The scent of age

Abstract

In many species, older males are often preferred mates because they carry 'good' genes that account for their viability. How females discern a male's age is a matter of question. However, for animals that rely heavily on chemical communication there is some indication that an animal's age can be determined by its scent. To investigate whether there are changes in body odours with age, and if so their composition, mice were trained in a Y-maze to discriminate urine odours of donor mice of different ages: Adult (3-10 months old) and Aged (more than 17 months old). Trained mice could discriminate between these two age groups by odour alone. To determine the chemical basis for these discriminations, studies were performed using gas chromatography and mass spectrometry. These analyses demonstrated differences in the ratio of urinary volatiles with age. The most prominent differences involved significantly greater amounts of 2-phenylacetamide and significantly lower amounts of methylbutyric acids in Aged animals relative to Adult animals. Fractionating and manipulating the levels of these compounds in the urine demonstrated that the mice can distinguish age based on variation in amounts of these specific compounds in the combined urine.

Citronellal Ingestion Decreases the Appeal of Male Mouse Urinary Pheromone for Female Mice

“…25) In a previous study, we found that aged B6 male mice developed an aging-associated odor that was attractive to female mice in an experimental setting, and that this attraction was due to increases in several volatile chemicals. 16,17) Another of our studies suggested that ingestion of mugwort and mushroom extract decreased the intensity of odors associated with aging in mice by decreasing specific urinary chemicals that normally increase in aged mice, although we found no evidence to suggest that xenobiotic chemicals from these edible herbs were released into the urine. 26) Moreover, using a standard odor training paradigm employing a Y maze, 7,8,27) we found that citronellal, which emits a lemony aroma and is present at high concentrations in the Japanese pepper (Xanthoxylum piperitum DC.…”

“…For example, individual body scents, present in the urine, are influenced by the differences in genetically encoded species information, 1,2) sex, [3][4][5][6] individual identity, [7][8][9] and kinship 10,11) of the owner, as well as information about the animal's current reproductive status, [12][13][14] virus infection status, 15) and age, [16][17][18][19][20] all of which can influence other animals' behavior and mate selection. It is generally believed that each of these characteristics must be relatively stable over a considerable period of time in an individual in order to influence body odors so that the individual can be recognized in multiple behavioral and social contexts.…”

In search of the chemical basis for MHC odourtypes

“…In addition to the MHCassociated chemosignals, mice release diverse chemical signals that communicate not only their unique odour signatures but also information such as gender, age, motivational state, sexual readiness and health status. Some of the sources and chemical identity of these signals in mice have been studied, including MUPs (Hurst et al 2001;Chamero et al 2007), exocrine glands secreting peptides (Kimoto et al 2005), urinary signals of virus infection (Yamazaki et al 2002) and the animal's age (Osada et al 2003(Osada et al , 2008, and volatile semiochemicals that are involved in sexual communication (e.g. 2-secbutyl-4,5-dihydrothiazole, 3,4-dehydro-exo-brevicomin and methylthiomethanethiol; Jemiolo et al 1986;Lin et al 2005).…”

Effect of an Orally Ingested Mugwort and Mushroom Extract Mixture on Urine Odor from Aged Mice

“…Mice were used since there is extensive information on the chemistry of mouse odors, [12][13][14][15] and we have knowledge of what odorous materials change with age. 16,17) There are some volatiles which are known to be mouse putative pheromones in mouse urine, 13,18) although we are not aware of any prior studies involving the agerelated change of these chemosignals. The change of volatiles with age has been suggested by the research of Robinson and colleague who showed that the composition of mouse urine varies with age.…”

“…The change of volatiles with age has been suggested by the research of Robinson and colleague who showed that the composition of mouse urine varies with age. 19,20) Our previous studies 16,17) indicate that, as mice age, their odors change, thus allowing older male mice to be discriminated from otherwise identical adult, sexually mature individuals. Moreover, we have provided evidence for the identity of some of the volatile compounds (e.g., 2-phenylacetamide, 2PA; indole, IND) underlying these changes and suggested that their presence may reflect age-related changes in the animal's immune system (for 2PA) and age-related changes of intestinal microbial flora and/or the metabolic activity of amino acid intermediates in the liver (for IND).…”