Review: Evolution of Dog

Abstract

Dog(Canis familiaris) is one of the terrestrial mammal with immense diversity in it's phenotype although they belong to a same species.Till the beginning of  industrial revolution there were a few variety of Dog with a very few changes in their gene pool.But as the wave of Industrial Revolution spread throughout the western world,the people living there were obsessed with perfection.They built factories,magnificent buildings and invented many things.So they want every thing perfect from their household to their livestock.They began with Cow and certainly  succeeded as a result of we see cows with variety of shape and size.Then came the term of dog so this triggered the massive diversification of the gene pool of the dog.Dog as small as Chihuahua
  to dog as big as Great Dane are found today.Humans have for years tailored dog according to their needs such as there are dogs for game purpose,dogs for guarding livestocks,there are dog for hunting.So humans have genetically engineered the dog according to its need.
Example-Dog called Sulimov dog created by Klim Sulimov i.e  only found in Russia is a result of a hybrid between the Jackal and Dog.The main objective of creating this dog variety is  for sniffing bombs or explosive material.Their sense of smell is so strong that they can sniff explosives of trace amount i.e smaller than grain of sand.So these are the instances how we have created wide range of variety of Dogs from a small group.Previously in the late 18th and 19th century when people were not aware of the genetic basis or what cause such large variety so what they were doing that they cross breed the dog with each other as well as with their ancestor mainly wolf,as a result they went on increasing the gene pool.This became the chief reason for tremendous diversity in their genes.  

Introduction

The domestic dog(Canis familiaris) as well as new type of dog called wolf-dog hybrid (also called a wolf hybrid or wolfdog) is a canid hybrid resulting from the mating of a wolf (various Canis lupus subspecies) and a dog (Canis lupus familiaris) can be found in different parts of the world.Dog history has been studied recently using mitochondrial DNA, which suggests that wolves and dogs split into different species around 100,000 years ago; but whether humans had anything to do with that, no one really knows. Recent mtDNA analysis , suggests that the origin and location of dog domestication, long thought to be in east Asia, is in some doubt.It is usually done taking the maternal mitochondria as it is very conserved throughout the evolutionary time history.
When we move back in the earth history the earliest evidence of dog human domestication found at a burial site in Germany called Bonn-Oberkassel has joint human and dog interments dated to 14,000 years ago. The earliest domesticated dog found in China is at the early Neolithic (7000-5800 BC) Jiahu site in Henan Province. European Mesolithic sites like Skateholm (5250-3700 BC) in Sweden have dog burials, proving the value of the furry beasts to hunter-gatherer settlements. Danger Cave in Utah is the earliest case of dog burial in the Americas, at about 11,000 years ago

