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Ecology Thermoregulation in Animals
by
Michael J. Angilletta

Introduction

Thermoregulation includes all phenomena in which an organism maintains a mean or variance of body temperature that deviates from a null expectation, defined by random use of thermal microclimates and passive exchange of heat with the environment. Early studies of thermoregulation focused on certain taxa that exhibit striking physiological or behavioral strategies, such as endothermic vertebrates and desert lizards. Subsequent research has shown that most organisms thermoregulate to some degree, although thermoregulatory strategies vary greatly among taxa. In the late 1970s and the 1980s, researchers not only continued to study patterns and mechanisms of thermoregulation, they also began to study the evolutionary factors that influence capacities for and strategies of thermoregulation. This period coincided with the appearance of a new discipline, evolutionary physiology, which was a natural outgrowth of ecological physiology (or physiological ecology). From this period to the present day, studies of thermoregulation have driven much of the conceptual development within ecological and evolutionary physiology, thereby strengthening our general understanding of regulatory behavior.

General Overviews

To understand the development of concepts and ideas within the field, one should consult several syntheses of knowledge about temperature and thermoregulation. Cossins and Bowler 1987, focusing on mechanisms of thermoregulation, was the first general synthesis of the field. McNab 2002 contains a more recent review of patterns and mechanisms of thermoregulation in vertebrates. Angilletta 2009 provides greater emphasis on the evolution of thermoregulation. Other books and articles provide excellent reviews of thermoregulation in specific taxa, including reptiles (Huey 1982), amphibians (Hutchison and Dupré 1992), crustaceans (Lagerspetz and Vainio 2006), insects (Chown and Nicolson 2004), and mammals and birds (Clarke and Rothery 2008). In addition, the Journal of Thermal Biology routinely publishes papers about thermoregulation.

Historical Development of the Concept

The concept of thermoregulation stems from observations that the body temperatures of organisms often deviate from the body temperatures that one would expect in the absence of regulation. Consequently, the development of the concept in inextricably tied to the development of a null expectation for body temperature. At first, researchers inferred thermoregulation from deviations between organismal temperatures and air temperatures. Heath 1964 shows that even inanimate objects would reach different temperatures from the surrounding air when exposed to solar radiation, thus warning against the use of air temperature as a null expectation. Shortly thereafter, Bakken and Gates 1975 introduces the concept of operative temperature, which now serves as an appropriate null for evaluating thermoregulatory performance. Hertz, et al. 1993 introduces several indices that enable one to quantify an animal’s thermoregulatory performance, given knowledge of its preferred temperature and the operative temperatures. Christian and Weavers 1996 introduces a related index to compare thermoregulatory performance, which also relies on preferred temperature and operative temperatures. More recently, Wills and Beaupre 2000 shows how randomization of operative temperatures can be used to infer thermoregulation when one does not know the preferred temperature, and Christian, et al. 2006 shows how a null expectation can be generated for an animal with thermal inertia.

  • Bakken, George S., and David M. Gates. 1975. Heat-transfer analysis of animals: Some implications for field ecology, physiology, and evolution. In Perspectives of biophysical ecology. Edited by David M. Gates and Rudolf B. Schmerl, 255–290. New York: Springer-Verlag.

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    Models the body temperature of an animal that experiences radiation, conduction, and convection to establish the concept of operative temperatures. This concept has become integral to the study of thermoregulation, because it serves as an appropriate null expectation for a nonregulating animal.

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  • Christian, Keith A., Christopher R. Tracy, and C. Richard Tracy. 2006. Evaluating thermoregulation in reptiles: An appropriate null model. American Naturalist 168.3: 421–430.

    DOI: 10.1086/506528Save Citation »Export Citation »E-mail Citation »

    Points out that large animals have thermal inertia, which makes an instantaneous measure of operative temperature less desirable. Solves this problem by simulating random movement and heat exchange to define a null distribution of body temperatures for a nonregulating animal with thermal inertia.

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  • Christian, Keith A., and Brian W. Weavers. 1996. Thermoregulation of monitor lizards in Australia: An evaluation of methods in thermal biology. Ecological Monographs 66.2: 139–157.

    DOI: 10.2307/2963472Save Citation »Export Citation »E-mail Citation »

    First intensive application of the thermoregulatory indices proposed by Hertz, et al. 1993; proposed a new index designed to quantify the degree to which individuals exploit thermally suitable microenvironments.

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  • Heath, James Edward. 1964. Reptilian thermoregulation: Evaluation of field studies. Science 146.3645: 784–785.

    DOI: 10.1126/science.146.3645.784Save Citation »Export Citation »E-mail Citation »

    A classic study showing that one cannot infer thermoregulation by comparing body temperatures to air temperatures. Heath found that beer cans exhibit temperatures that deviate from air temperature and resemble the body temperatures of certain animals, even though beer cans cannot thermoregulate.

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  • Hertz, Paul. E., Raymond B. Huey, and R. D. Stevenson. 1993. Evaluating temperature regulation by field-active ectotherms: The fallacy of the inappropriate question. American Naturalist 142.5: 796–818.

    DOI: 10.1086/285573Save Citation »Export Citation »E-mail Citation »

    A must-read paper for anyone interested in thermoregulation. Introduces indices to quantify the accuracy of thermoregulation, the environmental constraints on thermoregulation, and the effectiveness of thermoregulation given the environmental constraints. These indices have greatly influenced the way that researchers measure thermoregulation in natural environments.

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  • Wills, C. A., and S. J. Beaupre. 2000. An application of randomization for detecting evidence of thermoregulation in timber rattlesnakes (Crotalus horridus) from northwest Arkansas. Physiological and Biochemical Zoology 73.3: 325–334.

    DOI: 10.1086/316750Save Citation »Export Citation »E-mail Citation »

    Introduces a randomization approach for demonstrating that an animal’s body temperature deviates from the operative temperatures available in its environment. This approach enables one to test hypotheses about thermoregulation when preferred temperatures are unknown.

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Preferred Body Temperature

The concept of preferred body temperature has been integral to interpreting the temperatures of animals in their natural environments. Quantitative indices of thermoregulation are generally calculated as the absolute difference between observed body temperature and a preferred body temperature (or range of temperatures). Consequently, papers that discuss ways to define or measure preferred body temperatures are an important source for students of thermoregulation. Additionally, researchers have also considered whether preferred body temperatures reflect the coevolution of thermoregulatory behavior and thermal tolerance.

