1 Lecture 9 & 10: Evolution of Endothermy 2 Endothermy has evolved multiple times in both animals and plants: birds and mammals, or their ancestors 3 Endothermy has evolved multiple times in both animals and plants: some reptiles (brooding pythons, large sea turtles, maybe dinosaurs, pterosaurs) 4 Endothermy has evolved multiple times in both animals and plants: scombrid fishes (e.g., tunas and billfishes) lamnid sharks 5 Endothermy has evolved multiple times in both animals and plants: insects (e.g., moths, bees some beetles) 6 Endothermy has evolved multiple times in both animals and plants: at least eight genera of plants within the family Araceae 7 Endothermy is often considered to represent a "key innovation," i.e., a characteristic that allows a fundamentally new way of life and may lead to an adaptive radiation. If so, then we should be able to recognize clear benefits (advantatges) of endothermy, while also identifying costs (disadvantages). 8 Early comparative physiologists assumed that ectothermy was "primitive" and, in general, inferior to endothermy, e.g., "lower" vs. "higher" vertebrates. Now, it is recognized that many characteristics of "lower" vertebrates are actually specializations that promote a low-energy lifestyle. A general separation in average body sizes also exists. Low energy requirements go along with small body size: Costs/Benefits of Ectothermy/Endothermy 9 Body Mass Distributions and small endotherms have severe problems with heat loss because of unfavorable surface/volume ratios. K. S. Kilburn, Old Dominion University 10 Ectotherm Benefits: Do not spend direct metabolic energy on thermoregulation Can spend more on growth and reproduction Require less food overall than do endotherms Costs/Benefits of Ectothermy/Endothermy 11 Allometry of field metabolic rate based on doubly labeled water studies (excluding animals that were seasonally inactive [hibernating mammals, overwintering reptiles]). Note that the lowest mammal and the highest reptiles overlap! Lines are least-squares linear regressions plus 95% prediction intervals. Nagy, K. A., I. A. Girard, and T. K. Brown Energetics of free-ranging mammals, reptiles, and birds. Annual Review of Nutrition 19: 12 Nagy, K. A Field metabolic rate and body size. Journal of Experimental Biology 208: For all data: Note that birds tend to be higher than mammals. 13 Legend for previous slide: Nagy, K. A Field metabolic rate and body size. Journal of Experimental Biology 208: 14 Nagy, K. A Field metabolic rate and body size. Journal of Experimental Biology 208: 15 Ectotherm Benefits: Do not spend direct metabolic energy on thermoregulation Can spend more on growth and reproduction Require less food overall than do endotherms Costs/Benefits of Ectothermy/Endothermy Can spend less time in risky foraging activities Lose less water by evaporation because their metabolic rate is lower and because their Tb is generally lower Generally "preadapted" for life in hot deserts 16 Ectotherm Costs: Activity times more constrained on a daily and seasonal basis Cannot sustain high work rates aerobically (lower maximal aerobic speed) Costs/Benefits of Ectothermy/Endothermy 17 Endotherm Benefits: Are more independent of ambient temperature on a daily and seasonal basis, as well as latitudinally and altitudinally Can grow more rapidly Costs/Benefits of Ectothermy/Endothermy 18 Case, T. J On the evolution and adaptive significance of postnatal growth rates in the terrestrial vertebrates. Q. Rev. Biol. 53: Mammals similar to precocial birds; altricial birds are higher Slope for mammals = 0.72 GRAMS 19 Case, T. J On the evolution and adaptive significance of postnatal growth rates in the terrestrial vertebrates. Q. Rev. Biol. 53: Reptiles and fishes are lower than birds & mammals GRAMS 20 Endotherm Benefits: Are more independent of ambient temperature on a daily and seasonal basis, as well as latitudinally and altitudinally Can grow more rapidly Costs/Benefits of Ectothermy/Endothermy Can sustain high rates of work aerobically (higher maximal aerobic speed) Long-distance migrations McClellan, C. M., and A. J. Read Complexity and variation in loggerhead sea turtle