Animal domestication LECTURE 4

Domesticated animals amounting to how much biomass of the terrestrial vertebrates

• 2/3

What are they used for

• wool

• leather

• silk

• food

• movement→ transportation

Issues with close poximity to animals

• zoonotic disease

What is an important part of animla domestication

• Taming

• → dont want to get trampled!

Types of taming

• Learning-based taming→ many wild animals can under go

• Evolutionary reduction of aggression and fearfulness

Domestication differs from the standard mutualism

• control over the domesticated

• but can animals self-domesticate?

Dom plants vs Dom animals

• many more plants domesticated

Domesticated animals main ones

Big five (herbivores)

• sheep

• goats

• pigs

• cattle

• horses

Predators

• dogs

• cats

10 livestock

• camel

• yaks

• chickens

Wild relatives still alive?

• Yes for some

  → e.g red jungle fowl

But

• NO

  → wild horses endangered

When did animals gets domesticated

1. Dogs

2. Cats

3. cattle and pigs

4. horses and chickens

Where did domestication happen?

• mainly Eurasia

  → no early domestications in Africa (despite being ancestral home)

How is the origin of domesticated species mapped?

1. Zooarchaeological evidence

2. Genetic Evidence

1. Types of evidence?

• Behaviour of the species cannot be presered

  • (although some indirect clues e.g dental damage (due to bridle)

• Decreased body size

• reduced sexual dimorphisms→ due to herd managements

  • not evo change (so much be evidence of domestication NOT of evolution/change in species)

2. Difficulties of genetic evidence

1. Hybridisation with wild relatives + introgression→

   • cause overestimate the age of the domestic species

   • or number of independent domestication events

2. What is useful in genetic evidence?

• Whole genomes

• Ancient DNA

  → but still uncertainty

Found the domsetication ( two indepednet ones) in:

• cattle

• horses

• dogs

• pigs

Domestication of pigs→ well documented

Has caused domestic pigs to have higher genetic diversty than sympatric wild boar

This asymmetry of animal domstication

• bit of a mystery!

Where did vast majority of mammals originate from

Eurasia

WHY?

• answer below

Conditions for domestication

1. Diet

   • carnivorus livestock need x 10 more than herbivores

   • specialist diets also hard to maintain

2. Growth Rate

   • must grow rapidly

3. Failture ot bred in captivity

   • captive breeding is needed for later stages of domestication

4. Too aggressive

   • can be too damgerous

5. Tendency to panic

   • don’t want it to do itsefl harm

6. Inappropriate social structure

   • if dont live in heards, hard to livestock

   • also need dominance hierachy that humans can hijack

Ways in which animal domestication can happen

1. Early→ accidental Commensal pathway

   • attracted to humans as tamer, less fearful

   • selected themselves into a partnership with humans

     → Commensal pathway

2. Or Early→ Manage groups of prey species Prey Pathway

   • to the point they began to control breeding

     → Prey Pathway

   • (most through this path)

3. Directed pathway

   • bred to promote traits

   • once knew what domestication could do

Why most domestic mammal progenitors from South Eurasia

Biogeopgraphy and influence of early farming

Traits they had:

• non-tropical

• moderate migratory

• dependent on available drinking water

• grazing adaptation

Environment needed for this:

• cool

• semi-arid

• seasonaility→ migration

  • → follow the leader social interactions (humans can hijack)

WHERE is this environment found??

→ S. Eurasia→ Fertile Crescent

• also had the first dom plants

• so good for animals to eat

Once Neolithic farmers then expanded out of Fertile Crescent

• took their domesticated animals with them

Alternative explanation for Eurasian dominance

• Only turn to prey management when prey numbers decrease

• In Africa→ long co-habitation of humans and prey

  • → prey do not decrease

BUT

• In Americas→ humans were too successful at driving large mammals species extinct

INSTEAD→ Eurasia

• Goldilocks zone of

  • Humans being able to prey on the animals

  • Balanced with

  • Not so vulnerable they dispappeared before domestication

Main traits wanted for domestication

Main→ tamness

The rest of the traits→ depends on the animals

• frequent bouts of reproduction

  • breed more

• smaller brain and teeth

• different and variable colouration

• floppy ears

• shorter snout

• curly tail

Is this a domestication syndrome?

