Opercular Flaps as Sexual Ornaments For Male Longear Sunfish (Lepomis Megalotis)


Kaye Goddard

Date of Graduation

Summer 1996


Master of Science in Biology



Committee Chair

Alicia Mathis


Characteristics such as courtship displays and body size have been shown to influence mating success of male fishes. However, few examples of structural sexual ornaments exist in fishes, and ornamentation is typically limited to coloration. One possible example of a structural sexual ornament in a fish species may be the exaggerated opercular flaps of male longear sunfish (Lepomis megalotis). The opercular flaps are soft scaleless extensions of the opercula which are conspicuously colored, associated with exaggerated gestures and sexually dimorphic for length. I investigated the effects of male opercular flap length on female mate choice and on male resource holding power in four laboratory experiments by manipulating the opercular flap length of matched pairs of males. In a fifth experiment, I investigated the effects of male body condition on male opercular flap growth. Females spent significantly more time with, and displayed more to the longer-flapped males when the males' flaps were clipped and when the males' flaps were extended. When the opercular flaps were clipped, only longer original (unmanipulated) flap length produced a significantly greater frequency of male dominance, suggesting that flap length may be a reliable indicator of resource holding power. In addition, the opercular flaps grew significantly faster than pelvic fin spines, a nonsexually selected trait, despite condition. Thus, female longear sunfish may use opercular flap length to assess the quality of potential mates, and male longear sunfish may use opercular flap length of rival males to assess their resource holding power. The high growth rate of the opercular flaps suggest an advantage in increased length, thereby supporting results of the female choice and male competition experiments. These results suggest that the opercular flaps of male longear sunfish function as sexual ornaments and as an indicator of male quality.

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© Kaye Goddard