life history. Biology Letters 3: [long-distance movements, tied to endothermy?] Powered flight in relatively larger animals Intense feeding of offspring Enzymes can function more efficiently over a narrower temperature range 21 Endotherm Costs: Need a lot more food Need larger home ranges and spend more time foraging, conspicuously, and may be more apparent to predators Note that many ectotherms (e.g., lizards) combine activities (multitask), alternating between basking, foraging, signaling, defending their territories, looking for mates, watching for predators Costs/Benefits of Ectothermy/Endothermy Stopped here 4 Feb. 2014 22 Where did endothermy evolve in the lineage leading to modern mammals? What characterizes a modern mammal? Endothermy High Metabolic Rate Homeothermy Response to Lowered Ambient Temperature (shivering + non-shivering thermogenesis) Fur or Hair Live Birth Parental Care Lactation Large Brain 4-chambered Heart Most of these features are absent or unclear in the fossil record. 23 In the fossil record, mammals are defined mainly by the presence of a single bone (dentary) in the lower jaw. Other fossil-visible features include: Multi-cuspid Teeth, Differentiated Along the Jaw Secondary Palate Upright Posture Large Brains These changes occur gradually in the fossil record. If or how they are associated with endothermy is often unclear. Stopped here 3 Feb. 2015 24 The endothermy of birds and mammals is distinctive, because at rest it results primarily from metabolic heat production by visceral organs (and the brain) rather than by muscles. The endothermy of pythons, scombrid fishes, sharks, and sea turtles results primarily, but perhaps not exclusively, from myogenic heat production coupled with relatively large body size The endothermy of insects is also myogenically based, but given their small size, endothermy in insects also requires a highly effective insulation. 25 Only birds and mammals have metabolic rates high enough and insulation effective enough (or body size large enough) that they can maintain body temperatures elevated above ambient while at rest and in the absence of contractions by skeletal muscles. (If the slow swimming needed to ventilate the gills of obligate ram ventilators is equated with the effort needed to ventilate the lung of a bird or mammal, then it can be argued that some fishes also maintain elevated body temperatures while at rest, i.e., during slow swimming.) 26 Increased resting metabolic rate has been hypothesized to be associated with selection for: 1) thermal niche expansion (Bakken and Gates 1975; Crompton et al. 1978; Block et al. 1993) 2) homeothermy (stable body temperature) and increased metabolic efficiency (Heinrich 1977; Avery 1979) 3) commitment to inertial homeothermy followed by decreasing body size (McNab 1978) 4) postural changes that enhance exercise performance (Heath 1968, cf. Carrier 1987) 5) increased brain size (cf. Hulbert 1980) 27 6) increased aerobic capacity during exercise (Regal 1978; Bennett and Ruben 1979) 7) parental care (Case 1978; Farmer 1998, 2000; Koteja 2000) Case, T. J Endothermy and parental care in the terrestrial vertebrates. American Naturalist 112: Farmer, C. G Hot blood and warm eggs. Journal of Vertebrate Paleontology 18, suppl. 3 (Abstracts. Fifty-eighth Annual Meeting of the Society of Vertebrate Paleontology), 40A. Farmer, C. G Parental care: the key to understanding endothermy and other convergent features in birds and mammals. American Naturalist 155: Koteja, P Energy assimilation, parental care and evolution of endothermy. Proc. Royal. Soc. Lond. B 267: Angilletta, M. J. and M. W. Sears Parental care as a selective factor for the evolution of endothermy? American Naturalist 162: Farmer, C. G Reproduction: The adaptive significance of endothermy. American Naturalist 162: ) resting metabolic rate set to optimize cardiovascular O 2 transport (Krosniunas and Gerstner 2003) 28 Recent attempts to elucidate the selective regime(s) responsible for the evolution of avian and mammalian endothermy (i.e., ultimate causes) have focused principally on #6, which is now termed the aerobic capacity model. 