ESPINOZA, N.R.*; BLOB, R.W.; Erskine College; Clemson University: Swimming in painted turtles: testing kinematic similarity among members of a morphologically conservative lineage.
Use of representative species is widespread in evolutionary studies of locomotor diversity. Functional diversity is often expected in the context of morphological divergence among taxa, but what are the prospects for locomotor diversity among morphologically similar taxa? To examine this question, we collected three-dimensional kinematic data from swimming painted turtles and compared these to previous data from the closely related (and morphologically similar) red-eared slider (Trachemys scripta). Painted turtles (Chrysemys picta) belong to a restricted clade of deirochelyine emydid turtles that includes the chicken turtle (Deirochelys), sliders (Trachemys), and cooters (Pseudemys). Turtles rely primarily on their limbs to generate propulsive forces, and limb morphology is highly conserved across these taxa; in particular, the hindfoot is larger and possesses more substantial webbing between the digits than the forefoot. The timing of each major kinematic event (e.g. transition from protraction to retraction, peak elbow and knee extension) is generally similar in these species, but the taxa do exhibit some quantitiative kinematic differences. Painted turtles show greater extension (as much as 20°) of both the elbow and knee than sliders during the power stroke, possibly aiding thrust production. Paddle (foot) orientation also differs between these taxa. Painted turtles do not exhibit the discrete phase of high-drag forefoot orientation shown by sliders during recovery phase. In addition, painted turtles rotate the hindfoot into an orientation more nearly perpendicular to flow during thrust phase than sliders. These results demonstrate the potential for at least moderate kinematic diversity among closely related taxa despite morphological similarity.
