Thermal Sensitivity of Axolotl Feeding Behaviors

Musculoskeletal movement results from muscle contractions, recoil of elastic tendons, aponeuroses, and ligaments, or combinations thereof. Muscular and elastic contributions can vary both across behaviors and with changes in temperature. Skeletal muscles reach peak contraction speed at a temperature optimum with performance declining away from that optimum by approximately 50% per 10°C, following the Q10 principle. Elastic recoil action, however, is less temperature sensitive. We subjected Axolotls (Ambystoma mexicanum) to changes from warm (23°C), via medium (14°C), to cold (6°C) temperature across most of their thermal tolerance range, and recorded jaw kinematics during feeding on crickets. We sought to determine if suction feeding strikes and food processing chews involve elastic mechanisms and, specifically, if muscular versus elastic contribution vary with temperature for gape opening and closing. Measurements of peak and mean speed for gape opening and closing during strikes and chews across temperature treatments were compared with Q10-based predictions. We found that strike gape speed decreased significantly from warm and medium to cold treatments, indicating low thermal robustness, and no performance-enhancement due to elastic recoil. For chews, peak, and mean gape closing speeds, as well as peak gape opening speed, also decreased significantly from warm to cold treatments. However, peak gape opening and closing speeds for chews showed performance-enhancement, consistent with a previously demonstrated presence of elastic action in the Axolotl jaw system. Our results add to a relatively small body of evidence suggesting that elastic recoil plays significant roles in aquatic vertebrate feeding systems, and in cyclic food processing mechanisms.