Thermal tolerance and performance

Question 1

How do thermal window vary with the environment

Answer 1

• stable environment, smaller thermal window (polar & tropics)
• less stable regions, greater thermal window (temperate)

Question 2

What is thermal acclimation?

Answer 2

Any phenotypic response to altered environmental temperature that alters performance - Angilleta (2009)
can be developmental or reversible

Question 3

what does a thermal performance curve show?

Answer 3

how performance varies with temperature

Question 4

what is ctmax and ctmin?

Answer 4

critical thermal limits, beyond which survival is passive and time limited

Question 5

what are organisms performance curves influenced by?

Answer 5

the environment and evolutionary history

Question 6

Why are performance curves used?

Answer 6

To quantify and compare the thermal optima and thermal breaths of performance

Question 7

What is the breath of performance?

Answer 7

Range of temperature over which performance is high

Question 8

How do endotherm and ectotherm performance curves vary?

Answer 8

• Ectotherms performance varies with temp

- endotherms have a wider range over which performance is optima (TNZ)

Question 9

What is a thermal generalist?

Answer 9

can do well over a wide range of temperatures but have a lower ctmax

Question 10

What is a thermal generalist?

Answer 10

• Do well at a very narrow range of temp

Question 11

How does performance vary?

Answer 11

• seasonally (winter & summer)
• between environments and not static to the organism
• trait

Question 12

What limits performance?

Answer 12

OCLTT hypothesis

Question 13

what is the OCLTT hypothesis?

Answer 13

A drop in aerobic scope is the first mechanism to limit survival at the low and high ends of the thermal window

• away from optimum, performance starts to decline (i.e hemolin oxygenation starts to decline and drop in aerobic scope) - Pejus threshold marks this
• beyond this there is a drop in the organisms ability to supply tissues, as temp increases the oxygen available in water decreases but metabolic rate increases, hemolin conc continues to decrease and reaches a critical thermal limit (switch to anaerobic metabolism) Portner 2002

Question 14

What limits the capacity to supply the tissues with oxygen? - Portner 2002

Answer 14

• capacity to supply tissues limited by functional capacity of circulatory and ventilatory systems in the spider crab, in turn limiting thermal tolerance and performance
• as temp increases ventilation increase (reaches a capacity)
• past optimum pathological collapse in ventilation (same with heart rate)
• ventilation system doesn’t have ability to deliver oxygen to the tissues to fuel aerobic metabolism (switch to anaerobic metabolism), survival is passive

Question 15

Does oxygen transport capacity always limit performance?

Answer 15

Ern et al 2014

• oxygen transport capacity is maintained at high temperatures in the tropical giant FW prawn, other mechanisms are responsible for the loss of performance at high temp
• in some tropical species the cardiorespiratory systems are adapted to function at high temps, therefore the upper thermal limits may be determined by other mechanisms like loss of protein structure, membrane integrity, cellular function and the denaturation of enzymes

Question 16

why use performance curves?

Answer 16

• can infer relative fitness of organisms across different environments
• infer how organisms fitness may change as a result of changing thermal regimes
• idea of how different thermal environments might affect fitness
• responses can show both evolved and plastic shifts