Semiochemical

E. R. Mitchell, ed.. Management of Insect Pests with Semiochemicals, Plenum Press, New York, 1981. 

D. A. Nordlund, R. L. Jones, and W. J. Lewis, eds., Semiochemicals Their Role in Pest Control, Wiley-lnterscience, New York, 1981. 

The Chemistry of Pheromones and Other Semiochemicals I Volume Editor Schulz, S. 

The vertebrates produce, send and detect information which is conveyed by one or more molecular types. Chemical information of biological value (semiochemicals) which partly or wholly activates the accessory olfactory system (AOS) is transferred during intra- and inter-species communication. The compounds involved convey messages of social importance originating from the need to co-ordinate gamete release. It seems quite likely that gradual improvements by selection of semiochemical molecules and their receptors eventually enhanced the reproductive benefits both for the sender and for the receiver (Sorensen, 1996). The dual olfactory systems interpret chemical input to allow the discrimination of odour... 

Semiochemical analysis is especially mature in both genera and reveals some unexpected signal sources (Rasmussen et al., 1996 Rasmussen and Schulte, 1998 Riddle et al., 2000). 

The operation of each part of the vomeronasal sense, from the semiochemicals of frogs to the prevention of pregnancy in mice, is further considered in Chaps. 5 and 7. 

The singular and defining characteristic enjoyed by the AOS is the way in which its stimuli arrive. Entry of semiochemicals is by fluid-borne presentation via the nose, nose and mouth, or mouth alone. It is a method which avoids many of the vagaries of entirely air-borne delivery. Chemosignalling by whatever route is an inherently wasteful and inefficient way of communicating information because of the lack of control over the transmission medium. The signal that eventually... 

Amongst the secretions of specialised exocrine complexes, the ancillary products which act as sticky compounds are large, often proteinaceous, molecules. Their primary, secondary and tertiary structures being inherently complex are now seen as ideal informational vehicles — alone or in combination with volatile molecules. Much recent work (Sec. 3.2, below) has identified them as the key components involved in close range transmission, and in intra-nasal peri-receptor events. Proteins are semiochemically implicated when their selective removal or presentation alters responsiveness (Belcher et al., 1990 Mucignat-Caretta et al, 1995). 

With increases in group size and social complexity, and the consequent expansion of diversity in communication, there is presumably selection pressure for unambiguous signals. Over time, evolutionary change may reduce unwanted complexity and act to refine specificity. Whether this results in reliance on the properties of a single component rather than those of the pattern provided by a complex mixture is conjectural. A reasonable expectation is that emitted semiochemical(s) can be reliably produced, and that their contents are acted upon by selection. The improvements in control which can thus be attained are seen in the operation of stereospecificity (Miiller-Schwarze et al, 1976). 

Behavioural testing of protein fractions has not kept pace with semiochemical studies. Belcher et al. (1990) found that the mixed scent marks of the Saddle-backed Tamarin (S. fusicollis) comprise urine and genital/suprapubic gland secretions. Both sexes deposit mixtures of pheromonally active large molecules at, for example, exudate feeding... 

The prophecy on semiochemical systematics in the headline quotation at the start of this chapter remains just that — an intriguing speculation. Some single-component chemosignals do turn up as apparently the main active compound in a complex secretion. In male gerbils (Meriones) one volatile, phenylacetic acid, appears to represent the dominant male state (Thiesen, 1974). Individuality must be added by further components — dietary or variable sebum constituents in this case. Indeed, amongst mammals and some reptiles, complex mixtures seem to be the norm very few taxonomically relevant examples have emerged. 

Field and laboratory bioassay of chemosignals from related sympatric and allopatric species (overlapping and discrete distributions) are essential to an understanding of the relatedness or otherwise of functionally active compounds. The semiochemicals involved in speciation surely utilise the main and vomeronasal senses, but their relative contributions cannot be predicted at present. 

A recurrent refrain in the semiochemical literature is the lack of sustained and comprehensive studies covering all transmission stages from stereochemical detail to ethological nuances (Albone, 1984 and 1997). 

A previously unexplained observation of a link between nose and gonads — the so-called naso-genital relationship — can now be placed in context. Removal of the relay site for the pump-regulator (see above) by extirpation of the sphenopalatine ganglion was found to result in a state of pseudo-pregnancy (Rosen et al, 1940). Interruption of stimulus access would clearly prevent most uptake through loss of control over the pump. A diestrous state would be induced (Sec. 5.3 below) attributable to the lack of male urinary semiochemicals. 

Sensory processing of semiochemical stimuli, by the accessory pathway, is achieved by amplifying and streamlining the passage of... 

The anatomical separation achieved by reptiles parallels the divergence of the main/accessory receptor categories. AOS chemoreception is assumed to elaborate its semiochemical responses by selective gains in ligand-capture efficiency and by alterations of threshold values. Once... 

One well-analysed chemosignal system is that of the Red-bellied Newt (Cynops pyrrhogaster). Males of this species produce from the abdominal gland a semiochemical protein (sodefrin) with marked VNO activity as a female attractant (Kikuyama et al., 1997). Courtship displays of newts often contain tail-waving bouts, which direct cloacal or other secretions from the male toward female recipients (Fig. 3.1). A large stable molecule like sodefrin, alone or as part of a VNPr complex, is presumably suitable for such local transference. 

The ability to compare semiochemical patterns and to assess degrees of similarity is a likely mechanism underlying the establishment, and eventually the maintenance of genetic divergence. Amongst Tamarins (Saguinus spp.) and Marmosets, both for within- and between- (related) species distinctions, the complexity of their scent marks provides a discriminatory mechanism (Epple et ai, 1987 Smith et al., 1997). Mixed species groups of these monkeys are enabled to co-exist, to... 

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