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Body odour and sexual attraction in animals

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Insects

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Insects use extremely sensitive receptors to detect pheromone signals. Each pheromone signal can elicit a distinct response based on the gender and social status of the recipient[1]. In insects, sex pheromones can be detected in very minute concentrations in the environment[2]. Insect sex pheromones, usually released by the female to lure a male, are vital in the process by which insects locate each other for mating. The main purpose of releasing these sex pheromones is to attract a partner from a distance, however the sex pheromones also serve to evoke a courtship response and sexually excite the male prior to copulation.[3] Male insects can also release sex pheromones, but this is only for the purpose of sexually exciting the female, making her more receptive to the male's advances. Generally, the majority of insects are sensitive and selective to the sex pheromone of their own species.

Insects make use of two classes of pheromone signals; the pheremones that induce immediate or 'releaser' effects (for example, aggression or mating behaviours) and those that elicit long-lasting or ‘primer’ effects, such as physiological and hormonal changes[4].

 
A pair of mosquitos during mating season

There is a significant amount of research supporting body odour and sexual attraction in insects. Observations and laboratory experiments of Culiseta Inornata, identified a chemical substance involved in mating behavior, when exposed to this scent the male mosquitos were found to attempt sex with dead females and when exposed to the scent of virgin females, the males showed increased sexual activity through excited flight, searching and attempts to copulate with other males.[5] Further evidence comes from research on the commercial silkworm moth, Bombyx mori, a chemical produced in the abdominal sac of the female adult moth is released shortly after it's emergence from the cocoon, male moths were found to be immediately attracted to this scent demonstrated by a characteristic wing flutter and attempts to copulate[6]. The sex pheromones of the silkworm moths can elicit responses in the male antenna at concentrations of only a few hundred molecules per square centimeter[7].

Vertebrates

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For vertebrates, aquatic environments are an ideal medium for dispersing chemical signals over large areas. Aquatic vertebrates use chemical signals for a wide range of purposes, from attracting mates to distant nesting sites during spawning, to signalling reproductive readiness and regulating predator/prey interactions[8]. Research on goldfish has identified that the fish release hormones in various combinations, depending on the reproductive status of the releaser, and these different combinations can elicit varying degrees of male courtship in the recipient[9].

In terrestrial environments, chemosignals can be either volatile or non-volatile[10]. Accordingly, terrestrial vertebrates have two functionally and anatomically distinct olfactory systems: the main olfactory system, which is receptive to volatile cues, and the vomeronasal system, which is thought to process mostly non-volatile pheromones[11].

Mammals

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When it comes to sex, mammals use chemical signals (pheromones) to convey information to one and other. Mammal's heromones are air-borne chemical substances released in the urine or feces of animals or secreted from sweat glands that are perceived by the olfactory system and that elicit both behavioral and endocrine responses in conspecifics.[12] Mammals use sex pheromones to arouse, attract, and elicit specific behavioral responses from the opposite sex.[13] In mammals, chemical signals and the scent glands that secrete them have many features in common, for example, expression in only one sex, development only in adults, often only secreted in breeding season and used exclusively in mating.[14] For an odour to be exclusively result in sexual behavior, it must not only be perceived and preferred, but when absent there should be a decrease or complete elimination of sexual activity. This exclusivity has only been shown in golden hamsters[15] and the rhesus monkey.[16]

Mammalian pheromones can elicit both long-lasting effects that alter the hormone levels of the recipient animal, and short-term effects on its behavior[17]. For example, detection of male pheromones by female mice has been found to encourage onset of puberty, however the detection of female pheromones have been found to delay the onset of puberty[18].

Odour can influence mammalian mating both directly and indirectly. Odour may act as a direct benefit to females, for example by avoiding contagious diseases by using odour cues to choose a healthy mate[14]. Odour can also act as an indicator mechanism, a form of indirect benefit, for example when a male displays a particular trait such as strength of odour which is in proportion to their heritable viability, females choosing males with strong odours will gain genes for high viability to pass to their offspring.[19]

There is vast evidence for the use of pheromones in mating behaviors. For example, when boars become sexually aroused, they salivate profusely dispersing pheromones into the air. These pheromones attract receptive sows, causing it to adopt a specific mating posture, known as standing, which allows the male boar to mount it and therefore copulate.[20]

Species Specificity

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Regardless of the species, sex pheromones are often structurally similar and for that reason different species need to be able to respond to the correct pheromone. It is the variation in the ratios of each compound within a pheromone that yields species specificity[21]. The use of mixtures of compounds as pheromones is well documented in insects, research into male orchid bees demonstrates that specific odours mediate exclusive attraction within a species[22].

