Geographical distribution of DNA barcodes in Europe
The geographical distribution of the DNA barcodes of the study species
showed a strong bias with an under-representation of southern Europe. If
the barcodes available in BOLD are divided between those from countries
located at southern European Peninsulas (Italy, Iberia and the Balkans)
and the rest of the continent, the number is clearly imbalanced (73vs 204). Germany is the country in which most DNA barcodes are
available (60), followed by some of its neighbour countries (Austria,
Czech Republic, France and Netherlands) with more than 15 each (Table
2). The highest number in the northern countries is not related to their
area.
The species richness does not explain the geographical bias in DNA
barcodes either. Taking our study species as a model, the number of
species decreases significantly in a linear fashion from south to north
(y = 40.3354 - 0.5942x) (F1,24 = 393.44;
p<0.001. Fig. 2). By contrast, the relationship between the
number of barcodes and latitude is quadratic (y = -223.4723 + 9.8584x -
0.1013x2) (F3,25 = 10.16;
p<0.001. Fig. 2). By equalling to zero the derivative of the
previous function (y’ = 9.8584 - 0.2026x) we found that the number of
barcodes peaked at 48.66 degrees, it increased from the south to that
latitude and decreased northwards (Fig. 2). When the functions relating
latitude with species richness and number of DNA barcodes are plotted
together it can be seen that, in latitudes lower than 44 degrees, the
number of DNA barcodes is proportionally low compared to the number of
species (Fig. 2). This leaves the Iberian Peninsula (with a highest
latitude for a DNA barcode in BOLD of 42.74 ºN), among the
under-represented areas, as well as most parts of the other two
peninsulas of southern Europe (Italy and the Balkans) (Fig. 2).