Ontogenetic changes in endurance in water snakes (Natrix sipedon): physiological correlates and ecological consequences

F. Harvey Pough

ISSN: 0045-8511


Article may be found at: http://links.jstor.org/sici?sici=0045-8511(19780210)3%3A1978%3A1%3C69%3AOCIEIW%3E2.0.CO%3B2-L Adult northern water snakes (Natrix s. sipedon) can sustain maximum activity at 25 C for 42 min while newborn snakes are exhausted in 5 min. The increased endurance of large snakes is paralleled by an ontogenetic increase in blood oxygen capacity (BOC) and a decrease in blood oxygen affinity. The effect of these changes is to enhance oxygen transport and delivery in large water snakes. Whole-body lactic acid concentrations at exhaustion are 1.5 times higher in adults than in juveniles while endurance increases 8 times. Thus increased aerobic metabolism, produced partly by a 3-fold increase in BOC, provides much of the additional energy available to large water snakes. The ontogenetic change in endurance is reflected by differences in defensive behavior which is passive in juvenile water snakes and active in adults. Changes in prey selection can probably be traced to the ontogenetic difference in endurance. Because of their physiological differences, juvenile water snakes are ecologically quite different from adults.