Mammals odor discrimination

Mammals easily discriminate the odor of conspecifics from odors of other species. 

The anatomy of the northern fulmar s olfactory bulbs is better suited for powerful odor detection than for keen odor discrimination. The periglomerular and external tufted cells are relatively sparse. These cells are important for superior odor discrimination in macrosmatic mammals. The interior granule cells are also loosely organized (Meisami and Wenzel, 1987). 

It is not always clear how pheromone signals are detected in mammals. Most vertebrates, mice for example, have a VNO in addition to the main olfactory system. The VNO has two separate families of olfactory receptors Vlr, 137 functional receptors in mice V2r, 60 functional receptors in mice. The genes for these are only distantly related to those for the main olfactory receptors, suggesting that these systems evolved independently. As a general rule, it is the VNO and not the olfactory epithelium that is responsible for detecting pheromone molecules. However, it has been demonstrated that mice whose VNO has been surgically removed can discriminate MHC-determined odor types. This finding clearly implicates the main olfactory system in the detection of pheromones. 

In black-tailed deer, Odocoikus hemionus columbianus, fecal odors of sympatric predators (coyote, C. latrans, and mountain lion, Fdis concolor) in vials next to food pellets inhibited feeding, while those of allopatric predators (lion, Fdis leo, snow leopard, Uncia uncia) do not, or very little (Miiller-Schwarze, 1972 Fig. 12.3). Note that mammals discriminate between the odors of sym- and allopatric predators, while fish and rattlesnakes do not (pp. 359 and 364). Free-ranging adult female wapiti, Cervus elaphus canadensis, respond to the odors of dog urine, and cougar and wolf feces (presented as water slurry) with increased heart rates. It was concluded that the main effect of predator odors may be for assessing the risk of predation (Chabot etal, 1996). 

Olfaction is the primary modality for social recognition and communication in nocturnal rodents (Johnston, 1983 Halpin, 1986, 1991). For example, most mammals that have been tested discriminate between the odors of individual conspecifics that are not close relatives (e.g., Johnston, et al., 1993 Johnston Jernigan, 1994 Todrank Heth, 1996) and many species may use these individually distinctive odor cues for recognition of kin versus non-kin as well (e.g. Block, et al., 1981 Hepper, 1983). Most secretions that are individually discriminated also contain information about other attributes of the individual, such as the sex, reproductive state, and species of the odor donor (Johnston, 1983 Heth, Beauchamp, Nevo Yamazaki, 1996). 

Optical purity of enantiomers is of great importance in the chemistry of natural products, especially in the fields of flavors, fragrances, and pheromones. Since odor receptors in mammals and in insects can discriminate between enantiomers, it is important to know the enantiomeric composition of chiral molecules that impinge on these receptors. 

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