Evolutionary history

                      The modern carnivore families originated over 40–50 million years ago . The domestic dog belongs to the family Canidae which,in turn, is classified within the superfamily Canoidea and order Carnivora. Therefore, seals, bears, weasels and raccoon-like carnivores are more closelyrelated to canids than are cats, hyenas and mongooses . The Canidae is the most phylogenetically ancient lineage within the superfamily Canoidea,diverging from other carnivores over 50 million years ago. The canine karyo-type has little similarity to those in any other carnivore families   suggesting that large chromosome blocks and linkage groups may not be conserved .
Three subfamilies of canids have been recognized. The subfamilyHesperocyoninae includes the oldest and most primitive members of the family.This Oligocene to Miocene Age subfamily includes small to medium sized predators and lasted for over 20 million years. In the Middle Miocene, the Hesperocyoninae were replaced by Borophaginae, large bone-crushing dogs, that are often the most common predators in late Tertiary deposits but were extinct by the mid-Pliocene, about 4 million yearsago .The third subfamily, Caninae, includes all living representatives of the family and first appears in the late Miocene.Although canids belong to an ancient lineage, the 36 extant species are all very closely related and diverged only about 12–15 million years ago Based on mitochondrial DNA sequences, three distinct groups can be identified within the extant Canidae, including the red fox-like canids  the South American foxes, pampas foxes, and the wolf-like canids i.e the domestic dog, grey wolf, coyote, African hunting dog, dhole, Ethiopian wolf and jackals. Bush dog and maned wolf are two very divergent South American canids that cluster with wolf-like canids in some analyses.The grey fox, raccoon dog and bat-eared fox represent long distinct lineages. Evolutionary relationships are also suggested by chromosome similarity. Chromosome number and structure vary widely among canid species, from 36 metacentric chromosomes in the red fox to 78 acrocentric chromosomes in wolves, coyotes and jackals.However, the closely related wolf-like canids and South American canids all have high diploid numbers and acrocentric chromosomes.Similarly, the closely related fox-like canids have low diploid num-bers and metacentric chromosomes and share a common ancestry. But how exactly the dog domesticated from their nearest ancestor i.e the wolves it is quite difficult to answer.Evidence can only be found from the old archaeological site,because initial finding of dog remains from the archaeological site difficult to identify because of morphological similarity between the early domesticated dog and the wolves.So with the advancement of science and development of sophisticated technique we are able to trace as well as able to prove that dogs evolved from wolves. Molecular results imply an ancient origin of domestic dogs from wolves. In fact, wolves and humans lived in the same habitats for as much as 500,000 years and domestication might not have been apparent until the nature of artificial selection and dog conformation changed with the shift from hunter–gatherer cultures to more agrarian societies about 12,000 years ago The role that dogs had in hunter–gatherer cultures was perhaps restricted more to protection and hunting, and dogs may have lived less closely with humans,resulting in more morphological similarity to their wild brethren.The Romans were among the first to develop breeds of dogs that differed dramatically in conformation and sizealthough some morphologically divergent dogs were depicted by the ancient Egyptians and in western Asia 4000 years ago.Mastiffs and greyhounds were among these dogs and not extensively interbred with other dogs. In North America, the most ancient living breed is the Mexican hairless, or Xoloitzcuintli (Xolo) which is a hairless dog developed over 2000 years ago  Because the Xolo is a pre-Columbian breed, the progenitors of the Xolo either migrated with the first Americans across the Bering land bridge over 10,000 years ago or were domesticated independently from North American wolves. Molecular studies shows that the majority of breeds have moderate to high levels of genetic variability and the differentiation between them is mostly due to differences in the allelic frequencies .These results reflect the recent origin of many breeds from a diverse founding stock and subsequent interbreeding among breeds. The small differentiation between breeds seems to be the result of their recent isolation in modern times.However, ancient breeds, such as the dingo and the New Guinea singing dog were developed when human populations and their domestic dogs were more isolated and founding populations were potentially more inbred. Dingoes and singing dogs were introduced into Australia and New Guinea by ancient travelers as early as 6000 years ago and this long period of isolation and small founding population size has translated into limited genetic diffrentiation. It will probably never be guessed what course the evolving dogs might have followed. One can only come closer to a better understanding of the pathwaysand factors guiding evolving dogs by using approximations. It is hoped that the domestication experiments with foxes will shed some light on a long-disputed issue. Surely, the conditions of experimental re-creation of domestication in our days do not, even in rough outline, truly bring out the start of the ancient process. The task of the grand-scale experiment was to reproduce the major, as initially suggested, factor in the first steps of domestication – the strongest selection pressure on behavior. All animals from the very start of domestication were challenged by the same evolutionary situation of the pressure of selection – primarily natural – on the specific behavioral traits favouring adaptation to the novel social factor – human beings.
DOG ENGINEERING
When we see the present scenario 80% of the breed does not exist as we see today.Dog's improvement by agressive breeding or technically called Eugenics i.e in quest of perfection of a species by selecting breeding .So the shaping of man's best friend must just by an accident.Dogs are the decendent of the wolf but how the split happened from a fierce predator to a loyal friend happened no one knows.
According to Zoologist James Serpell,(University of Pennselvania) the ancient man simply wanted a pet and it is still now practised among the hunting tribes across the world of keeping baby wild animals whenever they encountered one.
The dog is malliable humans have tampered with it's forms such as looks,structure and other characters,such atonishing diversity among the dog is only possible is due to the canid DNA which is exceptional only in the animal kingdom.DNA is the basic instruction manual for every living organism i.e almost all of them follow the central DOGMA i.e DNA->RNA->Protein only a few aberration in the virus.So the total no of base pair or the combination of A,T,C,G is 2.4 billion base pairs.These sequences of A,C,G,T makes thousand of genes specefying each component of the dog.Due to selective intensive breeding dogs have more physical and behavioral characteristics than any mammal on this earth but yet all the dogs are genetically similar about 99.99% and the varioution i in their appearance,shape etc is because 0.2% in their gene.The researchers of NIH have found that a small change in the IGF-1 gene influence dog size from the Tennese chuwawa to the Great Dane.In Texas another group of researchers offers intriguing explanation why human able to transform dog so easily.They found some thing very interesting in the genomic code of the dog i.e tandem repeats.Tandem repeats are small section of DNA that repeat over and over like a single word  get repeated over and over in a sentence.These mutations can change the protein expression so leading to change cell function consequently overall function of dog.All living organnismim have tandem repeats in their genes but the dog have significantly more than most of the other organisim.
So the researcher found out that the link of the repeat correlated with the downturn ofthe dog's downturn or upturn in the dog's snouts.Like one number of repeat produce Boxer's snout and another no of repeat produces the Russian wolf hound.The notable change inthe shape of snout canbe seen in the bull Terrier's snout i.e is it has gone downward slide in just 45 years.This shows that mutations occuring in tandem repeats  can contribute to variety of size,shape,color etc.Certainly over the years humans have perfected the art of manipulating the dog but this resulted in some other serous mental as well as physical diseases.such as the gene that produces the black color inthe Dalmatians is related to deafness in them.Cancer,blindness,deafness,epilepsy are few of
the disease that human share with it's best friend.But again the pure breed rarely suffer from this type of diseases.So actually we can pin point the irregularities in dogs from  this pure breed dog.This happens because most the dog the dog evolve in a closed breeding polulation so no new genetic material get added to their genomic pool as a result it leads to expression of more recessive kind of genes.

