Society for the Study of Amphibians and Reptiles Energetic Cost of Predation : Aerobic Metabolism during Prey Ingestion by Juvenile Rattlesnakes , Crotalus durissus Author ( s ) :

-We investigated the cost of prey ingestion in the South American rattlesnake, Crotalus durissus, to see if the capacity to generate energy aerobically could be a constraint on the size of the prey that can be ingested. To accomplish this goal, we measured time and aerobic metabolism (inferred from oxygen consumption) of juvenile C. durissus ingesting prey ranging from 10 to 50% of their own body mass. Time needed for prey ingestion increased with prey size, with prey representing 10 and 20% of snake size being ingested with the same effort Whole animal rates of oxygen consumption increased linearly with prey size, but at a slower pace for snakes ingesting prey larger than 30% of their body mass. Aerobic factorial power input necessary for prey ingestion increased with prey size, and for snakes ingesting prey representing 50% of their body mass it equaled the aerobic factorial scope for exercise. For the maximum prey size tested, the aerobic derived energy necessary for prey ingestion represented 0.02% of the total energy content of the prey. Within the prey size range we studied, the cost of ingestion did not constitute any constraint on the size of the prey that can be ingested. These constraints are set by morphological (gape size), ecological (predation risk), and, probably, by physiological parameters, as suggested by the tendency of VO2 during ingestion to increase at a slower pace at relative larger prey sizes. Several evolutionary scenarios consider morphological modifications related to dietary demands as the main driving force for the impressive radiation experienced by snakes (Rieppel, 1980; Greene, 1983). Early in the evolution of this group, small modifications of the jaw apparatus permitted them to ingest prey of relatively large mass (Gans, 1961). This modification were associated with a shift in foraging mode, from frequent ingestion of small prey to infrequent ingestion of large prey (Greene, 1983). The feeding biology of snakes has been examined from several perspectives: predatorprey relationships (Arnold, 1993), kinematics of jaw apparatus during prey handling and ingestion (Cundall, 1987), dietary correlates of evolution (Greene, 1983), and physiological aspects of digestion (Andrade et al., 1997). Despite the attention given to morphological, behavioral, and ecological aspects of predation in snakes, some fundamental questions remain. For example, studies on the energetic correlates of predation in snakes are rare (Feder and Arnold, 1982). In lizards, studies on energetic expenditure associated with ingestion of different prey sizes have provided data that have clarified some aspects related to optimal foraging theory (Pough and Andrews, 1985), the constraints on feeding due to their morphological adaptation for a particular habitat (Andrews et al., 1987), the metabolic support (aerobic or anaerobic) during feeding (Preest, 1991), and the relationship between prey size and sexual size dimorphism (Preest, 1994). Nonetheless, extrapolation of these interpretations to snakes may be misleading, due to fundamental differences in feeding mechanisms between these groups (Gans, 1961). Herein, we quantify aerobic metabolism and the time expended by juvenile South American rattlesnakes, Crotalus durissus, in ingesting prey of relative different sizes. Crotalus durissus, like other viperids, possess very derived specializations associated with feeding and ingest prey of a wide size range (S. S. Santana, unpubl. data), which make it a suitable model to test the effects of prey size on feeding energetics in snakes. Since there is a lack of data on the relationship between energetic expenditure and prey ingestion in snakes (but see Feder and Arnold, 1982), we analyzed our data in two ways: (1) by comparing energy expenditure for ingesting different prey size with the maximum aerobic capacity of this species, and (2) by analyzing the relationship between energy input and return associated with the ingestion of different prey sizes. With this approach we attempted to determine how the physiological capabilities, in terms of oxygen consumption, vary with the ingestion of different relative prey sizes. The results will help to determine if these variation sets an upper limit to the size of the prey that can be ingested by juvenile C. durissus. MATERIAL AND METHODS Experimental Animals. -We used 15 juvenile Crotalus durissus of both sexes in this study. This content downloaded from 200.145. 191.239 on Thu, 28 Nov 2013 10:48:59 AM All use subject to JSTOR Terms and Conditions A. P. CRUZ-NETO ET AL. These snakes came from the same litter as those used in our previous study on the energetics of digestion in rattlesnakes (Andrade et al., 1997). Protocol for maintenance of the snakes in captivity are in Andrade et al. (1997). We fasted snakes for at least 10 d before the experiments in order to raise the level of hunger, and used only healthy snakes that were not in shedding