are no diagnostic morphological characters that uniquely define the new species, linear and geometric morphometric analyses reveal consistent differences in mean shell size and shape between tortoises from Reserva and Cerro Fatal. Tortoises from Reserva are larger in size and have a relatively larger carapace with higher anterior opening than the Cerro Fatal tortoises [ 20, 26, 27].

Distribution: The new species is only found on the eastern side of Santa Cruz Island occupying an area currently estimated at about 40 km 2 ( Fig 1 ).

Etymology. The new species is named in honor of Fausto Llerena Sánchez who devoted 43 years of service (1971–2014) 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, one of the first to explore tortoise habitat throughout the archipelago, and was well known for his work ethic, commitment to tortoise conservation, and collegiality. Several tortoise lineages in Galapagos remain extant in large part due to Don Fausto’s dedication, ingenuity, and patience.

Conclusion

Genetic and morphological data confirm the existence of two tortoise species on Santa Cruz Island. We describe the tortoises from Cerro Fatal as a new species, C. donfaustoi . The recognition of C. donfaustoi as a new species has important conservation implications for both taxa. The revised taxonomy reduces the range of C. porteri , with a population of several thousand individuals, to occupying only the western and southwestern parts of Santa Cruz Island. It also confines C. donfaustoi to the eastern part of Santa Cruz Island, with a much smaller population size estimated currently at ca. 250 individuals.

From a conservation standpoint, recognition of this new species will help promote efforts to protect and restore it, given that its low abundance, small geographic range, and reduced genetic diversity make it vulnerable. In particular, further investigation is needed to better determine C. donfaustoi ‘s population size and structure, range, movement patterns, location of nesting zones, and habitat requirements, as well as ongoing threats and effective ways to mitigate them. In an age of increasing human occupation of much of the higher elevations on Santa Cruz Island, maintaining the two species’ biological isolation is critical. Of particular importance is ensuring that no human-mediated transport of tortoises occurs between the two sides of Santa Cruz Island given that the two species’ ranges are now linked via a single agricultural zone.

Figures

Fig 1. Geographic distribution of the two known lineages of giant tortoises on Santa Cruz Island: Chelonoidis porteri (Reserva) and Chelonoidis sp. nov. (Cerro Fatal) (indicated in dark gray). Light gray area connecting the distribution areas of the two species indicates agricultural land. Modified from Russello et al. [11].

Fig 3. Polymorphic sites between Chelonoidis sp. nov. (Cerro Fatal — Santa Cruz), C. chathamensis (San Cristóbal), and C. porteri (Reserva — Santa Cruz). The position of diagnostic locations is relative to the Genbank record AY 956622 for porCF 1 from Cerro Fatal. - = gap position and K = G / T polymorphism.

Fig 6. A-E. The skull of the museum specimen UWZS 32700, holotype for Chelonoidis sp. nov. from Cerro Fatal in Santa Cruz (A: dorsal, B: ventral, C: occipital, D: frontal and E: lateral view).

Tables

Table 5. Morphometric data for UWZS 32700 compared to data presented in Crumly [53]. Sixteen measurements were taken from the skull of UWZS 32700 following those described by Crumly [53]. Measurements were taken to the nearest 0.01 mm using a Mitutoyo digital caliper.

	UWZS 32700	ephippium	guntheri	porteri	vicina	chathamensis
B	115.0	96.7	128.0	121.5	109.0	98.1
WAT	117.6	73.9	106.6	98.4	86.0	80.4
WO	40.2	25.1	35.4	37.0	28.4	28.4
HN	20.2	12.5	18.6	18.6	16.1	13.9
WN	24.5	17.0	25.1	23.1	21.3	18.5
LB	17.4	13.3	18.7	14.7	18.1	14.7
WB	19.2	14.6	19.1	17.1	15.8	13.8
WZ	18.6	9.3	14.3	13.3	12.6	10.1
WP	10.6	7.0	9.5	9.0	8.8	7.3
WS	12.9	7.3	12.0	9.5	9.6	7.9
DPV	3.2	3.2	4.2	4.2	3.7	3.1
LP	16.1	14.1	21.0	18.1	14.8	15.2
WFS	17.4	10.0	16.0	12.8	8.9	12.5
PW	30.5	19.2	25.9	26.1	21.9	19.0
APW	20.0	10.5	15.2	14.1	11.8	10.5
PC	11.2	8.6	10.6	13.3	8.5	8.2

Variable Species

B: Basicranial length; WAT: Width of skull at anterior tympanic opening; WO: Width between orbits; HN: Height of external narial opening; WN: Width of external narial opening; LB: Length of basisphenoid; WB: Width of basisphenoid; WZ: Width of quadratojugal; WP: Width of postorbital; WS: Width of jugal; DPV: Distance (greatest) from prepalatine foramina to vomer; LP: Length of preootic; WFS: Width of prootic at stapedial foramen; PW: Width of pterygoid waist; APW: Width of anterior premaxillae; PC: Length of sagittal contact of prefrontals.

doi:10.1371/journal.pone.0138779.t005