Vaughan H. Shoemaker

Observations on the Thermal Relations of Western Australian Lizards

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Energetics of Foraging in Breeding Adelie Penguins

We studied foraging energetics in Adelie Penguins (Pygoscelis adeliae) using doubly labeled water (DLW) and time-depth recorders (TDR). Measurements were made during three nesting stages: late incubation, the guard stage (when small chicks were con- tinuously guarded by at least one parent), and the subsequent creche stage (when large chicks were left unattended). Nest relief cycle times decreased from 229 h during incubation to 33.3 h during the creche stage, and the fraction of time birds spent swimming increased from 20.8% during incubation to 31.6% during the creche stage. The fraction of swim time spent in hunting dives and bottom time did not change significantly at different nesting stages. Field metabolic rates (FMR) were 2.73 x basal metabolic rate (BMR) during in- cubation, 3.03 x BMR during the guard stage, and 3.29 x BMR during the creche stage; due to high variance these values did not differ significantly. Estimated metabolic rate during swimming was 8.2 x BMR. Rates of prey capture (grams of krill per hour of swimming, per hour of hunting dives, and per hour of bottom time) did not change at different stages. Food provided to chicks was 20.9% (guard stage) to 23.3% (creche stage) of the food metabolized by adults. Our data suggest that (1) prey capture by Adelies is limited primarily by their ability to find krill swarms and not by limitations in harvest rates or energy efficiency after prey have been located, and (2) reproductive effort in Ad6lies does not require a large increase in either energy expenditures or foraging time.

Evaporative water loss, nitrogen excretion and osmoregulation in phyllomedusine frogs

Summary1.Minimal rates of evaporative water loss in tree frogs of genusPhyllomedusa (P. pailona, P. iherengi, P. hypochondrialis) were only 5–10% those of representatives of two related genera,Agalychnis annae andPachymedusa dacnicolor (Table 1).2.Phyllomedusa species,A. annae andP. dacnicolor all took up water rapidly (25–45% standard wt·hr−1) across the skin following prolonged water deprivation (Table 2).3.When fed mealworms (Tenebrio larvae) and deprived of additional water, body fluid concentrations increased more slowly inPhyllomedusa species than in representatives of three other genera (Agalychnis, Pachymedusa andHyla) tested. Of thePhyllomedusa species,P. sauvagei showed by far the lowest rate of increase (Table 4).4.The osmoregulatory ability of thePhyllomedusa species is primarily attributable to their ability to excrete urate. The fraction of total waste nitrogen production excreted as urate was 80% inP. sauvagei, ca. 45% inP. pailona andP. iherengi, and 24% inP. hypochondrialis. Urate excretion inAgalychnis, Pachymedusa andHyla was negligible (Tables 5 and 9).5.Increased water intake did not alter the rate of urate production in the three species tested (P. sauvagei, P. hypochondrialis andA. annae) (Table 6).6.Additional osmoregulatory benefit is derived byPhyllomedusa species from the binding of Na+, K+, and NH4+ to precipitated urate (Tables 5 and 7).7.On a diet of mealworms, energy losses via the feces and nitrogen wastes ranged from 14 to 18% of intake in the four species ofPhyllomedusa and inP. dacnicolor, and were about equally divided between the two avenues (Tables 8 and 9).8.These results suggest thatP. sauvagei could remain in water balance in nature on a diet of insects with little or no additional water intake.

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.

Reproductive effort in Adélie penguins

SummaryWe estimated reproductive effort (energy expenditures for reproduction, as opposed to maintenance) in Adélie penguins breeding at Palmer Station, Antarctica. Data on body composition changes and metabolic rate were obtained using isotopic methods. Adelie breeding behavior consists of an initial courtship stage (during which both sexes fast), incubation, the ‘guard’ stage (when chicks are 1 to 18–28 days old), and the ‘creche’ stage (from the end of guarding until chicks are 28–45 days old). Both males and females lost considerable mass during the initial stages of the reproductive season, but males fasted longer and lost more mass. Mass losses of both sexes consisted of 66% depot fat and 34% lean tissue. Mass and body composition remained constant once birds resumed feeding. The metabolic expenditure for the foraging necessary to accumulate the mass lost while fasting — one component of reproductive effort —was about 63 MJ in males and 39 MJ in females. Field metabolic rates (FMR) were low during courtship and while incubating, increasing more than 2-fold when birds resumed foraging. Although mean FMR increased between incubation and the creche stage, differences between stages were small and not significant. We used FMR data and an energy balance model to estimate the cost of feeding chicks. Results suggest a maintenance FMR of about 2.7 × basal metabolism (BMR), increasing to 3.4–3.6 × BMR during the creche stage. The reproductive effort (as metabolic expenditures) associated with feeding chicks is 31 MJ (males) to 36 MJ (females). Cumulative reproductive effort is 94 MJ in males and 75 MJ in females, or 5.3–6.2% of the annual energy budget. The reproductive effort devoted to chick care does not appear to be constrained by physiological or time limitations. Instead, selection to reduce the risk of predation may prevent the evolution of increased parental care.

