Winterkill, Oxygen Relations, and Energy Metabolism of a Submerged Dormant Amphibian, Rana Muscosa

Abstract

Both larval and metamorphosed Rana muscosa (mountain yellow—legged frog) over—winter for 6—9 mo in ice—covered lakes and streams at high elevation (≤3700 m) in California and Nevada. In some winters almost all the frogs in shallow lakes (<4 m deep) die. This mortality is associated with oxygen depletion, which occurs most rapidly in shallow lakes. However, tadpoles survive for months in nearly anoxic conditions when shallow lakes are frozen to the bottom. In the laboratory at low P02, oxygen metabolism of overwintering tadpoles at 4° differed from that of frogs. The critical oxygen tension (Pc) of tadpoles (1.98 kPa) was significantly lower than for frogs (4.04 kPa). Also, when P02 was greater than Pc, the resting oxygen consumption (V02) of tadpoles partially conformed to P02, whereas the resting V02 of frogs was constant. At the atmosphere P02 of their natural environment (P02 °13.3 kPa), however, the resting V02 of tadpoles was not significantly different from that of frogs. Tadpoles apparently have two advantages over frogs during winter: (1) a greater tolerance of low P02, and (2) a reduced consumption of energy and oxygen at low P02. Unlike a number of anuran species which become dormant on land at temperatures above 4°, the resting V02 of metamorphosed R. muscosa overwintering at 4° was nearly the same as for summer—acclimated individuals in air at 4°. During 7 mo dormancy, the standard metabolic rate of both tadpoles and frogs remained constant. Resulting V02 of frogs in water at 4°, and in air at 15° was related to the 0.83—0.85 power of body mass.

Tribute to R. G. Boutilier: The role for skeletal muscle in the hypoxia-induced hypometabolic responses of submerged frogs

“…However, laboratory behavioural studies Tattersall and Boutilier, 1999) further indicate that cold-submerged frogs remain relatively active when placed in O 2 and thermal gradients; they explore their environment and eventually settle in areas of optimal ambient O 2 content and temperature. This behaviour in non-uniform environments is consistent with the inability of frogs to survive prolonged and severe O 2 lack (Bradford, 1983;Boutilier et al, 1997). Submerged frogs exploit thermal and O 2 gradients in natural waterways to seek out cold water with high levels of dissolved O 2 and thereby achieve a state of slow, aerobic metabolism Tattersall and Boutilier, 1999).…”

Body size is not critical for criticalPO2 in scarabaeid and tenebrionid beetles

“…In the only prior interspecific comparison, P crit was found to be independent of body mass for grasshoppers (Greenlee et al, 2007). We are aware of no data to date that show how P crit varies with size among adults of a single species of insects, although in amphibians P crit was found to increase with increasing body size in Siren lacertina (Ultsch, 1974) and to not be significantly correlated with body size in the frog Rana muscosa (Bradford, 1983). …”

Reversing introduced species effects: Experimental removal of introduced fish leads to rapid recovery of a declining frog

“…When tadpoles hatched from the egg masses, I recorded the number of tadpoles attacked by trout during daily 20-min observation periods at each enclosure. R. muscosa tadpoles take several years to metamorphose (42), and some that hatched in previous years (Gosner stage Ͼ 36) were confined inside the enclosures during cage construction. Attacks on these tadpoles were recorded separately from attacks on the newly hatched tadpoles.…”

“…However, extensive museum records exist for this species (41), and these data have been used to confirm the decline of this once abundant montane frog (36). The mountain yellow-legged frog occurs mostly at high elevation (up to 3,700 m) and has a larval stage lasting up to 4 yr, making the species dependent on permanent bodies of water for successful reproduction (42). This frog apparently evolved without intense fish predation because nearly its entire range was historically fishless (41,43).…”