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The Complexity of Male Pheromones

As further evidence of complexity of male pheromone odor compared with female odorour research shows the preliminary characterization of caudal organ odors of Apodemus avicollis Melchior (Stoddart, u...

As further evidence of complexity of male pheromone odor compared with female odorour research shows the preliminary characterization of caudal organ odors of Apodemus avicollis Melchior (Stoddart, unpublished). Several peaks peculiar to the male are present and their identification and isolation are the subject of continuing pheromone studies.

Mention was made above of the dual role played by the scent producing apparatus of some small mammals. There seems little doubt that cutaneous glands play an active role in mate attraction. If this is not known from direct observation it is at least inferred from the fact that many such glands decrease in size during the period of sexual quiescence (Quay, 1953; Mitchell 1965, 1967; Stoddart, 1972a) according to

The fact that they operate for other pheromone purposes which, if not sexual, must be social, is shown by the fact that many, if not all species have scent organs active throughout the whole year. Little is known from eld studies about the effects of old age on the scent organs, but in the laboratory post reproductive Arvicola lose their scent pheromone organs altogether.

In Mesocricetus a great reduction of secretory activity occurs (Lipkow; 1954 Vrtis 1930). Ecological studies on small mammals seldom reveal se- nility, but when it does occur the effect of the scent organs is presumably similar to that of removal of the site of sex hormone production. This results in a drying up and cessation of function of the glandular tissue (Martan 1962; Mitchell 1965; Stoddart 1972a;Thiessen 1968).

Pheromone Scent Organs

Although pheromone scent organs may play a large part in the bringing together of two indivi duals to mate, there is no evidence that lack of the scent organs prevents successful breeding. There have been few studies conducted to investigate this, but one, using Meriones unguiculatus Milne-Edwards, has shown conclusively that presence of the mid-ventral scent organ is not essential to normal successful breeding (Mit- chell 1967).

This is not to say that scent is unimportant in mating. Indeed anosmic male hamsters show no copulatory behavior towards receptive females (Lisk et al. 1972) and anosmic rats show impaired sexual behavior (Larsson 1971). How- ever, the most obvious odor producing organs are not primarily for use in the intimate behavior surrounding mating.

There can be little doubt that pheromone olfaction offers the main pathway of social communication within populations of small mammals. Two factors above all others point to this. Firstly, glandular development is more enhanced in the male than in the female and his odor may contain more compounds than that of the female. Secondly, there is a high degree of specialized scent setting behaviour shown by many species of small mammals. 

If the pheromone odor was required only in the context of intimate behaviour there would be no need for a broadcasting behaviour. However, in several mainly subterranean species, a passive form of odor spreading has been adopted. These two factors leave us with little doubt that it is important for information about one individual in the population to be made known to the others, or at least some, and that this information has considerable social value.

Before discussing pheromone odor as a factor in the social biology of populations, it should be re-emphasized that more studies are needed now on populations under natural conditionsFree Reprint Articles, in order to indicate which olfactory messages are employed at times of greatest dynamic change in the population. Such indications would constitute a major breakthrough in small mammal population biology.

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Alexander P is a blogger that studies pheromones.

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