Definition and Measurement

Licht, et al. 1966 defined preferred body temperature as the mean temperature selected in an environment with minimal thermoregulatory costs or constraints, while also illustrating the way to measure preferred body temperatures in artificial thermal gradients. Sievert and Hutchison 1988 cautions against using thermal gradients that confound heat and light. Dillon, et al. 2009 and Angilletta 2009 discuss several effective designs for a thermal gradient. Regardless of the kind of thermal gradient, one must consider important issues regarding the measurement and interpretation of preferred body temperature. Reynolds and Casterlin 1979 considers changes in preferred body temperature resulting from acclimation, suggesting that researchers should give animals a sufficient time to acclimate to a thermal gradient. Barber and Crawford 1977 advances the idea that observed distributions of body temperatures could reflect a preferred range of temperatures rather than a single preferred temperature. Therefore, one might follow Hertz, et al. 1993 (cited under Historical Development of the Concept), which defines preferred body temperature as the central portion of the distribution of temperatures selected in a thermal gradient. Dillon, et al. 2009 covers a broad range of topics related to preferred body temperature, including methodological considerations, neurological mechanisms, genetic variation, developmental plasticity, and ecological significance.

  • Angilletta, Michael J. 2009. Thermal adaptation: A theoretical and empirical synthesis. Oxford: Oxford Univ. Press.

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    See Box 4.1 on page 92 for examples of thermal gradients used to measure preferred body temperatures in a variety of animals.

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  • Barber, Billy J., and Eugene C. Crawford Jr. 1977. A stochastic dual-limit hypothesis for behavioral thermoregulation in lizards. Physiological Zoology 50.1: 53–60.

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    Models the distribution of body temperatures that would result if thermoregulation were governed by upper and lower thresholds rather than a single thermal set-point.

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  • Dillon, M. E., G. Wang, P. A. Garrity, and R. B. Huey. 2009. Thermal preference in Drosophila. Journal of Thermal Biology 34.3: 109–119.

    DOI: 10.1016/j.jtherbio.2008.11.007Save Citation »Export Citation »E-mail Citation »

    A comprehensive look at the measurement and patterns of preferred body temperature in Drosophila, but covers many issues pertinent to other ectotherms.

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  • Licht, Paul, William R. Dawson, Vaughan H. Shoemaker, and A. R. Main. 1966. Observations on the thermal relations of western Australian lizards. Copeia 1966.1: 97–110.

    DOI: 10.2307/1440766Save Citation »Export Citation »E-mail Citation »

    The authors define preferred body temperature and use an artificial thermal gradient to measure this variable in several species of lizards.

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  • Reynolds, William Wallace, and Martha Elizabeth Casterlin. 1979. Behavioral thermoregulation and the “final preferendum” paradigm. American Zoologist 19.1: 211–224.

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    Reviews the concept of final preferendum, which essentially is the preferred temperature of an animal that has acclimated to the conditions of a thermal gradient; argues that studies of preferred body temperature should be designed such that animals reach their final preferendum.

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  • Sievert, Lynnette M., and Victor H. Hutchison. 1988. Light versus heat: Thermoregulatory behavior in a nocturnal lizard (Gekko gecko). Herpetologica 44.3: 266–273.

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    An experiment that underscores the need to separate sources of light and heat when estimating preferred body temperature.

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Relationship with Thermotolerance

Preferred body temperatures are thought to reflect the physiological benefits conferred by a particular temperature. Consistent with this idea, Dawson 1975 concludes that the preferred body temperatures of reptiles generally correspond to the temperatures that maximize rates of physiological performance (i.e., thermal optima). Beitinger and Fitzpatrick 1979 reviews more limited data for fish and concludes that preferred temperatures maximize rates of growth. These early reviews led to the hypothesis that thermoregulation and thermotolerance coevolve, which has been called the coadaptation hypothesis. Huey and Bennett 1987 presents the first phylogenetic comparative study of the coadaptation hypothesis, revealing a significant correlation between preferred temperature and the thermal optimum for sprinting in lizards. However, a reanalysis of the data by Garland, et al. 1991 casts doubt on the original conclusion. Angilletta, et al. 2002 reviews subsequent experimental and comparative tests of the coadaptation hypothesis. Angilletta, et al. 2006 develops a conceptual model that describes how thermoregulation and thermotolerance should coevolve. Some evolutionary models suggest that coadaptation should lead to a genetic correlation between thermoregulation and thermotolerance, as observed in Good 1993, an experiment with fruit flies. Martin and Huey 2008 shows that natural selection can favor genotypes that prefer temperatures below the thermal optimum for performance, particularly when individuals thermoregulate inaccurately.

  • Angilletta, Michael J., Jr., Albert F. Bennett, Helga Guderley, Carlos A. Navas, Frank Seebacher, and Robbie S. Wilson. 2006. Coadaptation: A unifying principle in evolutionary thermal biology. Physiological and Biochemical Zoology 79.2: 282–294.

    DOI: 10.1086/499990Save Citation »Export Citation »E-mail Citation »

    Figure 5 contains a conceptual model of the factors that influence the coadaptation of thermoregulation and thermotolerance.

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  • Angilletta, Michael J., Peter H. Niewiarowski, and Carlos A. Navas. 2002. The evolution of thermal physiology in ectotherms. Journal of Thermal Biology 27.4: 249–268.

    DOI: 10.1016/S0306-4565(01)00094-8Save Citation »Export Citation »E-mail Citation »

    Reviews comparative and experimental evidence that preferred temperatures are coadapted with thermal optima for physiological performances.

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  • Beitinger, Thomas L., and Lloyd C. Fitzpatrick. 1979. Physiological and ecological correlates of preferred temperature in fish. American Zoologist 19.1: 319–329.

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    Presents evidence that species of fish prefer a specific temperature, despite experiencing a wide range of thermal conditions in nature; reviews limited data showing that preferred temperatures of fishes are related to thermal optima for growth, and calls for more studies of this kind.

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  • Dawson, William R. 1975. On the physiological significance of the preferred body temperatures of reptiles. In Perspectives in biophysical ecology. Edited by David M. Gates and Rudolf B. Schmerl, 443–473. Berlin: Springer-Verlag.

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    A comprehensive review (at the time) of the correspondence between preferred body and optimal temperatures for physiological performance in reptiles; no quantitative or phylogenetic meta-analysis is included, because the paper predates these methods.

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  • Garland, Theodore, Raymond B. Huey, and Albert F. Bennett. 1991. Phylogeny and coadaptation of thermal physiology in lizards: A reanalysis. Evolution 45.8: 1969–1975.

    DOI: 10.2307/2409846Save Citation »Export Citation »E-mail Citation »

    A reanalysis of Huey and Bennett 1987, with better comparative methods and new phylogenetic information. Authors found less support for the coadaptation support than the original analysis.

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  • Good, Darrin S. 1993. Evolution of behaviours in Drosophila melanogaster in high temperatures: Genetic and environmental effects. Journal of Insect Physiology 39.7: 537–544.