29 Bennett and Ruben (1979) argued that selection for higher capacity for sustainable activity, supported by aerobic metabolic rate, was important during the evolution of endothermy. They noted that the energy (food) cost of increasing resting metabolic rate was high compared to the thermoregulatory benefits, especially for small increases in resting metabolism, for which thermoregulatory improvements would be insignificant. In contrast, any increase in maximal aerobic capacity will be reflected in higher capacity for sustainable activity. 30 The aerobic capacity model has two major parts. 1. directional selection related to activity capacity resulted in the evolution of a higher maximal aerobic metabolic rate. Increase in VO 2 max would increase maximal aerobic speed and thus enable animals to exercise longer at higher levels. This would be advantageous for many reasons, e.g., better at capturing prey or defending territories, able to traverse and hence forage over greater areas. However, higher aerobic capacity by itself would not result in endothermy of resting animals. 31 2. maximal and resting metabolism are somehow linked in a causal, mechanistic sense; thus, evolutionary changes in the two traits cannot occur independently. This idea was based on the empirical observation that in vertebrates maximal oxygen consumption during exercise (VO 2 max) is typically 5-10 times resting oxygen consumption. 32 "Thus there appears to be a consistent linkage between resting and maximal levels of oxygen consumption in the vertebrates. When an animal is in any given physiological state, oxygen consumption may increase an average of only five- to tenfold." (Bennett and Ruben 1979, p. 651) They saw what they interpreted as a relatively constant factorial aerobic scope, and viewed this as indicative of a fundamental property of vertebrate physiology. But they concluded that the mechanisms underlying such a relationship between activity and resting metabolic rate were unclear. 33 One simple verbal model is the Volkswagen - Ferrari analogy. Does not use much gas, but cannot go very fast. Goes really fast, but uses a lot of gas even when idling. 34 Whatever the mechanism might be, the aerobic capacity model assumes that selection for increased maximum aerobic capacity will necessarily result in increased resting metabolic rate and, eventually, endothermy. Note that this model is an interesting mix of ultimate and proximate explanations for why and how mammalian and avian endothermy evolved! Some of the other ideas about the evolution of endothermy (see slides 26-27) also mix these levels, which is not a bad thing. This would make a good exam question! 35 How can we test the aerobic capacity model? In general, a model can be tested by testing its predictions or by testing its assumptions. Let's go through 5 possible tests that get at one or the other. 36 1. If we intentionally selected for a higher VO 2 max, then resting metabolic rate would be predicted to increase more-or-less in parallel. Hayes and colleagues bred 4 replicate lines of laboratory house mice for high mass-independent VO 2 max during forced treadmill exercise (Wone et al Heredity). The selection criterion included body mass as a covariate, so selection was independent of effects of body mass on metabolic rate. 4 additional lines were maintained as non-selected controls. Compared with controls, VO 2 max significantly increased by 11.2% in lines bred for VO 2 max, while BMR did not change significantly (+2.5%). Koteja and colleagues bred 4 replicate lines of wild voles for swim-induced aerobic capacity (Stawski et al Comp. Biochem. Physiol. A 180:51-56) and got some correlated response in BMR, but not maintaining the same factorial increase (i.e., BMR did not increase nearly as much as VO 2 max). These studies offer, at most, weak support for the aerobic capacity model. Of course, the relevance of small living rodents for (large?) therapsids is unclear. 