Evolution of Dog Celeste, Dan, Jason, Tyler
Early Canid Domestication: Domestication Natural Selection & Artificial Selection (Human intervention) Domestication: Morphological, Physiological and Behavioral changes Mammals undergo similar changes in appearance and behavior: size coat color reproductive cycle Russian geneticist, Dmitry K. Belyaev believed domesticated animals underwent genetic changes in the course of selection Key Factor: Tamability
Breed Breed group Akita Inu Oriental Boxer No. dogs No. sires (% of males) No. dams (% No. founders of females) 21,155 1,329 (13) 2,115 (20) 223 Mastiff 195,358 8,518 (9) 24,601 (25) 4,032 English bulldog Mastiff 46,420 2,175 (11) 7,660 (36) 882 Chow chow Oriental 18,386 928 (11) 2,597 (27) 1,012 Rough collie Shepherd 83,864 4,190 (11) 13,232 (30) 5,285 Golden retriever Hunting 317,527 7,752 (5) 28,963 (18) 6,932 Greyhound Shepherd 1,060 103 (21) 159 (28) 81 German shepherd dog Shepherd 474,078 21,629 (9) 48,108 (20) 15,843 Labrador retriever Hunting 703,566 26,830 (8) 70,541 (20) 15,064 English springer spaniel Hunting 276,179 17,471 (13) 34,252 (24) 9,718 What can be done?
The Farm-Fox Experiment 1959 The Silver Foxe bred for tamability in a 40-year experiment exhibit remarkable transformations that suggest an interplay between behavioral genetics and development Hypothesis: Changes observed in domesticated animals result from genetic changes that occured in the course of selection and since tamability is rooted in biology, selecting for tameness and against aggression means selection for physiological changes in the systems that govern the body s hormones and neurochemicals.
Belyaev noted, domestication leads to morphological and physiological changes: Size: leading to appearance of dwarf and giant breeds Color: originally believed to function as camouflage Tail: dogs and pigs exhibited tails that curled up in a circle or semicircle Decrease in number of tail verberate in cats, dogs and sheep Ears became floppy: Darwin noted in chapter 1 of On the Origin of Species, not a single domestic animal can be named which has not in some country developed drooping ears - a feature not seen in any wild animal except the elephant Loss of seasonal rhythm of reproduction
For Belyaev s hypothesis to make evolutionary sense two things must be true... 1. 2. Variation in tamability must be determined at least partially by genes Domestication must place that animal under strong selective pressure So how did he do it? https://www.youtube.com/watch?v=0jfgnqscrny Findings: After 12 generations the basal levels of corticosteroids in the blood plasma, domesticated foxes dropped to slihgly more than half of control group Adrenal cortex responds less sharply to emotional stress Changes in serotonin system, thought to mediate the animal s aggressive behavior
Alternative Explanation 1. 2. Inbreeding True if...population carried a recessive mutant Heterozygote carriers Two reasons why inbreeding doesn t work Mating system: outbred foxes from commercial fox farms New traits are not recessive: they are controlled by dominant or incompletely dominant genes Domestication a by-product of quantitative traits But polygenes are very intricate so change can lead to a cascading effect Belyaev observed domesticated animals across the world share similar traits
Take home points Dogs evolved from grey wolves Evolution can be seen in a compressed sample - Domestication Behavior can be heritable with natural selection being the driving force Behavior is controlled by one gene that leads to a cascading effect Genetic bottlenecks and inbreeding have lead to a loss of genetic diversity in pedigree dogs Restrictive breeding practices - reduce effective population size and increase overall genetic drift among domestic dogs. Results in loss of genetic diversity within breeds.
Discussion Questions 1. Do you agree/disagree that tamability can be explained by QTL? 2. Why would genetic bottlenecks and inbreeding lead to an increase in linkage disequilibrium? 3. How could selection shadow be used as another hypothesis to the high percentages of dogs with cancers?
Answers 1. 2. 3. According to Belyaev, the answer is not that domestication selects for quantitative trait but it selects for a behavior. Although Belyaev believed that foxes were either tame or aggressive he pointed out the cascading morphological and physiological changes associated with such selection By selecting for specific traits over and over, homozygosity increased, driving the number of available alleles in the population in one direction increasing linkage disequilibrium. Dogs functioning as household pets and no longer just working animals, with an increase in the availability of veterinary care, they are living longer lifespans and genes which normally were deleterious later in life which selection never acted on are expressing.
Works Cited Adams, J. (2008) Genetics of Dog Breeding. Nature Education 1(1):144 Trut, Lyudila. Early Canid Domestication: The Farm-Fox Experiment. American Scientist Journal. (1999): 160-169. Vilà, Carles, Jesus E. Maldonado, and Robert K. Wayne. "Phylogenetic relationships, evolution, and genetic diversity of the domestic dog." Journal of Heredity 90.1 (1999): 71-77. Wayne, Robert K. "Molecular evolution of the dog family." Trends in Genetics9.6 (1993): 218-224. Schoenebeck, Jeffrey J., and Elaine A. Ostrander. "Insights Into Morphology And Disease From The Dog Genome Project." Annual Review Of Cell & Developmental Biology 30.1 (2014): 535-560. Dobson, Jane, Breed-Predispositions to Cancer in Pedigree Dogs, ISRN Veterinary Science, vol. 2013, Article ID 941275, 23 pages, 2013. Calboli, Federico, Sampson, J, Fretwell, N, Balding, D. Population Structure and Inbreeding from Pedigree Analysis of Purebred Dogs. Genetics May 2008 vol. 179 no. 1 593-601