Body Color Pattern and the Aggressive Behavior of Male Pumpkinseed Sunfish (Lepomis Gibbosus) During the Reproductive Season

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Abstract
Male pumpkinseed sunfish (Lepomis gibbosus) readily attacked plywood models placed into their nests. Models containing red features (iris, opercular flap) received more attacks and aggressive displays than models lacking these features or than models which had these features painted black. This indicates that in the pattern of the male pumpkinseed, the red portion of the opercular flap and the red iris are social releasers for aggressive behavior. These features fade in subordinate pumpkinseeds in the laboratory and also in female pumpkinseeds before they enter the male's nest during reproduction. This pattern change would therefore function to decrease aggressive behavior directed at these individuals. A conspicuous feature of the female pumpkinseed is the presence of lateral bars. When bars were added to models, reductions in aggressive behavior were consistently observed. Hence, bars appear to inhibit male aggression. Bluegill sunfish (L. macrochirus) nest sympatrically with pumpkinseeds and interspecific nest defense was commonly seen. A conspicuous feature of male bluegills is a dark spot in the area of the dorsal fin rays. When such a spot is added to models, increases in aggressive behavior were observed in male pumpkinseeds. Hence, this feature may provide a basis for interspecific recognition and reproductive isolation. Finally, pumpkinseeds responded more vigorously to models than did bluegills. This may imply that the former are more attuned to morphological features than the latter. Bluegills, on the other hand, may be more attuned to the behavior of nest intruders. This hypothesis agrees with differences in the nesting ecology of these species.