W5: Vertebrate Physiology (Evolution Of Endothermy) [Dr. Matt]

Question 1

Poikilotherm attributes? (2)

Answer 1

• Variable body temperature (Tb).
• Dependent on environmental temperature (Te).

Question 2

Homeotherm attributes? (2)

Answer 2

• Constant Tb.
• Independent of Te.

Question 3

How do Poikilotherms & Homeotherms differ, i.e., by what factor are they differentiated by?

Answer 3

Differentiated by their stability of body temperature.

Question 4

Types of metabolic strategies? (2)

Answer 4

• Ectothermy.
• Endothermy.

Question 5

Ectotherm attributes? (3)

Answer 5

• MR increases with Te.
• Most body heat from the environment.
• Many are poikilothermic.

Question 6

Egs of ectotherms? (4)

Answer 6

• Fish.
• Invertebrates.
• Reptiles.
• Amphibians.

Question 7

Describe the graphs specific to Ectotherms regarding Te (x-axis) & MR (y-axis)? (4)

Answer 7

1) Positive linear graph.

2) Exponential increase.

3) Increase then stabilise then increase.

4) Hill-like increase.

Question 8

Endotherm attributes? (4)

Answer 8

• MR changes with Te.
• Body heat produced internally.
• Many are homeothermic.
• Scholander-Irving model.

Question 9

Egs of Endotherms? (2)

Answer 9

• Birds.
• Mammals.

Question 10

Describe Endotherm graph? (5)

Answer 10

• x-axis = Te.
• y-axis = MR.
• First: negative linear decrease = heat production.
• Second: constant horizontal line = TNZ.
• Third: positive linear increase = heat dissipation.

Question 11

TNZ stands for?

Answer 11

Thermo-Neutral Zone.

Question 12

TNZ?

Answer 12

=

Question 13

Describe the graph of combined ectotherm & endotherm? (8)

Answer 13

• x-axis = Te.
• y-axis = MR.
• Ectotherm at Tfridge: starts off with a low MR but slightly increases MR to match fridge temperature.
• Endotherm at Tfridge: starts off with a very high MR at low Te but increases MR as Te increases to Tfridge.
• Ectotherm at Troom: increases MR further to match an increased Te.
• Endotherm at Troom: as Te increases it decreases MR, so when it gets to Troom MR is within the TNZ & is constant.
• Ectotherm at Tb: MR continues to increase with increasing Te, so its Tb matches that of the Te.
• Endotherm at Tb: MR increases at Tb, but overall MR changes with Te.

Question 14

Cons of Endothermy/Why is endothermy extremely costly? (4)

Answer 14

• At the same Tb, MR is much lower in ectotherms than in endotherms.
• The differences in MR becomes greater as Tb decreases.
• Same amount of food sustains ectotherms for much longer.
• Ectotherms have a higher proportion of energy to growth & reproduction than endotherms.

Question 15

Eg of Con 1 of Endothermy?

Answer 15

A reptile has 1/5 to 1/10 MR of a mammal.

Question 16

Eg of Con 2 of Endothermy?

Answer 16

At low Te, MR of a reptile can be 1-2% of mammals.

Question 17

Eg of Con 3 of Endothermy?

Answer 17

A 300g mammal needs 17x more food than a 300g reptile (same habitat/diet).

Question 18

Pros/Benefits of Endothermy? (4)

Answer 18

• Independent of Te.
• Stable internal environments.
• Higher maximum metabolic rates (= increased aerobic capacity).
• Parental care.

Question 19

Explain Pro 1 of Endothermy?

Answer 19

Independent of Te enables niche expansion.

Question 20

Explain Pro 2 of Endothermy?

Answer 20

Stable internal environments, which maintain stable temperatures for enzyme activities.

Question 21

Explain Pro 3 of Endothermy?

Answer 21

Higher maximum metabolic rates & increased aerobic capacity allows for locomotion & sustained activity.

Question 22

Explain Pro 4 of Endothermy?

Answer 22

Parental care as endotherms are able to:

• Optimise incubation.
• Shorten gestation.
• Have the ability to lactate.

Question 23

Thing to note about parental care?

Answer 23

All placental mammals share a single placental ancestor that survived the K-Pg boundary & radiated into all placental mammals.

Question 24

Evolution of Endothermy attributes? (3)

Answer 24

• One of the most important developments in vertebrate evolution.
• Evolved separately in mammals (synapsids) & birds (sauropsids) from ectothermic ancestors.
• Recent developments are now allowing for the evaluation of hypotheses.

Question 25

What are the recent developments that are now allowing for the evaluation of the hypotheses of the evolution of endothermy? (3)

Answer 25

- Fossils from Jurassic & Cretaceous eras. - Methods for character-state reconstruction. - Biochemical techniques such as bone histology (growth rates) & C and O isotopes (clumping in minerals, Tb).

Question 26

List the single-cause models? (4)

Answer 26

- Aerobic capacity model. - Parental care model. - Niche expansion model. - Body miniaturisation model.

Question 27

Aerobic capacity model attributes? (4)

Answer 27

- NS favoured capacity for sustained activity & locomotion, which increased MMR. - Parallel increases in resting metabolic rates (RMR). - Can be tested to an extent in living mammals. - Bennett & Ruben.

Question 28

Explain Parallel increases in RMR? (2)

Answer 28

- Became the basis for endothermic homeothermy. - By product of increased aerobic scope (MMR/RMR).

