In a paper from last week's PLoS One (also highlighted in today's Science Times), Thomsen et al. describe a method that may be used to extract DNA from insect specimens collected as far back as 188 years ago. Remarkably, this method also avoids destruction of the pinned insect (see photo - this beetle is post-extraction). Twenty of twenty museum specimens examined yielded good, if short (~200 bp), sequences from mitochondrial genes. There was also some limited success on insects that were even older from non-frozen conditions. One big caveat is that all of their tests were done on beetles, which obviously are some of the most durable of insects, but it was nonetheless exciting. Although they didn't test this, sounds like their DNA might also have been useful for other short fragments, i.e. microsatellites - opening up doors for tracking lots of interesting population biology of insects, including pests and maybe even vectors. Suddenly those cabinets and cabinets of pinned insects I'm surrounded by seem all the more interesting!
Saccularina sp.
2 weeks ago
6 comments:
How do microsatellites preserve? Do they have any tendency to be among the weaker (or stronger) stretches of DNA experiencing age-related fragmentation?
Yikes! You didn't find the amazing insect collection at the AMNH interesting before?
To Rich - being small, microsats can sometimes be amplified from old or degraded tissues. My former lab has had success in getting microsat data from old stained blood smears, for example.
To Roberto - I said I find them all the *more* interesting!
That they did this with beetles is even more remarkable. Because beetles are among the most impermeable of insects, they have an unfortunate tendency to retain water and rot inside before dessicating enough to preserve the DNA.
Minor note: credit for the extraction method goes to Gilbert etal 2007 though the extraction buffer itself traces back to Pfeiffer et al 2004.
As for microsats, Gilbert etal 2007 was able to amplify nuclear DNA from a 1952 specimen (28S), so maybe there's hope.
The impermeability of beetles may be an advantage here. It'll be interesting to see if this works with other arthropod groups. Don't see why it wouldn't but since bees and butterflies are softer, maybe they'll suffer some external morphological damage.
A little late on the comment, but we have managed to optimize non-destructive sampling of bumble bees as well, and have published a proof-of-concept comparative population genetics study in Molecular Ecology. (Lozier & Cameron, Molecular Ecology, Vol. 18, No. 9., pp. 1875-1886). For this study we used microsats, and we found pretty good amplification for most loci (though we stress the need for duplicate data for each sample) using forelegs only, which were then reassociated with specimens using genitalia vials. Interestingly, the best fragments were <200bp, with weaker ampl. for larger fragments.
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