DISEASE AND MEDICATION

A bull terrier called Tally suffers from the dog's version of OBSESSIVE COMPULSIVE DISORDER.At nine months old the Dog began chasing her Tail for hours and hours.The bull terriers pedigree dates back to 1830,first it was bred first  as a fighting dog.Bull terrier produced by crossing  bull dog and now extinct English terrier,the pointer was added few years later for size.According to Alice Moon-Fenelli of Tuft's University who studies bull terrier tells that we genetically selected dogs for their Predatory behaviours mainly,so in case of Tally or dogs who chases their own Tail it is like their predatory behaviour gone away.

So is there any technique available for all these human aided disease in dogs that evolved from wolves.Certainly Gustavo Aguirre of University of Pennsylvania and colleagues developed a technique for treating the blindness among the dog by injecting a virus carrying the healthy copy of genes .
 
So to study how we mold the dogs for such friendly behaviour  Adam Miklosi of Eotvos Lorand University  experimented in which  a group of Dogs and Wolves giving both of them the same amount of human exposure.Dogs have innate type of intelligence which no other animal can claim .According to Miklosi imitation is the basis of culture that is how we pass on knowledge from one generation to other.They devised an experiment in which they kept a piece of meat in a bucket and directed both the dog and wolf.It was found that that dog went on to that bucket which the master directed without investigating the other one but it was not in case of wolf.The wolf does not look for the help for human as seen in dogs despite the domestication.In another problem solving experiment between wolf and dog they tied a piece of meat inside a cage.What the dog did was it tried for dew minutes and later it looked at it's master for help.But the wolf kept  on trying untill it get's agitated and never looked toward for human intervention.So they found that dogs are much better in learning than wolves.So in the evolution of dogs human selected them in such a way that they imbibe the ability to learn and subsequently can use it in the need of problem solving situation.So dog's communicative skill developed after it's splits from wolves.