Question 29

Explain attribute 3 of Aerobic capacity model?

Answer 29

Can be tested using the relationship between metabolic rate at rest & during exercise.

Question 30

Egs of the relationship between MR at rest & during exercise? (3)

Answer 30

- Deer mice. - Rodents. - Dark-eyed juncos.

Question 31

Basal metabolic rate (BMR)?

Answer 31

= maintenance of energy requirements of the organs & tissues.

Question 32

Maximum metabolic rate (MMR)?

Answer 32

= energy used by skeletal muscles to produce physical work.

Question 33

Explain Deer mice?

Question 34

Explain Rodent species?

Question 35

Explain Dark-eyed juncos?

Question 36

Parental care model attributes? (3)

Answer 36

- NS for increases in RMR. - Suggested mechanism is mediated by thyroid hormones in the breeding season. - Links endothermy to fitness more directly.

Question 37

Results of natural selection for increases in RMR? (2)

Answer 37

- Enhanced capacity for incubation, - Enhanced parental care/food provisioning, which increases growth & decreases juvenile mortality.

Question 38

Egs of Parental care model? (2)

Answer 38

- Diamond pythons. - Burmese pythons. - Greater hedgehog tenrec.

Question 39

Explain Diamond pythons?

Question 40

Explain Burmese pythons?

Question 41

Explain Greater hedgehog tenrec?

Question 42

Aerobic capacity model VS Parental care model?

Answer 42

- Aerobic capacity model = increase in MMR. - Parental care model = increase in RMR.

Question 43

Body miniaturisation model?

Answer 43

= retain homeothermy.

Question 44

Three-phase iterative model?

Answer 44

= a phenology of the evolution of endothermy in birds & mammals.

Question 45

Three-phase iterative model attributes? (2)

Answer 45

- "Correlates" of endothermy. - Is able to explain the correlates of endothermy.

Question 46

Can a single-cause model explain all these correlates? (3)

Answer 46

- Evolution of endothermy "began" about 250mya. - Numerous benefits of endothermy, perhaps each was a driver at different times. - Proposed a three-phase iterative model.

Question 47

Name the three phases of the Three-phase iterative model?

Answer 47

- Phase 1. - Phase 2. - Phase 3.

Question 48

Phase 1 of model?

Answer 48

= parental care & land conquering.

Question 49

Phase 2?

Answer 49

= miniaturisation, thermoregulation & ecomorphological diversification.

Question 50

Phase 3?

Answer 50

= locomotion & climate adaptation.

Question 51

Phase 1 attributes? (3)

Answer 51

- Permian-Triassic. - Therapsids & archosaurs. - Initial endothermic pulses (RMR).

Question 52

Therapsids & archosaurs attributes? (3)

Answer 52

- Earliest ancestors of birds & mammals to show endothermy. - Commonalities. - Lacked insulation: thermoregulation via metabolic heat production unlikely.

Question 53

Commonalities between therapsids & archosaurs? (3)

Answer 53

- Large body size. - Homeothermy. - Oviparity.

Question 54

Initial endothermic pulses (RMR) attributes? (2)

Answer 54

- Parental care during egg brooding. - Likely benefits for aerobic capacity, which enabled colonising of dry land (niche expansion).

Question 55

Phase 2 attributes? (3)

Answer 55

- Late Triassic-Jurassic. - Common, concurrent innovations. - Parental care & locomotion selected for concurrently.

Question 56

Common, concurrent innovations in Phase 2? (5)

Answer 56

- Body size miniaturisation (retention of homeothermy). - Encephalisation (causes high metabolic demands of neuronal tissue). - Nocturnalism in mammals. - Enhanced body insulation (fur & feathers). - Ecomorphological diversification.

Question 57

Encephalisation?

Answer 57

= increased brain size.

Question 58

Phase 3 attributes? (3)

Answer 58

- Cretaceous & Cenozoic. - Locomotory specialisations. - Climate adaptation during the late Cenozoic era.

Question 59

Locomotory specialisations attributes? (2)

Answer 59

- Cursoriality in mammals (improves skeleton muscle performance). - Flapping flight in birds (causes increased demands of pectoral muscles).

Question 60

Climate adaption during the late Cenozoic era attributes? (2)

Answer 60

- Global cooling phases = highly seasonal, high-latitude cold habitats. - Birds & mammals developed advanced thermoregulatory abilities to colonise.

Question 61

Summarise the diagram that concerns the Three-phase iterative model?

Question 62

Explain Lovegrove, 2017?

Question 63

Explain Farmer, 2000?

Question 64

Recap: Endothermy vs Ectothermy? (4)

Answer 64

- Metabolic strategies in endotherms & ectotherms. - Endothermy is more costly than ectothermy. - Benefits of endothermy. - Evolution of endothermy from ectothermic ancestors.

Question 65

Recap: Single-cause models? (4)

Answer 65

- Aerobic capacity model = increase in maximum metabolic rates. - Parental care model = increase in resting metabolic rates. - Niche expansion model. - Body miniaturisation model = retain homeothermy.

Question 66

Recap: Three-phase iterative model? (3)

Answer 66

- Phase 1: = Permian-Triassic. = Parental care & locomotion capacity. - Phase 2: = Late Triassic-Jurassic. = Miniaturisation, thermoregulation (insulation), ecomorphological diversification. - Phase 3: = Cretaceous & Cenozoic. = Locomotory specialisations & climate adaptation.