Fragmented Museum DNA Traces Two Lost Galapagos Tortoise Lineages

DNA that was once considered too damaged to reveal much about the past has helped researchers identify two extinct giant tortoise lineages from the Galapagos Islands. According to reporting from Phys.org, a Yale-led team analyzed genetic material from dried bones held in museum collections. The specimens included five examples associated with two extinct lineages, whose histories had been difficult to reconstruct because the DNA had broken into fragments and included contamination. In some cases, researchers could read less than 1% of a specimen’s genome. Rather than discard those samples, the team combined several computational tools to assemble the available fragments and compare them with a reference evolutionary tree created from higher-quality genomes of living and historical tortoises. The analysis identified the extinct San Cristóbal and Santa Fe island lineages as distinct genetic groups. The findings were published in Proceedings of the Royal Society B under the title “Integration of ultra-low coverage whole-genome sequences for reconstructing the evolutionary history of Galapagos giant tortoises.” The study also bears on how the lineages may have disappeared. The researchers said sailors historically transported tortoises between Galapagos islands as food supplies. Some of those relocated animals survived and bred with tortoises from other islands, potentially allowing genetic material from extinct lineages to persist in hybrid descendants. That possibility could matter for conservation programs. Study lead author Alexander Ochoa said captive breeding involving such hybrids might, over future generations, help recover genetic components from the extinct lineages. The study does not establish that this recovery has already occurred, but it indicates that genes from the lost populations may still exist among living tortoises. The researchers said their computational approach could also be useful for studying other wildlife when available DNA is too incomplete for conventional genomic analysis. The work forms part of an ongoing Yale research effort focused on the genetic diversity of Galapagos giant tortoises.