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Missouri Southern State University logo

Thomas Zapletal

Biology Major
Physical and Biological Sciences Category


I am Thomas Zapletal, a senior biology student here at Missouri Southern State University. I have worked with Dr. Penning for almost a year and been involved in the reptile physiology lab since the beginning of January.  


Sexual dimorphism in reptiles is present in various forms such as bite force, mass, tail length, behavior and more. An example of this is in turtle species, a longer tail usually indicates that it is a male, however, a female has a short tail. During an ecological survey of Kellogg Lake in Carthage, MO, populations of Sternotherus odoratusTrachemys scripta, and Regina grahamii were found. Size was used as the measure of sexual dimorphism among these three species. During the survey, 93 S. odoratus were captured and results indicated that this population was heavily female skewed (p<0.0001) and there was no significant difference in size between males and females (p>0.75). Among the 48 T. scripta captured, 17 were juveniles, 14 were males, and 17 were females. Juveniles were indicated by no obvious external characters to distinguish from either males or females. There was no significant difference found between sexes (p>0.46) or in size between the sexes (p>0.87). Among the 15 R. grahamii captured, the data was heavily female skewed (p<0.0001) and that females were significantly heavier than the males captured (p < 0.02). Further data is needed to be collected to accurately determine if the S. ordoratus and R. grahamii populations were significantly different in a 1:1 sex ratio. 

Poster Presentation