Yes

BUT

• Not all the traits are found all together

How to find out what caused the appearance of these traits?

Genomics

• highlighting regions of genome associated with domestic traits

• indicating the pattern of selection that might have brought them about

E.g study comparing genomes of goats and sheep→ found a homologous region

→ region that differentiated domestic from wild individuals

e.g KITLG gene→ coat colour in mammals

• Goats→ region have higher diversity than wild

  • shows relaxed selection in domesticates

• Sheep→ low diversity in region

  • show positive selection

  • desire white wool

E.g study between pigs and wild boar gene

e.g MC1R gene→ affect coat colour

• Wild boar→ many mutations synonymous

  • indicate purifying selection

• Pigs→ 9 non-synonymous mutations

  • suggests new coat colour variants appeared thanks to relaxed selection in a relatively predator -press environemnt

  • THEN: strong positive selection that quickly fixed these MC1R variatns in different breeds

The genetic basis of phenotypic diverstiy of dogs

• 50 regions of the genome

• some traits = significant genetic variation at only 3 loci or less

→ likely the result of intense artificial selection for extreme phenotypes in different dog breed over the last 200 years

Overall this tells us that traits for domestication syndrome

• various traits were directly selected for

or

• result of the relaxed selection in a human-controlled environment

BUT: there is a different story→ Silver fox experiment

Silver fox experiment

1. captive silver foxes selected for tameness using criteria

2. within 6 generations, foxes inthe tame line were eager to eastablish human contact

3. whined when humans deparated

4. allowed themselves to be picked up, wagged their tails when humans arrives and licked their hands

5. Reproductive cycle also began earyl

6. From 10th generation→ other domestication traits began to appear:

   • floppy ears, piebald coats, shortened muzzle and upturned tail

But why would the selection of tameness alone cause the appearance of so many other aspects of domestication syndrome?

1. Genetic linkage?

   • NO: coz domestication genes are scattered throughout the genome

2. Selecting tameness→ accidently selecting for neoteny

   • prolonged expresseion of juvenile triats

   • into sexual matuirty:

     • e.g: behavourial or morphological factors

     • maturation of hypothalamic-pituitart adrenal axis→ give rise to a longer socialisation window

       • so animals can learn to regard humans as non-threatening

       • e.g in wolves this closes at 1.5 months but dogs 4-10 months

3. Most domestication syndrome traits would be influenced by neural crest cells

What is the neural crest?

• embryoninc migratory cell population

  • unique to vertebrates

• gives rise to melanocytes (pigment cells)

• bones and cartilage of the head

• pigmentation

• skull shape

• eat floppiness

ALSO
- adrenal glands→ hormones stress response

What is the hypothesis with the neural crest?

Domestication may be a mild neurocristopathy→ reduction in neural crest cell proliferation and/or function

Genetic support for this

• many genes associated with domestication are involved in neural crest specification and function

Critics of this?→ Dogs

• only dogs exhibit all traits of the domestication syndrome

BUT

• even in dogs the traits are inconsistently expressed in different breeds

  → no obvious correlation with temperament

Domesticated traits in humans?

• smaller teeth

• shorter snout

• variable skin and hair pigmentation

• tolerence for other members of species

→ slected for tameness, by outselves??

But how can self-domestication happen?

Already one way to describe initial stages of commensal domestication pathway that dogs followed:

1. enhanced coopertative communicaiton seen in domestic animals

2. resonance with the origin of the human language or culture

Evidence for this?

→ several genes show evidence of positive selection in humans→ similarly been selected for in domesticated animals!

But is this too much a simplistic view?

• do we really control our aggression better?

• Are we in fact wild animals, but with sufficient emotional flexibility and control to live in domestic environment?

  • has this come with a cost??

Example essay questions

1. Why were almost all major domestic animal species domesticated in southern Eurasia?

2. What might have caused the appearance of morphological traits of the domestication syndrome in domestic animals?