    DOI: 10.1016/0022-1910(93)90034-OSave Citation »Export Citation »E-mail Citation »

    The author found that populations of flies that evolved at higher temperatures preferred higher temperatures; this effect could not have been caused by direct selection for behavior, because little or no thermal variation existed within the selective environments.

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  • Huey, Raymond B., and Albert F. Bennett. 1987. Phylogenetic studies of coadaptation: Preferred temperatures versus optimal performance temperatures of lizards. Evolution 41.5: 1098–1115.

    DOI: 10.2307/2409194Save Citation »Export Citation »E-mail Citation »

    First quantitative test of the hypothesis that preferred temperature coevolves with the thermal optimum for physiological performance. A very influential study because of its use of phylogenetic comparative methods. See Garland, et al. 1991 for re-analysis of the data with different methods.

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  • Martin, Tara Laine, and Raymond B. Huey. 2008. Why “suboptimal” is optimal: Jensen’s inequality and ectotherm thermal preferences. American Naturalist 171.3: E102–E118.

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    A stimulating paper showing that an inaccurate thermoregulator should aim for a body temperature that lies below the optimal temperature for physiological performance; comparative data in support of the model are also presented.

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Proximate Mechanisms

Studies that describe how animals regulate their temperature help biologists to understand the costs of and constraints on thermoregulation. Proximate mechanisms of thermoregulation can be categorized as physiological, behavioral, or morphological. This section is organized according to these categories.

Physiological Mechanisms

Physiological control of body temperature includes any internal process by which animals regulate the production, dissipation, or distribution of heat. Scholander, et al. 1950, a classic paper, describes how mammals tune the production of metabolic heat according to the temperature of their environment. Kammer 1981 and Bartholomew 1982 discuss physiological regulation of body temperature by insects and reptiles, respectively. Seebacher and Franklin 2005 provides a more recent review of cardiovascular control of body temperature in reptiles. Bicego, et al. 2007 reviews a wide range of physiological mechanisms of thermoregulation in animals, emphasizing studies of vertebrates. Dzialowski and O’Connor 1999, Dzialowski and O’Connor 2001, and Dzialowski and O’Connor 2004 present a cohesive series of models and experiments that quantify the interaction of body size and blood flow during thermoregulation.

  • Bartholomew, George A. 1982. Physiological control of body temperature. In Biology of the Reptilia. Vol. 12, Physiology C: Physiological ecology. Edited by Carl Gans and F. Harvey Pough, 167–211. New York: Academic Press.

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    Not the most recent review of this subject, but it includes a useful comparison of physiological mechanisms between endothermic and ectothermic vertebrates. See Seebacher and Franklin 2005 for a more recent review of physiological thermoregulation by reptiles.

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  • Bicego, Kênia C., Renata C. H. Barros, and Luiz G. S. Branco. 2007. Physiology of temperature regulation: Comparative aspects. Comparative Biochemistry and Physiology, Part A: Molecular Integrative Physiology 147.3: 616–639.

    DOI: 10.1016/j.cbpa.2006.06.032Save Citation »Export Citation »E-mail Citation »

    A comprehensive review of physiological mechanisms of thermoregulation, including a broad coverage of vertebrate taxa and some references to invertebrate taxa.

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  • Dzialowski, Edward M., and Michael P. O’Connor. 1999. Utility of blood flow to the appendages in physiological control of heat exchange in reptiles. Journal of Thermal Biology 24.1: 21–32.

    DOI: 10.1016/S0306-4565(98)00034-5Save Citation »Export Citation »E-mail Citation »

    Mathematical models of thermoregulation by changes in blood flow; shows how body size and blood flow interact to determine heat exchange.

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  • Dzialowski, Edward M., and Michael P. O’Connor. 2001. Physiological control of warming and cooling during simulated shuttling and basking in lizards. Physiological and Biochemical Zoology 74.5: 679–693.

    DOI: 10.1086/322929Save Citation »Export Citation »E-mail Citation »

    Introduces techniques for measuring blood flow in small animals; shows that changes in blood flow were less effective for thermoregulation in smaller lizards than in larger ones.

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  • Dzialowski, Edward M., and Michael P. O’Connor. 2004. Importance of the limbs in the physiological control of heat exchange in Iguana iguana and Sceloporus undulatus. Journal of Thermal Biology 29.6: 299–305.

    DOI: 10.1016/j.jtherbio.2004.04.003Save Citation »Export Citation »E-mail Citation »

    A nice experiment isolating the thermoregulatory advantages of blood flow to limbs; changes in blood flow were only effective in the larger of two species.

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  • Kammer, A. E. 1981. Physiological mechanisms of thermoregulation. In Insect thermoregulation. Edited by Bernd Heinrich, 115–158. New York: John Wiley.

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    A review focused mainly on moths, dragonflies, beetles, and bees.

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  • Scholander, P. F., Raymond Hock, Vladimir Walters, Fred Johnson, and Laurence Irving. 1950. Heat regulation in some arctic and tropical mammals and birds. Biological Bulletin 99.2: 237–258.

    DOI: 10.2307/1538741Save Citation »Export Citation »E-mail Citation »

    A seminal paper presenting an impressive collection of data on the metabolic responses of mammals and birds to air temperature; shows that the capacity to generate metabolic heat relates to the environmental conditions that a species normally experiences.

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  • Seebacher, Frank, and Craig E. Franklin. 2005. Physiological mechanisms of thermoregulation in reptiles: A review. Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 175.8: 533–541.

    DOI: 10.1007/s00360-005-0007-1Save Citation »Export Citation »E-mail Citation »

    A concise and focused review that covers the physiological basis of preferred temperature and cardiovascular control of body temperature.

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Behavioral Mechanisms

Animals use many forms of behavior—such as orienting, posturing, and shuttling—to regulate body temperature. In heterogeneous environments, behavioral mechanisms of thermoregulation can be more effective than physiological mechanisms, as shown by the modeling exercises of Stevenson 1985. Casey 1981 provides an early review of behavioral thermoregulation by insects. More recently, Kemp and Krockenberger 2002 summarizes the use of thermoregulatory postures by butterflies. Belliure and Carrascal 2002 presents a clever experiment to verify that lizards can behaviorally distinguish rates of heating offered by different microclimates. Several authors have argued that behavior provides the flexibility to cope with thermal heterogeneity throughout the range of a species. Huey and Pascual 2009 presents evidence that flies adjust their timing of activity to deal with latitudinal variation in temperature. Similarly, Asbury and Adolph 2007 shows that lizards use microhabitat selection to deal with altitudinal variation in temperature. Despite their obvious reliance on physiological mechanisms, endotherms also engage in behavioral means of thermoregulation. Terrien, et al. 2011 reviews all forms of behavioral thermoregulation by mammals. McKechnie and Lovegrove 2001 shows that social behaviors of birds facilitate thermoregulation during cold periods.

