Evolutionary ecology of stripe-necked musk turtles (Sternotherus peltifer) in the Cahaba River drainage

Abstract

Stripe-necked musk turtles (Sternotherus peltifer) are one of the least-studied species of the southeastern United States’ diverse turtle fauna. Despite this, the environmental variation that exists within their geographic distribution makes them excellent study subjects for addressing questions about how the local environment drives adaptation in aquatic organisms at the population level. In this thesis, I examine variation in shell shape of S. peltifer from the Cahaba River drainage basin in central Alabama, USA. I then present the first data on clutch and egg size for the species and conduct a preliminary examination of reproductive allometry. The results of my analyses on both traditional and geometric morphometric measures indicate that S. peltifer from above the fall line have flatter shells than those from the coastal plain. This phenotypic pattern aligns with observations from other turtles, suggesting that some aspect of the environment above the fall line, such as flow rate, has led to local adaptation for flat shell shapes in turtles. Since morphological features such as pelvic aperture width or flat shell shapes may present a constraint on reproductive output in small turtles, I examined reproduction in S. peltifer from above the fall line. Clutch size and egg width both increased with female body size, suggesting that there is competition for allocation of resources to different aspects of reproduction. Pelvic aperture width also increased with female body size, and did not appear to present a constraint on egg width. These results highlight the importance of the local environment for affecting the morphological and life history evolution of aquatic organisms at the population level.