W5: Vertebrate Physiology (Evolution Of Endothermy) [Dr. Matt] Flashcards
Poikilotherm attributes? (2)
- Variable body temperature (Tb).
- Dependent on environmental temperature (Te).
Homeotherm attributes? (2)
- Constant Tb.
- Independent of Te.
How do Poikilotherms & Homeotherms differ, i.e., by what factor are they differentiated by?
Differentiated by their stability of body temperature.
Types of metabolic strategies? (2)
- Ectothermy.
- Endothermy.
Ectotherm attributes? (3)
- MR increases with Te.
- Most body heat from the environment.
- Many are poikilothermic.
Egs of ectotherms? (4)
- Fish.
- Invertebrates.
- Reptiles.
- Amphibians.
Describe the graphs specific to Ectotherms regarding Te (x-axis) & MR (y-axis)? (4)
1) Positive linear graph.
2) Exponential increase.
3) Increase then stabilise then increase.
4) Hill-like increase.
Endotherm attributes? (4)
- MR changes with Te.
- Body heat produced internally.
- Many are homeothermic.
- Scholander-Irving model.
Egs of Endotherms? (2)
- Birds.
- Mammals.
Describe Endotherm graph? (5)
- x-axis = Te.
- y-axis = MR.
- First: negative linear decrease = heat production.
- Second: constant horizontal line = TNZ.
- Third: positive linear increase = heat dissipation.
TNZ stands for?
Thermo-Neutral Zone.
TNZ?
=
Describe the graph of combined ectotherm & endotherm? (8)
- 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.
Cons of Endothermy/Why is endothermy extremely costly? (4)
- 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.
Eg of Con 1 of Endothermy?
A reptile has 1/5 to 1/10 MR of a mammal.
Eg of Con 2 of Endothermy?
At low Te, MR of a reptile can be 1-2% of mammals.
Eg of Con 3 of Endothermy?
A 300g mammal needs 17x more food than a 300g reptile (same habitat/diet).
Pros/Benefits of Endothermy? (4)
- Independent of Te.
- Stable internal environments.
- Higher maximum metabolic rates (= increased aerobic capacity).
- Parental care.
Explain Pro 1 of Endothermy?
Independent of Te enables niche expansion.
Explain Pro 2 of Endothermy?
Stable internal environments, which maintain stable temperatures for enzyme activities.
Explain Pro 3 of Endothermy?
Higher maximum metabolic rates & increased aerobic capacity allows for locomotion & sustained activity.
Explain Pro 4 of Endothermy?
Parental care as endotherms are able to:
- Optimise incubation.
- Shorten gestation.
- Have the ability to lactate.
Thing to note about parental care?
All placental mammals share a single placental ancestor that survived the K-Pg boundary & radiated into all placental mammals.
Evolution of Endothermy attributes? (3)
- 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.
What are the recent developments that are now allowing for the evaluation of the hypotheses of the evolution of endothermy? (3)
- 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).
List the single-cause models? (4)
- Aerobic capacity model.
- Parental care model.
- Niche expansion model.
- Body miniaturisation model.