  • Asbury, Dee A., and Stephen C. Adolph. 2007. Behavioural plasticity in an ecological generalist: Microhabitat use by western fence lizards. Evolutionary Ecology Research 9:801–815.

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    An experiment confirming the role of microhabitat selection during thermoregulation in three distinct environments; plasticity of behavior was more important than genetic variation.

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  • Belliure, Josabel, and Luis M. Carrascal. 2002. Influence of heat transmission mode on heating rates and on the selection of patches for heating in a Mediterranean lizard. Physiological and Biochemical Zoology 75.4: 369–376.

    DOI: 10.1086/342768Save Citation »Export Citation »E-mail Citation »

    Demonstrates that animals can adaptively choose between different modes of heating when rates of heating vary between the modes.

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  • Casey, T. M. 1981. Behavioral mechanisms of thermoregulation. In Insect thermoregulation. Edited by Bernd Heinrich, 79–114. New York: John Wiley.

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    A balanced review covering topics such as orientation, posture, and microhabitat selection in insects.

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  • Huey, Raymond B., and Marta Pascual. 2009. Partial thermoregulatory compensation by a rapidly evolving invasive species along a latitudinal cline. Ecology 90.7: 1715–1720.

    DOI: 10.1890/09-0097.1Save Citation »Export Citation »E-mail Citation »

    Shows that flies at higher latitudes shift their timing of activity, although these flies still experience lower body temperature than flies at lower latitudes. The authors approximated body temperature from air temperatures.

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  • Kemp, D. J., and A. K. Krockenberger. 2002. A novel method of behavioural thermoregulation in butterflies. Journal of Evolutionary Biology 15.6: 922–929.

    DOI: 10.1046/j.1420-9101.2002.00470.xSave Citation »Export Citation »E-mail Citation »

    Describes the use of posture to regulate heating in butterflies; Figure 1 provides an overview of various postures and their effectiveness for basking.

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  • McKechnie, Andrew E., and Barry G. Lovegrove. 2001. Thermoregulation and the energetic significance of clustering behavior in the white-backed mousebird (Colius colius). Physiological and Biochemical Zoology 74.2: 238–249.

    DOI: 10.1086/319669Save Citation »Export Citation »E-mail Citation »

    Shows that cooling of body temperature at night can be slowed through huddling behavior; cooling decreased as the size of the huddling group increased.

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  • Stevenson, R. D. 1985. The relative importance of behavioral and physiological adjustments controlling body temperature in terrestrial ectotherms. American Naturalist 126.3: 362–386.

    DOI: 10.1086/284423Save Citation »Export Citation »E-mail Citation »

    Models behavioral and physiological mechanisms of thermoregulation, concluding that behavioral mechanisms are far more effective when substantial spatial variation in radiation exists.

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  • Terrien, Jeremy, Martine Perret, and Fabienne Aujard. 2011. Behavioral thermoregulation in mammals: A review. Frontiers in Bioscience 16.1: 1428–1444.

    DOI: 10.2741/3797Save Citation »Export Citation »E-mail Citation »

    An up-to-date review of the behaviors that mammals use to avoid hyper- and hypothermia, as well as the effects of season, gender, and age on behavioral strategies.

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Morphological Mechanisms

Morphological properties, such as size and color, interact with behavior and physiology to determine the potential for thermoregulation. Size affects the thermoregulation of ectotherms and endotherms. Stevenson 1985 uses a model to show that an intermediate size affords the widest range of body temperatures to an ectotherm. Bartholomew 1981 discusses how large size facilitates thermoregulation by endotherms. Independent of size, color determines the amount of solar radiation absorbed by an organism, and hence its operative temperature in a given microclimate. Hamilton 1973 critically evaluates hypotheses about the function of color, including hypotheses related to thermoregulation. Kingsolver 1987 reports on experiments detailing how the melanization and positioning of wings enable butterflies to adjust their rate of heating; readers should also consult Kingsolver’s other papers on this subject (cited in Kingsolver 1987), as well as the critical appraisal in Heinrich 1990. Clusella Trullas, et al. 2007 reviews the evidence that species in cooler environments develop more melanism and asks whether melanism trades off with body size. Clusella-Trullas, et al. 2008 uses a phylogenetic comparative analysis to show that lizards that experience lower levels of solar radiation have evolved darker bodies, presumably to increase rates of warming while basking.

  • Bartholomew, George A. 1981. A matter of size: An examination of endothermy in insects and terrestrial vertebrates. In Insect thermoregulation. Edited by Bernd Heinrich, 45–78. New York: John Wiley.

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    Reviews the implications of body size for endothermic thermoregulators, giving balanced coverage of data for insects, mammals, and birds.

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  • Clusella-Trullas, S., J. S. Terblanche, T. M. Blackburn, and S. L. Chown. 2008. Testing the thermal melanism hypothesis: A macrophysiological approach. Functional Ecology 22.2: 232–238.

    DOI: 10.1111/j.1365-2435.2007.01377.xSave Citation »Export Citation »E-mail Citation »

    The authors found that species of lizards that experience more solar radiation have higher skin reflectance, supporting the hypothesis that coloration has evolved for thermoregulatory function.

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  • Clusella Trullas, S., J. H. van Wyk, and J. R. Spotila. 2007. Thermal melanism in ectotherms. Journal of Thermal Biology 32.5: 235–245.

    DOI: 10.1016/j.jtherbio.2007.01.013Save Citation »Export Citation »E-mail Citation »

    An excellent overview of the theory of thermal melanism and the support for four major hypotheses. Examples come primarily from studies of insects and reptiles.

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  • Hamilton, William James. 1973. Life’s color code. New York: McGraw-Hill.

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    An interesting book that discusses the functions of body color, with an emphasis on thermoregulation.

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  • Heinrich, Bernd. 1990. Is reflectance basking real? Journal of Experimental Biology 154.1: 31–43.

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    Argues that wing positioning by butterflies does not increase heat gain by reflecting radiation to the body, but rather reduces heat loss by convection.

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  • Kingsolver, Joel G. 1987. Evolution and coadaptation of thermoregulatory behavior and wing pigmentation pattern in pierid butterflies. Evolution 41.3: 472–490.

    DOI: 10.2307/2409250Save Citation »Export Citation »E-mail Citation »

    Describes experimental manipulation of wing melanism to illustrate its role in thermoregulation.

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  • Stevenson, R. D. 1985. Body size and limits to the daily range of body temperature in terrestrial ectotherms. American Naturalist 125.1: 102–117.

    DOI: 10.1086/284330Save Citation »Export Citation »E-mail Citation »

    Models the effects of body size on the capacity for behavioral thermoregulation; Figure 1 shows that animals of intermediate size can attain the widest range of body temperatures, because small animals have too little thermal inertia and large animals have too much.

