3. Biophysical Analyses of Energetics, Time-Space Utilization, and Distributional Limits

Porter, Warren P.; Tracy, G. Richard

doi:10.4159/harvard.9780674183384.c4

Cited by 110 publications

(94 citation statements)

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“…As previous studies have noted, the influence of thermal inertia (the resistance of a body to changing its temperature) is higher on cooling than on heating rates (Smith, 1976;Claussen and Art, 1981;Carothers et al, 1997;Zamora-Camacho et al, 2014) for live animals. This difference can be explained by behavioral or physiological adjustments to increase heat gain (Lillywhite, 1980;Blouin-Demers and Weatherhead, 2001) that buffer the effect of body size (thermal inertia), commonly observed in lizards (Porter and Tracy, 1983;Carrascal et al, 1992;Carothers et al, 1997;Heatwole and Taylor, 1987;Labra et al, 2009). Behavioral adjustments in the experimental conditions used here may be due to postural changes, a behavior not recorded in the present study that needs further attention.…”

Section: Discussionmentioning

confidence: 59%

“…For example, body size influences heating and cooling rates, final equilibrium temperatures and thermal inertia in reptiles (Porter and Tracy, 1983;Stevenson, 1985;Carothers et al, 1997;Heatwole and Taylor, 1987;Carrascal et al, 1992;Labra et al, 2009). The lower surface-to-volume ratio of larger animals implies higher heat conservation capacity, or thermal inertia, as Bergmann (1847) postulated.…”

Section: Introductionmentioning

confidence: 99%

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Effect of body mass and melanism on heat balance inLiolaemuslizards of thegoetschiclade

Azócar

Bonino

Perotti

et al. 2016

Journal of Experimental Biology

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The body temperature of ectotherms depends on the environmental temperatures and behavioral adjustments, but morphology may also have an effect. For example, in colder environments, animals tend to be larger and to show higher thermal inertia, as proposed by Bergmann's rule and the heat balance hypothesis (HBH). Additionally, dark coloration increases solar radiation absorption and should accelerate heat gain (thermal melanism hypothesis, TMH). We tested Bergmann's rule, the HBH and the TMH within the Liolaemus goetschi lizard clade, which shows variability in body size and melanic coloration. We measured heating and cooling rates of live and euthanized animals, and tested how morphology and color affect these rates. Live organisms show less variable and faster heating rates compared with cooling rates, suggesting behavioral and/or physiological adjustments. Our results support Bergmann's rule and the HBH, as larger species show slower heating and cooling rates. However, we did not find a clear pattern to support the TMH. The influence of dorsal melanism on heating by radiation was masked by the body size effect in live animals, and results from euthanized individuals also showed no clear effects of melanism on heating rates. Comparison among three groups of live individuals with different degrees of melanism did not clarify the influence of melanism on heating rates. However, when euthanized animals from the same three groups were compared, we observed that darker euthanized animals actually heat faster than lighter ones, favoring the TMH. Although unresolved aspects remain, body size and coloration influenced heat exchange, suggesting complex thermoregulatory strategies in these lizards, probably regulated through physiology and behavior, which may allow these small lizards to inhabit harsh weather environments.

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Section: Discussionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Effect of body mass and melanism on heat balance inLiolaemuslizards of thegoetschiclade

Azócar

Bonino

Perotti

et al. 2016

Journal of Experimental Biology

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“…Smaller eggs incubated faster (Fig. 4), which may positively influence hatching success in environments with very short seasons (Porter and Tracy, 1983). Based on results from yolk-removal experiments, eggs with halfof their mass in yolk removed hatched two days earlier at 30°C.…”

Section: Discussionmentioning

confidence: 99%

“…For example, consider a life-history trait (trait A) correlated with <C incubation time, hatchling size, juvenile growth rate, and sprint speed. These offspring traits are likely to affect fitness: incubation time may influence hatching success in environments with very short seasons (Porter and Tracy, 1983); hatchling size influences survival of lizards (Ferguson and Fox, 1984); growth rate affects the time and size at maturity (Sinervo, unpubl. ); and hatchling size, through its effects on sprint speed (Sinervo and Adolph, 1989;Tsuji et al, 1989), can potentially affect feeding success (Avery et al, 1982), predator avoidance (Christian and Tracy, 1981;Webb, 1986), and social dominance (Garland et al, 1990).…”

Section: Sizementioning

confidence: 99%

The Evolution of Maternal Investment in Lizards: An Experimental and Comparative Analysis of Egg Size and Its Effects on Offspring Performance

