Reproductive Isolation Between Pumpkinseed (Lepomis gibbosus) and Longear Sunfish (L. megalotis) (Centrarchidae) in the Thames River, Southwestern Ontario

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Abstract
In the middle branch of the Thames River, southwestern Ontario, nest construction and occupation by male pumpkinseeds (Lepomis gibbosus) began earlier and reached a peak earlier in the season than nesting by male longear sunfish (L. megalotis). Nevertheless the two species' breeding seasons broadly overlapped. All pumpkinseed nests occurred in backwater areas, where water flow is minimal, the substrate is a deep layer of detritus and mud, and aquatic plant growth is heavy. Some longear nests were in the backwaters, but most were in the main river, where water flow is variable, the substrate mainly sand and gravel, and vegetation sparse. Females of both species are nonterritorial and were found throughout the study area. Hybrid sunfish are present in the area and opportunities for interspecific breeding would seem to be greatest in backwaters, where males of both species may occupy nests close to each other. However, the only observed interbreeding was between female pumpkinseeds and male longears in the main river. Behavioral barriers to interbreeding occasionally break down under the turbulent social conditions associated with breeding in large longear colonies. Key words: sunfish, reproductive isolation, longear, pumpkinseed, habitat, season, behavior

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