Reproductive Patterns of Texas River Cooters (Pseudemys texana) and Red-Eared Sliders (Trachemys scripta elegans) at Spring Lake, Hays County, Texas




Mali, Ivana

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Clietonians are considered the most prolific atrmiote group, with some species laying up to 1000 eggs per year and nesting more than once during a single nesting season. Turtles have been used to test and developed optimality models predicting the strategy of maternal investment that will maximize maternal fitness within a population. Turtles are also ideal organisms for assessing the relationship of body size/body condition and reproductive fitness. I studied reproductive patterns of two species of emydine freshwater turtles. Texas river cooters (Pseudetnys texana) and red-eared sliders (Trachemys scripia elegans) at Spring Lake. Hays County. Texas during the 2009 nesting season, where I followed nesting turtles. After a female nested, I measured her plastron length, carapace length, carapace width, and determined her mass. Eggs were taken to Texas State University-Sail Marcos laboratory, where I measured egg length, egg width, and determined egg mass. I used simple linear regression to assess correlations between female body size (plastron length) and reproductive parameters (mean egg mass, mean egg length and width, mean clutch size and mass, and nest distance from wafer). Phenotype-habitat matching theory, (predicting increasing reproductive parameters with increasing body size) was followed for most of the reproductive parameters. However, those parameters did not show strong fit of data to the model (r2<0.3). I found 30 Texas river coolers and 9 red-eared sliders nesting twice in a single nesting season. I used paired t-tests to determine if clutch parameters (number of eggs, egg mass, total clutch mass) decrease with subsequent clutches laid during the same nesting season. Paired t-tests showed that mean egg mass, mean egg length and width decreased in subsequent clutches in Texas river coolers, blit the sample size for red-eared slider (n=9) was too small to make conclusions. Possible explanations for the weak correlation of body size with clutch parameters might be genetics of the population, weather conditions, or food availability. Repeating this study for several years would help get better understanding of reproductive patterns in those two populations. Optimal Egg Size theory tests showed contradictory results; while red-eared sliders supported OES, Texas river coolers did not. Therefore, it remains challenging to choose the correct optimality model for chelonians.



pseudemys, Trachemys scripta, sexual behavior in animals, habitats, Spring Lake, Texas


Mali, I. (2010). Reproductive patterns of Texas river cooters (Pseudemys texana) and red-eared sliders (Trachemys scripta elegans) at Spring Lake, Hays County, Texas (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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