Stress Flashcards
Animals have evolved mechanisms to cope with stress
These are behavioural and physiological.
These can be adaptive and promote survival
What is stress?
Biological response elicited by a perceived stressor Disrupts homeostasis (balance) Caused by changed environment in animals, e.g. Disease, parasites, finding food, man made stressors
Acute stress response
Fight or flight, from the HPA axis. Adrenal gland ultimately produces glucocorticoids, which initiate the response (HR BP digestion immune function)
Long term costs of activating the system:
- Damage to tissue and processes
- Detracts from the ability to digest food, reproduce and fight disease
Signal detection theory
Can use this to weigh up the benefits and costs of producing the HPA response.
Criterion of when to respond- if this is set too high they could be predated.
Cost of response < probability that noise came from predator x cost of it being a predator
Has natural selection acted on stress responses?
Can investigate through predation pressure: will probably change the level of stress response in prey
Example 1 of predation pressure acting on the stress response of prey
- predator naive island species, marine iguanas
Without predation for 5 million years, adapted. 150 YA dogs and cats arrived, high increase in mortality
Flight initiation distances are greater on Islands with acute predation. Iguanas are not wear so predators can get very close and attack.
Predation pressure increase HPA response, is much steeper in Islands with cats and dogs.
Appears that selection has acted on iguanas in Islands with acute predation risk. May not be enough to save the iguanas
Example 2 of predation pressure acting on stress response
- Belding squirrel alarm calls
Squirrels produce different alarm calls for different predators (trill - terrestrial , whistle - aerial)
Naive pups in box, played trill whistle squeal silence. Collected blood samples.
Only trills elicited a strong corticosteroid response. Perhaps it’s only adaptive to elicit HPA to terrestrial - have enough time to hide
How are animals coping with anthropogenic environmental change?
Example 1, blackbirds
City living birds nest close to human activity, while country living have less contact.
Measured stress responses of birds in lab after handling, found stress response was much higher for country living birds.
- adaptive response to living in city
Anthropogenic environmental change
Example 2, hoatzin chicks
Lower survival rates in areas with ecotourism, and is associated with higher stress response.
Chick dives into water when stressed, very risky
Tourist exposed juveniles have elevated corticosteroid levels than undisturbed birds
Conclusion on anthropogenic change
Stress responses vary across species
Hoatzin = sensitised, blackbird = habituated
HPA response helps animals deal with stress, and should increase fitness.
Stress and animal welfare
A stressed animal has poor welfare
CORT levels are often used as a welfare measure, as it’s seen as the ‘stress’ hormone
Differences in stress levels
Acute - short peak in levels in response to a temporary stressor
Chronic - long term elevated levels in response to long term stressor
Chronically elevated levels can be detrimental because:
They can suppress immune function
Decrease growth
Reduce cognitive function
Influence development
Why is CORT a good measure?
It’s direct
Measured directly, results from the stress response
Easily quantified
Found across species
