Lon L. McClanahan

Rate of water uptake through the integument of the desert toad, Bufo punctatus

Abstract 1. 1. The rates of water uptake across the total integument, ventral pectoral integument and ventral pelvic integument were compared in dehydrated Bufo punctatus . 2. 2. The ventral pectoral integument was found to take up insignificant quantities of water whereas the ventral pelvic integument was found to take water up at a mean rate of 423 mg/cm 2 per hr, and can account for approximately 70 per cent of the rate of water uptake in toads totally submerged. 3. 3. These data are consistent with observations on the rehydration behavior of the toad (i.e. rapid emergence after rains and pressing against moist substrates).

Uricotelism and Low Evaporative Water Loss in a South American Frog

A South American anuran (Phyllomedusa sauvagii) produced large amounts of semisolid urate when it was maintained on a diet of insects. Rates of evaporative water loss in Phyllomedusa sauvagii were only about 5 to 10 percent of those other anurans tested and were similar to those of lizards of comparable size.

Structure and Function of the Cocoon of a Ceratophryd Frog

Lepidobatrachus llanensis (Leptodactylidae) were found to form cocoons when exposed to dry conditions, either in air or soil. We studied the effect of cocoon formation on rates of water loss from intact animals. When first removed from water L. Ilanensis lost water at rates comparable to typical anurans under similar conditions (ca. 8 mg g-lhr-1), but within three to four days the cocoon began to form and water loss decreased 50 to 70% within a week. Rates of water loss from two individuals excavated after 150 days in dry soil were 1.08 and 0.55 mg g-lhr-1, or 7 to 14% of the rates of animals taken directly from water. While burrowed in relatively dry soil, L. llanensis differed from spadefoot toads (S. couchi) in not accumulating high concentrations of urea and thus did not reduce the water potential of their body fluids below that of the soil. Nevertheless, they lost less water and showed smaller increases in plasma electrolytes than did S. couchi under identical conditions.

Thermoregulatory Response to Heat in the Waterproof Frogs Phyllomedusa and Chiromantis

The thermal relations of waterproof frogs of two genera (Phyllomedusa and Chiromantis) were studied in an outdoor enclosure and, in the laboratory, in a thermal gradient, in a heated wind tunnel, and under an imposed radiant heat load. When allowed to move freely in a thermal gradient, no frogs showed a distinct preferred temperature, although Chiromantis spp. consistently avoided the cool end of the gradient. Both Chiromantis spp. and Phyllomedusa sauvagei voluntarily tolerated high body temperatures of 38 and 40 C, respectively. When subjected to a convective heat load, either outdoors or in the laboratory wind tunnel, both C. xerampelina and P. sauvagei allowed body temperature (Tb) to track air temperature (Ta) until Tb reached 38-39 C. Further increases in Ta resulted in little or no increase in Tb, whereas evaporative water loss (EWL) increased in direct proportion to the temperature difference (Ta − Tb) and with wind speed to the power of about 0.4. Phyllomedusa azurae increased water loss at a lower Tb (ca. 35-36 C) and did not regulate as precisely. A similar pattern was seen when frogs were subjected to rapid radiant heating. A sudden increase in EWL was observed when Chiromantis spp. reached a body temperature of 39 C and when P. azurae reached 35 C. Glands in the skin begin secretory activity when EWL increases, and the mechanism for thermoregulation in these frogs is apparently analogous to sweating.

Nitrogen excretion in the larvae of a land-nesting frog (Leptodactylus bufonius)

Abstract 1. 1. The larvae of the land-nesting frog, Leptodactylus bufonius, were found to produce predominant quantities of urea in the foam of the mud nests, as well as in water. 2. 2. The rate of ammonia excretion remained quite constant throughout development, whereas the rates of urea excretion closely followed the changes in rates of total nitrogen excretion. 3. 3. It is suggested that ureotelism may be widespread in many larval leptodac-tylids as well as other anuran larval forms living under conditions of restricted water.

Energetics, Salinity and Temperature Tolerance in the Mohave Tui Chub, Gila bicolor mohavensis

Metabolic performance at various temperatures and maximal swimming speeds, critical thermal maxima and minima, as well as salinity tolerance were examined in the Mohave tui chub, Gila bicolor mohavensis. Maximal metabolic rates, ca. 0.1 cc O2/g h were attained at 24 and 30 C at swimming speeds of 87 cm/sec. At 18 C fish could attain swimming speeds of only 45 cm/sec and consumed 0.1 cc 02/g h. Factorial metabolic scope dropped from 3.3 at 18 C to 1.57 at 30 C. The mean critical thermal maxima at three acclimation temperatures (18, 24, 30 C) were 33.5, 34.9 and 36.2 C, respectively. Mean critical thermal minima were 2.8, 4.8 and 7.2 C, respectively, for fish acclimated at 18, 24 and 30 C. Mohave chubs osmoregulate well up to salinities of 237 mOsm/1. Higher salinities induce weight loss and antidiuresis. Based on these experimental results it appears that the Mohave chub is not as adaptable to desert conditions as other desert fish, such as the pupfish (Cyprinodon). Therefore, careful consideration must be given to micro-environments when new refugia are sought for this endangered species.