Abstract
The taxonomy of giant Galapagos tortoises (Chelonoidis spp.) is currently based primarily on morphological characters and island of origin. Over the last decade, compelling genetic evidence has accumulated for multiple independent evolutionary lineages, spurring the need for taxonomic revision. On the island of Santa Cruz there is currently a single named species, C. porteri. Recent genetic and morphological studies have shown that, within this taxon, there are two evolutionarily and spatially distinct lineages on the western and eastern sectors of the island, known as the Reserva and Cerro Fatal populations, respectively. Analyses of DNA from natural populations and museum specimens, including the type specimen for C. porteri, confirm the genetic distinctiveness of these two lineages and support elevation of the Cerro Fatal tortoises to the rank of species. In this paper, we identify DNA characters that define this new species, and infer evolutionary relationships relative to other species of Galapagos tortoises.
Highlights
Giant Galapagos tortoises are icons of the Galapagos archipelago
The third haplotype carried by the C. porteri holotype (BMNH-1949) was novel, but only 3–4 mutational steps away from the four previously detected haplotypes found only in the extant tortoise lineage from Cerro Fatal
The lineage from Cerro Fatal is sister to the species from San Cristóbal Island (C. chathamensis), and both are included in a clade with species from the islands of Pinta (C. abingdoni), Española (C. hoodensis), and Santa Fe
Summary
Giant Galapagos tortoises are icons of the Galapagos archipelago They represent a classic example of an island adaptive radiation [1, 2], and are keystone herbivores [3]. Despite their prominence, the taxonomy of Galapagos tortoises has long been debated. On the basis of morphological data, Loveridge and Williams [6] established Geochelone (Fitzinger, 1835) as the most appropriate genus for Galapagos (and many other) tortoises, and placed all the Galapagos forms in one species (G. elephantopus) within the subgenus Chelonoidis (Fitzinger, 1856; containing mainland South American species). Despite a nomenclatural review by Pritchard [8] arguing for Geochelone and Chelonoidis as the appropriate genus and subgenus respectively, genetic data presented by Le, Raxworthy [9] indicated that Geochelone is polyphyletic and the generic status of Chelonoidis is supported
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