Dependance of Natural Pheromones

Until it does, the levels of dependence of naturally occurring rodent pheromones and other small mammal species upon olfactory communication cannot accurately be assessed. If odors are used for social purposes one might expect that the range of messages to be exchanged would be as large as the range of visual signals observed in social groups of large mammals.

This is a point of fundamental importance that appears implicit in many recent writings on scent communication in mammal pheromones.

The object of this chapter on pheromones is to review the existing evidence supporting this assumption and to illuminate the areas deserving the attention of ethologists and ecologists wherein further supporting evidence should be sought.

Before considering the components of pheromone organization it would be expedient for us to generalize on the way of life of most small mammals. By far the greatest proportion live either beneath the surface of the ground, or actually on the surface itself. Those living well above the surface, or in habitats where visual or acoustic social communication is possible, most frequently possess visual or acoustic adorn- ment (e.g. Balph and Balph 1966; Ewer 1968). For the large majority of small mammals the denseness of the habitat precludes the use of visual or acoustic com- munication for many components in the repertoire of the social behavior. No doubt visual and acoustic signals are used in close range behavior patterns such as are seen in courtship and mating, but they would be likely to be less efficient for ‘tele-advertizements relating to dominance status, sexual condition, territory or range owner- ship. This argument is not to say that visual and acoustic signalling is more highly advanced in an evolutionary sense than olfactory signalling, but rather more to say that natural selection has favored the spread of species with well developed pheromone producing organs in habitats which tend to preclude the use of visual and acoustic signals.

The conditioning fluid (but see Eisenberg 1963). Their discretion has necessitated the development of particular and specific behavior patterns (Frank 1957; Schultze- Westrum 1965; Thiessen et al. 1968) derived from existing patterns of behavior (Eibl-Eibesfeldt 1958).

Cutaneous glands appear to be largely under the control of sex hormones (Mar- tan 1962; Mitchell 1965; Stoddart 1972a) but this may not be so in every species (Pearson 1946). Castration, followed by hormone implant or injection therapy causes the glands to continue functioning normally, as far as is known. Lack of this therapy causes atrophy and involution of the glands.

Pheromone Chemical studies

Regrettably, rather little emphasis has been placed by ethologists and ecologists on the chemical composition of olfactory signals. This is one of the largest and most persistent gaps in our knowledge. We can not say with certainty that the same, or similar, groups of compounds occur in the olfactory secretions from even closely related species. All the known chemical analytical techniques have been employed to investigate the chemical composition of odors. Gas—liquid chromatography is favored by many workers since organic mixtures are readily separated, and this method allows the odor as produced by the animal to be examined.


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