(A) Samples of Pontogammarus robustoides used in this study. Yellow dots: sequences gathered from literature data, red dot: location of P. robustoides in Hungary, green dots: sequences added to dataset from own collection. (B) Zoom map of SE Hungary with the river system and the localities (red dots) where P. robustoides was collected in 2019. Numbering of the sampling sites started with #1 at the entry of the river to Hungary and ended with #22 at the mouth to River Tisza. Sites #2, 5, 7, 14, and 22 are not indicated on the map because P. robustoides had not been recorded at these five sites.