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60 results for “giant tortoises”
Data from: In the land of giants: habitat use and selection of the Aldabra giant tortoise on Aldabra Atoll
With habitat loss and fragmentation among the greatest threats to biodiversity, a better understanding of the habitat use of keystone species is critical in any conservation management strategy. Aldabra Atoll, in the Seychelles archipelago, has the largest population worldwide of giant tortoises. This endemic species (Aldabrachelys gigantea) could be vulnerable to habitat fragmentation and loss induced by climate change related reduction in rainfall. Here, we assess habitat use and selection by A. gigantea in its natural environment on Aldabra. We quantified the habitat areas of A. gigantea based on the first high-resolution terrestrial habitat map of Aldabra, produced for this purpose using satellite imagery. The resulting map was combined with four years of movement data to assess A. gigantea habitat use and selection at landscape and home range scales. Grassland or 'tortoise turf' habitat was most preferred by A. gigantea on Aldabra, at the landscape scale across seasons, followed by open mixed scrub. These two habitats cover only 30 km2 (19.2%) of the surface of the atoll (total area: 155.5 km2). At the home range scale, there was no significant preference shown and habitat was used randomly. Our results suggest that Aldabra's grassland habitat, despite its small area, is of great importance to A. gigantea. Conservation management actions for A. gigantea on Aldabra and elsewhere should therefore focus on the protection and maintenance of this habitat.
Data from: Lineage fusion in Galápagos giant tortoises
Although many classic radiations on islands are thought to be the result of repeated lineage splitting, the role of past fusion is rarely known because during these events, purebreds are rapidly replaced by a swarm of admixed individuals. Here we capture lineage fusion in action in a Galápagos giant tortoise species, Chelonoidis becki, from Wolf Volcano (Isabela Island). The long generation time of Galápagos tortoises and dense sampling (841 individuals) of genetic and demographic data were integral in detecting and characterizing this phenomenon. In C. becki we identified two genetically distinct, morphologically cryptic lineages. Historical reconstructions show that they colonized Wolf Volcano from Santiago Island in two temporally separated events, the first estimated to have occurred ~199 thousand years ago (KYA). Following arrival of the second wave of colonists, both lineages co-existed for approximately ~53 KY. Within that time they began fusing back together, as microsatellite data reveal widespread introgressive hybridization. Interestingly, greater mate selectivity seems to be exhibited by purebred females of one of the lineages. Forward-in-time simulations predict rapid extinction of the early arriving lineage. This study provides a rare example of reticulate evolution in action, and underscores the power of population genetics for understanding the past, present, and future consequences of evolutionary phenomena associated with lineage fusion.
Data from: Genetic rediscovery of an 'extinct' Galápagos giant tortoise species
Genes from recently extinct species can live on in the genomes of extant individuals of mixed ancestry. Recently, Poulakakis et al. detected genetic signatures of the giant Galápagos tortoise once endemic to Floreana Island (Chelonoidis elephantopus) within eleven hybrid individuals of otherwise pure C. becki on Volcano Wolf, Isabela Island. Movement of tortoises among islands by pirate and whaling ships was not uncommon during the 1800's, representing a likely mechanism by which individuals from Floreana were translocated to northern Isabela, despite being presumed extinct soon after Charles Darwin's historic voyage to the Galápagos Islands in 1835. These eleven hybrid individuals with C. elephantopus ancestry were thought to be the last genetic vestiges of a unique evolutionary lineage in the wild. Here we report that reproductively mature purebred tortoises of the recently 'extinct' C. elephantopus from Floreana Island are very likely still alive today, as identified and tracked through the genetic footprints' left in the genomes of very recent hybrid offspring on Volcano Wolf, Isabela Island. If found, these purebred C. elephantopus individuals could constitute core founders of a captive breeding program directed towards resurrecting this species.
Data from: Patterns of activity and body temperature of Aldabra giant tortoises in relation to environmental temperature
We studied the temperature relations of wild and zoo Aldabra giant tortoises (Aldabrachelys gigantea) focusing on: 1) the relationship between environmental temperature and tortoise activity patterns (n=8 wild individuals), and 2) on tortoise body temperature fluctuations, including how their core and external body temperatures vary in relation to different environmental temperature ranges (seasons; n=4 wild, and n=5 zoo individuals). In addition, we surveyed the literature to review the effect of body mass on core body temperature range in relation to environmental temperature in the Testudinidae. Diurnal activity of tortoises was bimodally distributed, and influenced by environmental temperature and season. The mean air temperature at which activity is maximised was 27.9˚C, with a range of 25.8–31.7˚C. Furthermore, air temperature predicted changes in the core body temperature better than did mass, and only during the coldest trial did tortoises with higher mass show more stable temperatures. Our results, together with the overall Testudinidae overview, suggest that, once variation in environmental temperature has been taken into account, there is little effect of mass on the temperature stability of tortoises. Moreover, the presence of thermal inertia in an individual tortoise depends on the environmental temperatures, and we found no evidence for inertial homeothermy. Finally, patterns of core and external body temperatures in comparison to environmental temperatures suggest that Aldabra giant tortoises act as mixed conformer-regulators. Our study provides a baseline to manage the thermal environment of wild and rewilded populations of an important island ecosystem engineer species in an era of climate change.
