2.4. Identification of individual mitochondrial genomes
A reference database of PCR-based bait fragments was established
for all specimens included in the shotgun pools, by collating
four mitochondrial gene fragments (cox1, cox2, cytb and rrnl). The
cox1 (50 and 30 region), cox2 and rrnl fragments were in part already
available from earlier work on the same specimens and thus
extracted from genbank. In addition, standard PCR reactions to
amplify cox1-30 and cytb were performed for species for which
none or only one fragment was available (see supplementary table
1 for bait regions per specimen and supplementary table 2 for reaction
conditions and primers list). Prior to Sanger sequencing the
PCR products were cleaned using a size-exclusion filter (Merck
Millipore). The chromatograms were assembled and manually edited
using Geneious.
The reference database of bait fragments was used for BLAST
searches against the complete collection of contigs. Only hits of
>98% pairwise similarity over >150 base pairs were considered a
match. Chimera formation was examined by checking whether
baits of different species hit the same contig. Where multiple bait
sequences from a single species showed matches with different
short (non-overlapping) contigs, their position in a phylogenetic
tree (ML tree, 1000 bootstrap replicates) was examined. If these
contigs were sister groups they were considered to represent different
portions of the same mitogenome and the sequences where
fused. The mitogenomes from this study have been submitted to
GenBank (accession numbers KU739421–KU739500; see supplementary
table 1 for details).