Breaking News – New Species of Galapagos Tortoise is Identified

Sorry for the introductory drama. Today, my pick for EvoLiteracy News includes a study just published -hours ago- in PLoS ONE. A characterization of a distinctive lineage of Galapagos Giant Tortoises. The study is rich in data; below I summarize its major points. Enjoy! – GPC

The two populations of Galapagos tortoises in Santa Cruz Island apparently belong to separate species. Click on image to enlarge.

First, the discussion over the “correct genus” of the Galapagos tortoises has been vivid since 1914, with three justified proposals: Testudo (14 species: 1914), Testudo elephantopus (all subspecies, 1955), Geochelone (as genus, 1957) and Chelonoidis (as sub-genus of Geochelone, 1957). The latest proposal is that all sub-species (13 or 14), or valid biological species, should be placed within Chelonoidis (2006), as legitimate taxa (the problem with Geochelone is that it seems to be polyphyletic, a fancy word to imply “artificial” rather than a natural group, as Chelonoidis).

Second, historic classifications of tortoise varieties based on carapace shape are informative, but taxonomically unreliable (i.e. saddleback, dome, intermediate, and unknown).

Third, populations from different islands represent independent evolutionary lineages, geographically isolated, even within islands, and are distinguishable genetically (via nuclear microsatellites).

The skull of the holotype (i.e. the representative specimen) used for description of Chelonoidis sp. nov. from Cerro Fatal, Santa Cruz. Click on image to enlarge.

Fourth, the new species is described for Santa Cruz Island. It belongs to a separate population (Chelonoidis donfaustoi sp. nov., from “Cerro Fatal,” estimated divergence 0.43 million years ago), genetically distinctive and only 20 Km distant from Chelonoidis porteri (from “Reserva,” estimated divergence 1.74 million years ago).

Fifth, the new species C. donfaustoi is genetically identifiable (via nuclear microsatellite and mitochondrial DNA), which suggests reproductive isolation.

Sixth, the new species has only 250 surviving individuals, which makes it one of the rarest, possibly one of the most endangered lineages of extant Galapagos tortoises.

CONCLUSION: The paper by Poulakakis et al. (total 12 authors), which was published today in PLoS ONE, is interesting and well documented. Keep in mind, however, that populations naturally –and not unusually– move, drift over time, colonize environments, become isolated, and gradually diversify (i.e. the foundation of species radiation). In this respect, the study adds specificity to our previous understanding of the Galapagos tortoises’ population genetics. It gives us additional hints about island connectivity during the  geologic past of the archipelago; for example, if we look closely into the mtDNA (mitochondrial) haplotype phylogeny of the extant and extinct tortoises, including museum specimens (below), the newly described “species” (C. donfaustoi) branches as sister taxa of the San Cristobal Island tortoise C. chathamensis, today a separate island, but likely connected to Santa Cruz in the past. Hopefully, the study by Poulakakis et al. generates support to conservation efforts (funding) of these magnificent giant tortoises. – GPC

Tree constructed from data including mitochondrial DNA haplotypes sampled from extant and extinct species, plus museum specimens of Galapagos tortoises. Click on image to enlarge.