Scaling of bite performance with head and carapace morphometrics in green turtles (Chelonia mydas)
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Adult green turtles (Chelonia mydas) are unusual relative to other sea turtles in that they are predominately herbivorous. This herbivorous diet is reflected in the serrated morphology of their beak, bite performance and the relative morphometrics of their heads. Recent bite performance data in loggerhead turtles (Caretta caretta), which are known for their durophagous capability, have demonstrated that bite force is correlated with head morphometrics. The objective of this study was to characterize bite force in green turtles and correlate bite performance with head and carapace morphometrics. We predicted that maximum bite force in green turtles would be less in magnitude relative to loggerheads, but would be positively correlated with head morphometrics. Therefore, mass, straight carapace length, straight carapace width, greatest head width, height, and length were collected with bite force from free-ranging green turtles from Punta Abreojos, Baja California Sur, Mexico and Otsuchi, Japan. Subjects ranged from 10.9 to 48. kg, with straight carapace length and width ranged from 40.6. cm to 71.9. cm (mean. =. 56.3. ±. 8.5. cm) and from 33.5. cm to 55.9. cm (mean. =. 44.8. ±. 5.7. cm), respectively. A bite force apparatus was used to collect bite performance from subjects. The maximum bite force was 303. N. Mean head width, head height, and head length were 8.7. ±. 1.2, 8.2. ±. 1.1, and 11.5. ±. 1.5. cm, respectively. Bite force was lower in magnitude than reported for loggerhead turtles as predicted but still strong enough to process algal and plant matter, as well as crush many hard prey items. Simultaneous measurements of body and head size, and the use of non-linear reduced major axis regression, show that bite force scaled isometrically relative to body size and head size. Simple correlation showed that all logged transformed morphometrics were good predictors of logged bite performance, but an AICc-based weighted regression showed that body mass, followed by head width and head height, were better predictors of bite force than carapace size. © 2013 Elsevier B.V.
author list (cited authors)
Marshall, C. D., Wang, J., Rocha-Olivares, A., Godinez-Reyes, C., Fisler, S., Narazaki, T., Sato, K., & Sterba-Boatwright, B. D.