37 2. If we estimated the additive genetic correlation between VO 2 max and resting metabolic rate, it would be positive and high. Genetic correlations can be estimated much more easily than doing a selection experiment (need fewer generations), but the evidence they provide is not as strong. In laboratory house mice, Dohm et al. (2001) found weak evidence for a positive additive genetic correlation. In wild voles, the additive genetic correlation between BMR and the swim-induced aerobic capacity was high and positive (Sadowska et al. 2005). Some support for the aerobic capacity model. 38 3. What about the phenotypic correlation between VO 2 max and resting metabolic rate? Estimates of the phenotypic correlations within species are much easier to obtain. They were compiled in Hayes and Garland (1995), and the following table gives their results with some updates: 39 40 Take-home message: phenotypic correlations tend to be positive. However, the picture for anuran amphibians is much less consistently positive 41 Gomes, F. R., J. G. Chau-Berlinck, J. E. P. W. Bicudo, C. A. Navas Intraspecific relationships between resting and activity metabolism in anuran amphibians: influence of ecology and behavior. Physiological and Biochemical Zoology 77: Studied 21 Neotropical species of anuran amphibians (frogs and toads) from different geographical areas that include remarkable diversity in behavior & thermal ecology. "The three possible trends (positive, negative, and absent correlations) were observed and appeared to be predictable from ecological and behavioral variables that relate to evolutionary physiological shifts in anurans. Positive correlations between VO 2 rest and VO 2 act were more common in species with active lifestyles (e.g., intense vocal activity) and in species that call at low temperatures (e.g., winter or high-elevation specialists)." 42 Gomes, F. R., J. G. Chau-Berlinck, J. E. P. W. Bicudo, C. A. Navas Intraspecific relationships between resting and activity metabolism in anuran amphibians: influence of ecology and behavior. Physiological and Biochemical Zoology 77: 43 Also, even when the correlations are positive, they are VO 2 max Not all analyzed phylogenetically (later lectures). Here is most recent example for rodents... 45 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: species or populations of rodents 46 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: Maximum metabolic rate in cold with helium-oxygen 47 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: r = 0.5 P < 0.001 48 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: Wiersma, P., M. A. Chappell, and J. B. Williams Cold- and exercise-induced peak metabolic rates in tropical birds. PNAS 104: Summary of Studies on Interspecific Correlations Tropical Birds P VO 2 max Wiersma et al., 2007 49 These positive interspecific correlations are consistent with the aerobic capacity model, but a similar pattern could arise if: selection favored high resting metabolic rate and maximal metabolic rate followed; selection simultaneously favored both high resting and maximal. Therefore, we cannot rule out alternative hypotheses based on this evidence. 50 5. If we studied basic physiology, we would find a necessary relationship between maximal and resting aerobic metabolic rates. For example, if mitochondria have a "minimum idling speed" or perhaps if "leaky membranes" are required for a high VO 2 max and also entail a cost at rest. Various suborganismal traits do differ consistently between mammals and reptiles 51 Various Suborganismal Traits Show Quantitative Differences Between Mammals and Reptiles Else, P. L., and A. J. Hulbert Comparison of the "mammal machine" and the "reptile machine": energy production. Am. J. Physiol. 240 (Regulatory Integrative Comp. Physiol. 9):R3-R9. "The difference in energy production capacity was not due to any single parameter but was a summation of several smaller differences. The mammal had relatively larger internal organs than the reptile, their organs had a greater proportion of mitochondria, and their mitochondria had a greater relative membrane surface area. These differences, it is suggested, may be due in part to different thyroid function in reptiles and mammals." 