Genetic Analysis of The Rapid Expansion of Banded Killifish (Fundulus diaphanus) in Illinois

The Illinois state-threatened Banded Killifish (Fundulus diaphanus) is comprised of an Eastern (F d. diaphanus) and Western subspecies (F. d. menona) that are known to inhabit vegetated glacial lakes and slow moving, vegetated streams. The Eastern subspecies occupies the Atlantic coast and inland to Lakes Ontario and Erie, whereas the Western subspecies ranges from Lake Erie, west to Lakes Huron and Michigan, and the upper Midwest. A recent range expansion of Banded Killifish into the Illinois and Mississippi rivers and Lake Michigan has prompted investigations into whether the rapid spread is due to native Western, non-native Eastern subspecies, or hybrids. We report here morphological and mtDNA analyses that suggest the majority of Banded Killifish that have expanded their range in Illinois are non-native Eastern Banded Killifish with some evidence of hybridization between the subspecies. The expansion of the non-native Eastern Banded Killifish could have implications for the listing status of Banded Killifish in the state of Illinois, as well as conservation efforts to manage for this ‘native invader’ that could harm the native Western Banded Killifish through mechanisms including hybridization and competition.