Ecomorphological variation in shell shape of the freshwater turtle Pseudemys concinna inhabiting different aquatic flow regimes

Abstract

Populations of species that inhabit a range of environments frequently display divergent morphologies that correlate with differences in ecological parameters. The velocity of water flow (i.e., flow velocity) is a critical feature of aquatic environments that has been shown to influence morphology in a broad range of taxa. The focus of this study was to evaluate the relationship between flow velocity and shell morphology for males and females of the semi-aquatic freshwater turtle Pseudemys concinna. For both sexes, the carapace and plastron show significant morphological differences between habitats characterized by slow-flowing (i.e., lentic) and fast-flowing (i.e., lotic) water. In general, the most prominent pattern for both sexes is that the shells of individuals from lotic habitats are more streamlined (small height-to-length ratio) than the shells of individuals from lentic habitats. Of the two shell components (carapace and plastron), the carapace shows greater divergence between habitats, particularly for males. These results are consistent with adaptations to flow velocity, and suggest that variation in shape may be more constrained in females. I also provide empirical evidence for an adaptive benefit of the observed shape change (i.e., drag reduction) and a brief comment on the relative roles of genetic divergence and phenotypic plasticity in generating shape differences observed in this species.

Sexual Dimorphism in the Greek Tortoise: A Test of the Body Shape Hypothesis

“…DISCUSSION When only shape (and not size) is taken into account, the shells of female G. insculpta and C. picta exhibit lower average stresses for a given load, and therefore may be said to be stronger than those of their male counterparts. Such a pattern is not unexpectedfemale turtles are known to develop taller, more rounded shells than males for many species (e.g., Tucker et al, 1998), and such shapes are conventionally considered to be better at resisting failure during loading from predators (e.g., Rivera, 2008;Stayton, 2009). The greater stresses exhibited by G. insculpta models with concave plastra are also expected-a concave structure tends to exhibit larger amounts of tension, compared with a flat structure, when stressed (Currey, 2006;Wainwright et al, 1982).…”

“…For example, the increased height of their shells may increase females' ability to resist loads (Tucker et al, 1998). However, although the taller shell is beneficial for protection and reproduction, it may negatively affect the hydrodynamic properties of female turtle shells by increasing drag (Rivera, 2008). The narrower, flatter shell of male turtles probably produces a lower drag coefficient (Rivera, 2008) and increases swimming performance, but this flatter shell may make the shell weaker during loading.…”

“…However, although the taller shell is beneficial for protection and reproduction, it may negatively affect the hydrodynamic properties of female turtle shells by increasing drag (Rivera, 2008). The narrower, flatter shell of male turtles probably produces a lower drag coefficient (Rivera, 2008) and increases swimming performance, but this flatter shell may make the shell weaker during loading. These potential functional differences can in turn affect other aspects of turtle natural history.…”

Swimming and jumping ability of 10 Great Plains fish species

“…Morphological differences have been documented between lotic and lentic populations based on specific ecological parameters such as water velocity. Water velocity was found to have altered the height to length ratio of the carapace of the turtle, Pseudemys concinna (Rivera 2008) and also changed growth rates and body condition of freshwater drum Aplodinotus grunniens (Rypel et al 2006). Morphological differences were found in blacktail shiner Cyprinella venusta as lentic individuals had deeper bodies and a shorter dorsal fin base that was located more anterior than lotic individuals (Haas et al 2010).…”

Hydrodynamic stability of the painted turtle (Chrysemys picta): effects of four-limbed rowing versus forelimb flapping in rigid-bodied tetrapods

“…Although a number of studies have examined aspects of swimming in aquatic turtles, including kinematics (Davenport et al, 1984;Pace et al, 2001;Renous et al, 2008;Zug, 1971), motor control (Blob et al, 2008;Gillis and Blob, 2001; Rivera and Blob, 2010), maneuverability (Heithaus et al, 2002;Rivera et al, 2006) and hydrodynamic implications of shell morphology (Aresco and Dobie, 2000;Claude et al, 2003;Lubcke and Wilson, 2007;Rivera, 2008;Rivera and Claude, 2008), relatively little is known about hydrodynamic stability in this lineage. Dougherty et al examined stability in post-hatchlings of two species of marine turtles [Caretta caretta (Linnaeus 1758) and Chelonia mydas (Linnaeus 1758)], providing a quantitative description of recoil motions throughout the limb cycle during rectilinear swimming using synchronous flapping (i.e.…”