Surprisingly, SF located at the western border of the region did not fall into any group composed of Cariaco drainage populations in the STRUCTURE analysis, and instead shared the cluster with the geographically distant San Juan drainage populations.
A similar relationship was inferred from natural archaeal Ferroplasma acid mine drainage populations (Eppley et al. 2007).
Clades BP1, BP2 (Blanco River drainage populations of E. pterophila) and BGP (Blanco & Guadalupe River E. pterophila) each contain populations assigned to E. pterophila[ 10], but form a polytomy in the 50% majority-rule tree with clade LT and several other populations.
In the second case, population GUAR, sampled in 2001, clustered to a great extent with San Juan populations but also showed considerable admixture with Cariaco genes, whereas CAS, sampled in 2011 from the same stream, grouped with the San Juan drainage populations.
Multidimensional scaling of genetic distances showed that Cariaco and San Juan drainage populations cluster separately with the only exception of the population CAS, which clustered together with San Juan populations (Additional file 2: Figure S1).
In this analysis, populations from the Cariaco drainage and San Juan drainage grouped separately, except for two anomalies; the SF population, which contains an admixture of alleles from San Juan drainage, and the CAS and GUAR populations, which group with San Juan drainage populations.
The values of drainage frequency of sub-watershed area exhibits positive correlation with drainage density values of the area, indicating the increase in the drain population with respect to drainage density.
A more complex picture emerges for the Ligurian drainages: populations from Central Liguria belong to group I, while populations from West (group II) and East Liguria (group IV) form their own groups, albeit with affinities to PV and TL, respectively.
Most mtDNA haplotypes clustered into two major well-supported lineages, one of which occurs exclusively among Cariaco drainage guppies (populations CC, CCAR, CUM, PER and SF, lineage C in Figure 4, Additional file 5: Figure S5).
Glaciation cycle-mediated changes in sea level and precipitation may be expected to produce changing levels of connectivity between adjacent drainages for populations of Dallia, which depend on highly connected coastal plain or wetland hydrological networks to move between adjacent river drainages.
