Darters (Percidae) are a vastly diverse group of fish, with the majority of species possessing a premaxillary frenum: a fleshy bridge of skin connecting the upper lip to the snout and reducing premaxillary protrusion. The purpose of the present study was to examine external and internal correlates of frenum development in three representative darters: Missouri saddled (Etheostoma tetrazonum), greenside (E. blennioides) and Johnny (E. nigrum). These species vary in the development of the frenum from fully developed (saddled darters), to intermediate (greenside darters), to completely absent (Johnny darters). We measured several external characters, focusing especially on the head region, and several cranial characters in cleared and stained specimens. Factor analysis was used to compare external and internal multivariate shape variables separately among these species. Greenside and Johnny darters differed significantly from saddled darters in having overall relatively smaller external characters in the head region with relatively higher protrusibility; greenside and saddled darters differed significantly from Johnny darters in having longer snouts and relatively lower protrusibility. Greenside and Johnny darters also had higher snout curvature than saddled darters. For internal characters, all three taxa differed significantly in having relatively small cranial characters relative to skull length and long, narrow ascending processes (greenside) or large cranial characters with short, wide ascending processes (saddled). Johnny darters were intermediate in regard to these characters. Greenside and saddled darters also had relatively long opening in-levers, while Johnny darters had relatively short opening in-levers. Regarding operculum size, no significant difference was found between the three species. We see these data and comparisons as providing a framework for functional hypotheses concerning frenum function and ecological morphology in darters. Future work should include sampling of more darter species, and especially increased sampling of greenside darter populations and clades, among which cranial characters are known to vary intraspecifically.
|Advisor:||Brunkow, Paul E.|
|Commitee:||Essner, Rick L., Jennings, David H.|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 58/01M(E), Masters Abstracts International|
|Subjects:||Morphology, Zoology, Animal sciences|
|Keywords:||Darters, Frenum, Greenside, Johnny, Morphology, Saddled|
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