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The role of the black nose in infrared radiation detection in dogs

Ytterberg, Agnes (2019) BIOK01 20191
Degree Projects in Biology
Popular Abstract
The dogged black nose in dogs

The different sensory systems of animals is a well-studied subject. Today it is virtually common knowledge that birds of prey have good sight, that bats use echolocation and that dogs have a good sense of smell. However, recent studies show that there is more to the noses of our precious dogs, then we for a long time knew. Apart from participating in the olfactory system the nose also possesses qualities that allows heat radiation sensing. It is the naked skin on the tip of the nose, called rhinarium, that is the star in this sensory mechanism of dogs. The rhinarium is, at its normal state, slightly wet and cold, which makes it particularly sensitive to warming. By comparison, herbivores have warm noses,... (More)
The dogged black nose in dogs

The different sensory systems of animals is a well-studied subject. Today it is virtually common knowledge that birds of prey have good sight, that bats use echolocation and that dogs have a good sense of smell. However, recent studies show that there is more to the noses of our precious dogs, then we for a long time knew. Apart from participating in the olfactory system the nose also possesses qualities that allows heat radiation sensing. It is the naked skin on the tip of the nose, called rhinarium, that is the star in this sensory mechanism of dogs. The rhinarium is, at its normal state, slightly wet and cold, which makes it particularly sensitive to warming. By comparison, herbivores have warm noses, which has a tactile function that aids the animals during foraging.
Another trait of the rhinarium is that in most terrestrial carnivores, it is black. Even white-furred predators living in arctic climates, like the polar bear (Ursus maritimus) and the arctic fox (Vulpes lagopus), have black noses despite of an obvious disadvantage in question of camouflage. One group of animals that instead possess a light-coloured nose is the felids and one other thing that separates them from the canids is that they are nocturnal. Could there be a connection here?
The pigmentation of dog rhinaria differs from that in for instance human skin, by having melanocytes that synthesizes the dark light-absorbing melanin pigment, in two layers in the skin instead of only one. In the context of heat radiation sensing this could mean that a dark-coloured nose absorbs light on a level protecting the cells sensing the heat radiation. Meanwhile, in light-coloured rhinaria the lack of melanin could imply that the light reaches further into the skin and therefore cause warming of the nose, making the heat radiation more difficult to detect.
In a two alternative forced choice experiment two dogs were tested in their ability to detect heat radiation. One of the dogs has a dark-coloured nose and the other has a light-coloured nose. To test the impact of light intensity the dogs were tested in two different light conditions where one was dim and the other one bright. Results from the tests of the dog with the light-coloured nose showed that the success rate was 2% higher in bright light than in dim light, implying bright light has no negative impact on the heat radiation ability of the dog. For the dog with a dark-coloured nose, the success rates were the exact same in the different light conditions, as expected. When tested against each other, the dogs showed no difference in their ability in either dim or in bright light.
From these results alone no conclusions about the impact of light intensity and the role of a dark-coloured nose in heat radiation sensing, can be made. Very little is still known about this sensory mechanism in dogs and further investigations of the dog nose is needed to be able to go further with the questions regarding the subject. It is clear that for many animals, having a black nose is an advantage. As melanin pigment protects the skin from UV radiation it is possible that the black skin of the rhinaria simply has a protective function. While nocturnal animals have the possibility to retrieve to a place of shadow during the day, the diurnal carnivores are often exposed to the sun when foraging. The dingo (Canis dingo) is one of few nocturnal canids but nonetheless possess a black rhinarium, making it an interesting target for future studies of the subject. While this study was an attempt to learn about the reason for its persistence, the black nose of dogs, and other carnivorans, continues to remain somewhat of a mystery.

Bachelor project for Bachelor degree in Biology 15 hp 2019
Biologiska institutionen, Lunds Universitet
Supervisor: Ronald Kröger
Mammalian Rhinarium Group (Less)
Please use this url to cite or link to this publication:
author
Ytterberg, Agnes
supervisor
organization
course
BIOK01 20191
year
type
M2 - Bachelor Degree
subject
language
English
id
8994882
date added to LUP
2019-09-13 11:53:33
date last changed
2019-09-13 11:53:33
@misc{8994882,
  author       = {{Ytterberg, Agnes}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{The role of the black nose in infrared radiation detection in dogs}},
  year         = {{2019}},
}