David T. Booth

Experimental Demonstration of the Energetic Cost of Parasitism in Free-Ranging Hosts

Although some parasites have obvious pathogenic effects, others appear to have subtle, indirect effects that are poorly understood, particularly in natural populations. Indirect effects may result from parasites altering host metabolic rate and hence host energy needs, yet no experimental studies have shown this to be the case for non-laboratory hosts. We report the results of a long-term field experiment designed to test the impact of parasites on host energetics. We measured the energetics of feral rock doves ( with populations of feather-feeding lice, traditionally considered to have little or no effect on host fitness. The lice reduced feather mass leading to increased thermal conductance and metabolic rate, as well as a steady reduction in host body mass over the course of the nine-month study. Our results demonstrate that even classically ‘benign’ parasites such as feather lice can reduce host condition through the accumulation of subtle energetic costs over time. We argue that experimental manipulations are a prerequisite for documenting such effects.

Influence of incubation temperature on hatchling phenotype in reptiles.

Incubation temperature influences hatchling phenotypes such as sex, size, shape, color, behavior, and locomotor performance in many reptiles, and there is growing concern that global warming might adversely affect reptile populations by altering frequencies of hatchling phenotypes. Here I overview a recent theoretical model used to predict hatchling sex of reptiles with temperature‐dependent sex determination. This model predicts that sex ratios will be fairly robust to moderate global warming as long as eggs experience substantial daily cyclic fluctuations in incubation temperatures so that embryos are exposed to temperatures that inhibit embryonic development for part of the day. I also review studies that examine the influence of incubation temperature on posthatch locomotion performance and growth because these are the traits that are likely to have the greatest effect on hatchling fitness. The majority of these studies used artificial constant‐temperature incubation, but some have addressed fluctuating incubation temperature regimes. Although the number of studies is small, it appears that fluctuating temperatures may enhance hatchling locomotor performance. This finding should not be surprising, given that the majority of natural reptile nests are relatively shallow and therefore experience daily fluctuations in incubation temperature.

Depth and temperature of the blue marlin, Makaira nigricans, observed by acoustic telemetry

Multiplex acoustic transmitters were used to monitor the depth, swimming speeds, body temperature and water temperature preference of six blue marlin, Makaira nigricans (Lacépède), near the Hawaiian islands in July and August 1989. The blue marlin ranged in size from 60 to 220 kg and were tracked for 1 to 5 d. All of the fish moved away from the point of capture and were followed up to 253 km from the island of Hawaii. The blue marlin tracked remained in the top 200 m of the water column, spending half the time in the upper 10 m, and rarely ventured below the thermocline. In the nearsurface waters the temperature was uniformly warm (25 to 27°C). The coldest water temperature, 17°C, was encountered on the deepest descent recorded (209 m). Depth changes occurred rapidly and excursions below 10 m were usually less than 60 min in duration. Muscle temperature was similar to water temperature except for a 2°C elevation in muscle temperature observed at the beginning of tracking one individual. This initial rise in body temperature was associated with the anaerobic muscle activity during capture and is an indication of the physiological stress involved in capture.

Temperature-dependent sex ratio in a bird.

To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1 : 1 at the average temperature found in natural mounds. Chicks from lower temperatures weigh less, which probably affects offspring survival, but are not smaller. Megapodes possess heteromorphic sex chromosomes like other birds, which eliminates temperature-dependent sex determination, as described for reptiles, as the mechanism behind the skewed sex ratios at high and low temperatures. Instead, our data suggest a sex-biased temperature-sensitive embryo mortality because mortality was greater at the lower and higher temperatures, and minimal at the middle temperature where the sex ratio was 1 : 1.

Incubation temperature, energy expenditure and hatchling size in the green turtle (Chelonia mydas), a species with temperature-sensitive sex determination

Eggs from the Heron Island, Great Barrier Reef, nesting population of green turtles (Chelonia mydas) were incubated at all-male-determining (26 degreesC) and all-female-determining (30 degreesC) temperatures. Oxygen consumption and embryonic growth were monitored throughout incubation, and hatchling masses and body dimensions were measured from both temperatures. Eggs hatched after 79 and 53 days incubation at 26 degreesC and 30 degreesC respectively. Oxygen consumption at both temperatures increased to a peak several days before hatching, a pattern typical of turtle embryos, and the rate of oxygen was higher at 30 degreesC than 26 degreesC. The total amount of energy consumed during incubation, and hatchling dimensions, were similar at both temperatures, but hatchlings from 26 degreesC had larger mass, larger yolk-free mass and smaller residual yolks than hatchlings from 30 degreesC. Because of the difference in mass of hatchlings, hatchlings from 30 degreesC had a higher production cost.

