Micro-CT X-rays do not fragment DNA in preserved bird skins

Most zoological systematics studies are currently based on morphological features, molecular traits or a combination of both to reconstruct animals phylogenetic history. Increasingly, morphological studies of museum specimens are using X-ray computed tomography to visualize internal morphology, because of its non-destructive nature. However, it is not known whether CT can fragment the size of DNA extracted from museum specimens, as has been demonstrated to occur in living cells. This question is of paramount importance for collections based research because X-rays may reduce the amount of data obtainable from specimens. In our study, we tested whether exposure of museum bird skins to typical CT X-ray energies (for visualization of the skeleton) increased DNA strand fragmentation, a key factor for the success of downstream molecular applications. For the present study, we extracted DNA from shavings of 24 prepared and dried bird skins (100+ years) footpads before and after CT scanning. The pre- and post-CT fragmentation profiles were assessed using a capillary electrophoresis high-precision instrument (Agilent Bioanalyzer). Comparison of the most common strand length in each DNA sample (relative mass) revealed no significant difference unexposed and exposed tissue (paired t-test p = 0.463). In conclusion, we found no further quantifiable degradation of DNA strand length under standard X-ray exposure obtained from our bird skins sample. Differences in museum preservation techniques probably had a greater effect on variation of pre-CT DNA fragmentation.