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Environmental Constraints

The micrometeorological conditions of an environment constrain the effectiveness of thermoregulation, as described in Porter and Gates 1969, Tracy 1976, and Gates 1980. Both Bakken 1992 and Dzialowski 2005 review methodologies for sampling operative temperatures, and Dzialowski 2005 reviews field studies of operative thermal environments. Studies by Grant and Dunham (Grant and Dunham 1988, Grant and Dunham 1990, Grant 1990) illustrate several sampling designs and show that opportunities for behavioral thermoregulation vary with time, altitude, and habitat.

Optimal Thermoregulation

Despite early notions that body temperatures are determined primarily by physical constraints, patterns of thermoregulation have undoubtedly been shaped by natural selection. The products of natural selection can be understood by analyzing the costs and benefits of particular phenotypes in particular environments. This approach, usually referred to as optimality modeling, has been used to study thermoregulatory strategies since Huey and Slatkin’s influential model of optimal thermoregulation (see Huey and Slatkin 1976, cited under Energetic Costs). This section highlights key papers that describe models and tests of optimal thermoregulation.

Energetic Costs

Huey and Slatkin 1976, a landmark paper, models the optimal strategy of thermoregulation given energetic costs and benefits. This paper stimulated numerous studies of thermoregulation in natural and artificial environments, which are summarized in Angilletta 2009. Withers and Campbell 1985 describes an elegant apparatus in the laboratory that was designed to manipulate the energetic cost of behavioral thermoregulation; the authors’ data strongly support the hypothesis that animals will thermoregulate less accurately when the costs are high. Blouin-Demers and Nadeau 2005 presents a broad phylogenetic comparative analysis of thermoregulation in natural environments; this analysis failed to support Huey and Slatkin’s model, finding instead that lizards thermoregulate more accurately when the energetic cost of thermoregulation seems high. However, Angilletta 2009 discusses a potential source of error in Blouin-Demers and Nadeau’s estimate of the energetic cost of thermoregulation. Angilletta, et al. 2010 applies Huey and Slatkin’s model to predict physiological thermoregulation by endotherms, finding qualitative support for the theory. The model predicts that thermoregulation by endotherms should depend on environmental temperature. Consistent with this idea, Soobramoney, et al. 2003 finds that thermoregulatory strategies of shrikes were related to environmental temperatures. Similarly, Geiser and Drury 2003 finds that marsupials altered their thermoregulatory strategy when provided with an artificial source of heat.

  • Angilletta, Michael J. 2009. Thermal adaptation: A theoretical and empirical synthesis. Oxford: Oxford Univ. Press.

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    Chapter 4 introduces Huey and Slatkin’s model in a less complicated form than the original, and summarizes empirical tests of the model (see Huey and Slatkin 1976). The same chapter also discusses how spatial variation in operative temperatures complicates interpretation of these tests.

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  • Angilletta, Michael J., Brandon S. Cooper, Matthew S. Schuler, and Justin G. Boyles. 2010. The evolution of thermal physiology in endotherms. Frontiers in Bioscience E2.3: 861–881.

    DOI: 10.2741/E148Save Citation »Export Citation »E-mail Citation »

    Applies models of optimal thermoregulation to endotherms, making qualitative predictions about the mean and variance of temperature in birds and mammals.

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  • Blouin-Demers, Gabriel, and Patrick Nadeau. 2005. The cost-benefit model of thermoregulation does not predict lizard thermoregulatory behavior. Ecology 86.3: 560–566.

    DOI: 10.1890/04-1403Save Citation »Export Citation »E-mail Citation »

    A phylogenetic comparative test of the hypothesis that a high cost of thermoregulation causes animals to thermoregulate less accurately; estimates the cost of thermoregulation as the absolute difference between the mean operative temperature of the environment and the mean preferred temperature of the species.

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  • Geiser, F., and R. L. Drury. 2003. Radiant heat affects thermoregulation and energy expenditure during rewarming from torpor. Journal of Comparative Physiology B: Biochemical Systemic and Environmental Physiology 173.1: 55–60.

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    The authors experimentally manipulated access to external heat and found that marsupials avoided torpor and relied on passive warming when external heat was available.

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  • Huey, Raymond B., and Montgomery Slatkin. 1976. Cost and benefits of lizard thermoregulation. Quarterly Review of Biology 51.3: 363–384.

    DOI: 10.1086/409470Save Citation »Export Citation »E-mail Citation »

    A highly influential paper that introduced the idea of optimization to the study of thermoregulation. The title suggests a limited taxonomic scope, but the model and ideas contained in the paper apply to all animals.

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  • Soobramoney, S., C. T. Downs, and N. J. Adams. 2003. Physiological variability in the fiscal shrike Lanius collaris along an altitudinal gradient in South Africa. Journal of Thermal Biology 28.8: 581–594.

    DOI: 10.1016/j.jtherbio.2003.08.004Save Citation »Export Citation »E-mail Citation »

    Thermoregulatory strategies of shrikes were related to the environmental temperature; shrikes from cooler environments maintained lower body temperatures, even after being moved to a warm environment.

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  • Withers, Philip C., and James D. Campbell. 1985. Effects of environmental cost on thermoregulation in the desert iguana. Physiological Zoology 58.3: 329–339.

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    Describes an ingenious experimental test of the hypothesis that energetic costs influence behavioral thermoregulation; the data strongly support the model in Huey and Slatkin 1976, which can be better seen from the plot of the data in Figure 4.18 on page 109 of Angilletta 2009.

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Physiological Condition

Certain physiological conditions can alter the optimal strategy of thermoregulation. For example, Huey 1982 (cited under General Overviews) notes that animals in the process of digesting and absorbing food require higher body temperatures to maximize rates of energy gain compared to fasted animals. Therefore, either feeding or fasting should elicit a shift in thermoregulatory strategy. This adaptive response has been documented in numerous lab experiments with fish and reptiles, but only Blouin-Demers and Weatherhead have tested this hypothesis in free-ranging animals (see Blouin-Demers and Weatherhead 2001). Humphries, et al. 2003 and Bozinovic, et al. 2007 show that energetic costs also affects the thermoregulatory strategies of endotherms, which must expend substantial quantities of energy to warm their bodies (see Endothermy). Similarly, reproductive condition can influence the optimal body temperature, as modeled and tested by Beuchat and Ellner 1987. Other studies have shown that levels of hydration (Maloney and Dawson 1998, Ladyman and Bradshaw 2003) or rates of dehydration (Tracy and Christian 2005) affect body temperature in a manner consistent with optimal thermoregulation. Mitchell, et al. 2002 reviews cases of selective brain cooling by endotherms, concluding that this strategy reduces evaporative cooling when the cost of losing water exceeds the benefit of thermoregulation.

