General statistical analysis
Before elucidating the relationships among the methylation states, environmental factors and individual characteristics, we used the Kolmogorov-Smirnov test to detect whether the assumptions of normality were satisfied. If not, a non-parametric test was employed. All statistical tests were performed in R v. 3.1.0. The spatial analysis, multiple regressions on distance matrices analysis (MRM) and multivariate variation partitioning were performed as has been shown before (Chen et al ., 2016). The details are as follows.