The righting response as a fitness index in freshwater turtles

Abstract

Theoretical evolutionary ecology assumes the existence of fitness variability in natural populations. As realistic measures of fitness are usually difficult to perform directly, integrating fitness indices are proposed in all taxa. In sauropsids, locomotor performances have been proposed as a good integrating index of fitness in natural populations. Concerning aquatic turtles, a performance trait that may be important for the survival of juveniles is the righting response of individuals when they are placed on their carapace. In the present study, we examined the righting response in juveniles of the red-eared slider turtle, Trachemys scripta elegans . We tested two different measures of the righting response for 170 juveniles from constant incubation temperature and for 86 juveniles from three sinusoidal fluctuating incubation temperatures that are considered as more representative of natural conditions in the nest. We compared the effects of offspring sex, maternal identity, juvenile growth rate, and juvenile survival (i.e. individual characteristics), as well as the nutritional status of juveniles (i.e. experimental conditions), on the two different measures of righting response and for each thermal incubation treatments of the eggs (i.e. experimental treatments). We observed that the effects of the individual characteristics were markedly different between the two measures of the righting response and between experimental treatments. These results highlight the importance of the choice of the measure and of the experimental conditions and treatments in the study of a phenotypic trait. Results obtained for only one performance measure under constant laboratory conditions must therefore be extrapolated to the field with caution. Our results also show that the righting response presents individual variability that is probably heritable and is indirectly correlated with survival. These findings support the validity of the righting response as a good candidate for a fitness index in aquatic turtles.

High levels of maternally transferred mercury disrupt magnetic responses of snapping turtle hatchlings (Chelydra serpentina)

“…We used turtles hatched in the laboratory from eggs that were collected from mothers with varying levels of mercury to minimize any influence of confounding factors that might differentially affect turtles captured in the field. Siblings of the hatchling turtles used in the magnetic alignment experiment were subjected to commonly used performance tests (righting response and movement speed) (Delmas et al, 2007;Bayley, 2002). We show that high levels of mercury eliminate the response of turtles to magnetic cues and discuss this change in response to key spatial stimuli in relation to their ecology and life history.…”

A question of scale: Replication and the effective evaluation of conservation interventions

“…Many headstarting programs accelerate hatchling growth rates beyond those of wild turtles, to ensure large body sizes before release (e.g., Haskell et al 1996;Vermont Fish & Wildlife Department 2009;Parks Canada 2012). The fine-scale relationship between body size and survivorship in wild hatchling turtles is unclear, with equivocal evidence both for and against the "bigger is better" hypothesis (Janzen 1993;Haskell et al 1996;Congdon et al 1999;Janzen et al 2000;Delmas et al 2007;Paterson et al 2014;Canessa et al 2016). Although sub-adult and adult freshwater turtles do experience lower mortality rates than juveniles (Enneson and Litzgus 2008), growth is energetically costly, and the physiological trade-offs of accelerated juvenile growth are not well understood (Wieser 1994;Bayne 2000;Dmitriew et al 2009;Dmitriew 2011).…”

Potential sources of intra-population variation in painted turtle (Chrysemys picta) hatchling overwintering strategy

“…Turtles that cannot right themselves are more likely to be predated, to desiccate and/or drown (Finkler and Claussen, 1997). Thus, righting ability is considered to represent a hatchling's future survival (Freedberg et al, 2004;Delmas et al, 2007). Hatchlings were processed within 24 h and released at their nests.…”