Figure 2. Root-to-tip distance versus collection date of the 132 LASV NP sequences.

A phylogenetic tree was inferred by a maximum likelihood method without molecular clock and the genetic distance from the root to the tip of the branches was correlated with the corresponding trapping dates. The regression analysis revealed a positive correlation between genetic distance and trapping date with R² = 0.22 (p < 0.005). The intercept of the regression line with the x-axis reflects the date at the root of the tree, i.e. the time of the MRCA.