Methods

Very distinct type of morphologies as a result of evolution a such as their skull as the skull shape and snout.Such as allometric growth andproportionate growth of the skull.So this is very typical to a dog as when it is a pup it skull size is different as compared to an adult dog,when compared to a cat their skull shape almost remains the same in a kitten as well as adult stage.This process of transformation is called Neoteny(Juvenillasition).
Mitochondrial studies
  1.one linked array og genes.
  2.one locus
  3.Central region sequence.
  4.Maternally inherited.
The sequence diversity in dogs is similar to that within wolves.
Average sequence divergence in dogs=2.06% +-0.07%.
Average sequence divergence in wolves =2.1% +-0.04%.
Control region consist of 261 base pair.
The majority of dog sequence has a single common origin.
Four origin or Interbreeding from wolves.
Archaeological Records
Domestic dogs 15-30,000 years ago hardly modified from their ancestors in terms of appearance.
Genetic studies
 It suggest multiple origin in the dog i.e East asia,Southwest Asia and Europe.
 High diversity in East asia shows an origin there.
 Founding by multiple matralines suggest origin about 15-40,000 years ago.
 Use of SNP array technique.

Results-Discussion

The dog has an ancient divergence about 55 millions years ago from other carnivores.
The extant Canidae has a relatively recent origin about 10 million years ago and is divided into three primary groupings.The dog is assigned to wolf like groups.
The dog is extremely close to the gray wolves form the molecular studies and show no evidence of origin from other wolf-like canids.
Dogs share more unique haplotypes with European and Middle eastern wolves.
So far human able to decipher the dog genome fully.What are the other practical implications other than knowing the evolutionary history.


In humans, common diseases show complex modes of inheritance, and as a result, they are frequently largely refractory to genetic analysis. Rodent systems are more tractable genetically, but the mutations typically represent induced rather than naturally arising alleles, and results are often of limited direct relevance to human disease because of profound differences in physiology. In contrast, the physiology, disease presentation and clinical response of dogs often mimic human diseases closely. Thus, positional cloning of genetic diseases in the dog can inform us about the genetic susceptibility to similar diseases in humans.
 Most modern dog breeds are relatively young, with the majority having been developed within the last 300 years. Many of these were derived from a small number of founders—as few as six, for instance, in the case of the modern Irish Wolfhound—that best represented the physical or behavioral traits breeders wished to feature. The natural history of some breeds has further restricted their genetic diversity over what is expected from breeding strategies alone. Catastrophic events in the last 100 years, such as the two world wars and the American depression, have produced severe bottlenecks in many breeds, at times reducing the effective breeding stock to only a few dogs. At the end of WWI, for instance, only five dogs of the Leonburger breed remained alive in Europe , and all Leonburgers alive today are believed to be descendents of those five. Genetic diversity in some breeds is further reduced by the presence of “popular sires.” These dogs have physical features which make them particularly successful in the show ring and hunting or performance events, and as a result they may produce over 100 litters in their lifetime.For many breeds, therefore, modern purebred dogs represent a limited genetic pool, with disease predispositions derived from one or a small number of recent genetic founders. Thus, modern dog breeds offer all the advantages of geographically isolated human populations, but with a higher degree of isolation, narrower bottlenecks, and much better genealogical records.The top 10 diseases in purebred dogs include several that are of major health concerns to humans such as cancer, epilepsy, allergy, retinal disease, cataracts, and heart disease. To date, disease loci have been genetically mapped or otherwise localized in the dog for many disorders including blindness,kidney,cancer,narcolepsy,rheumatoid arthritis,SCID,keratin-associated diseases,cystinuria,bleeding disorders ,ceroid lipofuscinosis , and copper toxicosis . In most cases investigators have been able to localize a disease locus to a modestly-sized interval of 10-20 million bp, although for some disorders such as several retinopathies,narcolepsy,cystinuria ,SCID ,bleeding disorders,and copper toxicosis the underlying mutations have been identified. In most of the latter situations, candidate gene approaches proved fruitful. Testing specific candidates, however, is unlikely to be useful for a majority of other loci that have been mapped.
In the following three sections, we consider the specific examples of retinitis pigmentosa, cancer and narcolepsy. These highlight, respectively, the ways in which pathways can be dissected by mapping several similar diseases in several distinct breeds; the utility of the domestic dog for mapping and cloning disease genes that are common in the human population but genetically intractable because of locus heterogeneity in humans; and, finally,the ways in which studying rare diseases in dogs can inform us about the biochemistry of common diseases in humans.



By neutralising the dogs wild nature we paradoxically assured it's survival.We eugenically shaping it's appearance and behaviour on an evolutionary speed way according to our specification and desires  ,for better,for worse and for us.