Abstract
Due in part to their large size, aggressive temperament, and difficulty in handling, there are few physiological studies of adult crocodilians in the literature. As a result, studies comparing individuals across an ontogenetic series and comparisons among species are also lacking. We addressed this gap in knowledge by measuring standard metabolic rates (SMR) of three species of crocodilians (Crocodylus porosus, C. johnsoni, and Alligator mississippiensis), and included individuals that ranged from 0.22 to 114 kg. Allometric scaling of SMR with body mass was similar among the species, but C. porosus had significantly higher SMR than did C. johnsoni or A. mississippiensis. Differences in SMR among species are potentially related to behavioural differences in levels of aggression; C. porosus are the most aggressive of the crocodilians measured, and have rates of standard metabolism that are approximately 36% higher at the grand mean body size than those measured for C. johnsoni or A. mississippiensis, which are among the least aggressive crocodilians.
Highlights
Crocodilians have been an important group in our understanding of animal nutrition, growth, and physiology
Standard metabolic rate was measured in 63 individuals: 35 C. porosus ranging in size from 0.22 to 114 kg, 21 C. johnsoni ranging from 0.34 to 48 kg, and 7 A. mississippiensis ranging from 1.29 to 104 kg (Fig 1)
C. porosus had a higher standard metabolic rate (SMR) than both C. johnsoni and A. mississippiensis (Scheffe S = 95.7 and 25.5 respectively, and P < 0.001 for both), but C. johnsoni and A. mississippiensis did not differ from one another (S = 1.1, P > 0.5)
Summary
Crocodilians (clade Crocodylia: Gavialidae, Alligatoridae, and Crocodylidae) have been an important group in our understanding of animal nutrition, growth, and physiology. As a result of their remarkable fecundity, rapid growth rates, and relative ease of captive propagation, crocodilians have long been a model for studies in reptilian nutritional physiology [1, 2]. A large majority of the published data regarding crocodilian physiology and metabolism has been collected from juveniles weighing less than ~3 kg, a size that is typically reached by most crocodilians within the first few years of life [3, 4]. The result is a potential demographic bias in the literature towards the study of young individuals that could yield a relatively myopic view of ontogenetic changes in physiological function that may accompany the extreme. Crocodilian metabolism growth and large body sizes achieved by crocodilians. The largest of the extant crocodilians, the saltwater crocodile (Crocodylus porosus), changes in body mass by more than four orders of magnitude across a lifetime from a ~60 g hatchling [5] to just over 1,000 kg in the very largest of adults [6]
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