Reviving Galapagos snails

Under this short title as eye-catcher, Villanea et al. (2016) recently published about an improved method to apply ancient-DNA techniques to identify material obtained from empty shells. The full abstract reads as follows: “Snail shells represent an abundant source of information about the organisms that build them, which is particularly vital and relevant for species that are locally or globally extinct. Access to genetic information from snail shells can be valuable, yet previous protocols for extraction of DNA from empty shells have met with extremely low success rates, particularly from shells weathered from long-term exposure to environmental conditions. Here we present two simple protocols for the extraction and amplification of DNA from empty land snail shells from specimens of Galápagos endemic snails, including presumably extinct species. We processed 35 shells of the genus Naesiotus (Bulimulidae) from the Galápagos islands, some from species that have not been observed alive in the past 50 years. We amplified and sequenced short fragments (≤244 bp) of mitochondrial DNA (mtDNA) from 18 specimens. Our results indicate that the implementation of an ancient DNA extraction protocol and careful primer design to target short DNA fragments can result in successful recovery of mtDNA data from such specimens”. The crux is that the method seems to circumvent largely the PCR inhibitors that are co-extracted when using degraded shells. The resulting tree is given below.

Villanea16

One of the co-authors wrote me “We are really excited about this approach as it will allow us to include rare and potentially extinct species to our considerations of the evolutionary history of the Naesiotus group”. Methodical seems the approach sound, although it remains vague what exactly the inhibitors are. Given the more laborious extractions during aDNA work, it seems to me that the PCR will remain the bottle-neck. With more PCRs needed, this will remain a relatively costly procedure.

Reference:
Villanea, F.A., Parent, C.E. & Kemp, B.M., 2016. Reviving Galapagos snails: ancient DNA extraction and amplification from shells of probably extinct Galapagos endemic land snails. – Journal of Molluscan Studies (early online access; doi: 10.1093/mollus/eyw011).

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