Fig. 3.

Invasion scenario testing of the recent southern expansion. Results from ABC model analyses with (A) general scenario explanation of invasion pathways of the Western Mediterranean Sea via 1) a stepping-stone range expansion from the Black Sea (Scenario 1, green circle) or 2) a direct reintroduction from its native range in the United States (Scenario 2, red squares) and (B) ABC model results for both scenarios where direct observation (yellow point) clearly indicates Scenario 1, with stepping-stone invasion from the Black Sea as the most likely explanation.