Comparisons of Aquatic Versus Terrestrial Predatory Strikes in the Pitviper, Agkistrodon piscivorus SHAWN E. VINCENT 1n , ANTHONY HERREL, 2 AND DUNCAN J. IRSCHICK 1 1 Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana 70118 2 Functional Morphology Laboratory, University of Antwerp, Antwerp, Belgium ABSTRACT Recent studies comparing terrestrial versus aquatic locomotion in animals have shown that changes in kinematics, muscular activation patterns, and performance across media are often dramatic. Surprisingly, however, despite the importance of feeding to the survival of most animals, few studies have compared differences in feeding behaviour between media. The present study compares prey-capture behaviour, strike success, strike velocity and acceleration, and prey- capture kinematics in a semi-aquatic pitviper (Agkistrodon piscivorus) when capturing both terrestrial (mice) and aquatic (fish) prey in a standardized laboratory setting. Strike velocity and acceleration did not differ significantly between media, but instead were positively correlated with initial prey distance. By contrast, the kinematics of terrestrial and aquatic strikes differed significantly in several aspects: max gape angle during the retraction phase, angular velocity of mouth closing during the strike, and the initial head angle before the strike. Terrestrial strikes were associated with higher gape angles during the retraction phase, higher angular velocities of mouth closure, and a more inclined head angle at the onset of the strike. Finally, strike success differed significantly between strike types, with terrestrial strikes being considerably more successful than aquatic strikes. Strike success likely differed due to the relatively slow mouth-closing velocity of aquatic strikes. J. Exp. Zool. 303A:476–488, 2005. r 2005 Wiley-Liss, Inc. INTRODUCTION Recent studies on animals moving in different environments have demonstrated significant changes in locomotor behaviour in response to the differences in the physical properties of the medium through which they move. For instance, anguillid eels undulating through water or across land alter the relative timing of the activation of their axial musculature between environments (Gillis, ’98). Additionally, studies comparing ter- restrial versus aquatic locomotion in birds, am- phibians, and lizards show that changes in kinematics, muscular activation patterns, and performance across media can be dramatic (e.g., Biewener and Gillis, ’99; Gillis and Biewener, 2000; Biewener and Corning, 2001; Ashley-Ross and Bechtel, 2004). Differences in locomotor patterns between water and land are largely believed to be a consequence of the difference in physical properties between the two media. Water is forty times more viscous and eight hundred times denser than air, so considerable drag forces will be generated when animals move through water, thereby strongly influencing how animals move within the aquatic medium (see e.g., Vogel, ’81). Although an increasing number of studies have examined differences in the kinematics of locomo- tion in water versus on land, fewer studies have examined differences in the feeding behaviour of animals feeding in different media (but see Lauder and Shaffer, ’85, ’88; Reilly and Lauder, ’88; Shaffer and Lauder, ’88). This lack of data comparing how individuals feed on land versus within water is surprising given the documented differences in locomotor behaviour, and the ob- vious importance of feeding ability to the fitness of an organism. Whereas a diversity of terrestrial Grant Sponsor: NSF; Grant number: IBN 9983003 to Duncan J. Irschick n Correspondence to: Shawn E. Vincent, Department of Ecology and Evolutionary Biology, 310 Dinwiddie Hall, Tulane University, New Orleans, LA 70118. E-mail: svincent@tulane.edu Received 15 July 2004; Accepted 15 November 2004 Published online in Wiley InterScience (www.interscience.wiley. com). DOI: 10.1002/jez.a.179. r 2005 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY 303A:476–488 (2005)