Hybridizing sisters: Evidence of bluegill-pumpkinseed hybridization in modified habitats at the confluence of two major Canadian waterways

Abstract

Urbanization and shoreline development are reshaping aquatic ecosystems, creating conditions that promote hybridization among fishes. This study investigates the potential hybridization between bluegill (Lepomis macrochirus) and pumpkinseed (Lepomis gibbosus) at the confluence of two major Canadian waterways and compares it to a long-established hybridization in Lake Opinicon, Ontario. We genetically confirm 17 bluegill–pumpkinseed hybrids in Montreal’s West Island, marking the first documented occurrence in Quebec. Hybrids from Montreal showed clearer classification into simple hybrid categories, suggesting a more recent hybridization than that observed in Lake Opinicon. Morphological, dietary, and isotopic analyses indicate that hybrids in both locations are more distinct from bluegill, with pure pumpkinseed becoming increasingly rare in Lake Opinicon. Notably, hybrids in Montreal are concentrated in heavily modified habitats, where altered environmental conditions appear associated with hybridization. This study captures an early stage of introgressive hybridization and highlights the importance of preserving critical habitat conditions to maintain the genetic integrity of key native fish species.