Lineage Identification and Genealogical Relationships Among Captive Galápagos Tortoises

Abstract

Genetic tools have become a critical complement to traditional approaches for meeting short- and long-term goals of ex situ conservation programs. The San Diego Zoo (SDZ) harbors a collection of wild-born and captive-born Galápagos giant tortoises (n = 22) of uncertain species designation and unknown genealogical relationships. Here, we used mitochondrial DNA haplotypic data and nuclear microsatellite genotypic data to identify the evolutionary lineage of wild-born and captive-born tortoises of unknown ancestry, to infer levels of relatedness among founders and captive-born tortoises, and assess putative pedigree relationships assigned by the SDZ studbook. Assignment tests revealed that 12 wild-born and five captive-born tortoises represent five different species from Isabela Island and one species from Santa Cruz Island, only five of which were consistent with current studbook designations. Three wild-born and one captive-born tortoise were of mixed ancestry. In addition, kinship analyses revealed two significant first-order relationship pairs between wild-born and captive-born tortoises, four second-order relationships (half-sibling) between wild-born and captive tortoises (full-sibs or parent-offspring), and one second-order relationship between two captive-born tortoises. Of particular note, we also reconstructed a first-order relationship between two wild-born individuals, violating the founder assumption. Overall, our results contribute to a worldwide effort in identifying genetically important Galápagos tortoises currently in captivity while revealing closely related founders, reconstructing genealogical relationships, and providing detailed management recommendations for the SDZ tortoises.