Data from: Genome-wide assessment of diversity and divergence among extant Galápagos giant tortoise species
Genome-wide assessments allow for fuller characterization of genetic diversity, finer-scale population delineation, and better detection of demographically significant units to guide conservation compared to those based on "traditional" markers. Galapagos giant tortoises (Chelonoidis spp.) have long provided a case study for how evolutionary genetics may be applied to advance species conservation. Ongoing efforts to bolster tortoise populations, which have declined by 90%, have been informed by analyses of mitochondrial DNA sequence and microsatellite genotypic data, but could benefit from genome-wide markers. Taking this next step, we used double-digest restriction-site associated DNA sequencing to collect genotypic data at >26,000 single nucleotide polymorphisms (SNPs) for 117 individuals representing all recognized extant Galapagos giant tortoise species. We then quantified genetic diversity, population structure, and compared results to estimates from mitochondrial DNA and microsatellite loci. Our analyses detected 12 genetic lineages concordant with the 11 named species as well as previously described structure within one species, C. becki. Furthermore, the SNPs provided increased resolution, detecting admixture in four individuals. SNP-based estimates of diversity and differentiation were significantly correlated with those derived from nuclear microsatellite loci and mitochondrial DNA sequences. The SNP toolkit presented here will serve as a resource for advancing efforts to understand tortoise evolution, species radiations, and aid conservation of the Galapagos tortoise species complex.
Data from: Population genomics through time provides insights into the consequences of decline and rapid demographic recovery through head-starting in a Galapagos giant tortoise
Population genetic theory related to the consequences of rapid population decline is well-developed, but there are very few empirical studies where sampling was conducted before and after a known bottleneck event. Such knowledge is of particular importance for species restoration, given links between genetic diversity and the probability of long-term persistence. To directly evaluate the relationship between current genetic diversity and past demographic events, we collected genome-wide single nucleotide polymorphism data from pre-bottleneck historical (c.1906) and post-bottleneck contemporary (c.2014) samples of Pinzón giant tortoises (Chelonoidis duncanensis; n=25 and 149 individuals, respectively) endemic to a single island in the Galapagos. Pinzón giant tortoises had a historically large population size that was reduced to just 150-200 individuals in the mid 20th century. Since then, Pinzón's tortoise population has recovered through an ex situ head-start program in which eggs or pre-emergent individuals were collected from natural nests on the island, reared ex situ in captivity until they were 4-5 years old, and subsequently repatriated. We found that the extent and distribution of genetic variation in the historical and contemporary samples was very similar, with the latter group not exhibiting the characteristic genetic patterns of recent population decline. No population structure was detected either spatially or temporally. We estimated an effective population size (Ne) of 58 (95% CI = 50-69) for the post-bottleneck population; no pre-bottleneck Ne point estimate was attainable (95% CI = 39-infinity) likely due to the sample size being lower than the true Ne. Overall, the historical sample provided a valuable benchmark for evaluating the head-start captive breeding program, revealing high retention of genetic variation and no skew in representation despite the documented bottleneck event. Moreover, this work demonstrates the effectiveness of head-starting in rescuing the Pinzón giant tortoise from almost certain extinction.
Fig 5 in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
Fig 5. Frequency distribution of genetic distances between different Galapagos giant tortoise species (A: microsatellite DNA, B: mitochondrial DNA). For each histogram, a dark gray column indicates where the observed genetic distance between the Cerro Fatal and Reserva tortoises falls. Left: Microsatellite genetic distances calculated from purebred individuals in the reference measured using FST (top) or RST (below). Right: DNA sequence genetic distances based on mtDNA haplotypes from purebred individuals in the reference database, measured using uncorrected p-distances (top), or maximum likelihood (ML)-corrected distances (below).
Fig 2 in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
Fig 2. (A) Bayesian Inference (BI) tree reconstructed from the dataset including all unique mtDNA control region haplotypes previously sampled from extant and extinct species as well as the three museum specimens of giant Galapagos tortoises analyzed in this study. Numbers on branches indicate posterior probabilities. Only the nodal support values for the major lineages are presented. Red and green colors identify museum samples analyzed in the present and previous studies, respectively. (B) Haplotype network showing matrilineal diversity recovered from 70 sequences of C. porteri from Reserva, 51 sequences of the lineage from Cerro Fatal, and 2 sequences of C. chathamensis from San Cristóbal Island. Twenty-five inferred mutations separate the haplogroups of Chelonoidis sp. nov. from Cerro Fatal from the ones from C. porteri from Reserva.