52 Various Suborganismal Traits Show Quantitative Differences Between Mammals and Reptiles Hulbert, A. J., and P. L. Else Basal metabolic rate: history, composition, regulation, and usefulness. Physiological and Biochemical Zoology 77: "Rolfe and Brown (1997) concluded that 10% of the oxygen consumed during BMR is consumed by nonmitochondrial processes, 20% is consumed by mitochondria to counteract the mitochondrial proton leak, and the remaining 70% is consumed for mitochondrial ATP production. At a whole-animal level, ATP production can be divided into 20%25% for Na +,K + -ATPase activity, 20%25% for protein synthesis, 5% for Ca 2+ -ATPase activity, 7% for gluconeogenesis, 2% for ureagenesis, 5% for actinomyosin-ATPase activity, and 6% for all other ATP-consuming processes. These estimates are averages over the entire animal, and the relative contribution of the different processes varies between tissues." 53 No single factor accounts for the higher resting metabolic rates of mammals versus lizards. A mechanism that would yield a necessary relationship between maximal and resting metabolic rates remains elusive... Also, how relevant are living vertebrates? Except for fossils, therapsids are not available for study, nor are the ancestors of modern birds. Various indicators of metabolic rate in fossils have been proposed, but do not seem definitive, and have not been tested experimentally, e.g., bone histology lung structure nasal turbinates as an example 54 Hillenius, W. J., and J. A. Ruben The evolution of endothermy in terrestrial vertebrates: Who? When? Why? Physiol. Biochemical Zoology 77: Fig. 6. Relationship of nasal passage cross- sectional area to body mass (M) in extant ectotherms (lizards & crocodilians; cross-sectional area = 0.11M 0.76 ) and endotherms (mammals & birds; cross-sectional area = 0.57M 0.68 ). Also plotted are three genera of Late Cretaceous dinosaurs - the hadrosaurid Hypacrosaurus and the theropods Tyrannosaurus (Nanotyrannus) and Ornithomimus - and five genera of Permo-Triassic therapsids: (1) a gorgonopsian, (2, 3) two primitive therocephalians, and the cyndonts (4) Diademodon and (5) Thrinaxodon. Values for dinosaurs and therapsids were not used in regression calculations. Modified from Ruben et al. (1996, 1997). Therapsids 55 Parental care and the evolution of mammalian/avian endothermy: two models. 56 Farmer, C. G Parental care: the key to understanding endothermy and other convergent features in birds and mammals. American Naturalist 155: Endothermy was driven by the development of active incubation, which would lead to the evolution of an increased metabolic heat production and control of an elevated body temperature. 2.The immediate advantages were an increased growth rate of the offspring and improved developmental stability. 57 3.Increased heat production was achieved by an increased leakiness of plasma membranes, particularly in the visceral organs. 4.High daily energy expenditure was partly a consequence of the foregoing increase in BMR. 5.Provisioning offspring with warmth and nutrition requires sustained vigorous exercise. A mix of ultimate and proximate explanations. 58 Koteja, P The evolution of concepts on the evolution of endothermy in birds and mammals. Physiological and Biochemical Zoology 77: 59 Koteja, P Energy assimilation, parental care and evolution of endothermy. Proceedings of the Royal Society of London B 267: Selection favored increased feeding of offspring by parents. Guarding of offspring first. Offspring ate scraps. So, selection favored parents who caught more than they ate, and returned to nest to eat it. 60 2.The increased total energy expenditure by parents (increased DEE) came with increased food requirements, and hence required an increased performance from the visceral organs, which resulted in an increased BMR, etc. --> positive feedback mechanism. (= "assimilation capacity model") 3.Selection also favored increased offspring growth rate. 4.Social structure is facilitated. Increase in brain size would cause some increase in BMR. 61 5.Eventually, when parents forage at or near maximal aerobic speed (MAS), selection favors increased VO 2 max. Would require increases in lots of suborganismal traits, if symmorphosis applies (later lecture)! 