title: Cold-blooded snipers: thermal independence of ballistic tongue projection in the salamander Hydromantes platycephalus.
abstract: Plethodontid salamanders of the genus Hydromantes capture prey using the most extreme tongue projection among salamanders, and can shoot the tongue a distance of 80% of body length in less than 20 msec. The tongue skeleton is projected from the body via an elastic-recoil mechanism that decouples muscle contraction from tongue projection, amplifying muscle power tenfold. We tested the hypothesis that the elastic-recoil mechanism also endows tongue projection with low thermal dependence by examining the kinematics and dynamics of tongue projection in Hydromantes platycephalus over a range of body temperatures (2-24°C). We found that H. platycephalus maintained tongue-projection performance over the tested temperature range and that tongue projection showed thermal independence (Q(10) values of 0.94-1.04) of all performance parameters including projection distance, average velocity, and peak instantaneous values of velocity, acceleration, and power. Nonelastic, muscle-powered tongue retraction, in contrast, responded to temperature changes significantly differently than elastic tongue projection; performance parameters of retraction displayed thermal dependence typical of muscle-powered movement (Q(10) values of 1.63-4.97). These results reveal that the elastic-recoil mechanism liberates tongue projection from the effects of temperature on muscle contractile rates. We suggest that relative thermal independence is a general characteristic of elastic-recoil mechanisms and may promote the evolution of these mechanisms in ectothermic animals.
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, Florida 33602, USA. sdeban@usf.edu
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Deban
authors.forename: Jason C
authors.initials: JC
authors.lastname: Richardson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D001831:Body Temperature; D004576:Electromyography; D005247:Feeding Behavior / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D011235:Predatory Behavior / Q000502:physiology*; D014059:Tongue / Q000502:physiology*; D014562:Caudata / Q000502:physiology*; D014741:Video Recording