Calculation of intra-specific genetic distance and geographical distance among populations
For each species, the maximum intra-specific genetic divergence and the geographical distance between localities were needed for further analyses (see below the section on statistical tests). For measuring genetic divergence, we first aligned all the sequences of each species separately using MUSCLE software (Edgard 2004) as implemented in MEGA 7 (Kumar, Strecher & Tamura 2016; default values). For each separate species alignment all pairwise genetic distances were calculated using the Kimura 2-parameter model (K2P%; Kimura 1980) as implemented in MEGA 7 (Kumar et al . 2016); we used K2P% because this is the method more frequently used in DNA barcoding studies (Bergsten et al . 2012; Gunay, Alten, Simsek, Aldemir & Linton 2015; Shen, Guan, Wang & Gan et al . 2016). The maximum genetic divergence for each pair of populations was the maximum genetic distance (K2P%) between any pair of individuals of those two populations. Pairwise geographical distances between populations were calculated using QGIS 2.18.9 (QGIS Development Team 2009) and later corroborated using the cosine-haversine formula (Robusto 1957).