Hybridization and Polyploidy in a Community of Three Sunfish Species (Pisces: Centrarchidae)

Abstract

Hall's Pond, a man-made reservoir in eastern Connecticut, contains three sunfish species: Lepomis gibbosus (pumpkinseed), L. cyanellus (green sunfish), and L. macrochirus (bluegill). In the past, gibbosus x cyanellus hybrids were extremely abundant, outnumbering both parent species. In laboratory crosses, diploid female gibbosus x cyanellus hybrids, backcrossed to males of both parent species, produced triploid offspring. Two types of triploids (gibbosus x cyanellus x cyanellus and gibbosus x cyanellus x macrochirus) occur naturally in Hall's Pond, and probably are the offspring of the diploid female hybrids. In contrast, male gibbosus x cyanellus hybrids show reduced fertility; although many were observed guarding nests with fry, most of the fry were not their progeny. During the study the number of gibbosus x cyanellus hybrids dropped dramatically; eventually they were no more common than the other sunfish hybrids in the pond. INTERSPECIFIC hybridization generally leads either to sterile F,'s or to fertile hybrids that utilize normal meiosis. Occasionally, however, hybridization disrupts meiosis so that hybrids produce viable gametes, but without recombination or reduction in ploidy; this disruption can lead to clonal hybrids, and it can lead to triploids. Clonal hybrids result when the unreduced eggs of female hybrids develop directly, either in the absence of sperm (partheno