REPORT ON PHEROMONES
Part 2
The research
The first identification of a pheromone took place in the Fifties thanks to a team of German researchers who choose the silk butterfly between the great amount of insect available in the silk worm farm. Half a million butterflies are necessary to obtain 6 ml. of the active molecule, bombikol (6 ml. of gram) necessary to make the bioessay that will allow to certify the effect of the molecule on the behaviour of the male butterfly.
The bombikol was obtained washing with solvent the glands that produce the pheromones of the butterfly, then separating by partition the various components of the pheromonal compound.
Various molecules were tested on males in the course of the bioessay and at the end was discovered that the molecule named bombikol was responsible of the behavioural response.
The method of the research involves therefore three steps: isolate various molecules from the compound, identify them and certify their effect in the course of bioessay.
Although today, thanks to the modern technologies, a single insect is sufficient to the study of its pheromonal compound, the task of the investigators is not less arduous because of difficulties inherent just to this field of research, particularly when dealing with pheromones of vertebrates that are much more complex.
In order to understand the puzzle in front of which the researchers found themselves, either biologist than chemist, we will list some of the difficulties with which they had to face.
- the pheromonal compound of the vertebrates contain sometimes dozens of molecule. The effect produced often is a synergy of three or more molecules. The possible combinations to try during the bioessay grow exponentially according to the complexity of the compound isolated.
- the bioessay to be persuasive must consider numerous factors very difficult to reproduce like the age of the animal, the period of the year because of the reproductive cycle, the outside environment in which the essay is made, just to name only some of them.
- the research requests the collaboration of chemists and biologists, that have completely different modalities of work.
The first vertebrates pheromone was isolated during the Sixties. The discovery of pheromones is therefore a very recent one. This shows well the state of knowledge that we really have when we think that this chemical language recently discovered is the most ancient way of communication of alive beings and that in the evolved forms of life it still controls in great part the reproductive function and many social behaviours.
The most important pheromones are the object of the next paragraph: the sexual pheromones
The sexual pheromones
A category of odorous signals produced by animals, humans included, has a sexual function. The production of these pheromones enrols in the context of a primordial process, the sexual selection.
The sexual selection has various aspects, the main ones is the choice of the partner, the competition between individuals of the same sex for the conquest of the partner and the competition to arrive first to the potential partner. All these mechanisms can be influenced by or sometimes entirely regulated by the pheromonal communication.
The sexual selection is responsible for the reproductive success of the single individuals of one species and for the same survival of that species.
Considering the ubiquity of chemical signals in the animal reign, we can understand that from the studies just began on the pheromones will emerge that these are the key factor in the most important mechanism of the reproduction, the selection of the sexual partner.
In the reproductive process, the female invests much more then the male. The effort of sperm production is not comparable with the one demanded from the maturation of the ovule up to the birth of the newborn. Therefore the female has a very limited reproductive ability while the male can try to transmit its genes fertilizing more than one single female during its “reproductive season”.
This biological fact is at the origin of the universal competition between males to conquer females.
Therefore are females who choose the male between their pretenders according to criteria like physical appearance, voice and surely also its smell.
Actually the reproductive process is a real duet of olfactory communication that begins with the female that publicize with her smell its availability to coupling and its state of ovulation. This pheromone stimulates both the sexual behaviour of the male and its production of sperm.
The sexual behaviour of the male comprises the production of pheromones in its turn that have the functions to communicate to the female information that will help her in the choice of the partner: state of health, sexual maturity, genetic compatibility and also the rank in the social hierarchy of the group. Often dominant males produce a pheromone that identifies them as such and it is not said that this, in a certain measure, is not the case also in the human species.
The pheromone of the dominant male is the favourite by females and, in some species, acts also on the other males of the group inhibiting their sexual behaviour.
An example that illustrates this well is the one of red snake. When the female exits from the lair in spring immediately is encircled by a hundred of males attracted by its scent (a pheromone). In the tangle that shapes, the males try to couple with the female. As soon as one of these succeeds, releases pheromones that make the others to disperse quickly.
Many sea animals as the curl or the sea worm depends entirely on a pheromonal duet for the success of reproduction. Chemical signals coordinate the production and the maturation of eggs and sperm and their release in the ocean.
For many species of vertebrates the initial role of pheromones in the reproductive process begins with determining the choice of the partner and we cannot discard the hypothesis that this is not valid in some measure also for our species.
In nature, the pheromonal smell of the male not only identifies it, but it reveals its intrinsic value: its genetic compatibility, its state of health, its diet, its state of sexual maturity and also its social rank inside the group. These information will allow females to choose the most appropriate partner between its pretenders.
For many vertebrates, the production of these pheromones is related directly to the level of androgens hormones present in the blood, like testosterone, because are these hormones that stimulate the glands manufacturer of pheromones. The pheromonal intensity of the male is also a criterion of important evaluation in the choice of the partner. The females of the “elephant butterfly” for example prefer males that produce a superior amount of pheromones.
Continues ...
