Lecture 8

Question 1

What are the short term/ acute effects of glucocorticoids (stress hormones in animals?

Answer 1

. Suppression of reproductive behaviour without affecting reproductive system
. Altered immune function
. Increased gluconeogenesis (mobilisation of energy stores)
. Increased foraging behaviour
. Promotion of escape (irruption behaviour during day
. Promotion of night restfulness

(Acute effects correspond to emergency life history stage)

Question 2

What are the long-term effects of glucocorticoids (stress hormones) in animals?

Answer 2

. Inhibitstion of the reproductive system
. Immune suppression, impaired disease resistance
. Loss of protein from skeletal muscle
. Accelerated neuronal degeneration
. Suppression of growth

Question 3

What happens if you administer corticosterone’s?

Answer 3

It can temporally stop reproductive behaviour although the reproduction may not change in size so the gonads will still be large but the birds won’t show any reproductive behaviour

Question 4

By administering corticosterone’s it can temporally stop reproductive behaviour, but what else can it affect?

Answer 4

Can affect the immune function e.g. when there is something like a storm and birds have to adjust the way they eat/ get energy so if food is scarce they may need to increase foraging behaviour or it may be beneficial to get out of a particular area so might fly away even is your nest is in that area

Question 5

How does the ‘capture, handling and restraint’ method to determine stress responsiveness in wild wilds work?

Answer 5

. Catch the bird. Take blood sample within 2 min of capture
. Bird subjected to standardised stressor
. Take blood at defined intervals (usually 5, 10, 30, 60 min) and measure the amount of corticosterone in the blood and over the hour you get a gradual increase

Question 6

Why when using the ‘capture, handling and restraint’ method to determine stress responsiveness in wild birds do you take a blood sample within 2 min of capture?

Answer 6

Is a baseline before the bird has experienced the stressor

Question 7

What is the standardised stressor that is used in the ‘capture, handling and restraint ‘ method to determine stress responsiveness in wild birds?

Answer 7

Being placed in a drawstring bag:
Place the bird in the bag for up to an hour. This is a physiological stressor maybe because it can’t move freely and is associated with being caught by a predator. It is not physically injured but it is enough of a stressor to activate the stress hormones

Question 8

What is good about using the ‘capture, handling and restraint ‘ method to determine stress responsiveness in wild birds?

Answer 8

It is a highly reproducible technique applicable across different species, seasons and habitats

Question 9

How can latitude affect stress response/ lower stress hormones?

Answer 9

Stress response can be reduced in high latitude breeding populations

Question 10

Give an example of a higher latitude that shows reduced stress hormones in more northerly populations

Answer 10

Shorebirds that breed Alaska e.g: Semipalmated sandpiper

Question 11

What is free (not total) corticosterone (stress responsiveness) related to?

Answer 11

The length of the breeding season

Question 12

What are glucocorticoids?

Answer 12

Lipid soluble hormones

Question 13

Since glucocorticoids are not proteins but lipid soluble hormones what is it hard for them to do?

Answer 13

To travel in the blood

Question 14

The lipid soluble hormones, glucocorticoids, are not proteins therefore it is hard for them to travel in the blood. So what do they need to do?

Answer 14

So it is difficult for them to travel in the blood unless they are associated with a protein which makes them much more water soluble. So, to get around the body they need to associate themselves with proteins
(So protein circulating in the blood binds to glucocorticoids)

Question 15

What are the proteins that glucocorticoids associate themselves with to get around the body called? Give an example of one

Answer 15

Binding globulins e.g. corticosteroid binding globulin (CBG)

Question 16

What is the free hormone hypothesis?

Answer 16

That the hormone (glucocorticoids) travels associated with that a protein but becomes unbound from the hormone once it gets into cells and when it is exerting it’s biological actions it is in a free form as it is unbound from that binding protein
(So protein (binding globulins circulating in the blood is proposed to modulate access of glucocorticoids to tissues)

Question 17

What is it that only the free hormone is believed to have?

Answer 17

The actual biological effects in the cells and is it is bound to the globulin then it is inactive

Question 18

What is the standard way of measuring corticosterone?

Answer 18

By the process called radioimmunoassay

Question 19

What does the process of of measuring corticosterone radioimmunoassay do?

Answer 19

Splits apart the hormone from its binding protein

Question 20

Why do researches typically measure the total corticosterone?

Answer 20

They are not able to see bound from free glucocorticoids but you can do that but it takes longer but it is possible because if you take some measurements at the same time you can for any given blood sample work out how much binding protein is in there but most people don’t do it

Question 21

Whether the hormone (glucocorticoids) is going to have biological effects can be regulated by what?

Answer 21

Regulated by whether it is bound to the binding protein or not

Question 22

Birds can regulate their response to corticosterone in fine detailed way. Give an example of this

Answer 22

For example they can regulate the amount of binding protein that they are producing

Question 23

How does birds regulating their amount of binding protein effect their response to corticosterone?

Answer 23

Because by regulating the amount of binding protein that they are producing can effect whether the corticosterone is going to have an effect on the biological effect in the tissues

Question 24

How can you measure corticosterone bound to CBG? Hence what can be estimated?

Answer 24

By measuring corticosterone concentrations, CBG binding capacity and affinity.
Hence can estimate ‘free’ corticosterone that exerts hormonal actions in tissues

Question 25

The does birds adjusting CBG concentrations provide the bird with?

Answer 25

A mechanism for fine-tuning its response to corticosterone (and therefore stressors)

Question 26

In what year was there extended snow cover, so extreme weather, in Alaska in spring?

Answer 26

2013

Question 27

The extended snow cover in Alaska 2013 meant it took birds longer to into their breeding grounds, how much did it delay their arrival by?

