Utility of arsenic-treated bird skins for DNA extraction

Background: Natural history museums receive a rapidly growing number of requests for tissue samples from preserved specimens for DNA-based studies. Traditionally, dried vertebrate specimens were treated with arsenic because of its toxicity and insect-repellent effect. Arsenic has negative effects on in vivo DNA repair enzymes and consequently may inhibit PCR performance. In bird collections, foot pad samples are often requested since the feet were not regularly treated with arsenic and because they are assumed to provide substantial amounts of DNA. However, the actual influence of arsenic on DNA analyses has never been tested. Findings: PCR success of both foot pad and body skin samples was significantly lower in arsenic-treated samples. In general, foot pads performed better than body skin samples. Moreover, PCR success depends on collection date in which younger samples yielded better results. While the addition of arsenic solution to the PCR mixture had a clear negative effect on PCR performance after the threshold of 5.4 μg/μl, such high doses of arsenic are highly unlikely to occur in dried zoological specimens. Conclusions: While lower PCR success in older samples might be due to age effects and/or DNA damage through arsenic treatment, our results show no inhibiting effect on DNA polymerase. We assume that DNA degradation proceeds more rapidly in thin tissue layers with low cell numbers that are susceptible to external abiotic influences. In contrast, in thicker parts of a specimen, such as foot pads, the outermost horny skin may act as an additional barrier. Since foot pads often performed better than body skin samples, the intention to preserve morphologically important structures of a specimen still conflicts with the aim to obtain optimal PCR success. Thus, body skin samples from recently collected specimens should be considered as alternative sources of DNA

Low mitochondrial DNA diversity in the endangered Bonelli’s Eagle (Hieraaetus fasciatus) from SW Europe (Iberia) and NW Africa

This study is an initial survey of the genetic diversity and population structure of the endangered Bonelli’s Eagle (Hieraaetus fasciatus) in SW Europe (Iberia) and NW Africa, two locations where the species has undergone a severe decrease in numbers during the last decades. It is also the first study in which the mitochondrial control region (CR) has been used to study the genetic diversity and population structure of this species. Samples were obtained from 72 individuals from Spain, Portugal and Morocco, and a 253-bp fragment of the mitochondrial control region was amplified and sequenced. Only three polymorphisms were present, indicating low nucleotide and haplotype diversity. No evidence of genetic structure was found. Several hypotheses may explain these results, including a possible greater genetic diversity in other regions of the mitochondrial genome or the existence of a presumed ancient bottleneck (last glaciation), possibly followed by a human-induced more recent one (twentieth century).This project was funded by the Terra Natura Foundation. L. Cadahía is supported by a grant of the Spanish Ministerio de Educación y Ciencia (reference AP2001-1444)