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Research projects

Background

The mammalian rhinarium is part of the integument, the skin. It is innervated by the nervus trigeminus and therefore separate from the olfactory system. The skin is a highly versatile sensory organ containing cells that can signal touch, pressure, vibration, pain, temperature, and hair movements. In addition, there are glands of various types producing sweat, fats and waxes, as well as odorants and pheromones. The functions of the specialized skin of the rhinarium are largely unknown today.

Spontaneous behaviour

We work mainly on live animals in zoos and on domestic animals owned by ourselves and various associates. Careful observations of spontaneous behaviors are performed in order to formulate hypotheses on rhinarium function.

Dog digging
Dogs are notorious for their digging dispositions and capacities. The rhinarium is used in various ways before and during digging for underground prey. Such observations of spontaneous behaviors are important for designing meaningful experiments.

 

Trained behaviour

Dogs are the main experimental animals because they have prominent rhinaria and are accessible and social. All of our animals love to come to the laboratory where they meet friendly people, make new experiences, get treats for doing simple tasks, and quite often can play with other dogs during the breaks. Even more exciting is field work where we study how the animals use their rhinaria under semi-natural conditions.

A dog is training
Thermograph of a dog having correctly chosen the warm penal from a distance of about 1 m and pushing it backwards in order to get access to a food reward

 

 

 

 

Temperature

A variety of mammals cool their rhinaria when awake and active, usually to a few degrees below ambient temperature, while the rhinarium is always warm and dry in a resting or sleeping mammal. We use thermal imaging for determining rhinarium temperatures in various species and under various conditions. The method detects heat radiating from surfaces and allows for measurements with minimal interference with the animals. Rhinarium temperatures in dangerous animals can be determined from safe distances.

Thermal image of an alert cat
Thermal image of an alert cat, including a temperature scale. The rhinarium is the coldest surface in the scene.

 

 

 

 

Development

Puppy

Rhinaria occur only in mammals and in all major mammalian groups, even in marsupials and monotremes (egg-laying mammals). This suggests that the rhinarium has evolved at the base of the mammalian branch and may have a function related to the mammalian way of reproduction and development. We investigate therefore also newborn mammals and perform longitudinal studies to follow their development.

Secretion

In many mammals, the skin of the rhinarium is moist in the alert animal. However, rhinarium skin is devoid of glands that might produce the moisture. We study the origin, composition and properties of this secretion in order to understand the functional significance of this feature occurring in disparate phylogenetic groups.

Nose with milky drops
A dog is intensely watching an approaching dog, forgetting to clean the nose by licking. Secretion from the rhinarium skin has accumulated as milky drops in the fur under the rhinarium

 

 

 

Molecular biology

DNA sequences of receptor proteins

Temperature-sensitive cells have receptor proteins forming membrane ion channels. Different types of these channels open and close at different temperatures, such that a wide range of temperatures can be signaled to the brain. The channel protein genes being present in various mammalian species are studied to reconstruct the evolution of rhinarium cooling. In domesticated animals, genetic analyses may reveal sensory defects in certain breeds and/or breeding lines.

Air flow

An animal investigating a target by olfaction has to direct exhaled air away from the odorant plume. Interestingly, a dog’s rhinarium may move extensively even if the animal cannot get olfactory information from an object of interest because of unfavorable wind direction. Dogs also quite frequently push their rhinaria against the ground. The flow of air around the rhinarium in various behavioral contexts is of interest for understanding the functions of the rhinarium and its movements.

Tissue structure

Rhinarium tissue structure is analyzed by light and electron microscopy. Collaborating zoos, farmers and veterinarians inform us if an animal has to be relieved from terminal illness or painful fatal injury. The network gives us access to more tissue samples than we can process, without harming any animal.

Dog rhinarium skin surface
(Scanning electron micrograph of dog rhinarium skin surface)

In animals with wet rhinaria, the outer surfaces of skin cells are richly folded on the nanometer scale. These folds develop in parallel with the keratinization of the cells. Such folding is absent in normal skin cells.

 

Evolution and ecology

We study a wide variety of mammals in order to understand how the rhinarium has evolved. Its function may be similar in distantly related species, while closely related mammals may use their rhinaria in different ways. As all sensory organs, the rhinarium filters vital information from the external world, thereby securing the survival of the animal in its environment in competition with other animals. However, in many cases it is unknown what type of information the animals obtain from their rhinaria.

A kinkajou
A kinkajou (Potos flavus), a relative to the raccoon in the family of Procyonidae, peeks from its home at Ystad Zoo. The prominent rhinarium is wet and cold if the animal is awake and alert, and dry and warm in resting kinkajous.

 

 

On duty

Dogs assist humans in countless ways. They search, guard, hunt, rescue, track, warn, and do hard physical work. They can even diagnose certain diseases, alert for upcoming epileptic seizures and guide the blind, much better than any technical device. Humans benefit from the keen senses, excellent social abilities and strong physique of dogs. By refining our understanding of the senses and physiology of dogs we can suggest improvements for both sides.

An Alsatian

Our studies help to select the breeds and individuals most suitable for certain tasks, we can guide humans to better understand and assist the dogs, and we can identify special needs the animals may have when solving particular problems or while being exposed to specific conditions.

 

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