Lecture 6 : PATHWAYS TO ANIMAL DOMESTICATION Flashcards
NEW SELECTIVE
PRESSURES
Behavioural attributes
most important
Placid, tractable, less
‘wary’, reduction in aggression
Not necessarily detected morphologically - the morphological might not have been intentional
DOMESTICATION SYNDROME IN ANIMALS
Package of traits that develop semi-concurrently
‘Paedomorphy’ (Juvenile traits) associated reduced aggression
Greater gregariousness and playfulness
Earlier sexuality maturity, more frequent receptivity
Smaller brain size, changes in neurological organisation
Shortening of the snout, tooth-size reduction, changes in tooth number
Smaller bodies, reduction in sexual dimorphism
Changes in coat colour, texture
FOX FARM EXPERIMENT
Experiment in silver fox breeding set up by Soviet scientist Dmitri Belyaev in 1959
Selection for behaviour would have broad effects on physiological development (which ones were more friendlier,agressive ones?)
After 40 generations, foxes displayed a suite of ‘domestication traits’
Pleiotropy: one gene influences two or more seemingly unrelated phenotypic traits - being friendly - aperance
REDUCED FEAR & AGGRESSION
Delayed development of ‘fear response’
Decreased levels of corticosteroids (stress hormones)
Higher levels of serotonin
Longer socialisation window
Domestication syndrome includes environmental factors (individual lifetime) and genetic changes (over several generations)
CHANGES IN PIGMENTATION
Changes in coat colour, loss of pigmentation - specially in the cranio/forehad
Piebald and star mutation
Dopamine (neurotransmitter), melanin (pigments), and adrenaline (hormones triggering ‘fight-or-flight’) part of the same biochemical pathway
PEDOMORPHOSIS
Alterations in the rate of
developmental
Neoteny
passing through fewer developmental
stages before reaching adulthood (resembles juvenile stage of its ancestor)
Earlier onset of sexual maturity
Retention of juvenile cranial morphology
Retention of juvenile behaviours (barking, playfulness)
CHANGES CRANIAL MORPHOLOGY
Often a reduction in brain size
Reduction in jaw size and tooth size
CHANGES IN HORN SHAPE AND SIZE
- the horn got smaller
- Relaxation of natural mating selection pressures (it was used for same sex fighting)
- or impact of new selective pressure?
domestic animals also tend to have more:
FLOPPY EARS AND ROLLED TAILS
CHANGES IN
REPRODUCTION
- Earlier onset of sexual maturity
- Increased receptivity - there is a bigger chance for animals to reproduce which in the wild their is less available mates-
WHAT SHOULD
WILD COWS
LOOK LIKE?
AUROCHSEN
Large
Aggressive, wary
Solid coloration
Seasonal reproduction
EXPLANATORY
MODEL
- Development of ‘domestication’
traits linked to neural crest cells
(NCCs)
NCCs: stem cells that first appear
during early embryogenesis and give
rise to different tissue types
Selection for ‘tameness’ leads to reduction of NCC derived tissues
reason why they have floppy ears and rolling tails
DOMESTICATION TRAITS RECAP
CONDITIONS OF DOMESTICATION
- They should be hardy;
- They should have an in-born liking for man;
- They should be comfort-loving ;
- They should be found useful to the savages;
- They should breed freely;
- They should be gregarious.
Intersection of nature and culture to produce the right circumstances for domestication
BIOLOGICAL PREREQUISITES
- Friendly: Short flight distance, generally placid
- Feeding: Generalized feeding behaviour
-
Fecund: Able to breed in captive, crowded, and unnatural
conditions. - Family values: Social animal with hierarchical dominance behavioural pattern
-
Flexibility: Adapt to new environments, non-shelter seeking,
readily habituated.
CULTURAL
PREREQUISITES
Need or desire that can fulfilled by protecting or breeding particular animal
Technology or lifestyle pattern to accommodate domestic species
-Sufficient subsistence base-
-Appropriate mobility patterns(active cultures/sendentarias)
In all domestic animals, the single most
important behavioral response to
domestication is reduced wariness and low reactivity to external stimuli
Maternal hormone states
produce epigenetic mutations in
NCC?
PATHWAYS TO ANIMAL DOMESTICATION: COMMENSAL,PREY, DIRECTED
COMMENSAL PATHWAY
Animals drawn to human settlements for to feed on refuse or other commensal prey
Selection for reduced flight distance
produces morphological change
Reduction in mandible and tooth size
Changes in cranial dimensions
Animals useful to humans continue along trajectory of domestication
Examples: Dogs, Pigs, Chickens, Guinea Pigs, Golden Hamster, Muscovy duck
NON-DOMESTICATED COMMENSAL ANIMALS?
rodents,pigeons,foxes,baratas,racoons
PREY PATHWAY
Initiated as humans developed game management strategies to secure dependable resource
Focus on hunting strategies to promote herd growth
Culling of young males, post-reproductive females
Observable differences in demographic profiles
Morphological changes may take place when animals are moved out of natural habitats
Examples: Goat, Sheep, Taurine and Zebu Cattle, Water
Buffalo, Mithan, Yak, Llama, Alpaca, pig?,
NON-DOMESTICATED PREY (TOO FLIGHTY AND BITEY
- zebra
- kudu
- gazelle
