Another attempt for a direct radiocarbon date on the Tarkio Valley sloths failed. Bob Feranec reports that the National Ocean Sciences AMS (Accelerator Mass Spectrometry) Facility at the Woods Hole Oceanographic Institution could not obtain a sufficient quantity of CO2 from the 2.5 milligram collagen sample that he collected via seven extractions from a molariform.
This news from Andy about our DNA tests:
I got a mitochondrial amp from one of the extracts, but I haven’t cloned it yet to check for contamination. I wasn’t able to get nuclear amplifications using our current stock of primers. It wouldn’t surprise me if we get endogenous DNA from this thing, but it may not be in high enough copy numbers to do much more than generate a few scraps. If we can determine that there is endogenous DNA via old school PCR and cloning(what I’m trying to do now), then the next step might be large scale extracts. We’d then use the concentrate to build libraries to go on GS (Genome Sequencer) FLX plates and try to shotgun generate at least a significant portion of the mitochondrial genome.
We received an urgent inquiry from Andy last week asking if we had used shellac on the ankle bone that we sent him. . . he was having problems dissolving the sample. Standard procedure after cleaning and grinding up the bone is soaking the fragments in ethylene diamine tetra acetic acid (EDTA) which dissolves the calcium and frees the DNA inside. We assured Andy we hadn’t used shellac or anything else, anticipating his tests and not wanting to introduce a foreign chemical that could interfere. We suggested the mystery coating might be one of the most impregnable known to man—greasy fingerprints and peanut butter and jelly. The bone is sturdy and it has been handled by at least 50,000 children! He went back and remixed his solutions. From the email we received at the end of the week, it looks like we’re moving forward again:
The experience Andy and his colleagues are getting with analyzing ancient bones, and using clean room facilities, body suits, facemasks, etc. to avoid contamination are the very skills that will be needed in twenty years when astronauts return from Mars with samples to test for traces of ancient life. [previous post: Ancient DNA Centre]
Then, as now, the challenge will be uncovering the biomolecular markers preserved inside and proving any positive findings derive from the sample and not mishandling. So we study our sloths to better understand them and the effects of global climate change, and prepare for the future. . . and maybe to visit the stars. . . . Dave
We sent a bone sample for DNA testing to the McMaster Ancient DNA Centre, McMaster University, Hamilton, Ontario two weeks ago. Andy Clack, a PhD student in the Centre, sent this encouraging reply:
I have the talus/ankle bone in the lab now… wow! That thing is like a rock. I couldn’t ask for a better specimen! I’m going to use a sterile dremel tool and a particular type of bit that generates less heat and produces shards of bone and not powder.
What kind of evidence of a disease would survive after 12,000 years? As a cause of death among animals, disease is probably a much more significant factor than predation, especially if they are under stress, though given the penchant of predators to pick out the weak and infirm, it may be difficult to distinguish (Shipman, 1981). A disease that could kill 3 sloths at once would have to have been dangerous and fast-acting, but can you prove it from fossils?
A hypervirulent disease has been suggested as a possible cause of the Pleistocene mass-extinction (MacPhee and Marx, 1997). The theory is humans or their dogs (or their fleas) brought a pathogen with them when they arrived in the New World, and while they were immune, the New World fauna was not, and large mammals died in unprecedented numbers–a dress rehearsal, if you will, for the devastation wreaked by measles, small pox, etc. when those pathogens arrived with Europeans 12,000 years later. But small pox didn’t exterminate dozens of species.