  • Beuchat, Carol A., and Stephen Ellner. 1987. A quantitative test of life history theory: Thermoregulation by a viviparous lizard. Ecological Monographs 57.1: 45–60.

    DOI: 10.2307/1942638Save Citation »Export Citation »E-mail Citation »

    The authors predicted drop in body temperature during pregnancy, using an optimality model, and found predictions were in close agreement with temperatures observed in the field; one of the few quantitative models of optimal thermoregulation that ties behavior to survival and reproduction.

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  • Blouin-Demers, Gabriel, and Patrick J. Weatherhead. 2001. An experimental test of the link between foraging, habitat selection and thermoregulation in black rat snakes Elaphe obsoleta obsoleta. Journal of Animal Ecology 70.6: 1006–1013.

    DOI: 10.1046/j.0021-8790.2001.00554.xSave Citation »Export Citation »E-mail Citation »

    Experimental feeding caused snakes to select more open habitat and raise body temperature; stands out over other studies because it included animals in a natural environment as well as animals in an artificial gradient.

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  • Bozinovic, Francisco, José L. P. Muñoz, Daniel E. Naya, and Ariovaldo P. Cruz-Neto. 2007. Adjusting energy expenditures to energy supply: Food availability regulates torpor use and organ size in the Chilean mouse-opossum Thylamys elegans. Journal of Comparative Physiology B: Biochemical Systemic and Environmental Physiology 177.4: 393–400.

    DOI: 10.1007/s00360-006-0137-0Save Citation »Export Citation »E-mail Citation »

    The authors controlled food intake to show that decreasing energy availability intensifies the depth and duration of torpor.

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  • Humphries, Murray M., Donald L. Kramer, and Donald W. Thomas. 2003. The role of energy availability in mammalian hibernation: An experimental test in free-ranging eastern chipmunks. Physiological and Biochemical Zoology 76.2: 180–186.

    DOI: 10.1086/367949Save Citation »Export Citation »E-mail Citation »

    An experimental study showing that the frequency and depth of torpor is determined partly by the availability of food; provides support for the novel idea that endothermic thermoregulation can be understood using an optimization approach.

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  • Ladyman, M., and D. Bradshaw. 2003. The influence of dehydration on the thermal preferences of the western tiger snake, Notechis scutatus. Journal of Comparative Physiology B: Biochemical Systemic and Environmental Physiology 173.3: 239–246.

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    Dehydrated snakes selected lower mean and maximal temperatures in a thermal gradient.

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  • Maloney, Shane K., and Terence J. Dawson. 1998. Changes in pattern of heat loss at high ambient temperature caused by water deprivation in a large flightless bird, the emu. Physiological Zoology 71.6: 712–719.

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    Dehydrated emus suffered prolonged panting and underwent hyperthermia when exposed to a high temperature; this result supports the idea that hydric costs affect thermoregulation by endotherms.

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  • Mitchell, Duncan, Shane K. Maloney, Claus Jessen, et al. 2002. Adaptive heterothermy and selective brain cooling in arid-zone mammals. Comparative Biochemistry and Physiology, Part B: Biochemistry Molecular Biology 131.4: 571–585.

    DOI: 10.1016/S1096-4959(02)00012-XSave Citation »Export Citation »E-mail Citation »

    The authors argue that certain mammals selectively cool their brains during heat stress, which inhibits the brain from engaging mechanisms of evaporative cooling and conserves water in the body.

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  • Tracy, Christopher R., and Keith A. Christian. 2005. Preferred temperature correlates with evaporative water loss in hylid frogs from northern Australia. Physiological and Biochemical Zoology 78.5: 839–846.

    DOI: 10.1086/432151Save Citation »Export Citation »E-mail Citation »

    The authors observed a very strong negative relationship between rates of water loss and preferred body temperature among species.

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Predation Risk

Huey and Slatkin 1976 (cited under Energetic Costs) discusses the effect of predation risk on optimal thermoregulation, but it does not model this cost explicitly. Several studies (Downes and Shine 1998; Downes 2001; Herczeg, et al. 2008) have shown that perceived predation risk, caused by chemical cues, affects behavioral thermoregulation by lizards. Gerald and Spezzano 2005 documents a similar phenomenon in snails. Other studies, such as Martin and Lopez 2001 and Polo, et al. 2005, have simulated predation risk by prodding or chasing animals. Polo, et al. 2005 is exceptional because the authors developed and tested a quantitative model of thermoregulatory responses to repeated attacks.

  • Downes, Sharon. 2001. Trading heat and food for safety: Costs of predator avoidance in a lizard. Ecology 82.10: 2870–2881.

    DOI: 10.1890/0012-9658(2001)082[2870:THAFFS]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    The authors added predatory scents to basking sites in experimental enclosures and observed a decrease in activity and growth.

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  • Downes, Sharon, and Richard Shine. 1998. Heat, safety or solitude? Using habitat selection experiments to identify a lizard’s priorities. Animal Behaviour 55.5: 1387–1396.

    DOI: 10.1006/anbe.1997.0705Save Citation »Export Citation »E-mail Citation »

    The authors manipulated predation cues and social conditions to show that lizards select a suboptimal temperature when faced with either predation risk or a superior competitor. Inferior competitors assumed more predation risk in the presence of a superior competitor.

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  • Gerald, Gerald W., and Lawrence C. Spezzano Jr. 2005. The influence of chemical cues and conspecific density on the temperature selection of a freshwater snail (Melanoides tuberculata). Journal of Thermal Biology 30.3: 237–245.

    DOI: 10.1016/j.jtherbio.2004.12.002Save Citation »Export Citation »E-mail Citation »

    Predatory cues caused random selection of sites within a thermal gradient.

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  • Herczeg, Gábor, Annika Herrero, Jarmo Saarikivi, Abigél Gonda, Maria Jäntti, and Juha Merilä. 2008. Experimental support for the cost-benefit model of lizard thermoregulation: The effects of predation risk and food supply. Oecologia 155.1: 1–10.

    DOI: 10.1007/s00442-007-0886-9Save Citation »Export Citation »E-mail Citation »

    Male lizards reduced their efforts to thermoregulate when their hear source was associated with a perceived predation risk (chemical cues of a predator); interestingly, pregnant females did not alter their thermoregulatory behavior in response to predation risk.

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  • Martin, José, and Pilar López. 2001. Repeated predatory attacks and multiple decisions to come out from a refuge in an alpine lizard. Behavioral Ecology 12.4: 386–389.

    DOI: 10.1093/beheco/12.4.386Save Citation »Export Citation »E-mail Citation »

    A field study showing that lizards spend less time hiding after a predatory attack as the difference between temperatures on the surface and in a refuge increases.

