Sex pheromones

Sex pheromones are pheromones released by an organism to attract an individual of the opposite sex, encourage them to mate with them, or perform some other function closely related with sexual reproduction. Sex pheromones specifically focus on indicating females for breeding, attracting the opposite sex, and conveying information on their species, age, sex and genotype after emitted by males. Volatile pheromones are characterized as sex pheromones or defensive pheromones and usually form a specific odor and are focused on alarm sensitivity. Non-volatile pheromones, or cuticular contact pheromones, are more closely related to social insects as they are usually detected by direct contact with chemoreceptors on specific parts of insects (i.e. antennae, feet).

Odours might be a kind of male "ornament" selected for by female choice; they meet the criteria Charles Darwin set out in The Descent of Man, and Selection in Relation to Sex. After many years of study the importance of chemical communication in this area is becoming clear.

Sex pheromones have evolved in many species. The many types of pheromones (i.e. alarm, aggregation, defense, sexual attraction) all have a common cause acting as chemical cues to trigger a response. However, sex pheromones are particularly associated with signaling mating behaviors or dominance. The odors released can be seen as a favorable trait selected by either the male or female leading to attraction and copulation. Chemical signaling can even be used to find genetically different mates and avoid inbreeding. Females are often choosy when deciding to mate with a male and chemical communication ensures that they find a high-quality mate that satisfies their reproduction needs.

Blepharisma japonicum is a ciliate protozoan that displays nuclear dimorphism, having a diploid micronucleus and a polyploid macronucleus. B. japonicum produces sexual pheromones that promote conjugation. There are two mating types (I and II), each type excreting a specific pheromone (termed gamone 1 and gamone 2, respectively). When sexually mature mating-type I cells are moderately starved, they autonomously produce and secrete gamone I. Gamone 1 specifically acts on mating-type II cells, transforming them so that they can unite with type I cells, and inducing them to secrete gamone 2. Gamone 2 then transforms type I cells so that they can unite with type II cells. Cells that can unite may then undergo conjugation.

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