How Selective Breeding Affects Communication

Genetics can influence behaviour through physical structure, and all behaviour depends on the physical capabilities of the animal. For example a dog could not show a direct stare if he did not have an eye type that allowed this.

Similarly the submissive grin would not be possible without the necessary facial muscles. As a species the domestic dog is highly unusual in the range and structure difference between individuals. Domestic dogs vary widely in appearance, particularly in size. The Shih Tzu, for example, is 20 to 28 cm (8 to 11 in) in height and weighs 4 to 7 kg (9 to 15 lb). The Irish wolfhound is at the other end of the scale, measuring about 71 to 94 cm (about 28 to 37 in) at the shoulder and weighing up to about 61 kg (about 135 lb). 

Coat colour, length, texture, and pattern also vary greatly. The muzzle may appear shortened, as in the Pekingese, or elongated, as in the Borzoi. Limbs are relatively short in the Basset Hound and Dachshund, but long in the Saluki. The long and slender legs and deep chest of the Saluki contributes to its ability to hunt by sight whereas the short legs of the Basset Hound make it perfectly placed for ground scent tracking.

The physical attributes of a particular breed are closely tied to the breeds original function and so influence the behaviours that are necessary to carry out that function. (L P Case, 2005)
Physical differences in appearance may also affect the ability of the dog to send and receive communications from both humans and other dogs, visually the dog uses body postures, facial expressions, Ear carriage, eye contact, and tail movement to communicate with others but some breeds possess traits that prevent or impede them from their ability to send or receive these signals, ears positioned lower on the head, or that have a pendulous flap as with Spaniels can alter facial expressions and the dog in the case of a spaniel is unable to prick up its ears. The thick coat of a Pomeranian or Samoyed can affect the dogs ability to signal using its body , and long hair in the facial area seen in the Bearded Collie and Old English Sheepdog can affect the dogs use of eye contact and the displaying of teeth, the length and weight of the hair can also prevent dogs from raising their hackles (beaver1981), 

this is also true of  many curly coated dogs for example the Poodle and Airedale. However the ridge of a Rhodesian Ridgeback gives the impression that its hackles are permanently raised which could cause it to be viewed suspiciously by other dogs

The curled tails of Pugs or artificially and naturally docked tails associated with Dobermans and Bulldogs distorts the visual signal of raised or lowered tails and inhibits normal tail wagging (interestingly those breeds that have a minimal tail tend to compensate by wagging the whole of the hind quarters)

Excessive skin folds around the face and the natural frown seen in Sharpei coupled with their very small button ears that are forward facing and held close to the head alter the ability to show normal facial expressions, ear positions and eye contact

When dogs misunderstand each other, trouble can occur. The breeds who most distinctly look like wolves are those with the clearest body language (such as German Shepherd Dogs). Those with peculiar anatomical features are most far-removed from the wolverine shape and so may be misunderstood. For example, a Bulldog who has excessive wrinkle, a naturally short, oddly shaped, or complete lack of tail, naturally dominant muscle bound stance (even when relaxed) and incredibly short muzzle usually causing the dog to permanently show teeth and heavy eyes with whites showing are giving out a host of conflicting and confusing signals. Black dogs are thought to appear featureless in the eyes of other dogs meaning subtle facial expressions may not be understood.