  1. ^ Dulac, Catherine; Torello, A. Thomas (July 2003). "Sensory systems: Molecular detection of pheromone signals in mammals: from genes to behaviour". Nature Reviews Neuroscience. 4 (7): 551–562. doi:10.1038/nrn1140.
  2. ^ Dulac, Catherine; Torello, A. Thomas. "Sensory systems: Molecular detection of pheromone signals in mammals: from genes to behaviour". Nature Reviews Neuroscience. 4 (7): 551–562. doi:10.1038/nrn1140.
  3. ^ Jacobson, Martin (1972). Insect Sex Pheromones. New York: Academic Press. p. 1.
  4. ^ Dulac, Catherine; Torello, A. Thomas (July 2003). "Sensory systems: Molecular detection of pheromone signals in mammals: from genes to behaviour". Nature Reviews Neuroscience. 4 (7): 551–562. doi:10.1038/nrn1140.
  5. ^ Kliewer, J. W.; Miura, T.; Husbands, R. C.; Hurst, C. H. (1 May 1966). "Sex Pheromones and Mating Behavior of Culiseta inornata (Diptera: Culicidae)". Annals of the Entomological Society of America. 59 (3): 530–533. doi:10.1093/aesa/59.3.530.
  6. ^ Butenandt, A; Beckmann, R; Stamm, D (1961). "Über den Sexuallockstoff des Seidenspinners, II. Konstitution und Konfiguration des Bombykols". Hoppe-Seyler´s Zeitschrift für physiologische Chemie. 324: 84–87.
  7. ^ Wilson, Edward O. "Pheromones". Scientific American. 208 (5): 100–114. doi:10.1038/scientificamerican0563-100.
  8. ^ Dulac, Catherine; Torello, A. Thomas (July 2003). "Sensory systems: Molecular detection of pheromone signals in mammals: from genes to behaviour". Nature Reviews Neuroscience. 4 (7): 551–562. doi:10.1038/nrn1140.
  9. ^ Poling, Kirsten R.; Fraser, E. Jane; Sorensen, Peter W. (2001-06-01). "The three steroidal components of the goldfish preovulatory pheromone signal evoke different behaviors in males". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. 4TH International Symposium on Fish Endocrinology. 129 (2–3): 645–651. doi:10.1016/S1096-4959(01)00361-X.
  10. ^ Dulac, Catherine; Torello, A. Thomas. "Sensory systems: Molecular detection of pheromone signals in mammals: from genes to behaviour". Nature Reviews Neuroscience. 4 (7): 551–562. doi:10.1038/nrn1140.
  11. ^ Broman, Prof Dr Ivar (1920-01-01). "Das Organon vomero-nasale Jacobsoni — ein Wassergeruchsorgan!". Anatomische Hefte (in German). 58 (1): 137–191. doi:10.1007/BF02033831. ISSN 0177-5154.
  12. ^ Rekwot, P.I.; Ogwu, D.; Oyedipe, E.O.; Sekoni, V.O. (March 2001). "The role of pheromones and biostimulation in animal reproduction". Animal Reproduction Science. 65 (3–4): 157–170. doi:10.1016/s0378-4320(00)00223-2.
  13. ^ The Neurobiology of Olfaction. Boca Raton, FL: CRC Press/Taylor & Francis. 2009.
  14. ^ a b Wyatt, Tristram D. (2003). Pheromones and animal behaviour : communication by smell and taste (Repr. with corrections 2004. ed.). Cambridge: Cambridge University Press. ISBN 9780521485265.
  15. ^ Murphy, M. R.; Schneider, G. E. (16 January 1970). "Olfactory Bulb Removal Eliminates Mating Behavior in the Male Golden Hamster". Science. 167 (3916): 302–304. doi:10.1126/science.167.3916.302.
  16. ^ Michael, R. P.; Keverne, E. B.; Bonsall, R. W. (28 May 1971). "Pheromones: Isolation of Male Sex Attractants from a Female Primate". Science. 172 (3986): 964–966. doi:10.1126/science.172.3986.964.
  17. ^ Halpern, M (March 1987). "The Organization and Function of the Vomeronasal System". Annual Review of Neuroscience. 10 (1): 325–362. doi:10.1146/annurev.ne.10.030187.001545.
  18. ^ Halpern, M. (1987-01-01). "The Organization and Function of the Vomeronasal System". Annual Review of Neuroscience. 10 (1): 325–362. doi:10.1146/annurev.ne.10.030187.001545. PMID 3032065.
  19. ^ Andersson, Malte (1994). Sexual selection. Princeton, NJ: Princeton Univ. Press. ISBN 9780691000572.
  20. ^ Dorries, Kathleen M.; Adkins-Regan, Elizabeth; Halpern, Bruce P. (1997). "Sensitivity and Behavioral Responses to the Pheromone Androstenone Are Not Mediated by the Vomeronasal Organ in Domestic Pigs". Brain, Behavior and Evolution. 49 (1): 53–62. doi:10.1159/000112981.
  21. ^ Dobele, Angela; Lindgreen, Adam; Beverland, Michael; Vanhamme, Joëlle; van Wijk, Robert (2007-07-01). "Why pass on viral messages? Because they connect emotionally". Business Horizons. 50 (4): 291–304. doi:10.1016/j.bushor.2007.01.004.
  22. ^ Zimmermann, Yvonne; Roubik, David W.; Eltz, Thomas (19 July 2006). "Species-specific attraction to pheromonal analogues in orchid bees". Behavioral Ecology and Sociobiology. 60 (6): 833–843. doi:10.1007/s00265-006-0227-8.
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