Skin Lipids, Water Loss, and Energy Metabolism in a South American Tree Frog (Phyllomedusa sauvagei)

Evaporative water loss in Phyllomedusa sauvagei is very low at ambient temperatures up to 30 C but increases precipitously between 35 and 40 C. Standard metabolic rate shows a constant Q10 (ca. 2.4) between 10 and 38 C. At ambient temperatures of 38–40 C there are pulsatile releases of clear fluid on the skin, and skin and core temperatures are maintained at 35–37 C. Some skin secretions of P. sauvagei contain lipids which are mainly wax esters. A film of the lipid retards evaporation from a water surface at temperatures below 35 C but is relatively ineffective at 38 C and above. This lipid appears to have a transition temperature strategically placed to minimize evaporative losses up to the point where thermal considerations outweigh those of water conservation.

Field Energetics and Food Consumption of the Galápagos Marine Iguana, Amblyrhynchus cristatus

Metabolic rates (doubly labeled water), daily time budgets, and feeding rates were determined for free-ranging marine iguanas on Isla Fernandina, Galápagos. Field metabolic rates were related to body mass according to the equation kJ/day = 0.079 g0.97 for all sizes of lizards, and kJ/day = 0.64 g0.68 for adults only. Hatchlings had surprisingly low field metabolic rates. The daily energy expenditure of a representative 1-kg adult (70.3 kJ/day) was 1.7 times resting metabolism. Metabolic cost of basking (1.9 times resting at 35 C) accounted for 37% of daily energy expenditure; foraging cost was only 8% of the daily cost of living. Foraging efficiency (metabolizable energy gained while foraging/energy spent while foraging) was 12.8, much higher than insectivorous lizards studied to date, but similar to two other herbivorous lizards that forage on land. The plant-eating lizards spend only about 1 h/day foraging, so their foraging expenses are much lower than those of insectivorous lizards which forage 3.5-10 h/day. Adult Amblyrhynchus consumed only algae (primarily Ulva lobata), and about 79% of the energy in their diet was available for metabolism. A 1-kg adult consumed about 8.6 g dry mass (or 37.4 g fresh mass) of food per day. The population of marine iguanas on Punta Espinosa (ca. 1,885 animals) would consume about 27,000-29,000 kg of fresh algae each year.

Osteoderms in Anurans

Dermal ossifications-- osteoderms- are more common in anurans than has been gen- erally acknowledged. In the hylid Phyllomedusa bicolor osteoderms are located in the dermis, cover the dorsal surface of the head and body, and are scattered on the lateral and ventral surfaces and the limbs. Each osteoderm consists of a vascularized bony basal plate (0.1 mm thick) from which bony lamellar spines protrude into the epidermis. The dorsal body osteoderms are approximately 3 mm2 in area. Similar osteoderms are present in Phyllomedusa vaillanti and Gastrotheca weilandii. In the pelobatid Megophrys nasuta osteoderms are present in the dorsal body skin and although comparable to the osteoderms of Phyllomedusa in size and shape they are histologically very dif- ferent. Megophrys osteoderms are avascular and composed of calcified collagen bundles in an orderly three-dimensional arrangement. The leptodactylid Hylactophryne augusti also has small bony osteoderms in the skin of the dorsum. They differ from the hylid osteoderms and resemble Megophrys osteoderms in being avascular and having a matrix composed of horizontal and vertical bundles of collagen. Larger dermal bony dorsal plates are present in Lepidobatrachus and Ceratophrys (Leptodactyl- idae) and in Brachycephalus (Brachycephalidae). Anuran osteoderms are structurally different from, and not homologous with, caecilian dermal scales. Given the histological differences among the various anuran osteoderms and the taxonomic diversity (Hylidae, Pelobatidae, Leptodactylidae, and Brachycephalidae), osteoderms appear to have been independently evolved a number of times within the Anura. It is suggested that the term dermal scale be restricted to the bony scale of fishes and caecilians, and osteoderms be used to denote the dermal scutes of anurans and reptiles. Textbooks on vertebrate anatomy clearly state that amphibians, with the

Heat Resistance of Some Australian Lizards

Survival times of Australian lizards representing 29 species of 16 genera in the Agamidae, Scincidae, Gekkonidae, and Pygopodidae, were determined at a series of high temperatures in the range in which this function shows strong thermal dependence. Most species were studied at 40.5?, 43.5?, and 46? C, but this range was expanded to include 37.5? or 47? C for a few. Results indicate some differences in heat resistance between

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.