INTRADRAINAGE VARIATION IN POPULATION STRUCTURE, SHAPE MORPHOLOGY, AND SEXUAL SIZE DIMORPHISM IN THE YELLOW-BLOTCHED SAWBACK, GRAPTEMYS FLAVIMACULATA
Graptemys flavimaculata (Yellow-blotched Sawback) is a small, highly aquatic turtle that is endemic to rivers and large creeks of the Pascagoula River system of southeastern Mississippi, USA. Little is known about geographic variation in population structure, shape morphology, and sexual size dimorphism (SSD) throughout the drainage. I captured and measured G. flavimaculata from three sites in 2005 and 2006. I analyzed female head width at two of these sites in 2008. Results indicate that body size and population structure vary across a geographic gradient; turtles from the Pascagoula River site were generally larger (both body mass and plastron length) relative to two upstream sites on two tributaries, the Leaf and Chickasawhay rivers. Additionally, body shape in females varied among populations, with Pascagoula River females having a more domed shape than upstream sites where turtles have a more streamlined shape. There was little difference in male shapes among sites. Female-biased SSD typified all three populations with SSD being less pronounced in the two upstream sites. Female head width was significantly different across sites (Pascagoula > Leaf), while there was no difference among sites for male claw length. Presumably, synergistic factors influence population structure, shape morphology, and sexual size dimorphism in Graptemys flavimaculata including: 1) food availability; 2) presence of competitors; 3) thermal environment; 4) presence of alligators; and 5) fluvial conditions.