rodents and behavioural light aversion

Question 1

What are Tinbergen’s 4 questions on behavioural research?

and how does it apply to rodents?

Answer 1

1. Function - What is it’s survival value?

Why do rodents need to detect differences in light levels?

2. Evolution - How did this behaviour evolve?

What caused the evolution of irradiance detection?

3. Ontogeny - When does this behaviour develop?

4. Causation - What are the mechanisms that cause this behaviour?

How do rodents detect changes in light?

Question 2

Why do rodents need to detect differences in light levels?

Answer 2

Predation pressure has generated anti-predator defences

• physiological
• morphological
• behavioural

prey species are most at risk of predation during foraging - creates a trade off eating and vigilance

-> detecting differences in light levels allow rodents to make better decisions on when and where to forage

Question 3

Why do rodents need to detect differences in light levels?

Answer 3

Perceiving risk and predicting when it is safe uses direct and indirect predation cues.

-direct cues

visual

tactile

auditory

olfactory

-indirect cues

habitat structure

illumination

Question 4

Why do rodents need to detect differences in light levels?

Answer 4

• Illumination
  (a) helps predators to see better
  (b) makes prey movement much more noticeable

Question 5

What caused the evolution of irradiance detection?

Answer 5

Nocturnal bottleneck hypothesis

• early mammals competed with reptiles (e.g. dinosaurs)
• reptiles are ectothermic -> active during the day
• predation pressure/competition from reptiles drove endothermy in mammals
• endothermy gave the ability to occupy other niches, including splitting temporal niches into day vs night activity

_______

-> successful nocturnal lifestyle requires:

a) detection of the onset of dusk

b) detection of changes in ambient light during darkness

Question 6

How do rodents detect changes in light?

Answer 6

1. Biological clock

-synchronises physiological and behavioural events around the 24 hr day

2. Changes in lighting at dawn/dusk

-most reliable indicator of what stage of the day it is

3. Light information

-interpreted by the master circadian pacemaker (suprachiasmatic nuclei)

Question 7

How do rodents detect changes in light?

Answer 7

whit a subset of cells on their retina that are intrinsically sensitive to the light

Photoreceptors

-Rods (image forming vision)

sensitive to light: therefore can operate in dim lighting

support right vision

-Cones (image forming vision)

less sensitive to light; require well lit environment to operate

allow colour vision

four types of cones (humans =3; birds =4; rodents =2)

-third/new receptor (non-image forming vision)

keeping circadian rhythm

pupillary light reflex

melanopsin (found in retinal ganglion cells) = photopigment in the new receptor that absorbs light (not present in rods/cones)

Question 8

why is research to study rodents and behavioural light aversion important?

Answer 8

“…research aims to improve
conservation outcomes in New Zealand by
testing new methods of preventing
reinvasion by rodents at sanctuaries…”

Question 9

How is rodents and behavioural light aversion research applied in the field in NZ?

Answer 9