Thursday 27th September - Domestication Flashcards
What is Domestication?
Defining domestication is difficult, components can include:
- Human-animal relationship.
- Human control over life cycle, esp. breeding.
- Symbiotic (mutualistic) relationship, benefiting both parties.
– Quality of life can be variable.
– Reproductive success often enhanced.
• Phenotypic changes (with genetic basis) from wild stock.
What is Domestication?
Domestication = “a sustained multigenerational, mutualistic relationship in which one organism assumes a significant degree of influence over the reproduction and care of another organism in order to secure a more predictable supply of a resource of interest, and through which the partner organism gains advantage over individuals that remain outside this relationship, thereby benefitting and often increasing the fitness of both the domesticator and the target domesticate.” (Zeder, 2015, p. 3191.)
Domestication = “the process by which specific changes in the behaviour, physiology, and life history of animals allow successful coexistence and reproduction in the proximity of humans.”
(Moller, 2012, p. 107.)
What is Domestication?
Other factors involved in domestication. Management.
- Control of animals’ environment.
- Manipulation of conditions.
Aspects of management are required for domestication, but do not predict it always occurring.
What is Domestication?
How to tell the difference between wild and domesticated?
- Middle-ground between wild and domesticated animals.
- How to delineate?
Feral = ?
Tame = ?
Feral = domesticated animals living away from human influence for multiple generations.
• Retain morphological aspects of domestication.
– E.g., brain size (often).
• Sometimes behavioural too.
– E.g., feral cats and their prey.
Tame = animals who are socialised with humans.
- Tractable, approachable.
- Not the same as domestication.
– Learned behaviour
(although genetics may influence how readily this occurs).
– Individual animal’s life history; not selection over generations.
Which Species are Domesticated?
Many species, for different purposes.
• Animals.
– Livestock.
– Work.
– Companion animals.
• Plants.
– Crops.
Certain traits make some species better candidates.
Effects of Domestication
Changes as a result of domestication.
• Selection pressures on wild animals relaxed (new environment).
– New selection pressures.
- Artificial selection.
- Probably multiple pressures involved.
Effects of Domestication There are phenotypic traits associated with domestication:
• Behavioural.
– Lowered reactivity to humans, incl. aggression.
– Note: motivation remains for many behaviours.
- E.g., nest-building in pigs.
- Physiological.
– Reduced stress response.
– Oestrous cycle.
• Early start, larger litters, more frequent cycles.
– Change in colour/patterns.
• Morphological.
– Reduced brain size (see upcoming slides).
– Decrease in body size.
• Not always reliable indicator.
Effects of Domestication Brain changes as a result of domestication.
• Selection for behaviour traits of reduced reactivity.
– Resulted in smaller brains.
Examples:
- Pigs, >30% reduction.
- Dogs, 30%.
- Herbivores, 14-24%.
Effects of Domestication
Effects of Domestication
Not all parts of the brain are affected uniformly.
• Some may increase: e.g., racing/homing pigeons, increase in memory and learning areas.
Mammals, limbic system structures are most affected.
• Structures associated with aggression, wariness, stress responses.
– Hippocampus, amygdala, hypothalamus.
• ‘Fight or flight’.
One of the key traits of domestic animals is a reduction in these behaviours. • Adaptive in their new environment.
Effects of Domestication
Some evidence that changes in brain size may be fixed
(at least for some species)
Feral dogs, sheep, goats, ferrets have similar brain mass to domesticates.
– Smaller than wild counterparts’.
– Despite generations apart from humans.
Example: Maselli et al. (2012) examined changes in brains in
wild vs. FLP vs. domestic pigs.
• Found a complete ‘recovery’ was not made.
– Brain mass was largely recovered in FLP.
– But molecular changes were not the same between wild and FLP
– so recovery of olfactory function didn’t occur.
• Despite presumed selection pressures.
Effects of Domestication
Pleiotropy = traits may arise as a result of selection for other traits.
• Thought that there is a genetic link between a number of traits commonly observed in domestic animals – associated with selection for tameness/less wariness.
Linked attributes include:
• Developmental timings.
– Neotony (morphology and behaviour).
– Sexual maturity at younger age.
– Juvenile behaviours retained in adulthood.
• ‘Domestication syndrome’ in mammals
– traits seem tied to selection for reduced wariness and aggression.
– Piebald, floppy ears, smaller brains, development trajectory changes.
• E.g., fox domestication experiments.
Effects of Domestication
Example: Belyaev’s fox domestication experiments.
• Commercially-bred foxes.
• Selected for ‘tameness’.
– Lack of aggression, fear.
– Display of tolerance, friendliness.
• Over generations, behaviour changes.
• Other effects too.
– Colouration, etc.
– Hormones in ‘tame’ foxes.
- Increased serotonin.
- Decreased corticosteroids.
- Changes in adrenal gland morphology.
How Did Domestication Occur?
Three pathways (Zeder, 2012):
• Commensal.
- Prey.
- Directed.
There can be more than one domestication event and/or pathway for a species.
How Did Domestication Occur?
Three pathways for most animal domesticates (Zeder, 2012):
• Prey pathway.
– Humans wanting more/predictable yield of prey/harvest.
– Most livestock (food).
– Humans initiated this relationship
– hunting. Introduced some management practices to maintain source.
• E.g., culling young males, older females.
