Evolution of Endothermy

Because endothermy is energetically expensive and evolved more than 100 million years ago (at least in

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Mammals3 log10 BMR = 0.614 -

0.69 log10 M

Birdsc b log10 BMR = 0.800 + 0.67 log10 M .Js^ Xj^ Repti|es

log10 body mass (g)

Figure 3 Relationship between metabolic rate and body mass in vertebrates. The data for amphibians, fish, and reptiles were normalized to 38 °C as described in White et al. Equation for birds was recalculated from Watts (used by McKechnie and Wolf) to ml O2 h_1. aLovegrove BG (2000) The zoogeography of mammalian basal metabolic rate. American Naturalist 156: 201-219. bWhiteCR, Phillips NF, and Seymour RS (2006) The scaling and temperature dependence of vertebrate metabolism. Biology Letters 2: 125-127. cMcKechnie AE and Wolf BO (2004) The allometry of avian basal metabolic rate: Good predictions need good data. Physiological and Biochemical Zoology 77: 502-521.

Table 2 Field metabolic rate (FMR) of endotherms and ectotherms of similar body mass

Species

Common name

Endotherm (ENDO)/ ectotherm (ECTO)

Body mass

(g)

FMR (kJd1)

Peromyscus maniculatusa

Deer mouse

ENDO

18.0

57.3

Erithacus rubeculab

Robin

ENDO

18.7

71.3

Mabuya striatac

Striped skink

ECTO

19.5

2.9

Thamnophis sirtalisd

Common garter snake

ECTO

22.0

5.2

Spermophilus parryie

Arctic ground squirrel

ENDO

630.0

817.0

Alectoris chukarf

Chukar

ENDO

440.0

306.2

Tiliqua scincoides9

Bluetongue lizard

ECTO

574.0

45.7

Aptenodytes patagonicush

King penguin

ENDO

12 900.0

7410.0

Chelonia mydas1

Green sea turtle

ECTO

16000.0

1867.0

aHayes JP (1989) Field and maximal metabolic rates of deer mice (Peromyscus maniculatus) at low and high altitudes. Physiological Zoology 62: 732-744.

bTatner P and Bryant DM (1993) Interspecific variation in daily energy expenditure during avian incubation. Journal of Zoology 231: 215-232.

cNagy KA and Knight MH (1989) Comparative field energetics of a Kalahari skink (Mabuya striata) and gecko (Pachydactylus bibroni). Copeia 1: 13-17.

dPeterson CC, Walton BM, and Bennett AF (1998) Intrapopulation variation in ecological energetics of the garter snake Thamnophis sirtalis, with analysis of the precision of doubly labeled water measurements. Physiological Zoology 71: 333-349.

eNagy KA (1994) Field bioenergetics of mammals: What determines field metabolic rates? Australian Journal of Zoology

fKam M, Degen AA, and Nagy KA (1987) Seasonal energy, water, and food consumption of Negev chukars and sand partridges. Ecology 68: 1029-1037.

gChristian KA, Webb JK, and Schultz TJ (2003) Energetics of bluetongue lizard (Tiligua scincoides) in a seasonal tropical environment. Oecologia 136: 515-523.

hKooyman GL, Cherel Y, Le Maho Y, et al. (1992) Diving behavior and energetics during foraging cycles in king penguins. Ecological Monographs 62: 143-163.

'Southwood AL, Reina RD, Jones VS, Speakman JR, and Jones DR (2006) Sesonal metabolism of juvenile green turtles (Chaledonia mydas) at Heron Island, Australia. Canadian Journal of Zoology 84: 125-135.

birds and mammals), the selective forces leading to the evolution of endothermy are unclear. The earliest hypotheses to explain the evolution of endothermy postulated that selection for higher resting metabolism led to an expanded thermal niche or increased thermal stability. Later, the aerobic capacity model posited that endothermy evolved as by-product of selection for high aerobic capacity (i.e., maximal oxygen consumption capacity during exercise). Based on data for extant organisms, aerobic capacity was argued to be inescapably

Table 3 A comparison of metabolic rates of endotherms and ectotherms of similar body mass

Endotherm (ENDO)/

Temperature

Body

Metabolic rate

Species

Common name

ectotherm (ECTO)

(°C)

mass (g)

(ml O2 h1)

Dipsosaurus dorsalisa

Desert iguana

ECTO

25

35

1.68

Dipsosaurus dorsalisa

Desert iguana

ECTO

30

35

2.45

Dipsosaurus dorsalisa

Desert iguana

ECTO

35

35

5.25

Dipsosaurus dorsalisa

Desert iguana

ECTO

40

35

6.30

Notoryctes caurinusb

North-western marsupial

ENDO

30.8

34

21.4

mole

Phyllostomus discolorc

Pale spear-nosed bat

ENDO

34.6

33.5

11.1

Gerbillus allenbyid

Allenby's gerbil

ENDO

36.3

35.3

38.8

Acanthodactylus

Fringe-toed lizard

ECTO

20

9.0

1.17

erythruruse

Acanthodactylus

Fringe-toed lizard

ECTO

25

9.0

1.62

erythruruse

Acanthodactylus

Fringe-toed lizard

ECTO

30

9.0

2.25

erythruruse

Acanthodactylus

Fringe-toed lizard

ECTO

35

9.0

3.15

erythruruse

Crocidura crosseif

Crosse's shrew

ENDO

34.3

10.2

(Continued )

Table 3 (Continued)

Endotherm (ENDO)/ Temperature Body Metabolic rate

Species Common name ectotherm (ECTO) (°C) mass (g) (ml O2 h1)

Perognathus Little pocket mouse ENDO 34.7 8.9 9.5

longimembris9

Pteronotus davyih Davy's naked-backed bat ENDO 38.8 9.4 24.4

aBennett AF and Dawson WR (1972) Aerobic and anaerobic metabolism during activity in the lizard Dipsosaurus dorsalis. Journal of Comparative Physiology 81: 289-299.

bWithers PC, Thompson GG, and Seymour RS (2000) Metabolic physiology of the north-western marsupial mole, Notoryctes caurinus (Marsupialia: Notoryctidae). Australian Journal of Zoology 48: 241-258.

cMcNab BK (1969) The economics of temperature regulation in neotropical bats. Comparative Biochemistry and Physiology 31: 227-268. dHaim A (1984) Adaptive variations in heat production within gerbils (genus Gerbillus) from different habitats. Oecologia 61: 49-52. ePough FH and Busack SD (1978) Metabolism and activity of the Spanish fringe-toed lizard (Lacertidae: Acanthodactylus erythurus). Journal of Thermal Biology 3: 203-205.

fSparti A (1990) Comparative temperature regulaton of African and European shrews. Comparative Biochemistry and Physiology A 97: 391-397. gChew RM, Lindberg RG, and Hayden P (1967) Temperature regulation in the little pocket mouse, Perognathus longimembris. Comparative Biochemistry and Physiology 21: 487-505.

hBonaccorso FJ, Arends A, Genoud M, Cantoni D, and Morton T (1992) Thermal ecology of moustached and ghost-faced bats (Mormoopidae) in Venezuela. Journal of Mammalogy 73: 365-378.

For endotherms, basal metabolic rate is shown. For ectotherms, standard metabolic rate over a range of temperatures is shown.

correlated with resting metabolism. The newest models suggest that endothermy evolved as consequence ofselec-tion for intense parental care. Which of these models for the evolution of endothermy is best is unresolved.

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