Fig 1 in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
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 6. A-E in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
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).
Fig 4 in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
Fig 4. Genetic membership from Bayesian assignment tests in STRUCTURE for the three museum individuals, relative to the genotypic database representing the Cerro Fatal (black) and Reserva (white) giant tortoise populations. Each bar represents an individual and the proportional color of each bar represents the percentage membership (i.e., Q-value) in each of the reference clusters. Museum individuals include the C. porteri holotype (#) and the two Cerro Fatal specimens tested as putative candidates for the Chelonoidis sp. nov. holotype (*).
Fig 3 in Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island
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 AY956622 for porCF1 from Cerro Fatal. - = gap position and K = G/T polymorphism.
Data from: A new lineage of Galapagos giant tortoises identified from museum samples
<p>The Galapagos Archipelago is recognized as a natural laboratory for studying evolutionary processes. San Cristóbal was one of the first islands colonized by tortoises, which radiated from there across the archipelago to inhabit 10 islands. Here, we sequenced the mitochondrial control region from six historical giant tortoises from San Cristóbal (five long deceased individuals found in a cave and one found alive during an expedition in 1906) and discovered that the five from the cave are from a clade that is distinct among known Galapagos giant tortoises but closely related to the species from Española and Pinta Islands. The haplotype individual collected alive in 1906 is in the same clade as the haplotype in the contemporary population. To search for traces of a second lineage in the contemporary population on San Cristóbal, we closely examined the population by sequencing the mitochondrial control region for 129 individuals and genotyping 70 of these for both 21 microsatellite loci and >12 000 genome-wide single nucleotide polymorphisms [SNPs]. The dataset archived here consists of a VCF file of the SNPs genotyped through ddRAD and a structure file of the 21 microsatellites with the genotypes for the same 64 individuals in each. Only a single mitochondrial haplotype was found, with no evidence to suggest substructure based on the nuclear markers.</p>
FIGURE 4 in A new species of extinct Late Quaternary giant tortoise from Hispaniola
FIGURE 4. Plastron and carapace fragments of Chelonoidis marcanoi sp. nov. from Pedernales Province, Dominican Republic: a, d, epiplastron fragment (MNHNSD FOS 23.1056), external and internal views; b, e, epiplastron fragment (MNHNSD FOS 23.1060), external and internal views; c, h, costal fragment (NHMUK PV R 36955), internal and external views; f–g, peripheral fragment (MNHNSD FOS 23.1061), external and internal views; i–j, fragment from border of carapacial rim, including two peripherals and part of costal plate (MNHNSD FOS 23.1062), external and internal views. Scale bar=2 cm.
FIGURE 1 in A new species of extinct Late Quaternary giant tortoise from Hispaniola
FIGURE 1. Map of Hispaniola, showing geotectonic boundaries and locations of cave sites from which giant tortoise fossils have been reported. Capital cities indicated with filled stars. Key: 1, Cueva del Papayo; 2, Cueva No. 12; 3, Cueva de las Tortugas; 4, Cueva del Muerto; 5, Cueva de las Caritas; 6, Bayaguana.
FIGURE 3 in A new species of extinct Late Quaternary giant tortoise from Hispaniola
FIGURE 3. Femora of Chelonoidis marcanoi sp. nov. from Pedernales Province, Dominican Republic: a–c, MNHNSD FOS 23.1063, left femur (young individual), lateral, anterior and medial views; d–e, MNHNSD FOS 23.1055, right distal femur, anterior and lateral views. Scale bar=2 cm.
FIGURE 2 in A new species of extinct Late Quaternary giant tortoise from Hispaniola
FIGURE 2. Humeri of Chelonoidis marcanoi sp. nov. from Pedernales Province, Dominican Republic: a–b, NHMUK PV R 36954 (holotype), right humerus, anterior and medial views; c–d, MNHNSD FOS 23.1064, left proximal humerus, medial and lateral views; e–f, MNHNSD FOS 23.1058, right humerus, anterior and lateral views; g–h, MNHNSD FOS 23.1054, left humerus, anterior and medial views; i, MNHNSD FOS 23.1059, right distal humerus, anterior view; j–k, MNHNSD FOS 23.1057, left humerus (young individual), anterior and medial views. Scale bar=2 cm.
FIGURE 6 in A new species of extinct Late Quaternary giant tortoise from Hispaniola
FIGURE 6. Schematic drawing of dermal bones of chelonian carapace (left) and plastron (right), indicating approximate estimated position of described shell fragments of Chelonois marcanoi sp. nov. from Pedernales Province, Dominican Republic. Original position on either the left or right side of the carapace is uncertain for the two specimens indicated with asterisks.
Data from: Theory, practice, and conservation in the age of genomics: the Galápagos giant tortoise as a case study
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Data from: Lineage fusion in Galápagos giant tortoises
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