All selected candidate genes need to be validated for their involvement in behav-ioural traits to close the circle. It will therefore be important to select appropriate behavioural tests for validation. The effect of environmental differences during testing has been intensely debated (Crabbe et al., 1999). These results indicate that it may be impossible to reproduce exactly the same behavioural phenotypes in different laboratories. However, it should be possible to determine with certainty that a particular gene can cause qualitative changes in specific behaviours. Such qualitative changes may be extremely important for the differentiation of very closely related individuals such as different species that belong to the Canidae family.
The definition of a species being the most inclusive reproductive population is a useful one because it puts boundaries on gene flow. This means that members within a species can mate and produce viable offspring. For most cases, this defi-nition is probably appropriate. The question is whether this defidefi-nition is appro-priate relative to the various species that make up the genus Canis. In fact, wolves, coyotes, jackals and dogs are inter-fertile, and crossbreeding still occurs in the wild. A better understanding of the genetics behind behavioural differences may help to distinguish man’s best friends from their wild ancestors.
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Introduction
The purpose of this chapter is not to cover sensory physiology completely but to stress some topics of special behavioural relevance and/or which deviate markedly from the acuity of our own senses. The function of the sensory system is to provide information to the animal about its chemical, physical biotic and abiotic environment and of the state of the body of the organism itself. With this information, the animal is able to behave in an appropriate way to the changes in these factors, or to change the factors themselves. The effect of the behaviour is further monitored by the organism. If the behaviour was successful it will be stopped and if not another behavioural strategy will be tried. The uptake of infor-mation by the sensory system is not a passive process; on the contrary, it is an active one for two reasons:
1. The physical or chemical influences are transformed into generator potentials and/or action potentials. These neurophysiologic parameters allow the process-ing of the input.
2. The sensory system is influenced by the state of the organism. For example, a dog which is hungry will react with predatory behaviour on seeing a rabbit with higher probability than a satiated dog. This means that motivation exerts an influ-ence on the sensory system by filtering the stimuli and altering the attention for special types of stimuli (Bubna-Littitz, 2005).
The sensory system plays a crucial role not only in the lives of each individ-ual, but also in intra- and interspecific communication. Dogs use acoustic, chem-ical (odours, pheromones) and visual signals. A signal is defined as behaviour
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