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  • Polo, Vicente, Pilar López, and José Martín. 2005. Balancing the thermal costs and benefits of refuge use to cope with persistent attacks from predators: A model and an experiment with an alpine lizard. Evolutionary Ecology Research 7.1: 23–35.

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    The authors accurately predicted the behavior of lizards using a model that balanced the benefit of basking against the safety of a refuge.

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Competition

Magnuson, et al. 1979 proposes that competition within and between species shapes the way that animals use thermal resources. The authors show that inferior competitors alter their thermal preferences when interacting with superior competitors. Medvick, et al. 1981 reports on an empirical test of this idea using bluegill sunfish. Conclusions based on these early studies of fish were later generalized to other taxa. For example, Downes and Shine 1998 shows that small lizards accepted energetically suboptimal temperatures when interacting with larger conspecifics. Downes and Bauwens 2002 shows that different species of lizards compete in a similar manner. Competition might also result in the coevolution of thermoregulatory strategies among species, as suggested by Verdu, et al. 2007.

  • Downes, Sharon, and Dirk Bauwens. 2002. An experimental demonstration of direct behavioural interference in two Mediterranean lacertid lizard species. Animal Behaviour 63.6: 1037–1046.

    DOI: 10.1006/anbe.2002.3022Save Citation »Export Citation »E-mail Citation »

    The dominant species forced the subordinate species to occupy microclimate that differed from its preferred microclimate.

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  • Downes, Sharon, and Richard Shine. 1998. Heat, safety or solitude? Using habitat selection experiments to identify a lizard’s priorities. Animal Behaviour 55.5: 1387–1396.

    DOI: 10.1006/anbe.1997.0705Save Citation »Export Citation »E-mail Citation »

    The authors manipulated predation cues and social conditions to show that lizards select a suboptimal temperature when faced with either predation risk or a superior competitor. Inferior competitors assumed more predation risk in the presence of a superior competitor.

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  • Magnuson, John J., Larry B. Crowder, and Patricia A. Medvick. 1979. Temperature as an ecological resource. American Zoologist 19.1: 331–343.

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    A provocative review describing how fish compete within and between species for access to thermal microclimates.

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  • Medvick, P. A., J. J. Magnuson, and S. Sharr. 1981. Behavioral thermoregulation and social interactions of bluegills, Lepomis macrochirus. Copeia 1981.1: 9–13.

    DOI: 10.2307/1444036Save Citation »Export Citation »E-mail Citation »

    The authors experimentally demonstrated that small fish select more extreme temperatures in the presence of large fish, indicating that competition within species can affect thermoregulatory decisions.

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  • Verdu, José R., Lucrecia Arellano, Catherine Numa, and Estafanía Mico. 2007. Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient. Ecological Entomology 32.5: 544–551.

    DOI: 10.1111/j.1365-2311.2007.00907.xSave Citation »Export Citation »E-mail Citation »

    Different species of beetles were active at different air temperatures; species that were active at low temperatures generated greater heat by metabolism to thermoregulate at similar levels to species that were active at high temperatures.

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Missed Opportunities

Behavioral thermoregulation often trades off with other beneficial activities, such as mating or feeding. Thus, the decision to thermoregulate results in missed opportunities. Although this cost of thermoregulation has been less appreciated than others, some papers on this subject should be considered by those who wish to understand thermoregulatory strategies. For example, Shine, et al. 2000 shows that garter snakes abandon thermoregulation during courtship and mating. Kessler and Lampert 2004 models the tradeoff between thermoregulation and feeding when preferred temperatures and preferred prey are located in different places; Kessler and Lampert also tested their model by recording the movements of aquatic invertebrates in a temperature-controlled water column. Wildhaber and Lamberson 2004 considers a similar tradeoff in fish.

  • Kessler, Kirsten, and Winfried. Lampert. 2004. Fitness optimization of Daphnia in a trade-off between food and temperature. Oecologia 140.3: 381–387.

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    The authors manipulated thermal gradients in large water columns to show that steep thermal gradients force individuals to trade off food for thermal benefits.

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  • Shine, R., P. S. Harlow, M. J. Elphick, M. M. Olsson, and R. T. Mason. 2000. Conflicts between courtship and thermoregulation: The thermal ecology of amorous male garter snakes (Thamnophis sirtalis parietalis, Colubridae). Physiological and Biochemical Zoology 73.4: 508–516.

    DOI: 10.1086/317734Save Citation »Export Citation »E-mail Citation »

    Male garter snakes place a greater emphasis on courtship than on thermoregulatory behavior, because the two behaviors are mutually exclusive and body temperature does not have a large effect on mating success.

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  • Wildhaber, Mark L., and P. J. Lamberson. 2004. Importance of the habitat choice behavior assumed when modeling the effects of food and temperature on fish populations. Ecological Modelling 175.4: 395–409.

    DOI: 10.1016/j.ecolmodel.2003.08.022Save Citation »Export Citation »E-mail Citation »

    The growth rate of fish depended on whether habitat was chosen based on food, temperature, or a combination of both.

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Endothermy

Endothermic thermoregulation—the regulation of body temperature via metabolic heat production—enables extremely precise control of body temperature, making it a subject of great interest to thermal biologists. To some extent, the literature on endothermic thermoregulation has developed independently of the literature on ectothermic thermoregulation. For this reason, endothermy will be treated separately here. Nevertheless, endothermic and ectothermic animals share many behavioral and physiological mechanisms of thermoregulation, despite the greater capacities of endotherms to produce and retain heat.

Occurrence of Endothermy Within Animals

As described in Scholander, et al. 1950 (cited under Physiological Mechanisms), endothermic thermoregulation commonly occurs within mammals and birds. Certain insects generate sufficient metabolic heat to elevate their body temperature during flight, as described in Heinrich 1974 and Harrison, et al. 1996. A few species of pythons endothermically regulate the temperature of their eggs during brooding, as described in Stahlschmidt and DeNardo 2011. Some fishes use endothermy to heat particular regions of the body (Block and Finnerty 1994). Grigg, et al. 2004 considers the diversity of endotherms and concludes that endotherms and ectotherms lie along a continuum of thermoregulatory strategies.

  • Block, Barbara A., and John R. Finnerty. 1994. Endothermy in fishes: A phylogenetic analysis of constraints, predispositions, and selection pressures. Environmental Biology of Fishes 40.3: 283–302.

    DOI: 10.1007/BF00002518Save Citation »Export Citation »E-mail Citation »

    Reviews two forms of endothermy occurring within certain fishes, and discusses the constraints on the evolution of endothermy within fishes.

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  • Grigg, Gordon C., Lyn A. Beard, and Michael L. Augee. 2004. The evolution of endothermy and its diversity in mammals and birds. Physiological and Biochemical Zoology 77.6: 982–997.

