What Post-Hoc Test is done when using Kruskal Wallis Test

[johnnyvelasquez]

The following is the output of a plot I created with statannotations:

p-value annotation legend:
ns: p <= 1.00e+00
*: 1.00e-02 < p <= 5.00e-02
**: 1.00e-03 < p <= 1.00e-02
***: 1.00e-04 < p <= 1.00e-03
****: p <= 1.00e-04

PRE-RT vs. 4WKSPD1: Kruskal-Wallis independent samples (pairwise between groups), P_val:1.294e-01 Stat=2.299e+00
4WKSPD1 vs. 8WKSPD1: Kruskal-Wallis independent samples (pairwise between groups), P_val:9.877e-01 Stat=2.367e-04
PRE-RT vs. 8WKSPD1: Kruskal-Wallis independent samples (pairwise between groups), P_val:2.266e-01 Stat=1.462e+00

I am not sure what post-hoc test was done to perform the pairwise comparisons between groups.