Temperature variation within and between nests of the green sea turtle, Chelonia mydas (Chelonia: Cheloniidae) on Heron Island, Great Barrier Reef

Four temperature data-loggers were placed in each of five green sea turtle nests on Heron Island in the 1998–99 nesting season. Temperatures in all nests increased as incubation progressed due to general sand heating and increased metabolic heat production of the developing embryos. Even at the top of nests no daily diurnal fluctuation in temperature was evident. The temperature of eggs in the middle of the nest increased above those in the nest periphery during the last third of incubation. However, this metabolic nest heating would have little effect on hatchling sex ratio because it occurred after the sex-determining period. Small differences in temperature between regions of a nest persisted throughout incubation and may be important in ensuring the production of at least some individuals of the opposite sex in nests that have temperatures close to either the all-male or all-female determining temperatures. Location and degree of shading of nests had little effect on mean nest temperature, but deeper nests were generally cooler and therefore were predicted to produce a higher proportion of males than were shallower nests. Nest temperature profile data indicated that the 1998–99 nesting season on Heron Island would have produced a strongly female-biased sex ratio amongst hatchlings.

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26°C were larger in size than hatchlings from 28 and 30°C, whilst in the second year hatchlings from 25.5°C were similar in size to hatchings from 30°C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28°C, hatchlings from eggs incubated at 25.5 and 26°C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30°C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea.

Effect of Temperature on Development of Mallee Fowl Leipoa ocellata Eggs

Mallee fowl eggs were successfully incubated over the temperature range 32-38 C. Greatest hatchability occurred at 34 C (80%); 22% hatched at 32 C, 44% at 36 C; and 38% at 38 C. Field data indicate that eggs can tolerate temperatures as low as 28 C for at least 4 days and that egg temperature can vary from 28 to 38 C during incubation. Birds did not regulate mound temperature as precisely as previously reported, 3-5 C variations in temperature were common. Energetic cost of development was found to be temperature dependent. Embryos developing at 32 C required 74% more energy than embryos developing at 38 C.

Effect of tail loss on reproductive output and its ecological significance in the skink Eulamprus quoyii

induced variation in body size of turtles hatching in natural nests. Oecologia 93:445-448. PLUMMER, M. V., AND H. L. SNELL. 1988. Nest site selection and water relations of eggs in the snake, Opheodrys aestivus. Copeia 1988:58-64. RATTERMAN, R. J., AND R. A. ACKERMAN. 1989. The water exchange and hydric microclimate of painted turtle (Chrysemys picta) eggs incubating in field nests. Physiol. Zool. 62:1059-1079. RHEN, T., AND J. W. LANG. 1995. Phenotypic plasticity for growth in the common snapping turtle: effects of incubation temperature, clutch, and their interactions. Amer. Natur. 146:726-747. ROOSENBURG, W. M., AND K. C. KELLEY. 1996. The effect of egg size and incubation temperature on growth in the turtle, Malaclemys terrapin. J. Herpetol. 30:198-204. SAS INSTITUTE. 1988. SAS/STAT Users Guide. SAS Institute, Cary, North Carolina. SPOTILA, J. R., L. C. ZIMMERMAN, C. A. BINCKLEY, J. S. GRUMBLES, D. C. ROSTAL, A. LIST JR., E. C. BEYER, K. M. PHILLIPS, AND S. J. KEMP. 1994. Effects of incubation conditions on sex determination, hatching success, and growth of hatchling desert tortoises, Gopherus agassizii. Herpetol. Monogr. 8:103116.

Nest temperature and respiratory gases during natural incubation in the broad-shelled river turtle, Chelodina expansa (Testudinata : Chelidae)

Temperature was monitored in three natural nests, and oxygen and carbon dioxide partial pressure monitored in one natural nest of the broad-shelled river turtle, Chelodina expansa, throughout incubation. Nest temperature decreased after nest construction in autumn, remained low during winter and gradually increased in spring to a maximum in summer. In a nest where temperature was recorded every hour, temperature typically fluctuated through a 2 degrees C cycle on a daily basis throughout the entire incubation period, and the nest always heated faster than it cooled. Oxygen and carbon dioxide partial pressures in this nest were similar to soil oxygen and carbon dioxide partial pressures for the first 5 months of incubation, but nest respiratory gas tensions deviated from the surrounding soil over the last three months of incubation. Nest respiratory gas tensions were not greatly different from those in the atmosphere above the ground except after periods of rain. After heavy rain during the last 3 months of incubation the nest became moderately hypoxic (P-O2 similar to 100 Torr) and hypercapnic (P-CO2 similar to 50 Torr) for several successive days. These short periods of hypoxia and hypercapnia were not lethal.