6.BMR thus increases, which increases DEE. 7.Positive feedback mechanism... A mix of ultimate and proximate explanations. But what about shivering, etc., in response to lowered temperature? This is not addressed by either Farmer or Koteja (or by the aerobic capacity model). 62 Koteja, P The evolution of concepts on the evolution of endothermy in birds and mammals. Physiological and Biochemical Zoology 77: 63 Extra Slides Follow... In 2014, this was only about 5 min short. Should add a bit. In 2015, this was about 15 min short. For next time, possibly cut some verbiage, eliminate redundancy, reorganize a bit, show McNab graph, explain some of the other models a bit more (e.g., quotes, figures). Could add more fossil work. Combine all endothermy stuff into one lecture, and expand the previous locomotion lecture. Add fish examples??? Farmer et al. unidirectional flow in varanid lung. 64 Sixth International Congress of Comparative Physiology and Biochemistry Symposium Papers: Evolution and Advantages of Endothermy Frappell, P. B., and P. J. Butler Minimal Metabolic Rate, What It Is, Its Usefulness, and Its Relationship to the Evolution of Endothermy: A Brief Synopsis. Physiological and Biochemical Zoology 77: Hulbert, A. J., and P. L. Else Basal Metabolic Rate: History, Composition, Regulation, and Usefulness. Physiological and Biochemical Zoology 77: Cruz-Neto, A. P., and F. Bozinovic The Relationship between Diet Quality and Basal Metabolic Rate in Endotherms: Insights from Intraspecific Analysis. Physiological and Biochemical Zoology 77: Ksiek, A., M. Konarzewski, and I. B. Lapo Anatomic and Energetic Correlates of Divergent Selection for Basal Metabolic Rate in Laboratory Mice Physiological and Biochemical Zoology 77: Speakman, J. R., E. Krl, and M. S. Johnson The Functional Significance of Individual Variation in Basal Metabolic Rate. Physiological and Biochemical Zoology 77: Lovegrove, B. G Locomotor Mode, Maximum Running Speed, and Basal Metabolic Rate in Placental Mammals. Physiological and Biochemical Zoology 77: White, C. R., and R. S. Seymour Does Basal Metabolic Rate Contain a Useful Signal? Mammalian BMR Allometry and Correlations with a Selection of Physiological, Ecological, and Life-History Variables. Physiological and Biochemical Zoology 77: Schleucher, E Torpor in Birds: Taxonomy, Energetics, and Ecology. Physiological and Biochemical Zoology 77: Else, P. L., N. Turner, and A. J. Hulbert The Evolution of Endothermy: Role for Membranes and Molecular Activity. Physiological and Biochemical Zoology 77: Prtner, H. O Climate Variability and the Energetic Pathways of Evolution: The Origin of Endothermy in Mammals and Birds. Physiological and Biochemical Zoology 77: Grigg, G. C., L. A. Beard, and M. L. Augee The Evolution of Endothermy and Its Diversity in Mammals and Birds. Physiological and Biochemical Zoology 77: Dickson, K. A., and J. B. Graham Evolution and Consequences of Endothermy in Fishes. Physiological and Biochemical Zoology 77: Hillenius, W. J., and J. A. Ruben The Evolution of Endothermy in Terrestrial Vertebrates: Who? When? Why? Physiological and Biochemical Zoology 77: Koteja, P The Evolution of Concepts on the Evolution of Endothermy in Birds and Mammals. Physiological and Biochemical Zoology 77: Seymour, R. S., C. L. Bennett-Stamper, S. D. Johnston, D. R. Carrier, and G. C. Grigg Evidence for Endothermic Ancestors of Crocodiles at the Stem of Archosaur Evolution. Physiological and Biochemical Zoology 77: Hillenius, W. J., and J. A. Ruben Getting Warmer, Getting Colder: Reconstructing Crocodylomorph Physiology. Physiological and Biochemical Zoology 77: Seymour, R. S Reply to Hillenius and Ruben. Physiological and Biochemical Zoology 77: 65 Stopped here 1 Feb. 2007 66 Sixth International Congress of Comparative Physiology and Biochemistry Symposium Papers: Evolution and Advantages of Endothermy Frappell, P. B., and P. J. Butler Minimal Metabolic Rate, What It Is, Its Usefulness, and Its Relationship to the Evolution of Endothermy: A Brief Synopsis. Physiological and Biochemical Zoology 77: Hulbert, A. J., and P. L. Else Basal Metabolic Rate: History, Composition, Regulation, and Usefulness. Physiological and