Artificially Selecting Dogs Answer Key

How did your friendly Fido become so unlike from his closest living relative, the wolf? Meet what scientists believe virtually humans' bogus selection pressures on the dog genome.

Any canis familiaris lover knows that Labrador retrievers are friendly, Dalmatians are hyper, and Australian shepherds are smart (Scott & Fuller, 1974). Some dog lovers likewise know that Labradors are susceptible to hip dysplasia, while deafness and kidney stones run in Dalmatians. But why is this the instance?

Convenance dogs for particular characteristics, or phenotypes, has been going on for centuries. Dogs are companions and workers, in service to humans, and they have thus been bred to accentuate desired traits. For example, Dalmatians have long been coach dogs, in part because of their striking looks and their comfort around horses. Bred for endurance, they can run alongside horse-fatigued carriages all day. When kept equally a housebound family pet, however, a Dalmatian'south excess of energy can make the dog seem wired and tin lead to less desirable behaviors, such equally gnawing on furniture.

Dogs' closest living relatives are wolves. Analysis of the ii species' genomes has revealed differences that some scientists believe are a upshot of dogs being subject to artificial selection imposed by humans. Information technology appears that with domestication, beginning as long as fourteen,000 years ago, came a relaxation of selective forces typical of nature (forces that continued in hostage on wolves), likewise equally an increment in variability in the dog genome compared with the genome of their ancestral stock (Björnerfeldt et al., 2006).

Dogs and Appearance

A photograph shows a brown boxer dog with white patches on its chest and nose, and black markings around its eyes, nose, and mouth. The dog is sitting on a lawn with a red house and two trees in the background. The dog is wearing a red canvas collar with a silver circular ring that has silver, rectangular identification tags hanging down in front of its chest.

Figure 1: Tasha, a boxer.

Tasha's Deoxyribonucleic acid was used for genome sequencing.

National Human Genome Inquiry Establish/Broad Institute.

One question that tugged at Swedish researcher Carles Vilà is how dogs can have such a wide diversity of phenotypes—imagine a tiny Chihuahua standing next to a Great Dane, or a Chinese shar-pei peering from under its peel folds at an Former English language sheepdog who peers back through its long hair. In fact, the variation among breeds of dogs is far greater than the variation among other completely distinct species in the family Canidae.

If dogs evolved from wolves, which seems to be the instance, and then wolves must have had the capacity for this diversity somewhere in their genomes. Thus, Vilà and his colleagues decided to compare the mitochondrial DNA of dogs and wolves in an attempt to understand the genetic consequences of these species' different lifestyles: domesticated versus wild. (Remember, both dogs and wolves evolved from a common ancestral wolf species, so wolves are an ideal command with which to study the consequences of dogs' life with humans.) The mitochondrial genome was used because of earlier piece of work by Vilà that showed the nuclear genomes of dogs and wolves to be too similar to study their molecular evolution. On the other hand, this research indicated that mitochondrial lineages are clearly distinguishable for the two species.

Vilà hypothesized that sure mutations—those that might be deleterious, just not strongly then—accumulated faster in populations in which natural selection had been relaxed, resulting in a decline in fitness. In other words, later on dogs started to alive with humans, less fit individuals were more probable to survive and reproduce than they were in the wild. In addition, information technology is highly likely that dogs were strongly selected for certain behavioral traits, such equally tameness. "Information technology is therefore possible that this procedure led to an increment in functional genetic variety throughout the entire dog genome," wrote Vilà, "including both genes and elements affecting factor expression." Such a relaxation of selective pressures might have led to the wide phenotypic diversity in dogs, likewise equally the multifariousness of diseases seen in dogs today (Figure 1).

Tameness

Many researchers have noted that beyond tameness, dogs appear to retain certain traits associated with juvenile wolves, especially behavioral traits such as whining, barking, and submissiveness. Russian geneticist Dmitry Belyaev focused on tamability equally a guiding feature. His idea was not only that early on humans would have selected the tamest animals to live with them, merely likewise that selecting for a unmarried trait could requite rising to an entire set up of changes in form, physiology, and beliefs. Belyaev thus launched an experiment that would concluding longer than his life, seeking to test whether selecting for tameness would indeed produce a set of domesticated traits similar to those seen in dogs (Trut, 1999).

