BIOL 3300 Vertebrate Zoology: Ectotherms - Herpetology

How do you heat yourself… electromagnetically or chemically? Ectothermy is THE key feature to understanding this diverse group! Importance of Ectothermy!

Control over body temp. spans from essentially none to fairly precise… Thermoregulators vs. thermoconformers T b is NOT constant… but diel pattern is! How do herps utilize ectothermy?

Figure 7.2 Lizards and frogs occurring at high elevations in Peru maintain different body temperatures and behave differently in response to temperature at the same locality. The lizard Liolaemus multiformis maintains a relatively high and constant body temperature throughout the day by basking. The toad Rhinella spinulosa reaches about 23°C in the morning by basking in sun and then retreats under a boulder at about 1050 hr. By repeated emergences and retreats, the toad maintains body temperatures below surface soil temperatures. Adapted from Pearson and Bradford, 1976.

How do herps utilize ectothermy? How could this lizard alter the amount of heat gained via radiation absorption?

Figure 7.4 The environments in which individual amphibians and reptiles live provide different opportunities for heat exchange based on the medium and the physical structure of the habitat. A reptile differs from the amphibians shown because water loss is much lower and influences body temperature much less. The reptile also is limited in its ability to absorb water directly from the environment. Adapted from Brattstrom, 1979.

Figure 7.3 Profile of body temperature characteristics of an ectotherm. Mean body temperature is based on field data taken on active animals. Set temperature is based on temperatures selected by individuals with external influences eliminated. See Table 7.1 for definitions.

Figure 7.16 Brooding temperature in a python. Python molurus bivittatus generates heat by rapid contractions of skeletal muscle while brooding eggs. The rate of muscle contractions increases, oxygen intake increases, and CO2 production increases during egg brooding. Adapted from Van Mierop and Barnard, 1978.

Don’t have to keep the thermostat at the same temperature Don’t have to burn the furnace… 1/7 to 1/10 of similar sized endotherm. ¡Tranquilo! What are the benefits?

E ctotherms are E fficient What are the benefits? EctothermsEndotherms Plethodon cinereus48K-rat0.8 Desmognathus ochrophaeus76-98Field Mouse1.8 Norops limifrons23-28Meadow Vole3.0 Uta stansburiana18-25Red squirrel1.3 Heterodon contortix81Least Weasel2.3 Python curtus6-33Savanna Sparrow1.1 Vipera berus49Marsh Wren0.5 Mean (n=12)50Mean (n=19)1.4 Source: Pough et al. 2004

Not always at optimal performance ( why? ) What are the disadvantages?

Figure 7.5 Theoretically, physiological and behavioral performances are maximized across a relatively narrow range of body temperatures in ectothermic vertebrates (left). Empirical data on Ameiva festiva demonstrate that performance is constrained by temperature. Adapted from Huey and Stevenson, 1979, and Van Berkum et al., 1986.

Figure 7.7 Green frogs, Lithobates clamitans, jump varying distances depending upon their body temperature but do most poorly at low and high temperatures. "a" and "b" refer to different sets of samples at 20°C. Adapted from Huey and Stevenson, 1979.

Figure 7.8 Body temperatures determine escape behaviors of active Agama savignyi. At high body temperatures, lizards rely on running (flight) for escape, reflecting the optimization of running speeds at high body temperatures. At lower body temperatures, alternative escape behaviors become more frequent. Defense occurs at three levels: level 1, gape and lunge; level 2, upright stance, body inflated, and tongue protruding; and level 3, all of the preceding plus attack, lashing with tail, and leaping off substrate to bite. Adapted from Hertz et al., 1982.

How do they work? Q 10 = Temperature coefficient how a 10° C temp. change affects the rate of a biological process. How are Heat, H 2 O and metabolism linked?

Temperate species have to deal with seasonally cold/deadly temperatures… How do they do this? What about cold temperatures?

Herpetofauna as a RULE are much smaller than birds or mammals. 80% lizards and 90% of frogs/salamanders <20g… Nearly all birds/mammals are >20g. Hardly any birds/mammals <5g… But, small frog adults <0.5g Smallest bird? Smallest mammal? Smallest herp? What is the influence on size? why?

Figure 7.6 A multitude of factors influence heat exchange and thus body temperatures and thermal ecology of amphibians and reptiles. The effects of some variables are direct, such as orientation and exposure during basking. Others are indirect. Predators, for example, can interfere with an amphibian or reptile's ability to use basking sites, thereby forcing it to maintain activity at suboptimal temperatures. Adapted from Hutchison and Dupré, 1992.

Figure 7.15 Thermal images of snakes showing that the head region differs dramatically from the body in temperature during cooling. (A) The head of the tropical rattlesnake Crotalus durissus barely cools just following apnea. (B) Four seconds later, the head of the same snake is much cooler following inspiration. (C) A different rattlesnake just after a high level of activity (tail rattling), showing significant respiratory head cooling. (D) A python showing whole-head cooling following gaping behavior and rapid respiratory rates, leading to high rates of evaporative water loss. Adapted from Tattersall et al., 2006.

Figure 7.22 Male spring peepers (Pseudacris crucifer) expend considerable energy calling to attract females during the breeding season. The rate of calling is related to reproductive success, which explains why males expend extra energy to call at higher rates. Adapted from Taigen et al., 1985.

Figure 7.26 The sidewinder, a sit-and-wait predator, expends considerably less energy under natural field conditions than the coachwhip, an actively foraging predator. Year-long profiles of daily energy expenditures (averaged by month) are illustrated. Open symbols indicate field metabolic rates based on doubly labeled water measurements, and closed symbols indicate standard metabolic rates. Adapted from Secor and Nagy, 1994.

Figure 7.21 Effects of body mass and temperature on the rate of oxygen uptake (metabolic rate) in a reptile and an amphibian under two different thermal regimes. Amphibians have lower metabolic rates than reptiles even after the effects of size and temperature are removed. Data from Bennett, 1982, and Whitford, Q10 ?!?