Biochemical Zoology 77: Cruz-Neto, A. P., and F. Bozinovic The Relationship between Diet Quality and Basal Metabolic Rate in Endotherms: Insights from Intraspecific Analysis. Physiological and Biochemical Zoology 77: Ksiek, A., M. Konarzewski, and I. B. Lapo Anatomic and Energetic Correlates of Divergent Selection for Basal Metabolic Rate in Laboratory Mice Physiological and Biochemical Zoology 77: Speakman, J. R., E. Krl, and M. S. Johnson The Functional Significance of Individual Variation in Basal Metabolic Rate. Physiological and Biochemical Zoology 77: Lovegrove, B. G Locomotor Mode, Maximum Running Speed, and Basal Metabolic Rate in Placental Mammals. Physiological and Biochemical Zoology 77: White, C. R., and R. S. Seymour Does Basal Metabolic Rate Contain a Useful Signal? Mammalian BMR Allometry and Correlations with a Selection of Physiological, Ecological, and Life-History Variables. Physiological and Biochemical Zoology 77: Schleucher, E Torpor in Birds: Taxonomy, Energetics, and Ecology. Physiological and Biochemical Zoology 77: Else, P. L., N. Turner, and A. J. Hulbert The Evolution of Endothermy: Role for Membranes and Molecular Activity. Physiological and Biochemical Zoology 77: Prtner, H. O Climate Variability and the Energetic Pathways of Evolution: The Origin of Endothermy in Mammals and Birds. Physiological and Biochemical Zoology 77: Grigg, G. C., L. A. Beard, and M. L. Augee The Evolution of Endothermy and Its Diversity in Mammals and Birds. Physiological and Biochemical Zoology 77: Dickson, K. A., and J. B. Graham Evolution and Consequences of Endothermy in Fishes. Physiological and Biochemical Zoology 77: Hillenius, W. J., and J. A. Ruben The Evolution of Endothermy in Terrestrial Vertebrates: Who? When? Why? Physiological and Biochemical Zoology 77: Koteja, P The Evolution of Concepts on the Evolution of Endothermy in Birds and Mammals. Physiological and Biochemical Zoology 77: Seymour, R. S., C. L. Bennett-Stamper, S. D. Johnston, D. R. Carrier, and G. C. Grigg Evidence for Endothermic Ancestors of Crocodiles at the Stem of Archosaur Evolution. Physiological and Biochemical Zoology 77: Hillenius, W. J., and J. A. Ruben Getting Warmer, Getting Colder: Reconstructing Crocodylomorph Physiology. Physiological and Biochemical Zoology 77: Seymour, R. S Reply to Hillenius and Ruben. Physiological and Biochemical Zoology 77: 67 Good graphs, but no phylogenetic analysis. Endothermy in African Platypleurine Cicadas: The Influence of Body Size and Habitat (Hemiptera: Cicadidae) Author(s) Allen F. Sanborn, Martin H. Villet, and Polly K. Phillips Identifiers Physiological and Biochemical Zoology, volume 77 (2004), pages 816823 DOI: / PubMed ID: Abstract The platypleurine cicadas have a wide distribution across Africa and southern Asia. We investigate endothermy as a thermoregulatory strategy in 11 South African species from five genera, with comparisons to the lone ectothermic platypleurine we found, in an attempt to ascertain any influence that habitat and/or body size have on the expression of endothermy in the platypleurine cicadas. Field measurements of body temperature (Tb) show that these animals regulate Tb through endogenous heat production. Heat production in the laboratory elevated Tb to the same range as in animals active in the field. Maximum Tb measured during calling activity when there was no access to solar radiation ranged from 13.2 to 22.3C above ambient temperature in the five species measured. The mean Tb during activity without access to solar radiation did not differ from the mean Tb during diurnal activity. All platypleurines exhibit a unique behavior for cicadas while warming endogenously, a temperature- dependent telescoping pulsation of the abdomen that probably functions in ventilation. Platypleurines generally call from trunks and branches within the canopy and appear to rely on endothermy even when the sun is available to elevate Tb, in contrast to the facultative endothermy exhibited by New World endothermic species. The two exceptions to this generalization we found within the platypleurines are Platypleura wahlbergi and Albanycada albigera, which were the