1990

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Abstract.-I used comparative and experimental analysis of egg size in a Sceloporus lizard to examine a fundamental tenet of life-history theory: the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. I analyzed latitudinal and elevational patterns ofegg life-history characteristics among populations and experimentally manipulated egg size and hatchling size by removing yolk from the eggs to examine the causal bases of population differences in offspring traits.Mean clutch size among populations increased to the north (seven vs. 12 eggs/clutch, California vs. Washington), whereas eggsize decreased (0.65 g vs. 0.40 g). The elevational patterns in southern California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically; these traits included incubation time, hatchling size, growth rate, and hatchling sprint performance.Hatchling viability of experimentally reduced eggs was remarkably high (-70%), even when up to 50% of the yolk was removed. The experimentally reduced eggs and hatchlings demonstrated the degree to which size influences each of the offspring life-history traits considered. Northern eggshatched sooner, in part because oftheir small size. Though growth rate is allometrically related to size within each population (i.e., smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate, as measured in the laboratory, are likely to reflect genetic differentiation in the underlying physiology of growth. Moreover, smaller juveniles, because of experimental reduction, had slower sprint speeds than larger juveniles. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is thus largely due to the fact that eggs are smaller in the Washington population.These results provide a basis for interpreting the evolutionary divergence of the suite of traits involved in the evolution ofmaternal investment per offspring in lizards. For example, evolutionary divergence in some offspringtraits functionally related to size (e.g., sprint speed) may be constrained, relative to traits that are determined by other aspects of development or physiology (e.g., growth). I also discuss issues relating to the evolution of maternal investment that could be tested in laboratory and natural populations using experimentally reduced offspring.

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“…If true, climate change may actually be making winter less of a limit to species distributions (by shortening winter) but may impose more physiological hardships to individuals (higher rates of dehydration and metabolism) that must be offset by growth and storage during the favorable season. While physiological (particularly thermal) limits to species' ranges are of increasing research importance, previous work has typically focused on limits imposed (or removed) during the growing season (for reviews, see Porter and Tracy, 1983;Pörtner, 2002;Helmuth et al, 2005) (but see also Ultsch, 1989). Thus, we advocate for increased attention to physiological limits imposed during the unfavorable season as well as to the ongoing alteration of those limits by anthropogenic climate change.…”

Section: Climate Change Winter Temperatures and Population Persistencementioning

confidence: 99%

Glycogen, not dehydration or lipids, limits winter survival of side-blotched lizards (Uta stansburiana)

Zani

Irwin

Rollyson

et al. 2012

Journal of Experimental Biology

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SUMMARYClimate change is causing winters to become milder (less cold and shorter). Recent studies of overwintering ectotherms have suggested that warmer winters increase metabolism and decrease winter survival and subsequent fecundity. Energetic constraints (insufficient energy stores) have been hypothesized as the cause of winter mortality but have not been tested explicitly. Thus, alternative sources of mortality, such as winter dehydration, cannot be ruled out. By employing an experimental design that compared the energetics and water content of lizards that died naturally during laboratory winter with those that survived up to the same point but were then sacrificed, we attempt to distinguish among multiple possible causes of mortality. We test the hypothesis that mortality is caused by insufficient energy stores in the liver, abdominal fat bodies, tail or carcass or through excessive water loss. We found that lizards that died naturally had marginally greater mass loss, lower water content, and less liver glycogen remaining than living animals sampled at the same time. Periodically moistening air during winter reduced water loss, but this did not affect survival, calling into question dehydration as a cause of death. Rather, our results implicate energy limitations in the form of liver glycogen, but not lipids, as the primary cause of mortality in overwintering lizards. When viewed through a lens of changing climates, our results suggest that if milder winters increase the metabolic rate of overwintering ectotherms, individuals may experience greater energetic demands. Increased energy use during winter may subsequently limit individual survival and possibly even impact population persistence.

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3. Biophysical Analyses of Energetics, Time-Space Utilization, and Distributional Limits

Cited by 110 publications

References 0 publications

Effect of body mass and melanism on heat balance inLiolaemuslizards of thegoetschiclade

Effect of body mass and melanism on heat balance inLiolaemuslizards of thegoetschiclade

The Evolution of Maternal Investment in Lizards: An Experimental and Comparative Analysis of Egg Size and Its Effects on Offspring Performance

Glycogen, not dehydration or lipids, limits winter survival of side-blotched lizards (Uta stansburiana)

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