Artificial Selection Flashcards
Define artificial selection
Selection by humans of a deliberately chosen trait or trait combination in a (usually captive) population. This differs from natural selection in that the criterion for survival and reproduction is the trait chosen, rather than fitness as determined by the entire genotype.
Would you expect artificial selection to work with, against or be ineffective with respect to natural selection?
The answer will depend on the example being considered (as well as the environment in which it exists). Artificial selection may oppose, amplify or be neutral in relation to natural selection.
Where does evidence come from for the domestication of the earliest animal species?
The dog is the animal with evidence for its domestication being the first and this has been found in Asia and Europe.
What was the first product that sheep were most likely to have been domesticated for?
Meat or mutton.
What other domesticated species is associated with the domestication of wheat?
Cats, and this is possibly related to their protection of stored grain from rodents, which would have been of great benefit to early humans.
What was domesticated from teosinte?
Maize or corn.
Name a domesticated species that cannot reproduce without human intervention.
Domesticated silkworms are dependent on humans for their survival as they have reduced mouthparts and require feeding and the adults cannot fly to meet mates. You may also have considered vanilla too, as it requires pollination.
Define ‘breed’ and ‘pedigree’
Breeds are a stock of animals or plants within a species having distinctive or homogeneous appearance and/or behaviour and typically having been produced by selective breeding over time. Pedigree refers to the recorded lineage of an animal with details of its dam and sire, grand dam and grand sire and so on, back through the generations of selected breeding.
Why might it be important to identify and preserve wild stocks of otherwise domesticated species?
It is important to identify wild populations accurately in order to protect their genetic diversity. These wild ‘cousins’ may then be used to further improve domesticated species; or, of increasing importance, to protect them from disease(s) by introducing new traits into the already domesticated stock from wild sources.
Livestock and pets that are cared for by humans are provided with food and shelter and protected from most predators. How would these living conditions alter the action of natural selection in domesticated populations?
Natural selection would be weakened for these particular characters that do not affect the fitness under domestication; that is, finding, eating and digesting food, the ability to recognise and escape predators, and tolerance of severe weather conditions. Put another way, animals that would normally not survive in the wild (because of their inability to find food, escape predators, etc.) would survive under these protected conditions.
Name a wild species in which relaxation of selection for escaping from predators has happened naturally. How did the animals’ behaviour differ from that of related populations that are exposed to predators?
Svalbard reindeer have had no natural predators for many thousands of years. Like domesticated cattle, these reindeer have less inclination to run away when approached. However, unlike many domesticated animals, Svalbard reindeer retain the capacity to forage and breed in a difficult climate. This example emphasises the similarities between evolution in artificial and natural environments, driven by artificial or natural selection, respectively.
On what kind of characters would natural selection continue to act in populations of domesticated animals?
Characters that affect fecundity (breeding success), such as age at sexual maturity, litter sizes and parental behaviour.
Would domesticated animals generally produce more or fewer offspring than their wild relations?
They would produce more offspring because protection by humans would prevent natural selection against traits such as heavily pregnant mothers becoming unable to escape from predators or find enough food. One notable difference between domesticated dogs and wolves is that most dogs come into oestrus and breed twice a year. Only the most primitive (i.e. earliest) breeds, including the Australian dingo and the Basenji (an African breed), resemble their wild ancestors in breeding only once a year.
Which special form of natural selection relating to reproduction could be eliminated entirely under domestication?
Sexual selection. Humans determine the resulting offspring’s genetic make-up by choosing which adults have the opportunity to breed. Sexually receptive females may be confined and therefore unable to choose amongst males. Furthermore, in both farmed animals and captive or managed wild populations, artificial insemination (AI) with fresh or frozen sperm may be used instead of mating.
What are the likely consequences of the isolation of breeding stock over time?
The same individuals breed with each other over and over again. As a consequence, the genetic diversity decreases because of inbreeding. Modern breeds are often inbred because they mate with genetically close relatives.
How can zoos avoid causing genetic bottlenecks in captive populations of wild animals?
By managing and only allowing, as far as possible, reproductive events to take place between individuals that will maintain genetic diversity. This may involve moving animals that are not related between zoological collections for breeding purposes, although the use of frozen sperm is becoming more widespread, which for some species avoids the need for such movement. Official records are maintained through the species studbooks, an example of which was shown in Figure 1.3. Thus lessons learnt from studies of domestication also guide conservation efforts to maintain biodiversity throughout the world.
Suggest a few reasons why domesticated animals, and even wild animals that have been tamed when young, might not be the best candidates for reintroduction to the wild.
Re-introduced animals need to be able to find food, defend themselves from predators, find mates, successfully rear their young, and so on. If they had been domesticated or tamed when young, they may struggle with any or all of these activities and fail to survive.
Define hybrid
The offspring of parents from different genetic lines. These may be from within a species, from different species (interspecific hybrid) or even different genera (intergeneric hybrid).
How are the size and shape of antlers of Svalbard reindeer different from those of the mainland subspecies?
The antlers of Svalbard reindeer are much smaller and simpler than those of the mainland subspecies.
Would dwarfism be more readily favoured by artificial selection in domesticated livestock than by natural selection in wild animals?
Yes. Provided the animals could breed successfully, issues such as impaired mobility associated with dwarfism would not reduce fecundity.
Would a dominant gene for dwarfism (or any other feature) be more easily selected than a recessive gene in domestic livestock?
Yes. Artificial selection would be much more efficient for retaining dominant genes because all animals that have the gene display the dwarf phenotype, therefore could be actively selected for with intensive breeding efforts.
Define piebald and pied.
Description of black and white patterning for domesticated animals. Body surface spot patterning of skin, hair, feathers or scales with often irregular or unsymmetrical patches of unpigmented white areas and pigmented black areas, in wild animals this is referred to as ‘pied’