    DOI: 10.1086/425188Save Citation »Export Citation »E-mail Citation »

    Discusses the evidence that the torpor of mammals and birds represents an ancestral trait, and proposes that the first endothermic mammals and birds were facultatively endothermic; these authors conclude that a continuum exists between ectothermic and endothermic thermoregulation.

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  • Harrison, John F., Jennifer H. Fewell, Stephen P. Roberts, and H. Glen Hall. 1996. Achievement of thermal stability by varying metabolic heat production in flying honeybees. Science 274.5284: 88–90.

    DOI: 10.1126/science.274.5284.88Save Citation »Export Citation »E-mail Citation »

    Demonstrates that honeybees increase their metabolic heat production during flight when air temperatures are lowered.

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  • Heinrich, B. 1974. Thermoregulation in endothermic insects. Science 185:747–756.

    DOI: 10.1126/science.185.4153.747Save Citation »Export Citation »E-mail Citation »

    Reviews the evidence for and mechanisms of endothermy in insects.

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  • Stahlschmidt, Zachary R., and Dale F. DeNardo. 2011. Parental care in snakes. In Reproductive biology and phylogeny of snakes. Edited by Robert D. Aldridge and David M. Sever, 673–702. Enfield, NH: Science Publishers.

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    Discusses the presence of endothermic thermoregulation in three species of pythons (pp. 686–687).

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Evolutionary Origins of Endothermy

Given the enormous energetic costs of endothermic thermoregulation, much has been written about the factors that might have caused endothermy to evolve. Plausible hypotheses and supporting evidences are reviewed in Hayes and Garland 1995. Early hypotheses focused on the greater physiological performance that comes from a high temperature (Hamilton 1973) or the greater metabolic efficiency that comes from a constant temperature (Heinrich 1977). However, the most influential hypothesis was proposed by Bennett and Ruben, who conjectured that endothermy evolved as a correlated response to selection for greater aerobic capacity (see Bennett and Ruben 1979). Those interested in Bennett and Ruben’s hypothesis should consult Hayes 2010, which presents a quantitative version of the model and clarifies the conditions for endothermy to evolve by correlated selection. Farmer 2000 criticizes this hypothesis and offers an alternative hypothesis based on the direct benefits of endothermy for parental care. Combining ideas about aerobic capacity and parental care, Koteja 2000 proposes that the need for intensive parental care in mammals and birds resulted in selection for aerobic capacity, with greater basal metabolism as a byproduct. Clarke and Pörtner 2010 argues the importance of metabolic performance as a benefit of endothermy, echoing a similar argument made in Hamilton 1973.

  • Bennett, A. F., and J. A. Ruben. 1979. Endothermy and activity in vertebrates. Science 206.4419: 649–654.

    DOI: 10.1126/science.493968Save Citation »Export Citation »E-mail Citation »

    An extremely influential paper that introduces the aerobic capacity hypothesis, in which endothermy is thought to have arisen as a byproduct of selection for a greater capacity for sustained activity; stimulated many empirical studies of the genetic correlation between basal and maximal metabolic rates.

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  • Clarke, Andrew, and Hans-Otto Pörtner. 2010. Temperature, metabolic power and the evolution of endothermy. Biological Reviews 85.4: 703–727.

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    Reviews the connection between body temperature and metabolic performance, arguing that endothermy evolved because of its positive impact on aerobic scope.

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  • Farmer, C. G. 2000. Parental care: The key to understanding endothermy and other convergent features in birds and mammals. American Naturalist 155.3: 326–334.

    DOI: 10.1086/303323Save Citation »Export Citation »E-mail Citation »

    Argues that endothermic thermoregulation evolved to control temperatures of offspring during parental care; presents anecdotal evidence in support of this hypothesis.

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  • Hamilton, William J. 1973. Life’s color code. New York: McGraw-Hill.

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    Chapter 1 introduces the hypothesis that homeothermy in mammals and birds evolved as a byproduct of selection for genotypes that maintain the highest possible temperature.

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  • Hayes, Jack P. 2010. Metabolic rates, genetic constraints, and the evolution of endothermy. Journal of Evolutionary Biology 23.9: 1868–1877.

    DOI: 10.1111/j.1420-9101.2010.02053.xSave Citation »Export Citation »E-mail Citation »

    A quantitative model of the conditions required for endothermy to evolve according to the aerobic capacity hypothesis; an excellent example of how a quantitative model can clarify the assumptions of a verbal model.

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  • Hayes, Jack P., and Theodore Garland Jr. 1995. The evolution of endothermy: Testing the aerobic capacity model. Evolution 49.5: 836–847.

    DOI: 10.2307/2410407Save Citation »Export Citation »E-mail Citation »

    A comprehensive review of hypotheses for the evolutionary origin of endothermy, and of the empirical support for these hypotheses.

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  • Heinrich, Bernd. 1977. Why have some animals evolved to regulate a high body temperature? American Naturalist 111.980: 623–640.

    DOI: 10.1086/283196Save Citation »Export Citation »E-mail Citation »

    Explores the role of metabolic performance in the origin and maintenance of thermoregulation by ectotherms and endotherms.

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  • Koteja, Pawel. 2000. Energy assimilation, parental care and the evolution of endothermy. Proceedings of the Royal Society B: Biological Sciences 267.1442: 479–484.

    DOI: 10.1098/rspb.2000.1025Save Citation »Export Citation »E-mail Citation »

    Proposes that endothermy could have evolved as a byproduct of selection for greater capacities to assimilate energy and provide parental care; this hypothesis builds on the ideas presented by Bennett and Ruben 1979 and Farmer 2000, with important modifications.

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Factors Affecting Endothermic Thermoregulation

As with ectothermic thermoregulation, the degree of endothermic thermoregulation should depend on the costs and benefits (see Optimal Thermoregulation). Although the classic work Scholander, et al. 1950 (cited under Physiological Mechanisms) stressed the constancy of body temperature within mammals and birds, more recent work has focused on quantifying and explaining variation in body temperature within and among species. Both Geiser 1998 and McKechnie and Lovegrove 2002 stress that mammals and birds exhibit various frequencies and depths of torpor (a temporary reduction in body temperature), which represents variation in thermoregulatory performance associated with phenotypic and environmental conditions. Humphries, et al. 2003 puts forth the idea that torpor imposes costs as well as energetic savings. McKechnie and Lovegrove 2002 reviews presumably adaptive patterns of endothermy and torpor in birds. Angilletta, et al. 2010 synthesizes these ideas in the context of Huey and Slatkin’s model of optimal thermoregulation (see Huey and Slatkin 1976, cited under Energetic Costs), arguing that costs and benefits determine the diverse patterns of body temperature in mammals and birds.

LAST MODIFIED: 05/23/2012

DOI: 10.1093/OBO/9780199830060-0007

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