L8 Boswell - The Arctic and Migration Flashcards
Describe the HPA axis doe the release of glucocorticoids due to stress
Hypothalamus - CRH (corticotrophin releasing hormone)
Pituitary - ACTH - (adreno-coritcotrophic hormone)
Adrenal Cortex - Glucocorticoids (corticosterone - mice and birds etc., cortisol - humans)
What are the acute effects of glucocorticoid release?
- Altered immune system
- Increases gluconeogenesis
- Promotion of escape behaviour during the day
- Promotion of a restful night sleep
- Suppression of reproductive behaviour with effecting the reproductive system
What are the long term effects of glucocorticoid release?
- Inhibition of the reproductive system
- Immune suppression, impaired disease resistance
- Loss of protein from skeletal muscle
- Accelerated neuronal degradation
- Suppression of growth in young animals
Why might inhibiting the adrenocortical response to stressors be beneficial on entering the Arctic?
Switching off the stress response might be energetically costly but could enhance reproductive fitness.
E.g. reduced stress to adverse weather would let the bird have the ability to stay onsite not escape, and then be ready in the breeding location when weather conditions are correct.
What are the neuroendocrine adaptions to short Arctic summers?
Weakened relationship between testosterone and aggression - accelerates breeding cycle to compensate for short arctic summer
Response to environmental stressors is generally moderated to allow nesting to proceed in adverse environmental conditions
What is the most efficient fuel source and why?
Fat - it is the most energy dense, containing only 5% water unlike carbohydrates and proteins which are both 70-80% water
What is pre-migratory fattening and how does it happen
It is stimulated in spring by long days, and achieved by increasing appetite.
Other supplementary cues from the environment act to fine tune the migration timing.
How fat a bird gets depends on how far it has to fly generally
gonads remain reduced
What does it mean that body mass is homostatically maintained at a seasonally appropriate level?
Non-seasonal animals such as rodents and humans, maintain a constant body weight, if they lose weight their body would try to get back to their original
Seasonal animals such as birds have a sliding set point’. This means that depending on the season is what tells them what weight they need to be
E.g. a mother hen gets fat before egg laying because she knows she wont leave the nest until they are finished. Even if in captivity food is placed in front of her she wont eat is as it is physiologically set she will lose the weight.
What are the 2 effects of corticosterone?
Basal (non-stressed) - concentration regulates food intake and fat deposition
Stress Induced - corticosterone secretion associated with activation the emergency life history stage