smallest species studied. The small size of P. wahlbergi appears to have altered their thermoregulatory strategy to one of facultative endothermy, whereby they use the sun when it is available to facilitate increases in Tb. Albanycada albigera is the only ectothermic platypleurine we found. The habitat and host plant association of A. albigera appear to have influenced the choice of ectothermy as a thermoregulatory strategy, as the species possesses the metabolic machinery to elevate to the Tb range observed in the endothermic species. Therefore, size and habitat appear to influence the expression of thermoregulatory strategies in African platypleurine cicadas. 68 Intraspecific Relationships between Resting and Activity Metabolism in Anuran Amphibians: Influence of Ecology and Behavior Author(s) Fernando R. Gomes, Jos Guilherme Chau-Berlinck, Jos Eduardo P. W. Bicudo, and Carlos A. Navas Identifiers Physiological and Biochemical Zoology, volume 77 (2004), pages 197208 DOI: / PubMed ID: Abstract The aerobic capacity model, as well as other models for the evolution of aerobic metabolism and the origin of endothermy, requires a mechanistic link between rates of resting and activity oxygen consumption (VN/Ao2rest and VN/Ao2act). The existence of such link is still controversial, but studies with anuran amphibians support a correlation between VN/Ao2rest and VN/Ao2act at both the intraspecific and interspecific levels. Because results at the intraspecific level are based only on a few species, we test for the generality of a link between these two metabolic variables in anurans by studying the intraspecific correlational patterns between mass-independent VN/Ao2rest and VN/Ao2act in anurans. We focus on 21 Neotropical species from different geographical areas that include remarkable diversity in behavior and thermal ecology. Although uncorrelated, VN/Ao2rest and VN/Ao2act seem to be consistent among individuals. Diverse intraspecific phenotypic correlational trends were detected, indicating that the intraspecific relationships between VN/Ao2rest and VN/Ao2act might be very diverse in anurans. The three possible trends (positive, negative, and absent correlations) were observed and appeared to be predictable from ecological and behavioral variables that relate to evolutionary physiological shifts in anurans. Positive correlations between VN/Ao2rest and VN/Ao2act were more common in species with active lifestyles (e.g., intense vocal activity) and in species that call at low temperatures (e.g., winter or high-elevation specialists). 69 Seymour et al., 2004 70 Seymour et al., 2004 71 Seymour et al., 2004 72 Seymour et al., 2004 73 Seymour et al., 2004 74 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: 75 Rezende, E. L., F. Bozinovic, and T. Garland, Jr Climatic adaptation and the evolution of basal and maximum rates of metabolism in rodents. Evolution 58: 76 From 41095LECT.DOC Problems of defining 1st mammal: (see Ridley, 1996, pages ) 1. How do you define a mammal? 2. modern mammals have hair or fur, lactation, live birth, parental care, high metabolic rates, ability to maintain high body temperature in face of cold via shivering, etc. 3. only skeletal characteristics can be seen in fossil record 4. so, define 1st mammals as having a single bone, the dentary, in the lower jaw (TRANSPARENCY 1 from Lecture 14) 5. skulls may indicate presence of vibrissae 6. bone histology may give clues as to metabolic rate 7. were therapsids warm-blooded? 8. predator-prey relationships -- Bakker 9. were dinosaurs warm-blooded? 10. biomechanical/energetic arguments a. must be warm-blooded to fly --> pterosaurs must have been --> ancestors of both pterosaurs and Archaeopteryx must have been??? 11. Comparative Method may help, and so must know evolutionary relationships!!! Difficulties in defining "first" in a clade emphasize the gradual nature of evolutionary change, even among major grades. 77 78 Possible exam question: Discuss two different models for the evolution of mammalian and avian endothermy. Who developed these models? How do the components of the models fall into the categories of ultimate and proximate explanation?