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, 4 (7), e6272

Morphometrics Parallel Genetics in a Newly Discovered and Endangered Taxon of Galápagos Tortoise

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Morphometrics Parallel Genetics in a Newly Discovered and Endangered Taxon of Galápagos Tortoise

Ylenia Chiari et al. PLoS One.

Abstract

Galápagos tortoises represent the only surviving lineage of giant tortoises that exhibit two different types of shell morphology. The taxonomy of Galápagos tortoises was initially based mainly on diagnostic morphological characters of the shell, but has been clarified by molecular studies indicating that most islands harbor monophyletic lineages, with the exception of Isabela and Santa Cruz. On Santa Cruz there is strong genetic differentiation between the two tortoise populations (Cerro Fatal and La Reserva) exhibiting domed shell morphology. Here we integrate nuclear microsatellite and mitochondrial data with statistical analyses of shell shape morphology to evaluate whether the genetic distinction and variability of the two domed tortoise populations is paralleled by differences in shell shape. Based on our results, morphometric analyses support the genetic distinction of the two populations and also reveal that the level of genetic variation is associated with morphological shell shape variation in both populations. The Cerro Fatal population possesses lower levels of morphological and genetic variation compared to the La Reserva population. Because the turtle shell is a complex heritable trait, our results suggest that, for the Cerro Fatal population, non-neutral loci have probably experienced a parallel decrease in variability as that observed for the genetic data.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Graph of the linear discriminant analysis.
Linear discriminant analysis along the first and second discriminant axes (LD1 and LD2, respectively). LD1 and LD2 account for 66% and 22% discriminant power, respectively. Black circles = Cerro Fatal males. White circles = La Reserva males. Black triangles = Cerro Fatal females. White triangles = La Reserva females.
Figure 2
Figure 2. Map of Santa Cruz Island with sampling localities highlighted.
Map insets indicate the geographic location of the Galápagos archipelago, west of the Ecuadorian coast, as well as the location of Santa Cruz in the archipelago. Altitude is shown on the map in meters. The shaded area represents the agricultural zone. Grey (Cerro Fatal) and white (La Reserva) circles denote samples used for the genetic analysis (including the subset of samples used for morphometric analysis, see Materials and Methods). Thicker black lines on Santa Cruz indicate the known distribution area of each of the studied populations.
Figure 3
Figure 3. Measurements obtained on the shell.
Carapace (left and center) and plastron (right) of a Galápagos tortoise with the measurements used for this study indicated (see Supporting Information S1 for details on how measurements were taken).

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