Answer 27

4-5 daysc

Question 28

What were the consequences of the delayed arrival of birds to their Alaska breeding grounds in 2013?

Answer 28

. Difficult to find food | . So faced energetic challenges when they arrived on the breeding grounds

Question 29

How did the extreme weather/ extended snow cover in Alaska 2013 effect longspurs and white crowned sparrows differently?

Answer 29

. They had less muscle and reduced fat stores in longspurs . White-crowned sparrows had reduced muscle and increased fat

Question 30

How did the stress response (Corticosterone) in white-crowned sparrows and longspurs change in the 2013 extreme weather in their Alaska breeding grounds?

Answer 30

. The white-crowned sparrows showed no difference in stress response . The stress response was increased in longspurs

Question 31

Why did longspurs stress response (Corticosterone) increase in the extreme weather in their Alaskan breeding grounds in 2013?

Answer 31

May have changed their strategy in response to reduced fat stores and muscle. Prioritising survival over reproduction

Question 32

In the extreme weather in Alaska, 2013, both male and female longspurs had elevated levels of corticosterone which we would not expect from these birds breeding at higher latitudes. What would we expect? What does this indicate?

Answer 32

We would expect that they would switch off their areas response so this indicates that there is a trade off for each individual bird as it prioritises its survival over its reproductive success. (So when the conditions are sort of ok they seem to prioritise their reproductive success but in these extreme conditions the longspur are choosing to prioritise it’s survival)

Question 33

Summarise what neuroendocrine adaptions to short Arctic summers include

Answer 33

. Weakened relationship between testosterone and aggression (so thy are not wasting time with territorial phase and get very quickly into the nesting cycle and to the point at which they are starting to feed young) . Response to environmental stressors are modulated to allow nesting to proceed in adverse environmental conditions (saves time) . (Note thee are separate adaptions, beware of confusing testosterone and corticosterone in exam answers)

Question 34

Lipids are lipophilic, what does this mean?

Answer 34

That you can store lots of carbon in them so you can store long carbon chains so you can store a lot of energy in a very small amount of space (so good for long distance journeys)

Question 35

Lipids aren’t soluble so what does this mean? Compare this to other fuel stores

Answer 35

That they have very little water associated with them compared to alternatives such as glycogen (a carbohydrate) or protein- so to store these you need a lot more water to accompany the energy source so lipids can store a lot of energy in a very small space (so good for long distance journeys)

Question 36

What do the level of premigratory fattening (migratory fat stores) depend on?

Answer 36

. How far they have to travel | . Whether they feed or not while they are travelling

Question 37

Explain premigratory fattening (fat stores) of the Gambel’s white crowned sparrow (how much they store, why this much)

Answer 37

Up to 30% body mass fast store because these will stop to feed because they are not actually travelling over water so they have the opportunity to stop and feed when they want

Question 38

It is birds that cross ecological barriers that show the most extreme changes. Give an example

Answer 38

The garden warbler which has to cross the Sahara desert and the Mediterranean so they can’t stop and feed

Question 39

What is the ‘record holder’ for migratory fat stores as % body mass?

Answer 39

Up to 50% in ruby-throated hummingbird- has to cross the Gulf of Mexico

Question 40

What are the other environmental cues other than long days that act to fine-tune migration timing?

Answer 40

Supplementary, modifying and synchronising information. Local cues in the environment so food availability and temp and whether or not it is showing a stress response (these are all applying to migratory physiology just as they are to reproductive physiology)

Question 41

A body mass tracking system in the brain ensures what?

Answer 41

That the animal is at an appropriate mass for a given stage in its annual cycle

Question 42

What is basal corticosterone correlated with?

Answer 42

Migratory fat deposit so changes in body mass are very closely correlated to the levels of corticosterone

Question 43

What does the correlation between the levels of corticosterone and changes in body mass/ migratory fat deposition show?

Answer 43

That corticosterone doesn’t just come into play when animals are given a stressor it also has fundamental functions

Question 44

Because corticosterone doesn’t just come into play when animals are given a stressor but also has fundamental functions that what do the animals need? Why is this?

Answer 44

Need a minimum level to be able to feed properly and deposit fat

Question 45

Why is having a minimum level of corticosterone important?

Answer 45

Because it has important metabolic functions independent to its role to respond to stressors

Question 46

How did they experiment the effects of a Corticosterone receptor antagonist on migratory feeding? What were the results?

Answer 46

If you inject RU486 at the same time as corticosterone then it completely blocks the action of corticosterone in changing fat store. Use the drug in wintering birds and it didn’t have any effect on how much they were eating. They then looked at spring migratory birds and it decreased their weight so suggests corticosterone promotes appetite in the breeding season

Question 47

What happens if you inject RU486 at the same time as corticosterone?

Answer 47

It completely blocks the action of corticosterone in changing fat store

Question 48

What are the two effects of corticosterone?

Answer 48

. Basal (non-stressed) concentrations regulate food intake and fat deposition . Stress-induced corticosterone secretion is associated with activating the emergency life history stage

Question 49

White collared sparrows in captivity were exposed to natural photoperiod, what effect did this have the body mass? Why did this happen?

Answer 49

That body mass increases in spring around April and some arrive at the breeding grounds around May. This body mass increase is due to body fat storage because they are becoming hungry at that time of year, so part of the brain is regulating appetite so fuel source

Question 50

Give the example of the a natural fasting animal; brooding hen (what makes her do it, how long for etc.)

Answer 50

The hen will sit on her eggs for about three weeks and her behaviour and physiology will change so that she can sit on her eggs for as long as she can do the internal tracking system in the brain switches down her appetite