Belyaev chose the silvery fox for his experiment; this species is related to the dog, just information technology is not domesticated. The initial foxes in Belyaev's experiment were not trained in any way, but simply tested for tameness at an early on age. Starting at age one month, a homo researcher would try to feed and pet the foxes, either alone or in the company of other foxes. The animals' responses varied from aggressive behaviors (such as biting), to indifference, to seeking interaction with the person more with the other foxes. The tamest foxes were then selected for breeding the next generation, although fresh genes were supplied through continual outbreeding.

Belyaev and his colleagues did indeed create a population of foxes that differed in temperament and behavior from their wild cousins. The foxes changed physically as well, with alterations in glaze color appearing as early as the eighth generation—typically a loss of pigment resulting in white patches. The foxes also developed floppy ears and curved tails, mirroring traits seen in dogs as well as other domesticated species.

One of Belyaev'due south hypotheses was therefore satisfied: Selecting for one trait (behavior) also changed other traits (here, aspects of the foxes' physical grade). A common thread in many of the observed changes across the generations in this experiment was that the timing of key developmental steps had been altered. Belyaev predicted that hormonal and neurochemical differences would exist evident, and that such changes would be regulatory in nature and would control early on development in a top-downwardly mode. In particular, two developmental milestones were different in the tamer foxes: their eyes opened several days earlier, and their fear response kicked in about iii weeks later than the norm for wild foxes. These ii events might accept worked together to increase the openness of young foxes to interacting with humans and doing and then without fear. At the same time, Belyaev constitute reduced levels of the stress hormone corticosterone in the domesticated foxes. Even the changes in coat color were linked to changes in the timing of development.

The Canis familiaris-Human Human relationship

In add-on to tameness, some other unique trait of dogs is their ability to empathize humans. For example, if you betoken or even shift your gaze toward a certain object (say, a jar that contains dog treats), a dog will probable investigate the object (Hare & Tomasello, 2005). Even our closest brute relatives, chimpanzees, practice not have this skill. Brian Hare, a High german researcher, posits that this is an example of convergent evolution—the emergence of a trait (referred to by Hare equally "social skills") that developed independently in two species. Hare's working hypothesis is that domestication comes commencement, and after the fearfulness response has been tuned down plenty, the evolution of social skills tin can accept identify.

Domestication of dogs has occurred over many millennia. More recently, the advent of controlled convenance practices has segregated genetic variability into singled-out phenotypes. In fact, the evolution of the majority of canis familiaris breeds is a relatively contempo phenomenon, offset with selective breeding practices during the past 200 years. Today, various breeds demonstrate a huge variability in size and shape, too as coat characteristics. Behavioral traits have also been bred based on humans' use of dogs for herding, hunting, guarding, and companionship. Phenotypic variation amongst dogs is currently partitioned into more than than 350 singled-out breeds worldwide; these breeds are largely closed populations that receive piddling genetic variation beyond that which existed in the original founders (Ostrander & Wayne, 2005).

"These restrictive breeding practices reduce effective population size and increase overall genetic drift amid domestic dogs, resulting in the loss of genetic diversity inside breeds and greater departure among them," writes Ostrander, who participated in a landmark study of the genomic relationship of 85 different dog breeds. "For case, variation among breeds accounts for 27% of total genetic variation, equally opposed to 5-10% amid human populations" (Parker et al., 2004). At present that the dog genome has been sequenced, the potential to learn more about man's best friend, and mayhap ourselves, has increased (Ellegren, 2005).

References and Recommended Reading

Belyaev, D. K. Destabilizing choice as a factor in domestication. Journal of Heredity 70, 301-308 (1979)

Björnerfeldt, Due south., et al. Relaxation of selective constraint on dog mitochondrial Deoxyribonucleic acid following domestication. Genome Research 16, 990–994 (2006) doi:10.1101/gr.5117706

Ellegren, H. Genomics: The canis familiaris has its day. Nature 438, 745–746 (2005) doi:10.1038/438745a (link to commodity)

Hare, B., & Tomasello, One thousand. Human-like social skills in dogs? Trends in Cerebral Sciences 9, 439–444 (2005)

Ostrander, Due east. A., & Wayne, R. 1000. The canine genome. Genome Research xv, 1706–1716 (2005) doi:x.1101/gr.3736605

Parker, H. G., et al. Genetic structure of the purebred domestic dog. Science 304, 1160–1164 (2004) doi:10.1126/science.1097406

Scott, J. P., & Fuller, J. L. Genetics and the Social Behaviour of the Canis familiaris (Academy of Chicago Printing, 1974)

Trut, L. Early Canid domestication: The farm-fox experiment. American Scientist 87, 160–169 (1999)