Breeding Belayev’s Pets by J. Phil Gibson, University of Oklahoma • Objectives: • Understand how artificial selection supports Darwin’s Theory of Evolution by Natural Selection • Understand how artificial selection can change characteristics of a breeding population. • Investigate changes that occur as a result of domestication.
CQ#1 Which of these forms of data did Darwin not use in developing his Theory of Natural Selection? • fossils • domesticated species • Mendelian genetics • structural homology • Darwin used all of these forms of data
CQ#2 Domestication involves selectively breeding for . . . • many separate, genetically-based traits specifically chosen by the breeder. • genetically-based traits that arise at random due to the species’ need for those traits. • some genetically-based traits and unpredictable changes in other traits that were not specifically chosen. • genetically-based and environmentally caused traits.
Darwin’s Data In addition to examples of adaptation, structural homology, the fossil record, and biogeography, Darwin used domesticated species as support for his theory evolution. Why do you think domesticated species would be an important part of his theory?
Darwin’s & Inheritance Because Mendel’s work was not yet known and discovery of DNA was almost a century in the future, domesticated species provided the only information on heritable traits and how breeders can change in a lineage over time, a process Darwin called ARTIFICIAL SELECTION which is similar to NATURAL SELECTION.
Artificial Selection Pigeons, cattle, and other domesticated species provided Darwin with examples of how breeders choose individuals with particular traits and by allowing those individuals to breed, desired parental traits become more common and the population changes over time.
Darwin’s Observations In addition to traits intentionally chosen by breeders, Darwin noted this observation in The Origin of Species, “. . . not a single domestic animal can be named which has not in some country developed drooping ears.”
Darwin’s Observations Not only drooping ears, but other unexpected traits also appear in domesticated species including piebald coloration (most domesticated mammals), wavy hair (sheep, poodles, horses, pigs, goats, mice, guinea pigs), rolled tails (dogs, pigs), shorter tails (dogs, cats, sheep), and changes in reproductive cycles (domesticated mammals excluding sheep). What could this mean?
Dogs, the first domesticated animal species, were domesticated from gray wolves in Southwest Asia over 15,000 years ago. Canis lupus Canis lupus familiaris
Two questions about dogs in particular and domestication in general have interested biologists for many years.1. What changes occur during domestication?2. How quickly could domestication occurr?How would you approach this problem scientifically ? Dogs of King Antef from Egyptian relief (2323 BC. to 2134 BC).
The Farm-Fox Experiment In 1959, Dr. Dimitry K. Belyaev, Director of the Institute of Cytology and Genetics in the U.S.S.R. began investigating the genetics of dog domestication by selectively breeding another canine, silver foxes, from local fur production farms. Vulpes vulpes
CQ#3 Dr. Belyaev hypothesized that variation in tameness is linked to genes. Domestication is a strong selective pressure that will change tameness of a fox population over time. How long do you think it will take for a population to become “tame” or considered domesticated? • Very quickly, just a few generations • Moderate time, a slow start but quickly after the first generations of breeding. • Fairly slow, a gradual change over many generations
The Farm-Fox Experiment Procedure • Fox pups (called kits) were scored for tameness and assigned to classes: • Class 3: flee or aggressive response to experimenter • Class 2: allow petting but no emotional response to experimenter • Class 1: friendly to experimenter (wag tail, whine, etc.) • Bred the most friendly Elite Class 1 (E1) foxes over many generations. What specific changes would you expect to observe over time as the experiment proceeded?
Farm-Fox Experiment Results The number of E1 foxes increased in frequency and showed significant increases in “dog-like” behavior (docile, eager to please, lick hands, compete for attention) in relatively few generations.
Farm-Fox Experiment Results But, there were other changes as well.
CQ#4 The results so far indicate. . . • domestication is a slow process. • selecting on one trait can lead to changes in another, unselected trait. • fox domestication has little to do with dog domestication. • domestication proceeds by changing one trait at a time. • None of the above.
Farm-Fox Experiment Data In addition to appearance, other changes occurred. The time when different maturation events occur in dogs and foxes are show below. Complete the figure for when you think these events should occur in domesticated foxes. DAYS WEEKS 7 8 9 10 11 12 13 14 15 16 17 18 19 4 6 8 10 12 DOGS WILD FOXES DOMESTICATED FOXES eyes fully open response window of to sound socialization
The Farm-Fox Experiment Having seen the changes produced by selective breeding, what should the researchers study next to support the idea that artificial selection for tameness has produced an evolutionary change in the fox population? Think of a follow-up research question, develop an hypothesis, and design an experiment you would conduct to test it.
CQ#5 • Studies have found changes in hormone levels such as corticosteroids rise at 2-4 months in wild foxes, but come much later in domesticated fox. If all of the observed these changes are genetically based, what would you expect if they bred for aggressive instead of docile behavior. • aggression should decrease in those lineages • b. aggression should increase in those lineages • c. no changes should occur in those lineages
CQ#6 As predicted, fox lineages bred for aggression became more so. Comparisons of the docile and aggressive foxes have identified multiple genetic differences between them. This indicates that . . . • domestication involves relatively few genes. • domestication affect genes for traits being selected as well as other traits. • domestication changes only those traits selected. • domestication is basically the same as training an animal to behave.
Epilogue Genetic analysis of the aggressive and domesticated silver fox lineages have identified two regions that are distinct between them. Studies of these regions and the genome of other domesticated species will not only provide deeper insights into the genetic changes caused by domestication but may also provide insights into changes that occurred in human evolution as well.
CQ#7 Suppose researchers were to take a kit from an aggressive mother fox and have it nursed by a docile mother fox What would you predict would happen? • The kit would become docile due to hormones in her milk. • The kit would cause the docile mother to become aggressive. • The kit would be more easily trained than if the aggressive mother raised it. • The kit would mature to become an aggressive adult. • No predictions can be made because breeding is unpredictable.
Deeper Thinking You have rescued a puppy from a local animal shelter. As it grows, you and your friends make different guesses about what breeds its parents were. Using accurate terminology, describe or diagram how this company’s offer could possibly work. • One day you notice a web site that announces it can tell you the breeds of dog produced your lovable mutt simply by sending them a swab of the cells from the inside of your puppy’s mouth.