Genetic differentiation
The redundancy analysis (RDA) performed on 74,137 SNPs obtained by
RAD-sequencing, including location (Barcelona, Montpellier or Warsaw),
habitat (urban vs. forest), and sex as explanatory variables was highly
significant (P < 0.001) but explained only a small fraction
(i.e. less than 2%) of the total variance (R² = 0.018, Figure
2A, SI Table S1). All three variables were significant (location: P =
0.001 ; habitat: P = 0.004; sex: P = 0.001) revealing small genetic
structuration between groups. Partial RDA revealed that the net
variation explained by habitat (R² = 0.004, P = 0.001) was inferior
to the net variation explained by location (R² = 0.012, P = 0.001)
but higher than sex (R² = 0.002, P = 0.004, Table S1). As expected,
when removing the Z chromosome from the data, sex became non-significant
(P = 0.260), whereas the effects of other variables remained
significant and of similar magnitude (Table S2).
Genome-wide differentiation between populations was relatively low on
average (mean FST = 0.019), in the order of 1 to 2%
between habitats for each location
(FSTBarcelone(rur-urb) = 0.018+-0.001 ;
FSTMontpellier(rur-urb) = 0.012+-0.001 ;
FSTWarsaw(rur-urb) = 0.018+-0.001, Table 1), suggesting
relatively high gene flow and limited genetic drift among populations.
Mean FST on autosomes was lower (mean
FST = 0.014, Table S3) than on the Z chromosome (mean
FST = 0.022, Table S4).